New Searches for Dark Matter and Dark Sectors I - Rouven Essig

so thank you very much for that traduction hmm so before I begin I want to get to know my audience a little bit who is a post stockholder okay who is a grad student who isn't the best time of their life you know you about to you really have a job going into the next semester whew you okay so who is a who is going to fly this here it's a good distribution okay and then younger I guess their one else is probably hands I get an idea okay so most of you actually younger okay good okay so very good so the topics I'm going to cover our new searches for document and dark sectors and I'll explain a little bit more whether it is but the topics for the three lectures are I'll begin with the introduction your Y sub G be dark sectors then we'll talk about exhilarate based searches for dark photons I'll introduce a very simple dark sector which is a very good some sort of a nice 20 models and then we'll also consider Dark Matter that's light and can be produced at accelerator accelerators colliders beam dump experiments and things like that and then I'll talk about our detection of subsidy document there's a lot of work in this direction over the last few years and then I'll end with sort of a the next decade where could we hope what could we hope to learn in the next decade what kind of experiments might come online over the next decade and what kind of models are these experiments probing going often so a doc sector is I'll define it a bit later in more precisely but a dark sectors basically collection of particles that is neutral under the standard model forces so it doesn't interact with any of the standard model forces instead of interact with some new forces and to make it interesting we often imagine that these the sector does have some interaction with the standard model sector so it's not completely decoupled that that is of course something that that is a possibility but it is something we to make it more exciting you know there's many reasons to think that it might actually be coupled to us and then the question is how do we look for that and where should we look for that so when I was preparing these lectures I was thinking back to when I was a student nine years ago I wasn't this great time way I really had a job I was going to go to slack in 2008 and it was some before and you know thinking back it was a really exciting time the LHC was about to turn on with all its promise and in the year in 2000 a few years later after that but it was you know on the rise and people were preparing further very exciting people were reporting very interesting results from indirect detection experiments the pamela satellites so an axis of cosmic ray positrons at energies above 10 GeV and that was super exciting because there might be a signal Dark Matter dark and annihilating - you know charged particles that give you this axis of cosmic rays and the cool thing was that it was not some standard thing it wasn't like a normal wimp it couldn't be a normal one but had to be something more interesting the Fermi gamma-ray Space Telescope was about to you know was was just launched and in June 2008 actually and that was going to revolutionize potentially our search for document are looking for indirect detection signals in addition there were tons of detection experiments that were taking data some of them had reported the nominees for a long long time so I'm sure that we have heard about Sudama who has not heard about gamma okay so dama he's an animal relation sigma and modulation of the signal in the detector and they reported evidence for dark matter since 1997 and you know at that time things were sort of really coming together there was a lot of data coming it was a really exciting time and I bring this up for two reasons so I think now things are a bit different I don't think that the next decade is going to have as much data coming as you know that that is that we think is going to reduce things where we're sure going to revolutionize things as it were maybe nine years ago I think you know the NSC turning on there was super exciting and your sir of course might be great surprises coming from the Latino that is he's only collected a tiny fraction with data but I think the next decade there's a question my way things you know where we going to see the new breakthrough and it's not clear as it was perhaps as we thought it was you know nine years ago when I was starting my postdoc the document anomalies that were exciting at the time they've largely disappeared I think you know they did most people don't take them seriously anymore as as evidence for dark matter and you know there's question about well should we be looking the second reason that I want to set up bring this up is you know around that time the idea of dark side has really started emerging especially below the GV scale now the idea of dark sega's was around well before that people talked about your mirror dark matter hidden hidden valleys before that no Strasser and Zurich and burn talked about MeV scale dark matter several years before that and fire as well but you know in 2008 with these anomalies it was really exciting because it really sort of gave us an idea that there might be this new GV scale sector that we could look for and that was started with work by nima Neel Doug and Tracy and then also Maxine pastor loves Adam Duritz and because of a lotion and it was a really exciting time the code we just realized that they could all be the stuff sitting at the GV scale below and we didn't even wouldn't even know about it and we need a new experiments to find out what it is and then the way if it's there so I think you have since then there's been a lot of development in the field a lot of searches for these subjects sectors there's a lot more searches that can be done and that people are planning at future colliders and I'll talk a little about this and I think also you're things have progressed so another topic that's sort of emerging over the last few years is the idea of subtly dark matter so not just that there's some mediators at the light scale but also that dark matter itself could be below the GeV scale and that that is actually a very good place to look for dark matter no guarantees of finding anything but it's a good place to look for it and the question is you know well one one thing you might ask is am i confident now as it was passed in 2008 that we're going to find new physics beyond the standard model in the next few years and I don't think I am right now but I'm still very excited because the searches that are being proposed the experiment that are being done they are really probing new space and stuff could just be it could be an amazing explosion of new particles and and and new new advances of finding new physics so I'm still very excited I'm super excited by all these searches and it's really a topic that has been you ever say growing in the last few years and building up and there's a lot of theory work and now let's be followed up with real experiments so new experiments look for this so I'll tell you about stuff that is coming up the next few years and in the next few lectures and - for review so we just put out the community put out a report a white paper on what kind of research this could be done looking for light dark matter beyond wimp dark matter and that review is called the cosmic rhythms workshop it's white paper and you can look at it here and the other reviews so there was a workshop last year where there was also summary afterwards which was the dark suckers workshop so that's 1608 zero eight six three two and an older one 13 11 point zero zero to nine this was written for Snowmass effort and as you can see there's a lot of