 Okay, great. So thanks for the invitation to give a talk at the conference and also to lecture at this very diverse summer school and have the opportunity to interact with students from particularly diverse backgrounds. So what I want to give a talk today is a pretty broad overview of what's going on in dark matter direct detection and where I think the future is going to be over the next 10 years. So let me start by, I've titled the talk Beyond the WIMP. And so you might want to ask the question, well, what's wrong with the WIMP? Why are we looking beyond the WIMP? And to do that, I think we need to spend some time looking at where our experimental status currently is. So this is, I think, probably the most by far useful plot to have come out of the snow mass process. And it gives us a summary of where the direct detection experiments are at. So here's a plot of the dark matter scattering cross section off of a nucleus as a function of the dark matter mass. And you can see this huge diversity of experiments pushing down in cross section. You can see that they cover the dark matter mass range above about 10 GeV. And the solid lines are the current constraints. So they're going down to the level of about 10 to the minus 45 centimeter squared. I'll tell you why that's significant in just a minute. And you can see also this neutrino background. So that sits around 10 to the minus 48 centimeter squared for a weak scale cross section. And to just parse this in terms of the most important physics on this plot, people talk about the fact that we're looking for the weakly interacting massive particle. And strictly speaking, that's not really true. And the reason why that's not really true is that weak interactions, namely scattering through the Z boson, has already been ruled out. So that scattering cross section is on the order of 10 to the minus 39 centimeter squared. And that's not ruled out by something like five to six orders of magnitude. What we're actually probing right now in what is symbolized here by this red blob is scattering through the Higgs boson. And that benchmark is around the level of 10 to the minus 45 to 10 to the minus 46 centimeter squared. There are big errors on that for reasons I'll discuss in just a minute. And the other thing I wanted to draw your attention to is the fact that the sensitivity of these experiments really rapidly dies around 10 GUB. Now the reason why Higgs scattering dark matter has such a smaller cross section is effectively just the fact that the Higgs coupling to the nucleons is much smaller because you couple proportional to the mass. So the dominant contribution is going to be through a loop of top quarks. And so when you compute this for sort of typical cross sections, so this is the down type Haxeno fraction of the dark matter if you put this in the context of the MSSM, for moderate tan beta you can get very large cross sections. But if you put in 125 GV Higgs tan beta of one you can rapidly see why it is that we're focused on this region here of around 10 to the minus 45 centimeter squared. Now that said, looking at this plot you would infer that by the time that we get down to the neutrino background down here we would have basically killed the neutrino within the MSSM. That's deceptive though and the reason why that is deceptive is because pure states within the MSSM do not couple to the Higgs boson. So if you just write down the Feynman diagrams for coupling to the Higgs boson you need a mixture of Weno Haxeno or Beno Haxeno in order to actually get a coupling to the Higgs. If you have a pure Beno, a pure Weno or a pure Haxeno you just don't generate a scattering cross section. So strictly speaking you can add zero direct detection cross section at tree level. Now on the other hand if you did have a pure state, a pure Weno or a pure Haxeno for example, even if you wouldn't see it in direct detection, in a direct detection experiment it could show up through its annihilation processes. So if you look towards the galactic center and you look for particles coming from those annihilation processes you can have dark matter annihilating to W and Z bosons and then eventually downstream you get photons and charge particles out of the deal and you can go and look for those. And you can compute this scattering cross section and it turns out to be huge. So that's what's shown in this plot. This is the annihilation cross section in this case it's to a line gamma gamma or gamma Z as a function of the dark matter mass and I want to draw your attention to this two to three TEV window because that's where a thermal Weno dark matter candidate lives. This is what the theory predicts and here in the solid line everything above that is what's currently constrained by the Hess experiment. And you'll notice that there's already some tension there. Now I wouldn't call this ruled out yet and the reason why I wouldn't call it ruled out yet is because there are theoretical uncertainties. For example the density profile of dark matter towards the galactic center is folded into this calculation. On the other hand if you look like look at what a future Trenkov telescope like the CTA can do that's what's shown is this beige line and you can see that it can rule out this window actually to an order of magnitude. So we're going to be able to put some pretty strong constraints on pure Weno dark matter. The other thing to say that's really important is these experiments are getting so good that we're not only probing the tree level cross section but in some cases we can actually get the one loop process. So I said that pure Weno doesn't give rise to a coupling to the Higgs boson. However, you can actually compute a one loop diagram exchanging W bosons. And you can compute the size of that scattering cross section. So here's for the Weno. Pure electroweak triplet, pure electroweak doublet. This is a scattering cross section in a direct detection experiment. So if you'll recall 10 to the minus 48 centimeters squared is about where the neutrino floor is at. And you can see that at the one loop level we're