Collider Physics from the Bottom Up - Nima Arkani-Hamed

okay so I had I planned to do a three different topics in my three lectures but I went a factor of two slower yesterday than I thought so I think most of today will probably be spent finishing the topic of my what I wanted to do yesterday the topic I was going to talk about today the the title was the collider physics from the bottom up and was going to talk about practically how you can use some of these recent ideas about calculating scattering amplitudes which which have been largely developed from for massless theories and some fancy supersymmetric theories even were most of the project of most of the progress has happened to just introduce you to a formalism that's that my collaborators and I've been developing recently as paper should come out and uh by the end of the summer hopefully where you can do these things for anything arbitrary mass of particles any mass any spin and and one of its practical consequences and that's what I it's possible to explain in a in the lecture of the of the appropriate period at least the rules is if you want to calculate any tree-level two to two scattering amplitude for any purpose you want standard model BSM if you want to imagine that you're colliding a gluon with some with a top quark producing a spin three half excitation of a top quark that decays back to a KK graviton and the top if I told you that you're going to do that calculation you'd probably be a little scared right and mad graph doesn't know how to do it so but you can compute it in two or three lines in real time so that was supposed to be the topic of today's lecture I probably won't be able to fit everything but but perhaps something that we can do if people are interested in that subject and formally is we could talk about it after hours next week sometime and we can maybe a chat about it then at any rate my my normal working hours are not at this time of day it's very hard to stay up this late so also you'd catch me in a better place mentally okay so what I want to do is is continue the theme of the discussion from yesterday where the heck is everybody what happened to Suzy what happened to a wimps and as I mentioned already yesterday the story seems to be one of having a basic idea of the kind of big picture of what particle physics looks like with the kind of unification remarkably happening at a high energy scale which is pretty close to a scale where a lot of things seem to be going on gravity string scale the inflationary scale the even more directly the scale circumstantially directly the scale associated with the Murano neutrino masses and and finding the first version of the idea failed right the most naive non super symmetric version fails you have proton decay but there was a nagging elephant in the room there was a hierarchy problem you solve that now things start working better the coupling is unified perfect percent level precision at a scale that's high enough that you don't have to worry about the model independent proton decay from X&Y gauge boson exchange the sort of height of excitement is the early 90s when everything seems to be on track and you get of course this other thing falling into your lap not just in supersymmetry pretty generically in theories that solve the hierarchy problem of getting a good Dark Matter candidate and I also alluded to on the other hand the sort of both the nagging niggling worries about why we could have seen the effect of all the stuff that was supposed to be at the TV scale a long time ago indirectly and increasingly as time went on and we looked for the particles at accelerators the difficulty with not having seen them there that supersymmetry is a theory of the wnz particles could have shown up at lap it could have shown up at even earlier than left but I couldn't should have left one you can fill up at left two is good the Tevatron and so there are many people as I emphasized the last time not the majority but a sizable minority of people who were already saying and you know 1999-2000 there's something a little bit wrong now of course everyone also knew that there was a huge thing wrong the whole time the cosmological constant and what we finished talking about last time maybe this is a whole subject we spend hours talking about but is that it's possible as a Weinberg pointed out that there could be an entirely different sort of explanation for the cosmological constant the convenience a lead if and sort of explanation for any seeming naturalness problem if we give up the idea that the underlying theory produces a unique vacuum or two or three vacuum and imagine that while the underlying theory might be dead unique complete unique it produces an exponentially large number of vacuum now I gave you a little example of what such a toy model of a landscape might look like just to make it very concrete you saw how simple it was okay what's not some totally crazy thing you just added a few hundred scalar fields to the standard model and and you got an exponential in that number number a vacuum right and so that made it possible to without having any crazy adjustments for the parameters of the theory made it possible to find a vacuum where the cost module constant is what it was or the higgs mass is what it is without making any crazy demands of the parameters of the underlying theory the question then becomes transmuted to another one now it's possible why is that the one that we find ourselves in and the second that happens other other kinds of explanations become possible and I pointed out this little plot that we drew independent of any of these words it's an interesting fact that if we take the cause module content and make it a little bigger the universe becomes empty if we take the higgs mass squared make it a little bit more negative the universe quickly only has a hydrogen atoms in it and nothing else right those those facts which in the conventional picture of the world just view as curious coincidences if you now imagine that you might have a gargantuan number of a q1 that they're somehow populated out there somewhere that puts a further condition on where you might find yourself right you're obviously not going to find yourself in the place where it's empty so no matter what ignoring any more detailed questions of measures and how you judge one place you could be versus another place you could be it's obvious you're not going to be in a place where the cosmological constant is plunking or gud ian and have any kind of reasonable structure form okay so so those arguments were made for the cosmo jewel constant in 87 by C Weinberg the argument about atoms was made by Donohue at all in the late 90s and so these things were known they were they were now what was the I can tell you my attitude towards these things back then was a grad student in early postdoc is that okay it's true we don't have any good other good explanation for the smallness of the cosmological constant one that we can actually stare at what we do have is the magic mystery mechanism that's going to make the cosmological constant zero for some fancy reason we'll someday discover um and it's true that so we have this argument that that if you made the Higgs mask word more negative we wouldn't have any atoms but here is saying for the Higgs unlike for the cosmos concept there are natural solutions to the hierarchy problem beautiful natural solutions with a hierarchy problem like supersymmetry but on top of it get you gauge coupling unification in dark matter so for sort of concreteness and sharpness this so I've drawn a picture of a balance of scales am I sort of thinking of which one of these two pictures of the world were correct the the precision and and a concreteness of this idea greatly overwhelmed all of these other considerations at least for me it's yeah these things are possible but you can sort of make up just so stories for y parameters turned out the way they were you know many other periods early on in the history of physics maybe this is again a bad time to make arguments like this and in any case if it's all going to be anthropic environmental multiversal whatever you want to call it why the heck would it seem like we're on the right track with everything working out like that and then you have to quiet the little voice in the back of your head that's it oh but then they're all those niggling things weren't there with the absence of deaf DNC's and mediums and so on so but anyway that was a that was a picture of the scale oh by the way let me make a quick little homework exercise for you we talked about what's bad about the universe when the Higgs mask where it gets more negative why can't the higgs mass squared be more positive then what what what would happen if let's say we took the standard model we made the Higgs mass plus 100 GeV squared what do you think would happen huh nope nothing is massless nothing particularly qualitatively changes about the world qualitatively changes a little bit quantitative but not qualitatively so this is a good exercise to do if you've never done it before think about what the Higgs looks what the standard model looks like in a theory without a Higgs and the answer is that the strong interactions are Technicolor the strong interactions condense the fermions and they break electroweak symmetry okay so what's the W in the Z mass is being you know 80 MeV instead of 80 GeV all right so so su 2 cross T 1 is broken now what about the fermions well even the fermions if the Higgs is there if you integrate out the Higgs it gives you what let's say even say four electrons you know Ellie I integrate out the Higgs it couples to quarks okay Q you so in the low-energy theory I have this effective operator over MH squared roughly speaking times the cacao couplings here okay lambda e lambda quark and so when this thing gets a valve order of the QCD scale the light fermions also get a mass so everything is the same okay of course the fermions are much much lighter but nothing super qualitative changes about the world so that's sort of interesting we don't even need the Higgs to break electroweak symmetry give Fermi on net walk in we we need something to break the chiral symmetries of the Fermi on so that's what the Higgs is doing here in order to generate a fermion masses but but the Higgs is not crucially involved in electroweak symmetry breaking otherwise okay so it's a nice exercise for you to think about what the world could look like in this case because and I want you to see if you can unpackage this statement that in a world like this there