white I'm giving reference for white papers the hope is that you know the funding agencies will take these white papers and actually turn them into real funding for these experiments and then you know there's real advances but there's a lot of ideas from the community that are being summarized so this paper also contains topics that should appear ground will cover so I also like dark matter and then I'll focus on on only part of that only part of that what's in that report so the existence of dark matter is perhaps you know I think the best motivation to consider a dark sector it's 25% of the dark of the energy and universe is roughly dark matter fibers in invisible and 70% is some dark energy and the fact that there is dark meta that you know we haven't seen interact with other labs Oh at least at least with large interactions that suggested that maybe it is in a dark sector maybe it has some tiny interactions but we to explain why these tiny interactions or not there a simple explanation is that the document is just not charged directly understand the model forces so I think the list of a dark sector is something that is motivated by the existence of dark matter and then we can ask all kinds of questions about how it might interact okay so so what I want to do to begin is I want to quickly give a brief review of the dark on a landscape and last week you heard a little bit about sort of a big picture overview but I think it's good to just begin again what's that so we have a mass axis we ask Waker dark and Ally this will scale 10 - -20 - Evi roughly that is the lower bound on dark matter if you ask with the de Broglie wavelength of dark matter with a mass with that mass and you ask what is fit into a dwarf galaxy that's the lower bound of the mass that it could have so if you make the mass lighter the de Broglie wavelength of darkman and dwarf fairies will be larger and you couldn't form structure on that scale so basically bosonic dark matter who wanted to be or any dark matter we wanted to be above the scale there's a bound for fermions which is about a few hundred Evy 100 of E in that scale you can ask the same question take a dwarf galaxy and you want to put in Fermi are now in the dwarf galaxy and you want to pack them all in because of the power of the exclusion principle there's only so much you can pack in and it turns out that you have at around 100 ev1 kV or so that's the lower bound on semiotic dark matter so everything below or that's underneath kV or so below that is the sonic that Dark Matter could be an axon to take the QC accion it could be pseudoscalar it could be a vector boson and that's the stuff that Peter is going to talk about much more detail by how to look for that okay then we can ask there's another scale roughly ka v up 200 te v so in this scale would be thermal dark matter so if you have dark matter that is in thermal contact with Stata model in the early universe so at very early you know and very early universe the universe was hot the dark matter is past annihilating the standard model particles and vice-versa that's how freeze art works if you put the if you ask what is the mass what's the lowest possible mass of dark matter it turns out that's about a kv so the reason is that as you make the mass lighter it takes longer for that particle to become non relativistic and structure forms differently do you know I mean structure in order to form structure in order to make clumps dark matter the particle of course needs to be nonrelativistic so it takes longer to make the dark matter for the doctor to become nonrelativistic and it turns out that if you want to form dwarf galaxies again so again this is first time we hear about dwarf galaxies so this is what the bound would need to be kV now if it is really in thermal contact then so for example the cup of the electromagnetic charge so a couple scales of electron positrons or photons and then it can also mess up BBN in particular all the ineffective measurement the number of roads with degrees of freedom of it in the universe so we know that's roughly three from neutrinos and if you've got dark matter that's interacting with electromagnetic charge particles and it's in thermal equilibrium at the time that neutrinos decouple you affect the temperature or the photon boss and you heat it up and you mess up how that relationship occurs in the standard model we would be free and will be different and that's roughly put the bound of an MeV so what I'm going to do we can make this part a little bit dotted so you might imagine there's some exceptions to this but in principle law and MeV you have to worry about bounds from an effective in BBN so if you really want to have in thermal contact then it should probably be above an enemy the upper bound 100 T V comes from unitarity so if you make the dark matter too heavy the cross section will be too small from unitarity considerations and you just can't defeat enough of the Dark Matter in order to satisfy the relic abundance and then you get get you produce too much dark matter if it's in thermal contact and it has enough above 100 TV and it's left to rough up the bounds again there's exceptions but this is a rough you know a good good picture okay you can of course go higher so once you go about the tank scale your things you can consider composite dark matter if you go much much higher like 30 solar masses or so then you might imagine that you've got primordial black holes which could explain the LIGO signal that's very exciting a lot of work on that but we're not going to consider that here today for in these lectures so good now the traditional wimp sits around here few gv2 you know TV or tender TV depending on what you want to consider a wimp and what we want to focus on is below that scale what a road doesn't make sense it's a few gv2 TV and what we're going to do is consider things below the scale so below the GeV scale and so I'll talk about things roughly down to Millie evey but most of my focus will be mega Eevee up to GeV okay okay any questions so far okay so last week you heard about a tons of particular you know tons of different models that could sit tons of different documented candidates across all this whole space stay on the tree nodes you know are a great candidate sure was discussed you know sitting around the KD scale that's a burgeoning dark on a candidate you'll hear about the lot of stuff as I said from other people but let's talk about wimps for a second and then we'll move on to the next thing okay so despite the fact that I'm talking about searches for document of beyond rooms so not worms I want to just you know make sure there's no confusion I do you think that wimps are great candidates and that people should be looking for them I just think that the exponential program for them is well-established it needs to be completed there's huge experiments the jeat so-called g2 generation two experiments superseded mass and algae that are going after that those are very important experiments then HC has done amazing work you're looking for wimps possibly there could be producer colliders there will be much more of that coming and Fermi has food on prefer me and others other satellites parents as well and look for indirect detection signals so I think that's all great stuff and once are great and once a great for a reason main you put two things because of the wimp so-called with miracle which is the statement that a particle that has interaction with the center more the weak force which and the mass of order the weak scale hundred GB recipe can give you automatic the right relic abundance if it's in thermal equilibrium would have done a model in the early universe just some thermal freeze out so I think that's a super exciting the