going to be able to get for 125 GeV Higgs the pure triplet case. The Higgs-Eno case lives in this unfortunate cancellation. I think we need to maybe look at other effects maybe multi-nucleon effects that could maybe help lift this. Pure Higgs-Eno will be hard. Beano, pure Beano is also hard. You can calculate the one loop contribution. I don't want to go into detail on this plot. Suffice it to say that this is the neutrino background. And these are the cross sections predicted for various scenarios. And you can see that they're below the neutrino background. So that's going to be hard to get. Still, we're going to be able to hit a lot of the parameter space. And I also don't want to go into details on this plot. But the reason why I'm showing it, you can see that it has supersymmetric parameters here for Beano Higgs-Eno dark matter in the tan beta mu plane. What's shaded is what's going to be gotten by xenon one-ton experiment. And you can see that's what left in this scenario is a sliver where you've tuned away the couplings to the Higgs boson at tree level. So the bottom line is we're not going to be able to rule out the neutrino, or the sort of standard WIMP candidate. But it's going to look like an increasingly tuned scenario by the time that we get through an experiment like the LZ experiment. So we're talking about once we get down to sort of 10 to the minus 47 centimeters squared kinds of scattering cross sections, we're really going to be pushing hard on the scenario. And so I think that there is a very strong case to be made, both theoretically and experimentally, that we need to be looking beyond the WIMP scenario. And there are two reasons for it. First is that for some time now, theorists have been looking at models beyond the WIMP in a pretty serious way. And what we found is that there are very simple natural models that reside elsewhere. And when I say elsewhere, I don't mean just the axion. Things beyond that are not just the axion or the WIMP are very nice models that reside there. And so in particular, if you're looking for particle dark matter, which is confined to this region here, there's an enormous amount of model parameter space that you're just not touching at all. So that's the first point. The second point is that experiments are pointing us in that direction. We have all of this pressure on the weak scale, not only in direct and indirect detection, which is what I've been talking about so far, but just the fact that LHC is doing all these searches, trying to turn over every single rock that we can, looking for new physics at the weak scale. Now, it may be one year from now, we found physics beyond the standard model at the weak scale, in which case we'll all be focused on that again. But I think it's really important that we try to spread our searches a little bit more broadly and design experiments that are not really only focused on the weak scale. So let me start and give you a couple of examples of natural models that reside elsewhere. And one that has gotten some traction is the example of asymmetric dark matter. So that is actually shown right here is these very three very light colored gray blobs on this plot. And this is examples of models. So they have sort of a natural mass scale that resides between about 1 and 10 GeV. And the reason why that's notable is because these direct detection experiments have sensitivity that dies around 10 GeV. So if you have a dark matter candidate currently whose mass is 5 GeV, even if the scattering cross section is huge, you're just going to miss it. Now, this idea that dark matter might have a particle, anti-particle asymmetry is old, it actually dates back to the late 70s when people were trying to solve the solar neutrino problem by collecting dark matter in the center of the sun. And the reason why the asymmetry was important was because it doesn't self-annihilate. And so this was a way to accumulate a lot of dark matter in the center of the sun, which could actually change the transport properties in the sun and hence potentially solve the solar neutrino problem. Now, we know that the solar neutrino problem was solved by other means. On the other hand, if you just look at this as a dark matter candidate, it's extremely simple to construct these models. And let me give you an example of how this works. So what's new? Well, the idea was that you just stop focusing only on the weak scale. And as soon as you stop focusing only on the weak scale, what you realize is that there's all sorts of other kinds of interactions that can easily communicate dark matter density between the visible and dark matter sectors. And one way that you can do that is through a higher-dimension operator. So you just imagine that you take any type of operator that looks like an r-parity violating operator, let's suppose you want to hold onto supersymmetry. So for example, I can take a neutron, UDD. This is usually viewed as being bad within supersymmetry. However, if you now have this r-parity violating interaction talk to the dark matter sector, which you see that it does, it doesn't carry any standard model charges, but it does carry baryon number. So if I have some interaction between this neutron here, this effective neutron and the dark matter, what it does is to transfer whatever asymmetry I had in the visible sector. If I had a primordial baryon asymmetry and I have this interaction through this higher-dimension operator, what it will do is to have these two talk to each other through this higher-dimension operator. And so if I have a matter anti-matter asymmetry, one part in 10 to the 10, I can't visualize that with a bar graph, but that's what it is, then what it is going to do through this barrier, this higher-dimension operator is communicate that to the dark matter, and I'm left with a small dark matter anti-dark matter asymmetry. And so just from the fact that we know that the baryon to dark matter ratio in terms of energy densities in the universe is a fifth, I come out with sort of a natural mass scale. There's slop on this, depending on what exactly the