could be no baryons and this has very much to do with some of the physics that Michael Dean was talking about the physics of the anomaly now the su2 anomaly that violates barren and lepton number okay and in the standard model that's violation of baron and lepton number keeps going but it's stopped because the gauge coupling can't get too big because the group is Higgs by the Higgs okay so at around 100 GeV so the size of these effects that we get from from electroweak from the electroweak anomaly are exponentially small however in the world where it's QCD itself breaking electroweak symmetry the W and the Z are much lighter than the proton and so the electroweak violation of grand lepton number proceeds in the early universe completely unchecked as you drop beneath the mass of the proton and all the baryons are converted to neutrinos okay so if the if the Higgs did not break electroweak symmetry we could not have a universe with baryons in it okay we'd have a universe with the completely filled with super duper duper duper duper light neutrinos because they're going to be even lighter than this if we have the usual dimension five operators pour in neutrino masses okay so that's kind of cool that that on one side on one side if we made the Higgs mass squared more positive we have radically radically different universe there's something qualitative that's helped by having the Higgs break electroweak symmetry but on the other side as we make the higgs mass squared more and more negative we lose atoms almost instantly okay now so to say it to say is the tension one more time did here our attention is that here we're sitting at the TeV scale and on the one hand we have the attention of unification and Dark Matter and solving the hierarchy problem of course okay that says there's a lot of stuff here lots here on the other hand we we have everything else all the niggling things let's say there should be nothing nearby right and of course the CC looming as this big worry in the back of your mind so on all of that which led to that picture but I know I was actually sort of literally drawing these imbalances in in a meeting at Cambridge in 2005 where all these things were being discussed and I can say that back already in 2005 and certainly today I would draw the picture like this maybe not even quite as extreme Lee tilted of that but somewhat tilted in the opposite direction of and the thing which has changed you could still imagine some mechanism like this okay but structure Adams weighing that down the same thing on on the other side I won't draw it again but the thing that changed for me around 2004 2005 was the realization that if if these environmental things were going to have a role to play in particle physics it did not have to mean that it was a standard model and nothing else up all the way up to the punk scale that there are there are other possibilities and in fact there's this very simplest possibility which was one where you don't have to give up any of the concrete successes okay everything keeps going just like it was before if you want to say it in the story that we're saying you notice these other everything is going great except these little niggling worries that you haven't seen anything and the CC is standing there above you making you worry about whether you should take these notions of tuning SuperDuper seriously this opens the possibility even thinking about something like the landscape opens the possibility of thinking about models of particle physics that are not just a standard model that would look crazy from a conventional point of view completely crazy from a conventional point of view but become more more plausible seeming or at least seem possible from this point of view if you think that that there might be a huge landscape out there and what made this possible is for me the picture of split Susie okay so let me first so just define defined what it is so what Susie is just the MS SM okay so it's just supersymmetry but in a peculiar range of its parameter space okay it's a range of its parameter space for the fermions of Susy so the fermions meaning the gauge inos and perhaps maybe the Higgs e knows H up and H down eggsy no open it down are in the neighborhood of the TeV scale but the scalars are much heavier okay and in the what what we called the minimal version of slits Uzi the minimal version has a splitting between the scalars and the gauge Eno's that's parametrically alpha alpha over 4pi okay and numerically it could be about a factor of 10 to the minus 2 to 10 to the minus 3 so we're thinking about scalars between you know hundred to a thousand pev you could think of even heavier scalars and in the original papers we talked about even heavier scalars by the way this is an idea with a long history many people ran into this kind of spectrum so the the main thing that happened in this period is that some number of us stopped being ashamed of it and said that this is something that might actually happen because most people who ran into it and this kind of spectrum has been running to as I said many many times said well what's what's wrong with this spectrum what's wrong with it is that it's horrendously finely-tuned right now it's not as finely tuned because the stop for example would be up at a thousand to Evie okay it's not as finely tuned as things going all the way up to the Planck scale which is a usual part in 10 to the 30 but it's fine tuned to a part in a million or a partner a hundred thousand or part in 10,000 right okay and so this is where the scalars are now why would you like something like this just from the top down forget about the rest of the issues more phenomena glitters I'm going to talk about why is this even possible after all you think after you break supersymmetry okay all the super partners get a mass why aren't the masses comparable well of course there's a difference between the fermions and the scalars what is the difference right the fermions can have a chiral symmetry and the scale is don't so in order to give the scalars of mass all you have to do is break supersymmetry in order to give the fermions the mass you have to break supersymmetry and the chiral symmetry okay so it's definitely not crazy the fermions might be lighter in fact what what is what is the chiral symmetry if you're a supersymmetry person what is the chiral symmetry we're talking about that protects let's say the mass of the gauge e knows it's an R symmetry okay and so we are forced to break our symmetry eventually in a super symmetric Theory there's no other way to cancel the cosmological constant other than having a vacuum expectation value for the super potential the brakes the R symmetry so ultimately the gravity no is a non zero mass supersymmetry is broken we have to break the r symmetry but it could well be that that's fed down to the fermions at at the expense of extra loop orders and i don't want to spend much time talking about models but it's true that in the early 80s the first simplest theories of supersymmetry breaking have this kind of spectrum in the late 90s early 2000s when people ran into fancier more sophisticated things like anomaly mediation so the incredibly simple pictures if you just break supersymmetry into sectors somewhere and just let some universal effects feed the information to the rest of the of the physics again there if you didn't do anything clever or smart the scalars ended up being a loop factor heavier than the gauge Eno's okay so this kind of spectrum with the Lupus splitting between the scalars and gauge inos is easy it's what you know the most garden-variety supersymmetric theories that break supersymmetry want to do but we weren't letting them do it okay we weren't letting them do it because that kind of spectrum would be phenomenologically dead right now but if you want to make the theory natural because if you have the scalars at a few hundred GV you'd have to have the glue we know at a few GeV okay now in fact that wasn't ruled out you know even in the mid 80s there was a some thought that maybe you had like bluey knows lying around there but eventually you know that's definitely not what things are looking like so if you wanted to let super symmetric models of supersymmetry breaking do what they want to do you would have to raise the scale so the bottom was then the hundreds of GeV or T V range and then the top would be so heavy that it was obviously unnatural from the standard point of view now just just to say the obvious you see the amount of fine-tuning it talking about here is completely intolerable if you're a mono vacuum you know we have to find one unique theory person a partner million is already is horrible partner hundred is terrible part and ten is terrible that's what we're talking about yesterday but if you're thinking and I'll try to make it more precise a little later if you're a if you're imagining there's some mechanism that's dealing with a cosmological constant problem that's 60 or 90 or 120 orders of magnitude problem then six orders of magnitude here are there seems like nothing in comparison okay so whatever there is that's violating our notion of naturalness is violating it really badly on the CC and the Higgs as a small cousin of this problem does not seem to be a big deal you know little factor of a million here or there okay so that's what the spectrum that's what the spectrum looks like the motivation is that from the top down the spectrum actually happens all the time but what are the consequences first of all gauge coupling unification works just as well in this theory as in the standard supersymmetric theories so in other words if you just take all the scalars and push them up to 100 or a thousand TV you do not ruin the success of gauge coupling unification okay um let me just just just just raise your hands how many people would think that if i push the scalars to the ten of the 14 GeV super far away that that would ruin unification so everyone understands why why the scalars are unimportant for unification all right so let me let me explain this quickly you've all seen this picture of the unified couplings right so we let me draw the picture again we're looking at alpha 1 inverse alpha 2 inverse alpha 3 inverse and from the purposes of this argument they're running coupling so let me just draw little runners okay little runners and so what is special what's special is that they're all running running running and they meet it at a point right so let's jump the reference frame of runner alpha 2 inverse okay so she's sitting there and she sees runner alpha 3 inverse