observation where there's anything do with nature whether it's how document is produced we don't know but I think that does certainly an interesting observation and of course the second reason is that we think that there should be new physics near the weak scale anyway because of the hierarchy problem so the fact that a particle at that scale that might add that if it's such a particle stable and if it has interaction of the weak force could be the Dark Matter candidate it's very suggested that these things might have the same solution now winds so I think this does motivate once there's a ton of searches for wimps and very quickly because when you'll get this but you've got the dark matter and I understand D'Amato particles depending on how you rotate this diagram there's various searches that you get annihilation annihilation with indirect detection going from left to right you can have scattering darkness scattering of nuclei for example or of new things that I'll talk about in the third lecture which can give you direct detection signals an underground detectives and of course going from right to left you can produce this at the collider and as I said there's a big important program going on for that so even though they're important I think it's good to think beyond the web and there's several reasons to do that we have not seen them we've not seen any convincing evidence for wimps I think we had ample opportunity to do that so Fermi has done as an example Fermi has done an amazing job and it's just favored dark matter particles that are that ability of wimps would annihilate to standard model particles and is to favor them up 200 GB or so in various channels and and as a legal disclaimer I'm going to put yet the other reason is that the NHC has no has not seen any new physics yet so anything that might solve the hierarchy problem and wizards come along and with it that you might get a dark on a kind of coming along with it that has not materialized either and again the legal disclaimer and the other thing is that your whims are produced in the early universe from thermal freeze out but there's a whole variety of different production mechanisms that exist for dark matter stock when I could produce from some initial asymmetry you know baryons the reason there's a barrier around abundance the reason we have baryons for Berens and anti burials is because of some initial asymmetry we don't get know how that arose in the early universe but there's no reason why the dark matter shouldn't arise from some similar initial asymmetry and given that it is reasonable you know - yeah that that's a totally fine production mechanism in fact nature's chosen that already initialized symmetry has chosen that production mechanism for the standard model particles baryons so several known what several possible I should say and last week I think you've heard about freeze in simps elders Willis etc so freeze out so more free does not the only possibility and then one thing that I think is very interesting and maybe not get enough attention from particle physicists yes there's a so-called small-scale crisis of lambda-cdm so we take n body simulation of dark matter and you see how structure forms it works really well on larger scales larger than galactic scales roughly you know tens of ten kilo Pascal are than tens of kiloparsecs but once you get to smaller scales things become a bit more description between the observations and n-body simulations and that might be because you know including darion is a complicated thing specially from first principles so you have to make some assumptions when you include baryonic effect and that might be a totally fine explanation so it might just be a wimp cold collision is dark matter particle that except you know works once include the baryon effect could explain all this but it might also be indicative of a new of non-trivial dark matter dynamics so it might be indicative of self induction in the dark sector so doctrine ourself into actions then they could explain some of these and in the discussion session maybe we can talk more about this but is the core business classes a problem missing satellites the too big to fail and then hmm a recent one is called the diversity of rotation curves okay we sort of that last one few of you who's not heard of it more okay so very very briefly we can also do this more in the discussion session if you look at the so you look at galactic rotation curves right you can measure the Stars the speed of the stars going around the center and spiral galaxies for example and you can just infer from that how much mass that has to be within that radius and let's take galaxies that have a common mass scale like a total mass so same similar mass galaxies so one measure of how much mass how massive they are is by looking at the velocity of the stars large radii so some circular velocity and if we take galaxies of similar size and roughly what we expect is that they look like this and this you would get from you know assuming you're called Dark Matter simulation that's what you get from dark metal simulations even when you include some very odd effects depending on how you do them and instead what you see is a whole different range diverse range of possibilities for how the stars behave as a function of radius so if you look at different galaxies sometimes you see data that looks like this sometimes it goes like this sometimes of course degrees but there's a whole different range even though at high radii it all seems to be the same and the prediction from just lambda-cdm would be the solid line so if you want to know more about this this is actually was pretty recently pointed out it's a very nice review or on SIEM self interacting dark matter to explain some of these issues by Toulon and you I'll even give you them well as you don't have it so 2017 so it's pretty recent but it's so summarizes all these various issues and how self and that can Dark Matter may or may not explain some of these things ok c'mon be use to explain to this so I think that thing claims to that effect but I don't know so I'm not extra enough to answer this properly yeah so I don't know ok let's see this is a better way of doing this anyway ok okay so as I said our focus will be GV down down to Milly V but mostly those down to mega Evie so big and Evie and here in that range we have generically we we don't call these wimps so we have our mass axis again we have the GV scale here so wimps are sitting above here and our focus will be below this and generically here that's our main focus but we will go down also to mini V and Peter will take over below that so in general there's different ways of defining things of course but we we can call this hidden sector dark matter or dark sector dark matter and below this screen call this so it continues we can call this ultra light dark matter so here our sweeper zonic ultralights mazanik and hidden sector dark matter can of course extend much much higher but in so below the GV scale we don't call them wimps okay at least not in these lecture series now you can ask the question why is the why can't you have a wimp below the GV scale and let's quickly review that so there's something called the Lee Weinberg bound for wimps and reviewing this will also be useful to show how we can have light dark matter so if we take a just a prototypical wimp so something that interacts with the Z boson we know this is you know yeah basically ruled out for various reasons but let's just imagine we have that I'm going to give you another reason why it's ruled out for very light dark matter so consider the dark matter mass less than the weak scale so we're getting want to go to the light scale so less the mass of the W or the Z boson and such