model is, which is about five times the proton mass or around 5G EV. And so what you're left with then is I need to annihilate away now this particle anti-particle asymmetry. The way this is done in the standard model is I have a force, known as the photon. And so for example, what happens in the standard model in the early universe is I have, once you drop below, temperatures drop below the electron mass, I have E plus E minus annihilates of photons. Well, exactly in the analogous thing is gonna happen in the dark matter sector. Now I have some dark photons sitting in the dark matter sector. All I've done is to extend the dark matter sector by U1, you can make it arbitrarily simple. And so the overall model building lesson that we've learned from this exercise is that it's easy to build light, dark matter sectors just by secluding it, okay? You could either seclude it by putting in a higher dimension operator to communicate between these two sectors, or you could just have some small parameter, but a low mass scale that communicates between the two, okay? And so the overall thing that we've learned is if we wanna extend from 10G EV down, it's very easy to do that by just having the dark matter sector be its own sector of particles. So I could have, for example, dark matter and highlighting to whatever this additional U1 is that is in the dark matter sector. And then the way that it could communicate, for example, I said either through a higher dimension operator or for example, I could put in a kinetic mixing parameter. And that kinetic mixing parameter then would allow me to communicate to the standard model and I've secluded it through this small parameter. And in addition, if you still wanna hold on to naturalness, you can make this natural by having this visible sector here, which would be the standard model in most cases, communicate to Susie Braking. And then since the dark matter is secluded from the visible sector, the Susie Braking has to grow through whatever this barrier is. So in this case, it's this small parameter sitting right here. And so the amount of Susie Braking that would be transmitted through this small parameter here sets whatever the dark matter mass scale is. And so if you have a small coupling between these two sectors, what that naturally generates is just a lower mass sector in the dark matter sector. And you didn't have to work hard at all. All that you have is one single small parameter, which is naturally small anyway, a kinetic mixing parameter. And in general, then I can easily generate a low mass scale in the dark matter sector. Now this has positive observational implications. One of the positive observational implications as soon as I've extended the dark matter sector by this U1, and I said I wanna generate that mass scale, then that naturally gives rise to an observable scattering cross section, which is shown here. And so people have one of the very positive things that's happened over the last five to seven or eight years is that people have been, theorists in particular have been focused on trying to develop new types of experiments that will be able to look for dark matter particles or a dark sector with mass well below the 10G EV scale. So in this case, what they did was to say, well, how is it that I can look for a dark U1 with a mass scale now that is well below this GEV mass scale? Okay, and so shown here in gray, so this is the effective coupling of this dark force. You'll notice that it's small, two electrons, and then you imagine, well, okay, how would I look for a force that's very light but weakly coupled to the standard model? And the way that you can do that, for example, is through a beam dump experiment. And so what these people did was to go and design beam dump experiments where you could fill in much of this parameter space and notice in much of this parameter space, the couplings are not particularly small. So the natural sort of extension of this is this plot that I've been showing sort of cuts off at a GEV and dark matter mass. I said asymmetric dark matter resides in this one to 10G EV range, has a natural mass scale there, but what is it that resides down here and how is it that I would go and look for it in direct detection experiment? So first of all, you have to satisfy some basic kinematics. So elastics gathering tells you that the amount of energy that you can deposit through a momentum transfer of dark matter off of a nucleon or electron, which is shown here is just the momentum transfer over twice the nucleon or electron mass. Typical velocity of dark matter in the galactic halo is 10 to the minus three. So one MEV dark matter corresponds to an EV of energy deposited in electrons and 30 MEV dark matter corresponds to one EV deposit of energy on nucleons. So in either case, if you can have a sensitivity to one EV of energy deposit on either electrons or nucleons, you can push down the sensitivity of your experiments all the way to 30 MEV or one MEV. Okay, so we're talking about three orders of magnitude extension in dark matter mass just by being able to push down the threshold of these direct detection experiments. So just to give you an idea of where we're at currently, so up to this point, the CDMS experiment has been sort of the state of the art. Okay, so coming back again to this plot, you have the CDMS experiment, it dies around 10G EV. The reason why it does that is because the current threshold of this experiment is about 5K EV. You can see that there are some new proposals now which are shown as these dashed lines. Super CDMS is really gonna focus on looking at light dark matter and they're gonna do that effectively just by lowering their energy sensitivity and the in principle thing that will stop them from going down even further is just the band gap in these semiconductors. So CDMS and super CDMS are germanium and silicon semiconductors. And so as long as you can pull an electron from the valence band into the conduction band, in principle you can have sensitivity to these dark matter candidates. And in fact, this isn't just sort of