up 1 and verse and alpha 3 inverse heading towards her with some relative velocities right so what is the relative velocity of runner alpha 3 inverse well it's given by the difference between the beta functions b3 minus b2 and this relative velocity here is given once again by the difference between the beta functions b2 minus b1 okay so the fact that unification works is related simply to that took to the ratio so unification is telling us that b3 minus b2 over b2 minus b1 has got to be more or less what it is in the MSS M right you can do the computation for yourself to see what the number turns out to be okay but it's that ratio velocities is the right one that's what you need for a unification so notice that only depends on the difference between the beta function so any matter that makes identical contributions to the beta functions of s u3 s u2 and u1 is completely irrelevant to whether the coupling is unified it matters what the strength of the unified coupling is it doesn't even affect where they unify okay because because only the because it doesn't affect what these velocities are now what kind of matter multiplets make exactly the same contributions 2 3 2 & 1 anything that fits in a gut multiplet okay and so the fact the very fact of the standard model unifies into a gut multiplet tells you that none of the standard model fermions or in supersymmetry the scalar partners are important for gauge couple unification ok is that clear now who is important for gauge couple unification so it's ironic unification that the hint for unification the fact that unification works is precisely because there are things in the standard model that are not complete multiplets okay otherwise everything would not work okay so what are the things that matter in the standard model itself it's the it's the it's the gauge bosons their contraries in the data function is very important and the Higgs because it's a scalar and have small coefficient the Higgs is not all that important but that's what determines the picture of the wrong picture of unification in the standard bottle itself now let's let's take supersymmetry and let's add the particles in turn let's say I add the gay genome just the gay genomes okay genomes are a little bit cool because if we just add the gay gene O's your there are incomplete multiplets so you are changing you are changing the beta functions right but since you're changing them since their beta function is precisely proportional to what the beta function was just for the gluon just for the just for the corresponding gauge bosons um the amount you're changing them is to just rescale b3 minus b2 to a slightly smaller number right it's a little less so you're canceling off a little bit so your rescaling b3 minus b2 and b2 minus b1 - slightly smaller numbers so if you just took the standard model and added the gauge inos then you would get precisely the same picture of gauge coupling unification as in the standard model but just stretched out a little bit okay because it's the same picture but the runners are moving a little slowly so that would mean that the miss of the unification would take place not at 10 to the 14 GeV but actually turns out much higher closer to the Planck scale okay but it still doesn't work it still works as well as the standard model so finally it's the Higgs inos which are the split multiplet that does most of the heavy lifting okay and when you finally put in the Higgs II know as it changes these it changes this thing so that finally everything everything unified so so the most important particles for unification are the Higgs II know and the gauge Eno's matters somewhat as well but those are the things that we need the scalars are completely irrelevant okay so if you're so why do we need the scalars for we need to scale those for natural notes nothing else okay so if we get rid of the scalars gait shuffle unification is fine okay what about dark matter well talk a little about more about dark matter in a second and as we'll see this whole story for why we haven't seen supersymmetry is very closely related to why we haven't seen dark matter in this in this picture in fact the two problems are literally flip sides of each other as well as I'll explain but but before we get into that level of detail who could the Dark Matter be well it could be the same as we always talked about Susie could be the lightest neutrally knows they're the fermions okay so we don't need the scalars for dark matter either so we can have dark matter so unification is okay we can have dark matter is okay and now what happens to all of the phenomenological problems what happens to flavor-changing a neutral currents they're gone happens the EDM they're gone okay ah it's the scalars at the TV scale that has the marginal couplings to the standard model fermions that have the opportunity to break the and and also in in their masses and mixing the among themselves that had the opportunity to badly break all the flavor symmetries okay so so all the phenomenological problems the tensions the nagging stuff are just gone okay so EDM FC NCS all this stuff or just gone alright so so that's it that's the that's via picture um I'll say in a tiny bit of details again this would be more for supersymmetry aficionados this picture of supersymmetric is troubling revision is totally beautiful at detail at two loops the tulip prediction ultimately use this case you offered me the prediction for alpha s @ MZ the the atul prediction is something like point one to eight okay and that's a little high that's a little higher than point one one eight which is what it is for alpha s @ MZ now it's kind of easy to fix this up if you imagine you have some somewhat large threshold correction to gage couplings near the gut scale so people would talk about putting in particles at ten to the fifteen or ten to the fourteen GeV to fix that up fine in minimal slit Susie that threshold is given to at low energies instead because you know you didn't quite get everyone at the TV scale some of them got hooked up to a hundred or a thousand TV and so that means that with no need of large threshold Corrections at the gut scale your prediction is alpha acid MZ is around one one five one one six quite a bit closer to one one eight so it's not a huge deal but to the extent that it's a small thing it's a small thing that goes in the right direction okay so that was a picture and to emphasize again you know in principle I don't have to say anything about landscapes multiverses all of that stuff I could just say this is a model it's completely concrete model right I could just say this is this is the model why would people yell at you if you said this is the model people would yell at you because you're saying that here is a supersymmetric theory that's finely tuned okay you're it's like you're it's like you're doing violence to the very point of the idea you say no it's got to be supersymmetric theories it's deliberately finely tuned right and we're going to have this sort of splitting and and and all of that um and it you could respond to say I'm sorry you're supersymmetric theories already finely tuned it's already finely tuned by at least sixty orders of magnitude for the for the cosmological constant so you can't be on this fine-tuning high horse okay but you could always go back again going back to the same thing I said a few times ago always go back yes but that's the magic mystery mechanism okay so whenever if you're ever doing something actually concrete what you're forced to do in your actual formulas is to put some consonants in and the super potential to perfectly delicately cancel the cause of logical constants generated by supersymmetry breaking you're actually fine-tuning massively the whole time okay but and what the landscape picture does is just give you a character a cartoon it's not remotely a theory yet and I'll if I have time I'll speak a little bit more about it but it gives you a kind of a cartoon for what might be going on that could make this kind of picture a little more plausible let me bring this back down okay so any questions about the set up yeah unification yeah actually it's actually amusing because if you if you ask what what what could you keep let's say you only kept the Higgs II knows okay uh purely purely as a question of like how well it unifies purely Higgs inos are sort of halfway between the MSM and the standard model for what it looks but it's not it's not a precise unification at all and it's a somewhat low quasi unification scale at ten to the fourteen GeV so if we just did the exercise that's what particles could I shove in at the t v-- scale YTV scale because of usual arguments about wimps dark matter okay but once you decide you're going to shove new particles of the weak field we just do the exercise what could you possibly add to give me precision unification as we see in the in in in Susie without any extra funding thresholds that's the exercise that Giudice and Roman Eno did and you land quickly on exactly the same spectrum okay so Higgs II knows and gaijin owes now it's amusing but that's precisely the spectrum you get if there was supersymmetry at high energies somewhere okay yes there isn't what what do you - ooh of the muon you mean the anomalous G - ooh of the muon uh yes I'm giving up on explaining that in fact I mean it's highly debatable if it's there by the way this is why I mean this it's it's funny uh I've said many times I'm talking about this but when many of us started talking about this over a decade ago for a year when I was giving talks to conferences some people would literally scream at me okay I mean I'm not I'm not joking this was uh this was the height of heresy to say that something like this might be true to use the word supersymmetry and fine tuning in the same sentence people I respected greatly would stare at me with baleful hating eyes as I was giving a talk on these subjects and so the whole time but so ironically despite the fact that it's this theory that's inspired by tuning in the landscape and so on it was vulnerable to disprove from day one any anomaly if it's true kills this theory okay because there's no reason to have any violations of the stamp that's that's the point we have a great explanation for the accidental symmetries of the standard model so all the tenon amélie's and there are many they're much more impressive than muon G - ooh that came and went were a threat to this picture okay but again it gives you a counter example that if there's tuning it doesn't have to mean that it's a standard model right and and