dark then it can annihilate to standard model particles through the Z okay and we can write down the cross section so there's some write some lagrangian we have got some the G Fermi the the Fermi scale so one of a MW squared one of them v squared roughly with the right coupling constants and we've got Chi some gamma matrix Khaybar and F gamma F and the cross section knowledge cross section is going to scale as G Fermi squared times the mass of the Dark Matter over PI and this goes as the Pico bond times M KY / v GV roughly yeah good oh wait square okay now YP cabin water normalize it to that because that's the WIMP Merkel right so wimp the typical weekend dashing cross section is a pika bond and that gives me the right relic abundance or rusty a peak abundance is what I need to get the right relic abundance and that's go skating as a function of mass and what you can see is that as I lower the mass of the Dark Matter lo v GV the cross-section decreases and the abundance the document abundance is going to go as one over the cross section so the abundance increases so as the lower the dark kind of mass the cross-section is too small in order for the dot going to be too peed it away to be annihilated way and I'm going to have too much dark matter okay and that's the bound so we need the wimp to be above a few GeV now it's easy to evade this bound but we can't do it in the standard model we can't do it withstand a model forces one way to evade the bound is that we can introduce light mediators okay so let's do that and the way to do that well one simple way of doing that is that we just consider some effect of the prime model so they'd bound by introducing light mediator so the same annihilation of the above I'm just going to call it a different thing like a D Prime and it's gonna have some coupling which here some barbecue couplings G Chi psi barbecue couplings GF 2 micron and water fermions and this cross-section will and I'm going to consider a light Z prime mass and this cross-section will then scale differently so now you don't integrate out the Z and then get the G Fermi up like a day now you got a now it's going to be bit different so you've got a g chi-squared gf squared just each of these couplings squared in the cross-section there's going to be a mass of the Dark Matter squared above and then ma prime sorry M G prime to the fourth in the bottom and again we can normalize it to a Pico bond and put some numbers to this so g KY let's imagine it's 0.5 squared keifa gf imagine zero point zero one zero zero one squared there's a m chi squared so let's pick it 100 MV and then times by a GeV for example for the mediator okay so we're putting these numbers you get roughly a pika bond and this is totally fine okay so there's no problem with having 100 MeV Dark Matter particle for example and what we've done is just lower the Z boson to the mediator map so that's fine and I think this is interesting so you're even pretty small couplings these couplings are not huge right they're 10 to minus 3 for example this one this is pretty big but not that big either you can get the right relic abundance as long as you're willing to have like mediators and of course light mediators that's what you have in a dark sector okay so if you want to look for light dark matter which really talking about dark sectors now just to turn this argument around a little bit here we get the right relic abundance from thermo freeze-out what we have are couplings they're not that small right and we could imagine that this is something that I could Ida or a beam dump you know an electron positron Collider or a beam dump experiment could see or even very special experiments could see if you have the sensitivity to see light dark matter and if we ask about what kind of models they could be you know what what models are we not searching for with current techniques with the wind searches and which models should we be searching for the sub GV scale is a very interesting area because you can have you can get the right relic abundance from thermal freeze-out and other ways you can get the right relic abundance from the things that were mentioned last week like the simp and alder and Friesen in each of those cases there's some connection to the standard model between the Darkman in the standard model and you in some thermal contact in these various mechanisms and because in some thermal contact that means that the couplings can't be that small because otherwise you wouldn't be in thermal contact so the coupling viewing the document and then the standard model particles and since the copies are not that small you can hope to look for these and accelerators and an indirect detection experiments as long as you have the sensitivity right and as long as you're doing the right types of experiments and right types of searches and that's what I'll be talking about what kind of service could be done to look for this but sort of a general point the most your many discoverable models things that we could find that we could discover on thermal contact and the companies are not that small actually pretty sizable so it's important to sort of look for for these things I think and since the you know GB scale and up has been covered very well we should be going to litem asses to see if Dark Knight could be hiding there of course dark matter could be you know might have tiny interactions or no interaction with the standard model particles and then we're just out of luck but if we ask where else should we be looking this sub G B scale is a very very good area to look because you can have models with pretty sizable couplings if there's some kind of thermal contact which makes things very predictive and in the last lecture when I'll talk about so the next decade models and projections I'll talk a little about some of these models you really heard about but I'll just put them you know on a plot and see what the target is way in in the interaction strength do they need to lie to get the right relic abundance and what projections are there from prospective colliders and digest action experiments look for them and then just to make the point again I sort of said already but you know so we said the sub GB scale is a good place to look because the Babaji v there's a lot of experiments going on already subjugate is that if you want to be in somewhat contact the copies can't be that small so it seems like a very discoverable area so you should probe it and see if there's anything lying there but if you go to light right below an MeV and you want to have some more contact then of course there's a bound again from BBN that doesn't mean that there aren't models they that you should be looking for absolutely are but they it's more it's it's not there's not a clear target as such but for some of these models with thermal contact going down to an MeV scale from GV to MIT is a very useful thing very good thing to do okay so let's now talk about dark sectors and set up a simple model so again the dark sector is a collection of particles that are neutrons down the model forces and it's interaction with some new force so we have is some standard model sector and some dark sector the word Dark Sector hidden sector Hidden Valley they all mean the same thing Dark Matter could be part of this dark sector the standard model has the matter and the forces right all of this here the dark sector could be super simple or it could be arbitrarily complicated we have no idea okay and of course to make progress to start something you consider simple things and you build on that and you keep building on that if that is all that exists that's not the most exciting thing that's possible but if we want to ask what kind of models should we be looking for what kind of dark Sider should we be looking for then we need to be able to produce it in in the lab or look for it in some other way and so then typically people talk about portals so there's some portal between the darks activists and emotive sector some connection now again the possibilities for the different portals are immense in principle okay so you can write down all kinds of high dimensional operators you can write down you know all kinds of possible connections but we can simplify things a little bit to ask and ask the question if we had a dark sector which portals are the most important which one should we be looking for first okay and then dancer actually becomes much the you focus in on a much more narrow subset so which portals are most important so which portal is most important that depends on the mediator that does this connection between the standard model and dark sector so we can have various types of mediators you can have a scalar we can have a vector boson we can have a pseudo scalar we can have fermions connecting and each of these particles so depends on the spin and the parity of the mediator and you can ask in each case what is the lowest dimensional operator that we can write down and this is actually dictated by the standard model symmetries so you can't cut arbitrary the Steiner model symmetries dictate which portals you can write down so for example if we have a scalar then we can write down into action mu Phi plus lambda v squared times H - H where H is the Higgs of course and Phi is some new scalar some singlet and understand the model and this gives us the Higgs portal and the dimension of that portal is just four okay if we have a fermion so here scalar Phi term you on some n then I can write a nun operator that connects it to the fermion so there's some coupling Y sub n is my N and I can connect it to LH where L is the lepton fc2 wdsu.com doublet in the standard model and this is called a neutrino portal and also it has dimension for then I can write down take it back to boson including a prime you can write down into action epsilon over 2 cosine Peter W and I'm being careful with a normalization as you'll see a bit later and there's some interaction between the hyper-charged and the hidden u 1 so what I have is a u 1 gauge boson and that can mix with the hyper charge and this one mixing parameter Epsilon okay and Peter W is the Weinberg mixing angle just feel a week so that I will talk more about this so this will be our main focus the vector I'll say very briefly few words about this and of course the other portal I'm going to leave to Peter so that's the axiom portal so that accent portal is dimension 5 but let me just write down business writing this down so that's the vector portal and also it's dimension 4 and then finally just do I've got some pseudoscalar doesn't have to be the QCD accion it could be some other so another two skater students gather a then I can write down into action which is a over F sub it F sub a so some scale some high mass scale and F mu nu F finger tilde and this is dimension five so it's not a normalizable but for absolutely scared of the most important little and so the Fermi on portal let me just write down oh yeah I'll get to that in seconds okay so that will focus on the vector portal the kinetic Mexican portal for pseudoscalar portal you can see the lectures by Michael design talked about this as well last week and Peter Graham will talk about this week very searches for that then the neutrino portal you had Andre talk about this and neutrinos I assume I'm not quite sure all the things he covered but that that would be something that he may have covered and for scaler portal I am just going to mention very briefly some references yeah so I think high-dimensional operas are you know we don't know how dark networks to us but to us so that that's totally fine thing to consider the way I'm arguing for it here is that we're going to ask what's the most important portal and that's to be the one with the lowest dimension you know the right room through localizable one case of the scaler there's even super or normalizable piece to it by hdh but that so I'm just arguing from that point of view it's more like motivating these you know the next set of searches that we'll talk about but you're right you know we again we have no idea out what talking to does to us but if you want to organize your thinking about what should we be looking for there's a certainly good thing to look for because it's has the lowest dimension it's not suppressed by a high mass scale okay with the exception of the pseudoscalar but you know so so the vector there's no mask of suppression we'll talk about that in a few minutes bit more and so those are the most important possible connections to it to a dark sector okay so for the scaler and you just make some comments so so if you ask if you just take that what I've written there the mute Phi plus Lambda Phi squared H th and you ask what is the connection what is the connection of a Phi 2 standard model fermions so it comes of course from the Higgs mixing and what you get from that operator is an interaction between the Phi and standard model fermions with the coefficient of MU of x MF or the MH squared so the F so the standard model fermions okay and what you see is that that interaction because you're coupling through the Higgs you're mixing with the Higgs and because the Higgs mixes the X couples two fermions proportional to the mass of the therming on you see that the scalar basically the way it couples to particular fermion is through the mass so no mass so like so coming to the first generation is very small and coming to the third generation quarks is your more important as a larger coupling so this portal is most constrained by third generation meson decay searches [Music] but it's a perfectly fine portal to consider and many people have and if you want to see more discussion about this you can look at this paper here and references therein so this paper doesn't do a good job actually either but it's good references which should do a better job okay good now okay so going a little bit further than what with Harry's question was you know why not other things so you can consider other things so you can also consider things where you might couple to the baryon currents so some global symmetry of the standard model even if it's anomalous you can consider that and those are fine those are fine things to consider they require more model building you know if you have a few couple of some anomalous symmetry some novice level symmetry and you gauge it so you you have to introduce some other fermions at the weak scales at some higher a little bit scale a little bit above that to counsel the nominees but you can do that that's just a model building thing there's you know possible there's more constraints on that and in principle that you have to worry about but at the lower energy factor theory that's a fine thing to consider so you shouldn't just think that that's the only thing the vector portal that I'll talk about here is very special as we'll see it couples to both leptons and quarks you can also consider things that just couple to quarks or they're just couple two leptons they're slightly maybe ugly a little bit but they're fine things to consider and for logically we want to have searches for this new experiment that we think about we want to be able to prou both kept on couplings and also quote cup into quirks okay okay so let's spend focus on the vector portal and just do some very basic quickly talk about the basics of that portal and they co-ops kinetic mixing and then what we'll see is how we can produce the particles and how what kind of searches we should be doing okay so kinetic mixing basics