if we have time we'll talk about some top-down motivations while you might have had supersymmetry in the ultraviolet maybe you need supersymmetry in the ultraviolet because of quantum gravity maybe you need supersymmetry in the ultraviolet to protect the stability of all the metastable vacuo in the landscape there's all sorts of reasons you might have supersymmetry somewhere beneath the Planck scale it was only natural mnestheus for that scale to be all the way right down over our head and even if you allow some rough idea of a kind of a notion of a pressure and we'll quote well I'll show you some little examples in a bit something that might select for things that are that to address another problem like the tsetse problem you might have to make things look a little bit more tuned on the hierarchy side even without saying anything more concrete about it makes this kind of picture possible but that's all that's all philosophy let's now stop talking about the philosophy this picture also made a quite concrete prediction for the Higgs mass okay and I'll draw draw draw the plot um but here's 110 GeV remember things get heavier logarithmic lee with where the stops are and so and so this is really just by solving the our GES so there'd be a 10 to the 4 GeV for the scalars now 10 to the 6 GV 10 to the 8 TV and so depending on whether the quartet coupling and the ultraviolet starts at G squared which is large tan beta or or for tan beta of order 1 it starts at a smaller value you can go all the way to 10 beta equals 1 which is a which is a somewhat tuned you get a picture like something like so the higgs mass has got to lie in this kind of window and now if we put an upper bound we don't want the scalars to be just from the theoretical considerations more than this loop factor a factor of a hundred or a thousand so we're talking about scalars maybe around a thousand TV okay so anyway so if we sort of put a cut around here you get a rough range for the Higgs mass which turned out to be between 135 GeV and 120 GV okay now so that was a again very long before the LHC these we could make these arguments so of course 125 is perfectly fine 125 is is in that range and that's also echoing what I told you before that yesterday even just by looking at the one loop blog but just to get the quartic big enough the stop should be somewhere between ten and a thousand T V okay sorry it doesn't matter for this argument the the the new parameter for example sorry I should have said that of course this picture he also solves the MU problem because the the tuning of mu could be the thing that's tuning the Higgs okay so the Higgs is tuned now once you admit that the Higgs is soon you say well mu is U but it's an important point you see mu cannot be much larger than the overall scale the soft masses okay if it was then then there would be then the Higgs would not be around and all the arguments that we talked about about atoms and the absence of baryons would tell you that doesn't go so you have to have a you have to have a higgs scalar down around the weak scale and so the only way that can happen wherever the soft masses are is that mu has to be somewhere in the neighborhood of where the soft masses are in order to even be able to cancel mu squared against MH squared and other things to find a light scaler know that you're talking about the mass squared parameter in the Lagrangian I'm talking about the quartet coupling of the eggs but so this is a confusion if you're if you're if you don't work in the subject people talk about the higgs mass in two different ways there's the M squared the parameter and the Lagrangian then there's a quartet coupling okay the M squared parameter Lagrangian determines the valve which ultimately determines MW okay when we talk about the Higgs mass in this context are really meaning the ratio of the Higgs mass of the W mass which is controlled by the Higgs quartet coupling okay and so it's the Higgs Corte coupling again in natural Susy completely natural Susy the Higgs should have been lighter than 90 GeV it's 125 which is within shouting distance of the Z but uh but logarithmic ly removed from it and if you just estimate how big that log has got to be it tells you the scalars have got to be between 10 and 1000 TV okay now if you just use that argument to use the log to estimate where something should be it might sound ridiculous to use a log something so insensitive as a log to estimate where a particle might be but I invite you to remember the story of precision electroweak Corrections where the logarithmic sensitivity of the precision electric parameter so the Higgs mass were used to predict ahead of time that the Higgs had to be between 80 and you know 200 GeV okay so that log was was was in that case accurately used to predict despite the fact that people would make lots of fun of it ahead of time again as I said we don't really know why but whenever you get to do something concrete with numbers in it you should try because it tends to work better than it has any right to in this case if we extrapolate of course we can do fancier things of course we can do model building of course we can do lots of other things but if you just do the simplest possible thing the simplest possible reading of the situation is that the stops are between ten and a thousand TV and at this point I should say that there are some qualitative difference between the ten TV number and a thousand TV number when it comes to flavor physics because if you to say that the theory wasn't natural but the stops and the rest of the scores are still at ten TeV you're in better shape with flavor chain neutral currents but you solve some model building to do not as not as difficult as before but you solve a little bit of work to do if the scale is slide all the way up to a thousand TV everything is gone okay you don't have to so you don't have to do any special model building of any sort in order to not have seen flavor-changing neutral currents so far and there's some other important experimental differences but I'll get to that in a moment okay any other questions about this yeah any I mean that that's that that's the that's the amusing thing okay you don't have to work hard to the extent you have to work it's typically in the opposite direction but but just does give you one simple example just imagine you break supersymmetry in the hidden sector with no special care to isolate the scalars from them no sequestering no extra model building you just break supersymmetry in a hidden sector then precisely because you only need to break supersymmetry for for scalars to get a mass just garden-variety one of my entire dimension operators will give the scalars a mass but the gauge Eno's cannot get a mass cannot get a mass from that effect if the if the fields that break supersymmetry aren't pure singlets and so the leading effect for Gugino masses is anomaly mediation and is a loop factor down from where the gravity no and the scalars are okay so that's in fact there are two sets of papers on the anomaly mediation idea the Randall Sundaram paper and the paper by by the CERN group and and Ramlal syndrome has the has the more clever and ingenious idea of sequestering that the CERN group did not so the certain group had scalars at 30 T V RS didn't the sort of people RS is a much better idea okay but okay but it needs some some picture that you're here and they're there and there's a little bit of extra structure and so that's that's why I'm saying the spectrum is not the some original thing has come up many many times it's just that mostly people were ashamed of it because it seems to violate your notion of naturalness but given these much larger 10 to the 60 90 120 numbers floating around it might not be such a big deal all right now let me transition so ah I'll talk more about the experimental signatures associated with this but given that the main motivation here to have any particles at the week scale or near the week scale is that the lightest particle should be the dark matter let's now turn to asking where the dark matter should be in this picture okay and and actually before this picture let me just ask more generally where should whip speed and so now so if we've bought into the idea of wimps ah should M wimpy 10 GeV should it be 100 GeV should it be a thousand GeV okay and all of these things make huge differences ah you know at the level of precision of the WIMP miracle you can tolerate all of them but they obviously make huge differences to where they make huge differences to what you should be looking for experimentally and I think again the attitude of most people was at M Webster probably hundreds of GeV and so you know it would say it should be hundreds of GeV and accessible to the LHC all right now why should that be because the whip is the lightest particle in some sector that's solving the hierarchy problem all those particles can't be too far away from the weak scale right they have to be three 400 GV at heaviest so the lightest of all of them and better not be too much heavier than that so it had better be down in the hundreds of GeV range okay so the hundreds of gb and accessible to the LHC is completely correlated with a perfectly natural theory okay now now we have two surprises though seemingly two different surprises we have surprise one which is that we haven't seen nothing yet at LHC right nothing new yet at LHC that surprise one and surprise two is that we have not seen wimps in direct detection okay and I think what's not widely appreciated enough is that these are essentially the same surprise okay so in other words not seeing wimps indirect detection is very closely related to the little hierarchy problem itself okay in order to explain why you know everyone does these cartoons for the wit miracle and you do squiggles for the cross-section and you say yeah the math should be hundreds of GeV but let's let's ask the very simple and concrete question let's say that the W in wimp stands for literally the weak interactions not a buttload of other interactions that might be comparable literally the weak interactions okay so let's imagine that sort of simplest dumbest picture I use this word a lot I hope you don't think of it as pejorative mostly dumb is I I think it was something good okay dumb means that you're not being clever being clever is bad being clever is bad because because clever cleverness is a human thing ingenuity is a human thing if you say that an idea is clever you're damning it with the faintest of phrases what what you want is a deep idea not a clever idea so anyway when I say dumb this is actually good okay so the the Adamas idea is that that's that the dark matter is just some like you know it's an electric doublet or an electric triplet you know just something which a couples of the weak interactions and you know just so we don't have to worry about whether it's heavy or light it's a Fermi on okay these are extremely simple ideas for what it might be and they also have the advantage that there's no free parameters other than their Maps right so you can just compute perfectly compute what's the relic abundance is and you can calculate what maps they have to have for the relic abundance to be dark matter okay so probably many of you know the right answer if you have an electric doublet how heavy does it have to be to be dark matter one to evey one point two TV or something I'll remember the exact number if you have an electric triplet how heavy does it have to be to be the dark matter it's around three TV okay this is not the theorists trying to hide from the experiments you know this is just the dumbest simplest theory where it what's the particle to be is not at hundreds of GeV where it wants to be is that a TV or three TV okay it's a multi TV scale in fact is what completely boring natural simple wimps want to be alright so why was that not what everyone was talking about okay well what one reason is well if it's super symmetry in the we knows our bottom of the spectrum there the triplet of the bottom the spectrum there are three TV that's not a natural theory right if the bottom of the spectrum is a three TV obviously it's not it's not a natural theory even if I don't say anything about split Susie or anything else so that was one reason but there is a ah but there is a more but there is a more a very nice and more structural reason let me illustrate it again it's true in many theories let me illustrate in the context of Susie and the content of Susie the neutrally knows well we have the we know and the Higgs II knows and we have the B know okay now let's imagine there was no electric symmetry breaking okay so so that these were pure States they weren't all mixed up with each other then if the dark matter was one of these guys how much of it would you get well in order for it to be right the bottom of the spectrum would have to be it you know one TV or three TV so so it'd have to be very very heavy if you wanted the theory to be natural and have these guys a lot lighter you would get much much less dark matter from them okay what about these guys these guys hardly have any interactions at all so they're free that abundance which scales like one over the cross section would be humongous so if all these particles were in the hundreds of GeV range which is what you need from naturalness then these guys would give you way too little and these guys would give you way too much but fortunately precisely if they're there right around the weak scale because of naturalness after electroweak symmetry breaking you would expect electroweak symmetry breaking to be an order one perturbation to this mass spectrum and so the actual neutrally nodes would be a healthy admixture of we know B no Z no so you could go somewhere in between the two of them okay and that's good because that's that's that's the right number that we need so in order for the classic neutralino picture of supersymmetry to work it's crucial that the superpartner spectrum is significantly perturbed by lecture weak symmetry breaking which means the superpartners at least these ones have got to be right around the weak scale okay and now you see why there's a why there is a correlation between the have we seen wimps problem and the hierarchy problem because as you start saying to partners we've got to be heavier and heavier then the then the chance that electroweak symmetry breaking can significantly perturb the spectrum get smaller and smaller okay and then what happens is that you have to live with the pure state and if it is the pure States it has to be pure we know or pure Higgs Eno and that's a TeV doublet or a 3tv triplet the other possibility is there is another possibility which is that the the spectra themselves have some fine-tuning in them so you so it's not perfectly natural but the spectra themselves have some fine-tuning a minimum in ups such that even though the electroweak symmetry breaking contribution is small there is enough degeneracy so that it gives a big mixing effect okay so that that general phenomenon is what's called the well tempering phenomenon okay but from this point of view once you see that the theory is going to start the superpartners are delayed you haven't seen them yet then the only way you either get way too much or way too little a dark matter if these guys are in the hundreds of GeV range and so there's two possibilities so there's two qualitative pictures for dark matter one is that some mixture of the we know eggsy no vino something like that is still at hundreds of GeV but tuned to do so okay so that's this sort of well tempered picture and the other one is well we know at three TeV Higgs II know at one TeV okay there it's not tuned for dark matter okay not tuned for getting the right ralick abundance but of course the bottom of the spectrum is even heavier than before okay so once once you're not seeing the superpartners if you still want the fermions to be Dark Matter these are the kind of two pictures that you have to choose between and there's no good reason to choose one over the other I think they're the two qualitative possibilities this one looks a little more complicated because you're you're tuning more in order to make it happen but again maybe dark matter is important for environmental reasons and that tuning might be justified by some other criterion when we wrote our paper about the subject I think this was the aspect that interested me the most that if something like this was going on it would be yet another surprise because you would discover that in the dark matter sector itself you wouldn't see any scalars where the Dark Matter detector itself we see film or accident okay but if you just want to run the dark matter story is absolutely simply as possible yeah the bottom of the spectrum could be at one TV or a three TV okay so once again the expectation the dark matter was at hundreds of GeV crucially tied to the expectation of perfect naturalness and that's also what allowed the Dark Matter to have a kind of an order one-ish coupling to the Higgs that's very important because as you remember from Neal's talk there are kind of two natural ranges for the cross-section that a width could have of scattering off a scattering of nuclei there's a cross-section of order 10 to the minus thirty eight centimeter squared which is what just what you get from Z exchange and that was dead in the early 90s already from the first experiments at CDMS but it's but it's also theoretically rather trivial to get around a lot of theories don't have it okay but it's the Higgs exchange cross-section that's roughly at the level of 10 to the minus 44 centimeters squared that's what our current experiments are going after 10 to the minus 40 for 10 to the minus 45 centimeter squared and so the expectation that these that these neutrinos would show up in a big wayne direct detection was crucially reliant on on the idea that there was a lot of mixing between the different states okay now once we get rid once we get rid of the scalars and they get heavier in this framework you would still have you know decent big size couplings to the Higgs and so the well-tempered is getting more and more squeezed by direct detection but now let's talk about this the simplest picture for dark matter again the dumbest picture from day one completely invisible to direct detection okay through no fault of the theory no malice on our part no trying to run away from the experimentalist it's just what the theory does right because without any of the other particles around though none of these things have direct coupling to the Higgs okay let's imagine you have a pure Higgs ìno or a pure we know the leading okay so if we have anyone of it doesn't matter the leading interactions with the standard model nuclei come from double W exchange diagrams like this those also diagrams which involve double use and a Higgs so this would be the dark matter this would be the standard model quarks let's say and there's even a malevolent interference cancellation between these two diagrams okay such that with 125 GeV Higgs it sort of canceled it down to 0.1 of what each term would have been otherwise okay and so the final cross-sections that you get I forget exactly but the final cross-sections are more like tremolo minus 46 centimeters squared for these series and that's it it's pretty close to the neutrino floor and if you're not going to see them in the direct detection experiment so so the simplest picture for whips predicted 30 years ago any time people would have done this calculation wimps at a TeV or 3 TV that were invisible to any of the direct detection experiments that we've done sits right ok so let's summarize where we are then and let me also say that in this kind of picture in this kind of picture uh what are we looking for experimentally with the split Susie at the LHC we're not seeing the scalars but there's a chance that you could see the fermions because again the fermions have to be in the neighborhood of the TV scale for dark matter okay but in this sort of picture of the we know cigs iNOS be knows were one hundreds of GeV while maybe the gluey nose again colored particles get a little heavier so maybe the glowy nose are at a few TeV and in this kind of picture you would expect yeah you might make the gluey no at the LHC okay we can maybe make lumia nose up to two and a half three TeV ultimately pushing it at the LHC we have access to electroweak states maybe up to four 500 PV although if we're doing sort of direct production like this can be a little quite a bit harder to see but anyway this was a case where you so might expect to see particles at the LHC what about this you know at the bottom of the spectrum is at three TeV at the gluey now is still three four or five times heavier does not just forget it right so this kind of picture is LHC acceptable this is LHC inaccessible and again these were not things that were said after the fact they're said very clearly because they're trivial and obvious they're said before hit by the way um one of the nice things about potentially having 100 TV collider is that the simplest dumbest theories of dark matter are