so given how much attention this thing gets you should know about it if you don't who's who's done who knows what duck photon is and things of that most of you who does not know don't be shy whew okay so most of its review but not everyone so let's just quickly do that so what we're going to consider is a dark sector which is super simple just a u1 an abelian gauge group and it's a Higgs u 1 so we're going to sort us there's some that the gauge boson mediating the interaction is massive okay we don't really care about exactly how or what scale is gauge at what scale it's broken the gauge symmetry but at the end if at some time I might make some comments about that but we're in consider just the mediator so there's a u 1 prime Higgs the mediator is going to be called a prime because I'm giving the lectures Maxine possible giving lectures will be called V and the kinetic mixing parameter is going to be called epsilon Maxime possible of what others were giving it would be Kappa and there's other notations like you boson and a sub D and Chi for the for the mixing etc so they're all means the same thing but we'll call it a prime and epsilon and what we're interested in is a low-mass part of it right so this kinetic mixing portal interacts with the hyper-charged so we didn't do one exactly hyper-charged but we're interested in in it at low energies and that case it actually is just interacting with the electromagnetic u1 so u1 electromagnetic determine a current so at low energies so what that means is below it actually so many breaking what we have is a Lagrangian which is so F Indian news connections for the high pitch for the electromagnetic currents then we've got the hidden u1 we've got a mixing parameter and because I'm ready cutting to the to the left minute current there's no cosine theta W D anymore okay so that's can absorb that the same epsilon as defined before and then I've got into action with the of the photon to the electromagnetic carrying of course and of the dark boat on to any hidden sector stuff so any hints like the particles that are charged under the u one prime under the hidden do one and so this so the J dark here would be well going to write down the electric current but the J dark is Khaybar gamma mu Chi that's other things okay so where Kaiba Dark Matter okay now in order to remove this kinetic mixing term we can do a field redefinition and what we can do is we can take remove mixing time and by doing this we filtered venetian we want to make sure that we don't get into generating a mass for the photon so I forgot one important to so there's a mass for the photon here for the dark hole time so when we do this feel it efficient we don't want introduce the mass of the photon so one way to do that is that we take the dark photon field just to itself and the photon field to the photon field that's a small mixing with the dark photon and that case you know this mass term this a prime doesn't change so there's no you're not mixing the photo into it so there's no mass of the photon coming so you're still going to be the mass eigenstate bases and but what this term does here is that basically gets rid of the canary mixing term and it introduces a coupling of the dark photon to the electromagnetic currents so doing this gives that main effect that we care about is that this turn here the coupling of the photon to the dark to the irishman a current changes and now becomes now gets an additional piece which is epsilon times e times the dark photon to the electromagnetic current okay so what this means that all standard model electrically charged particles have a dark Milly charge okay so I'm really charged under the dark u 1 so we can do this diagrammatically some diagrams we've got F and s bar we have the photon so kinetic mixing here and use the dark photon so if you just consider this is a diagram what we have here is a propagator one-way Q squared this epsilon it's melted by Q square here from the mixing so this is in the original basis and that's the same thing as just having a different basis will be considered the dark folds on with the coupling to f bar F so any standard model particle with a coupling of epsilon times E ok so the dark border comes to anything that has an electric charge so the quarks from the charged leptons and just to be a bit more precise so the gamma couples to FF doesn't actually have unit charge in terms of electron charge so there's some QF here so there's also going to be some QF here okay where QF is in units of e so for an electron if Q F which is one or minus one now this simple Dark Sector can do a lot and of course we can dress it up to make it do even more but what we have now is a new mediator the caboose electric charge we can look for that we have a mediator that immediates document into actions so we can add document ourself scattering just in the dark sector that can give yourself into acting dark matter you have ways to produce the mediator so you have ways to produce the dark matter so if we sample in the early universe I might have an interaction like this where the dark matter could annihilate your standard model particles or vice versa this is how we could set our relic abundance from thermal freeze our search is the same thing as a Z prime model they said now for doing a prime and I've set it up like this so that's and of course you can turn the diagram around you can have dark by Department you have the dark kind of sketch of sano model particles and you can produce it from right to left you can have standard model particles produced akai as well we can introduce some additional dynamics in the dark sector we can split the masses so we got an elastic dark matter Chi 1 Chi 2 we can see how that changes the phonology good I'll get to that in a second yeah okay so the a prime can be the dark matter if its mass is much less than the electron mass if its mass is much higher than the electron mass and it decays too quickly but yeah so that's that's sort of the simple thing and it does a lot and that's a good simplified model which we can work with yes no so the map the photon is massless there's no the you one extra mechanism is unbroken not to the mass so because in this base exchange right there's no there's no mass that the photon picks up so I can always choose the basis in such a way that the photon is massless okay now in certain bases I might think there's a mass but then one has to be careful and you can just it doesn't actually have a mass oh yeah say that again sorry yeah so I've neglected high-order things yeah so so if you do the whole thing there's a magician terms which I've neglected you can include those it doesn't change that question for example it doesn't change the question of what whether the photon gets a mass okay now you know the Z boson for example so the Higgs well I've mentioned that a bit later but if you go to higher masses then the coupling that I've written down here is not as simple it doesn't just cover the electromagnetic charge there's also mixing with the Z okay so for example the dark folks on can decay to neutrinos there's through the Z mixing a little bit because it mixes written the original mix things with hyper-charged right just that the low energy is the most important consequence of this is this here okay so if you want to know more details about you know the base is changing etc yes I'm principle right what you have is you've got three neutral gauge bosons you've got the dark photon the photon and the Z boson and in principle you can ask what the math-science States of those three you can diagonalize the mass matrix at no energies that's the most important thing here but you there are important effects for military precision measurements that also constrain parameter