in even 3tv we knows or one TV Higgs Eidos are are possible to produce and see if you will really want to cover some of the that the case of the exam is a little harder so some more work will have to be done but pretty close to covering the entire parameter space of a sort of obvious dumbest pictures for what dark matter could be in other words if you wanted to probe dark matter now that we know that what the WIPP miracle or or good wimps could mean something that's multi TV quite naturally what you need is something that's in electroweak factory a multi TV electroweak Factory the Higgs of the LHC is a multi TV colored particle Factory and a few hundred GeV Electric Factory and 100 TV colliders just shoves everything up by a factor of ten from there so hundred TV Collider could produce 20 TVs colored particles ah but would be able to produce one to three TV electroweak states with high enough rates to be able to see them experimentally okay Oh finally I want to make an important comments about this is that there is one thing that you could hope that you could see this is an indirect detection because there's a sizable annihilation cross-section for these guys in the center of the galaxy the gamma gamma - a photons and in fact if you take the simplest NFW profile if you just take we knows and nothing else if you say there 100% of dark matter this was actually already excluded by half okay so now this relies a lot on some on some astrophysics that maybe it's not quite the end of building profiles it's a little bit of coring maybe accion's are half the Dark Matter which is perfectly reasonable from this kind of picture right accion's are half the Dark Matter this is half the dark matter in which case the rates go down by a factor of four and things fine again the Higgs inos are totally fine but in any case a possible probe of these states are continuing to look at the center of the galaxy and our chart the future our Cherenkov telescopes are going to be a very useful ok but ok it's still possible that we could produce a the gluey nose of this model at the LHC so I just want to tell you the two salient predictions and how does the gluey no decay if we produce it now this is the this is the lovely thing if you just take the effective Lagrangian for gluey nose we know is v knows maybe Higgs e knows it's a very simple fact that there is no marginal couplings you can write down between any of these guys so all the leading interactions are higher dimensional they're all dimension six operators and that means that the glue Ino is stable in first approximation and only decays because of the presence of heavier state okay so for example I could draw I could draw a tree diagram with like a stop here I make a stop because it's plausibly the lightest of all the scale is this stop now is that a hundred or a thousand TeV okay ah but a go to a stop a top I could have a B no this is my favorite decay chain because it's I think what happens in the most simple version of these ideas even though I don't have time to explain it so that's how one gluey no decays alright and that's it that's a pretty spectacular decay and you have this on on both sides right your pair producing the gluey no so you have this on both sides so you get the Higgs will go to be B bar so you'll get eight B's and four W's in every event okay the standard bottle background for this is known as zero there's one more one more qualitative thing the most interesting qualitative thing about this decay is the following is that the stop is heavy okay and so the gluey no lifetime is going to be parametrically long and if the stop if the glue Eno's at around two TeV and the stop is at around 500 TeV then the Blooey no decays with a noticeable displacement of around a millimeter or so from maybe a few hundred microns from the abeam pipe if the stops are at 100 T V we might not see the displacement but it's possible also to see displacement okay so I bring this up not only because it's the it's the sort of smoking gun signal for this model but also to just remind us that we have this picture that we haven't seen anything at the LHC any even convincing you know two and a half three signal anomalies and if you have the sort of conventional picture that if you're going to see an anomaly it has to start small and grow and grow and grow you can do this back of the envelope estimate I'm sure you've all done that if you don't see roughly speaking if you don't see two sigma X s now you're not going to see a five Sigma X s after you get ten times more data okay but this is the kind of signal where it doesn't look like that right you just have to just has to happen once or twice and it's so spectacular that that it's not a question of accumulating lots and lots of lots and lots of data to be able to beat down via background so you only need an order one number of events for discovery okay so that's the main LHC signal you could also imagine producing these guys directly of the electroweak guys directly but I want to move on to the to the main non LHC signal yes sorry on top and a beam oh sorry that's a beam oh okay okay so the other signal our electric dipole moments and remember a one loop electric dipole moments were a problem with low energy supersymmetry the CP phases have to be small by about a factor of 100 or so however in split this is the main contribution to an EDM that you get is through is through a two loop diagram we draw it a little draw a little schematically but what's going on here that's the Higgs what's going on in here is let's say you have a we know an egg Zeno and okay if I if I really finish it there's a big Z no optics you know down hyper-charged and then I even quick another Higgs there too it's bad okay and this gives you a so it's a tulip effect so whereas before things were 100 times too big now we're down by another loop factor and so they're in the neighborhood of the experimental limit okay so of course you should look and slightly more detail and so this is a plot for the EDM as a function of the mass of the lightest car Gino and in GeV so this is a kind of the 2/10 of the three and I'll draw so this is the this is the EDM the ten to the minus twenty nine centimeters be centimeters ten to the minus twenty eight centimeters in ten to the minus 27 centimeters and the plot looks something like this and up here it's when the second charge Ino over the first charge Ino the mass wedding is around one and a half and here it's when the mass wedding is bigger it's around four which suppresses the EDM okay so now in ancient times the well not in ancient times actually before the latest round of experiments but after many many years of amazing experiments by Gene Cummins and his group the limit on the electron EDM was around ten to the minus twenty seventy centimeters okay so so we were not particularly close to that but there was an amazing experiment being done by Gerry Gabriele's John Doyle and Dave DeMille that just in the last little while really took the first big leap in our in in limiting the EDM in a long time by about an order of magnitudes now down at ten to the minus twenty eight centimeters and they promised us another order of magnitude maybe more okay so so even this is now okay we're still fine with ten to minus but it's starting to get interesting very very interesting if they get down to a ton of the -29 of course there are some assumptions going here that there is a Mac that there's a big CP violating phase that's one important assumption the other important assumption unfortunately is that it's important that the Higgs inos are like okay you see if I make these things II knows heavier to then this effect is even further suppressed okay so and I didn't spend much time talking about the structure of the model but the but the Higgs II knows you know from the top-down point of view they could be they could be down where the genomes are they could up be up where the scalars are doesn't make all that much of a difference from the structure of the model perhaps a little simpler if you have them all up all the things that aren't protected by our symmetry up together with the scalars and in that case so on the dead dead absolute simplest case the most minimal case case where the Higgs inos are are up also at hundreds of TV then de is around 10 to the minus 31 centimeters each centimeters so it would still be too small to these experiments this is okay any questions so um so again completing the story we started with we started with gut and unification and everything going great and proton decay but there was a hierarchy problem you solve the hierarchy problem now things are going again you have a perfect gauge coupling unification Dark Matter niggling problems huge worry about the CC and now we're just taking another small rotation right we're not throwing everything out we're not ripping everything up and starting all over again which maybe we should be and I'll spend a few minutes talking about that okay but if you don't want to do that if you don't want to think that all the hints were garbage or even most of the hints were garbage um this is the only picture of the world that I know where every hint from the last 30 years met something okay they all meant something and they all have a role to play in the in the final story now as I've said a number of times already we don't need to have a landscape or anthropic soar anything like that to talk about this picture it's just that it would look loony in the conventional worldview and in the caricature of the world provided by anthropic s-- it might not be loony of course it's such a caricature we understand it so poorly that it's not it's not clear how important it is how loony or not it looks but you know gives us a picture for how things might work and I want to spend a few minutes before wrapping up today I want to just want to spend a few minutes making some more general remarks and giving you some more pictures for what the landscape might look like that that could make some or other aspects of these problems the easier or harder something that always comes up in these discussions is look if you're going to say that cause Marvel constant is fine-tune the Higgs mass is a is a fine-tuned come on there's so many other things in the standard model that we don't understand which will obviously not be solved anthropic Lee for example the value of vub or VCD right nothing in the world cares about no no property of the long-distance world cares about the value of the you be or BCB so why are there three generations I could have four I could have to make not too much difference actually anyway one might be problematic slightly but anyway or theta QCD perfect right that's the perfect example who the hell cares if theta Q C V was order one okay the neutron would have a big EDM that no one would notice unless they're you know experimentalists in the 20th century doing detailed experiments has no impact on the long-distance world whatsoever the lifetime of the proton people talk about this one a lifetime of the proton did not have to be remotely as long as it is right in order to be perfectly fine with anthropic so obviously you don't want the proton lifetime to be of order you know it has to be at least the age of the universe it has to be quite a bit longer than that in order for the protons decaying in your body every now and then not to not to boil you up but there's a long way or does it magnitude between that limit and 10 to the 34 years so so you say all those things obviously there are other things that are not in tropic well so what no one says that everything has got to be one way or everything has got to be another it's perfectly possible that some things are selected for anthropic ly and some things are not so that's that that does not bother me at all there's a there's a bigger question there's a kind of a grander question of how we're supposed to make decisions about how likely it is or not once you grant that there is a landscape how likely is it not that we find this vacuum or that vacuum and there's there's the largest version of this problem which is to figure out if you believe in this picture if you think this do you take this picture seriously that all these back you are populated somewhere out there that you somehow have to put a measure on this space right and once you start trying to put a measure on the space you run into an enormous number of conceptual problems you might say well it's the region of the universe with the biggest volume which should be the most likely just to give you an example but how do you decide what spatial surface to draw to decide how you measure the volume okay and whenever you get confused in physics you normally say well okay let me just there's an actual finite problem I can do some actual calculation if we're talking about probabilities for example probabilities are completely meaningful things when you're a frequentist you do the experiment over and over it over again you get an answer right well we're not in that situation here okay so that's already something which is puzzling there's the pre question even of how we're supposed to apply quantum mechanics to the entire universe there's another pre question that's sitting underneath all of this but if you put all those things aside you try to be more pragmatic and invent some kind of measure you run into the difficulty that we have genuine infinities in this problem okay the universe and this eternally inflating sense becomes truly infinite every you know kind of vacuum is populate an infinite number of times and so you have to figure out how to deal with questions like if you want to think of it like this what fraction of integers are even you might say a hat but if you group them as two four three six eight five okay well that now it looks like 2/3 right whenever you have truly infinite things to deal with you have great ambiguities in how you make sense of probabilities so this question of a measure is the is the is the sort of largest conceptual difficulty in this business it's not even obvious we should be talking about a measure it's not obvious how to think of one even if you ignore all these deeper you know huge important questions about about how it makes sense to apply quantum mechanics to the entire universe or how we should go about thinking about even pragmatically it's just the fact that that incredibly committed wonderful people have spent ten years of your life working on this problem from my point of view with essentially nothing to show for it okay so it's obviously a very hard problem or the wrong problem so but I want to remind you that this is just for a second step to try to justify to yourself why you ended up in this vacuum or that vacuum having the landscape to begin with made it possible just made it possible for a underlying theory with no crazy mechanism in it to make something like we see around us actually possible so that's that's not the that's not a subject of philosophy or debate another thing that I want to emphasize is that there's a lot of discussion of how it's all philosophy and crap those are useless discussions the more important discussions are that it's very suspicious to talk about regions in the universe that we can't see behind our horizon that's where all that's all these other vac you are right and because our universe is accelerating we're not going to see the other vacuum either right so if they're there they're there on our minds eye of the theorist doing the calculation but light from them will never make it to us so we should be suspicious deeply suspicious of invoking regions of space-time that we can't even in principle see in order to sort of explain some feature of the world we see here and I think when I brought this up yesterday I said quickly and I'll say quickly again that's actually a research problem in principle we're very far from really being able to answer it but it's not obvious that when there are regions behind horizon you shouldn't talk about them in more practical calculations for example when we do the calculation of density perturbations in inflation those perturbations exit the cosmology horizon during inflation and they come back in long long later right so obviously if you're just a dumb guy you're doing the calculation they go out of the horizon if you freak out though they're outside the horizon and stop and say no no I'm scared I don't want to talk about it would be a dumb thing to do right yeah they go out they eventually come back in you see them right we're not supposed to be scared as theorists we're supposed to do it first right it's easier to ask for forgiveness than for permission and so there are so that's that's that's that's a case now you could complain in that case that well the reason it was legitimate to talk about is it eventually came back into the horizon okay good I'm not saying I have an answer to this question I'm saying it's not obvious either way that and it's an actual science problem okay so it's possible that someone might make progress on that science problem that's the sort of biggest that's the biggest conceptual obstacle and the most exciting theoretical problems in this in this business I think is trying to make sense of that of that picture I think we're so far away from making sense of it that it's not funny but it is though it's a almost well posed problem however I want to stress that there's an aspect of this story that is not philosophy which is that in principle it could be very hard because the particles might be very heavy but in principle you could make like let's say my toy landscape model was correct okay in principle you could make those 500 scalars you could just produce them in an accelerator okay you could produce them in is confirmed that they're they're confirmed they have a potential that looks like that and therefore confirm that there's two to the five hundred other states okay you could even in principle make little bubbles of the other vacuums right you know we can make little domain walls it could be very very hard but you you make enough coherence collisions of particles you bring them together you can even make some of the other vacuum a little bubble of the other vacuum and then another one another one you could shoot a particle inside and say hey the Higgs mass here is bigger than it was outside and it comes back and it tells you right so the fact that there could be but zillions of different possible vacuole whose parameters inside vary that is something that's in principle confirmable by experiments in our universe okay it's very difficult only because we imagine these particles are very heavy but it's not something that's in principle prohibited by some complications with horizons and cosmology and all the rest of it so while it's true that if we saw that it would be very striking it would we at least know that we're not alone we cannot possibly be unique there's billions of other metastable States we would know that we would still be left with the question of how its populated cosmologically and all the rest of it but I think it would be pretty powerful indication that that a picture like this has some some role to play in in understanding fundamental physics I think it's actually an interesting area of phenomenology to think about probing landscapes caylor's you know we if you think that anything like this is right there should be hundreds of extra scalars in our four-dimensional effective theory okay so and and it's interesting to look for what the signal is not oh just one or two singlets are but of hundreds of them okay because there can be qualitative differences when there are such large numbers the number of possible decay chains you can get can start getting exponentially long or exponentially many there's a lot of interesting things to do you might imagine that some of this part of the landscape is dragged down to the weak scale for various reasons related to tuning down the Higgs in which case we could be looking for 50 or 100 scalars mixing with the Higgs and the phenomenology of one or two singlets mixing what the Higgs has been studied to death but as I said lots of qualitatively new things happen when you have 50 or 100 of them so but anyway so I but that's it that's that's a very specific particular comment but more generally it is possible that we can that we can see some of these other sectors ah that we can see in principles possible that we can see that there is indeed a huge landscape of evacuee what I also wanted to say that it's possible if we knew a little bit more concretely about what this landscape the vacuole looks like that our picture for what can vary what can't vary and even what has to be explained with measures and what doesn't might change it's possible I'm not saying this is what the actual landscape looks like if there is one but it's possible that the landscape could have property such that the notion of a measure is irrelevant essentially irrelevant to some of these problems so let me give you just just the caricature imagine that there's two parts of the landscape and this is in fact the sort of simplest way in which the cause module