space which you don't quite see in this way I've set it up here but if you want to know more details then you can look at well there is papers but you can look at this one for example I think there's a paper by that young towers on and this one here okay so we don't set it who asked the question okay yeah we yeah here I haven't written something down I can add a mask to invoke I it could be get it from the Higgs mechanism so I could get it from the Dark Age mechanism there could be some carbon coupling between the KY and the Higgs yeah that's a simple way of giving it but I I don't really care right now for the thermal applications but that's one way to do it yeah that's right one field that's right I don't think there's good motivation it's the simplest yeah it's as simple you it has to be a u1 right so what you can imagine that there is a hidden sector you can imagine some non abelian gauge group right so you can have fermions the Kies charge with some non abelian gauge symmetry that some non abelian gauge symmetry that's totally fine people have considered that in the past as well it makes actually make the phonology very interesting there's different signals that you want to look for and maybe I'll mention that briefly this time at some point but otherwise it's really this is just simple what you could imagine that there's some s UN dark cross u1 high-pitch are you one prime the one prime does the hyper-charged mixing and then you can you know mix all the SU N and you want Fields break all the symmetries etc and then you've got basically a whole bunch of dark gauge bosons that have a small kinetic mixing worth with standard model particles and that leads to interesting phonology but in this case to keep it simple you know we have one field but certainly people have consider more complicated things as well and where your motivation I don't think there's a good one except simplicity especially in this venue pedagogically it's easy to start the simplest okay okay okay so as I was saying this sort of does a lot of stuff already you're SIEM self and dark and dark matter you can get it get the right vertical burns from thermal freeze out just as a sort of as a preview of what I'll do in the last lecture a little bit is that you can calculate what the cross section is for this process of course is trivial to calculate this and you can fix the parameters or certain combinations of parameters if you want to get the right relic abundance and that then gives you a target that experiments could aim for to probe this particular for a simple dark sector okay and that's a lot of a lot of work has gone over into that the last few years and there's some exciting searches that people are planning some exciting experiments and I'll talk a bit about that just very briefly about you know what is the your what are the values of epsilon that you might care about what are the values of the doc photomask that you might care about so the epsilon you know it's a dimension for operator maybe I'll find the right board see oh it's gone every doesn't okay so the dimension for operator and it could just be a UV boundary condition so you can write down this dimension for operator and it's your marginal parameter so it could be generated from very high scale it's arbitrary we don't know what it is it could be one principal threateningly or it could be super tiny we can imagine scenarios where the kinetic mixing is absent at some high scale so for example if we embed one of the you ones the hyper-charged you want for example into a grand unified theory then we would only generate the kinetic mixing term below that scale so then we would say okay at the gut scale at zero and then below that scaler could generate it and the way I could generate it is for example through some loop of heavy particles which interact both with hyper-charged and with the docq one so so the first answer is that it's arbitrary let me draw there's an arm missing good okay so yeah so UV they see it's sensitive to physics at some cup of lambda whatever that might be and some about UV boundary condition but you can imagine that it's absent a high scale so the way to do that for examples that you embed the u1 hyper-charged intergranular theory or even the one into some grand unified theory and then it could be generated below that scale so can we generate at low scales lower scales doesn't have to be very low through loops so one for example what you could have is dark photon some loop of particles with the hyper-charged gauge boson B mu and these are some particles in that loop it could be many particles in that loop and they could be very heavy and you just calculate what epsilon could be whether what it is so there's some g1 that's hyper-charged coupling to these particles so these probably will charge of course under both you want Prime and you want hyper-charged so g1 g dark is a loop so there's a 6 and PI squared and then you can have a log of some scale cut of scale over m pi and this key one is you know 0.1 0.3 or soul-g doc is whatever you want it to be could be you know order 1.1 or somewhere that 65 square that's one of 100 roughly the log we could take it to be order 1 if these scales are similar or we take it be much larger but you can needed to get you know 10 to the minus 3 to 10 to minus 2 from this simple thing and you can do more complicated things where you embed the ones and hyper-charged there's some symmetries that that then the force that the simple one group is finished and it cancels and then you can have a two loop diagram for example and get small absalons but basically epson is arbitrary but it certainly is not unreasonable to imagine that it's sort of a loop factor down one okay so the tenemos to 10 to minus three were you in a bit lower than that okay yeah with the dark photon model yeah so there certainly I mean not not any toy would work so you have to be bit get to do the right thing okay so and so many for ma prime here the a prime math and principles arbitrary what the dark photon masses now you can imagine that it's set by the week scale so whatever sets the week scale so from adding some Susy breaking setting the week scale then we can imagine that the kinetic mixing parameter between the stand model and the Dark Sector secludes the Dark Sector from the super summary breaking and the only math scale that the Dark Sector gets is Epsilon suppress compared to the week scale so you can imagine some Dark Sector mass scale that is epsilon times the week scale if it only feels the susi breaking through some kinetic mixing but again that depends on the model but certainly it's unreasonable to imagine that a dark sector could be you know below is look just below the week scale in general so something that's that's you know GV or even MeV or whatever is totally reasonable and some models but you're more definitely speaking it's an arbitrary thing okay okay so what we'll do first now is we'll consider the the super simplest Dark Sector where we just have the dark photon and you're going to consider various searches for it and once we have some tool box built up then what we can do is we can consider your the Dark Matter in addition to that and look see how the searches with logic changes once we have a dark sector the Dark Matter and the reason to go through these models you know again like the simple the simple model is very simple it's a useful for logical toolbox if you like to see what kind of technology is possible what things you should be looking for at colliders at beam dump experiments and other experiments but of course you know there's more complicated things are possible but these are the things that people have taught about a lot the last few years and you should at least be aware of them