constant and the hierarchy problems could be correlated with each other imagine you have two regions of landscape in this region you have Susie you have Susie at a TV perfect okay if you're a particle business along you say that's obviously where I live right solve our everything in natural everything is great but you count it you count than you count and you find it that there are 10 to the 40 vacua here so despite the fact that just with your particle business hat you say that's obviously where I live ah there just aren't enough vacuo to solve to find a small enough cosmological constant it's ten to one hundred and twenty that you need so you would love to live there but this big pressure of finding a non empty universe says that you cannot be there okay so this makes slightly more concrete this vague idea that whatever solves the ceci it's such a bigger problem it'll drag the hierarchy problem around with it well here's a here's a picture because there could be another region here out here let's say the Suzi breaking scale is 10 to the 6 TV just making up numbers but you count on you counting calcium you find 10 to 150 vacu appear okay well great despite the fact that you have to fine tune for electroweak symmetry breaking you're forced to be here you're forced to be here because only here can you solve the hierarchy problem okay and uh this would be sorry only here can you solve the cosmological constant problem only here can you find a non empty universe right so this is a concrete example of how if the numbers turn out to not all be gargantuan like ten of the thousand but if they're all the sort of neighborhood of these ten to the hundred twenties that we're talking about it's possible that just the rough neighborhood that we end up is just selected just by finding one vacuum that has things that look like our world or you know not exactly one but by the class of them that that that that for example allow a non-empty universe okay so if something if the if the landscape looks something like this then we'd still need measures for even more detailed questions but we'd be very happy to say yeah of course the Susy breaking scale is going to be a ten of the 60d and whatever other patterns might come along with that would be forced on us alright so I'm out of time but let me then just close with a couple of comments I've set it up set it already a couple of times but one of the things that I actually like about the picture of the landscape is it has a certain degree of conservatism to it you are taking ingredients that are there normal ingredients scalars nothing nothing fancy in the toy model that I talked about just for being concrete even more things came along for the ride like in that landscape the only things that varied even significantly with the Higgs maps and the cosmological constant so that was tailor-made to make you is non unhappy as possible yes not unhappy as possible the actual string theory landscape well the corners of the string theory landscape the people have studied a lot that sort of to be string theory landscape say in those corners it doesn't look the landscape doesn't look much much like that it looks rather different many other things very everything seems seems to vary that's all perfectly fine I'm not sure that's the even if you believe you believe in the string theory that's not the corner of the landscape that I would have imagined that we would find ourselves in in the standard model anyway again by the general philosophy that things shouldn't get too much worse things that seemed to work before we should keep going with and just rotates them slightly until we get to a better answers the old-fashioned picture of the perturbative heterotic string was spectacular it gave us gauge coupling unification ISM it incorporated a lot of the ideas about unification that worked found some interesting new mechanisms that solved all problems so if I have to guess myself any preserved gauge couple unification very very importantly ok if I had to guess myself where at some corner of the landscape that's in the neighborhood of those things and what the what the landscape looks like around there the string theory landscape nobody knows ok absolutely nobody knows what it looks like there there's hardly anything that's not remotely to the same degree of activity is with the Flex Bakula it's much harder to get your handle on what it looks like there so who knows as a model builder is a phenomenology I'm very happy to make hypothesis that all the distributions are a little bit narrow you know they're all like 10% narrow and in that picture the dimensionless constants wouldn't even vary very much but exactly the dimension full operators like the Higgs masculine cosmological constant could change by 10 percent in plot units and that's a humongous deal okay so it's not crazy if you just make that hypothesis of a little bit of narrowness in the distributions we could even just have the parameters that are the most troublesome ones very but but putting that aside what I like about this picture and and of course the fact that the only theory we've seen in you know 50 years has that has that amount of magic in it that are much larger than what the theorists studying it have seen is the string theory if anything was going to provide you with an exception to these pressures pushing through these directions you would have hoped that it was string theory would pull out some insane miracle out of at at which it might still do but but the fact that that that to the contrary it seems that string theory itself while being a unique theory has this feature of producing billions of possible long-distance world is and to me another sort of small addition to the arguments for taking the landscape seriously if we didn't have Weinberg in the CC I would give a crap about what the string theorists we're giving we're finding with their landscape that say ok come back when you've matched the real world right and then then we'll talk but it's the fact that we've seen these separate strains of arguments going in the same direction that all all gives it more more credibility but putting all this inside what I like about this is approach is that we're not we're not doing clever model building or adding this mechanism or this or it's something that sort of comes out in a relatively simple way the cosmology which is the sort of most troubling and strange part also is what comes out of the most obvious way when you solve the equations but I really like about it though is that the question that it brings to the fore is ultimately this question of how we have to how we can apply cosmology the physics sorry having how we apply quantum mechanics to cosmology how we think about these these quantum cosmological questions and it's not like this is a new question this is a question that was there from the very beginning of people thinking about quantum mechanics and cosmology the second we had these two subjects the question was there so when people talked about having a theory of everything and predicting all the constant - doing all this stuff what was going on is that I think they must have had it a hope that that question the question of determining the structure of the standard model at low energies would factorize somehow from the question of understanding the cosmology in the big and now the accelerating universe and all that somehow the problems with just factorize and because those problems are so difficult and hard we have no idea how to get get going on them but it is true that the physics has a way of not letting to factorize important problems okay and so that's actually to me an attractive part of the subject even though it makes it much much harder to make a theoretical progress on momentarily is that you know we're not making up some things for some part of the problem while ignoring other things that were there all along anyway right in this pictures you really have to attack the big conceptual problems that were lying around at the same time as the more immediate ones that you thought would be relevant to thinking about particle physics my own personal view right now if certainly the landscape is the most plausible by far the most plausible explanation we have for the smallness of the cosmological constant the plausibility of its of these atomic principle type explanations or other things like that for the hierarchy problem are much less convincing to me but there's something to them they're not zero there ah and I think of a whole theoretical structure at least for myself as I've said a few times as a caricature it's not a theory it shouldn't it's kind of a fantasy perhaps for how some things might work if we understand a lot of other things later but it's definitely not a theory yet and so I started my lecture yesterday that by saying if you put a gun to my head in the middle of the night and asked what what do I think why haven't you seen Susie or wimped the what I told you the the picture of the world that I've told you in these two lectures is what I would say hopefully more briefly because they might get impatient and fire the gun but um but and it's largely because of what I said that it's it's the only picture of the world that I know there everything has everything we learned experimental in last 30 years and theoretically have some has some role to play in it my confidence that it is not so super-high and I definitely think it's worth thinking about completely radically different things and the disadvantage to the trajectory of going with what worked and then changing a little and then changing a little and changing a little is that you might just be in the basin of attraction of the wrong idea from the start and then you'll just stay there forever so I told you I was going to factor of 2 more slowly I'm actually going to factor of 3 more slowly than I had intended to these lectures but perhaps perhaps next week either formally or informally before my final lecture about future accelerators which I definitely want to give I could also tell you Nate told you some of the things that that he was thinking about but we could also speak informally about some some crazy ideas for what might be going on and I'm very happy to share all my crazy ideas with you and some of them are some of them are reasonable some of them are really loony but anyway we can have a lot of fun discussing them all right thanks a lot

Channel: Institute for Advanced Study

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Id: mRMF4b0GcCw

Length: 97min 36sec (5856 seconds)

Published: Fri Jul 21 2017