I think because it's become a mature enough feel to you know that everyone should know a little about it to think so before so before we consider the dark matter forget the dark matter we would make it heavy in the simplified model then it's not important for technology and what we have is just the dot photon and we can ask how can we produce it how does it decay what do we look for so consider a prize by itself in order to know what it what to look for we can first discuss for the case and there's two very distinct regimes one way the dark photo mass is about the lightest electromagnetic knee will actually charge particles the electron so about twice miniature mass divided MeV and one way it's below that and above that it can of course the K two electrons and positrons below that it cannot and that makes a huge difference to the phonology particular above it what you have is just a very simple decay to electrons and positrons or any other standard model fermions are electrically charged and the decay rate is given by 1 over 3 alpha epsilon squared ma Prime and then there's some kinematic factors okay so that's the exact to carried to a dish from the positrons it's causing it to get your muons the expression is actually the same except that you would replace with the electron with the me on and then it can also decay to QQ bar now of course Q Bar is complicated because there's a strong force etcetera there to worry about so what we can do is in general we can talk about the case two hydrants and you know what the heck Decatur hydrants looks like so if we take electron positron collisions and you you understand the model you collide it and you see what comes out so they can be electron positives coming out be plus or minus hadrons etc you see resonances we see the role omega resonance the JPI resonance those old famous experiments that were done and people have measured what the photon would do how the photon comes to passing - well and the other and had rows in general and the dark Bodrum of course is just mixing with a photon so we just take that information and use it for a had rooms and way to do that is that we can write the Hat on decay width to be the MU plus or minus decay with times a function that's usually called R and R is defined to be equal minus shadrin's of the cross-section for each person - muons and that is the measured quantity and you take the percent of mass energy for this process of we set the center mass energy equal to Ma prime okay does everyone know what R is right okay if you don't you should but we thought that's so standard thing but that's what we can do so now we can just use data base you get the whole decay with and then what the branching relation looks like is the following so we've branching ratio function of the dark photon mass again we care about light stuff so let's focus on the low masses let's take it to be above 2m e we'll get to the other one you know one second let's make this one and there's a half so below twice the muon mass it can only Decatur you party - so the hundred the branch of a cheater standing by the party goes 100% to be plus or minus once you get to the tumor on threshold then the dark floating indicating muons as well so then the branching ratio to electrons drops and we just finished showing it like this this is 0.8 GeV you'll see why it does that in a second so here it comes in this is me plus or minus ping and then around seven eight hundred MeV what happens a drones yeah so pi plus or minus and PI plus PI minus PI 0 Y R oh yeah and Omega okay so the role is a big very wide resonance so what you get is something like this so this is PI plus PI - this is from the role the row is very wide its width so its massive 775 nad its width is 150 MeV and the Omega is much narrower but a basically sits in the middle here and that's dominate decays to pi plus or minus at 0 and that's much narrower so its width is HN may be its master 782 MeV okay so you've got the decay t plus n minus mu plus or minus mucousy - approach Tea Party - once the mass effect master of the mass these additional terms that contain the masses once they become negligible and then you've got the pi plus or minus cos 0 and pi plus or minus decays and then it's easy to calculate what the total decay length is and it's point one centimeters for a coupling of 10 minus 5 of epsilon squared + 1 GeV over MA Prime and then I've got a 1 over ineffective and that in effect of what I mean is I just mean a number of possible decay modes so it's basically given by these terms they so sum of a leptons electrons and tau so of course if you go to higher right you can also indicated towels tapas or - etc so in general this an effective is given by some of the e - towel there's a square root I'm going to be lazy that square root is just the square root Day and then there's a parenthesis which is just the same thing with the mass replace by lepton and then plus the square root with the muon from yuan times 1 plus R so in general that's the number and effective ways to find here but what you see is that the decay length can be very very small so the K can be prompt if the epsilon is larger than you know 10 to minus 3 to the minus 4 can devise 3 to my skewer so it can be slightly displaced if you've got a decay or an epsilon of ten minus five ish kind of minus six or so of course depending on the mass as well and the epsilon is much smaller than that then the decay length will be Hugh which can easily be meters hundred meters etc so in order to probe even the super simple dark sector just the dock photon you need a whole range of experiments just to look for it okay you need things that are sensitive to prompt decays to displace the case and to long loop the case and yeah so that that's okay and then very quickly yeah good time one second so clearly above in any moon to MEA can't be dark matter because of just decays way too quickly can't be long-lived but the low enemy below in MeV splode twice the electron mass it can be long-lived because the only possible decay mode for the dedicated neutrinos but at super-tiny that the dominant decay mode is into three photons through a loop of charged particles and the lifetime for this is one second if you take an epsilon of 0.03 over epsilon here any over ma prime to the ninth power okay there were some brave people at calculators actually precisely so hurry remaining and McDermott and Patel calculators very precisely so if you want to know the latest various calculation its possess you to some very recently and the facts are important just near the master sholde otherwise this formula is good so close to twice the electron mass but that's roughly how it scales and you can see that this is easily long-lived I can make it easy longer lived in the universe H of the universe especially if I make the dark hole to mass more okay and then again there's all possible kinds of all possible kinds of searches that you might want to do for this dog photon and because it maths well you know log scale it's a very long way down to zero and infinite way down to zero so you want to do a whole bunch of different kinds of searches to look for dark photos like potentially dark matter I think Peters going to talk about that some of those searches okay good but we're not going to focus on this we're going to focus on the high in that stuff okay and I should stop right be in charge okay yeah okay so let me stop here and then we'll quickly do a few of the searches and then we'll add Dark Matter and look see how the search that will talk about get changed and then regards detection okay [Applause]

Channel: Institute for Advanced Study

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Length: 88min 3sec (5283 seconds)

Published: Tue Jul 25 2017