pie in the sky pushing down from 10G EV dark matter sensitivity all the way down to tens of MEV. People have actually gone and done this. So they did this in particular for the xenon data. So this was the theory paper in 2011 where they looked at the scattering cross-section as a function of dark matter mass and they said if I had an experiment with one kilogram year of sensitivity and they looked at xenon which was here and germanium semiconductor experiments such as what super CDMS does, what is it that I can reach? And this is what they said. Now of course they haven't gotten to the point yet where these experiments are background free. So they're still trying to characterize and deal with their backgrounds. But nevertheless what they were able to do with the xenon 10 data was to go and use one, two and three electron ionization thresholds, I don't have time to explain what that means. And they drew a constraint now and the thing I want to emphasize is they went all the way down to 10 MEV in mass. So three orders of magnitude and they actually managed to probe part of this parameter space which is theoretically interesting. Now if you want to go to even lower masses, what is the in-principle thing that you might be interested in even lower masses? Well you might be interested in getting down to the warm dark matter limit. So we know from the Lyman-Alpha forest that a dark matter behaves like individual particles that the constraint on that observationally from the Lyman-Alpha forest is around a KEV. Going lighter than that, the dark matter is just too light, it doesn't cluster well enough. So if you want to get down to KEV, you can't actually just use elastic scattering because of the fact that you get this one on electron mass or nucleon mass to actually be able to get down to KEV dark matter, you actually have to be able to access the entire energy of the dark matter. So if you want to get to KEV energies, you need deposited energies of one milli-EV and then actually be able to extract all of that energy. So how is it that you do that? Well our idea was to actually make use of superconductors. And what is significant about the superconductors? Well first of all the electrons are pretty tightly bound in the sense that they're buried in a Fermi-C. So they have non-zero velocities. The electrons, these valence electrons and the superconductors have velocities which are on the order of 10 to the minus two. But even though they have velocities which are 10 to the minus two, so they're fairly tightly bound, the Cooper pairs, you have these coherent states. The coherent states have very small binding energies. They have milli-EV kinds of binding energies. Well milli-EV, if you want to get down to KEV, that's about the right energy scale. That's the first thing. And the second thing is that because the velocity electrons is 10 to the minus two, you actually have a hope of being able to extract all of the kinetic energy of the dark matter. So those are the two things that might make this helpful to you. And so the other interesting thing that's about this is that once you deposit more than a milli-EV of energy, at that point the electrons actually behave as free electrons in a Fermi C. So once you get significantly above that milli-EV threshold, what happens is you ram an electron and you create quasi-particles. So you imagine, you interact with one of the electrons in one of these Cooper pairs, you break the Cooper pair and that reverberates throughout the lattice. You have this quasi-particle that's bouncing around inside the superconductor and as it does it, it breaks a whole bunch of other Cooper pairs. And so the question is how does it, that you actually extract that energy out of the superconductor? Okay, and so we spent quite a bit of time talking with an experimentalist on Super CDMS, okay, and this is his design. And the idea is that you would have a superconducting substrate, in this case of aluminum, and then you would have on the surface of this some collection mechanism that would ultimately be tied to a TES that could absorb these milli-EV types of energies. And one of the reasons why this works is because the quasi-particles actually have a very long lifetime. So once you've created a bunch of these quasi-particles, they bounce around until they can be absorbed onto the TES on the surface of this object. So what's the calculation that you do? Well, the price that you pay for interacting with electrons in the Fermi-C is that you have polyblocking essentially. So the surface here is at around 10 EV. And remember, we're only depositing a milli-EV of energy. So if I'm only depositing a milli-EV of energy, the polyblocking is telling you that you can only pull out from the very surface of this sphere. And so the kinematics doesn't actually allow you to deposit energy in an arbitrary configuration. You have to satisfy the polystatistics. So when you're at a milli-EV of energy, so you know this very standard kind of plot of the population at zero temperature of electrons, you can only pull electrons for a milli-EV deposited energy from within this Fermi surface. And as you go to higher and higher deposited energies, you can pull electrons from deeper and deeper in the Fermi-C. And so more and more face-to-face opens up to you. So when you put in all the factors, this is what the rate ends up looking like. So here is the rate in number of events per kilogram year, per log energy, as a function of the deposited energy. Okay, so here we've plotted for 10 K-EV dark matter and for 100 M-EV dark matter. We've put in two cases, one where the mediator mass is well below, the momentum transfer in the event, and one where the momentum transfer, the mediator mass is well above. And you can see that you actually get a big enhancement for the light mediators because the rate is peaked at this low recoil energy. Okay, so for talking about having sensitivity to milli-EV energies, you actually win a lot by having this light mediator. So now the next thing you should be asking is, well, okay. So you've shown, the thing that I wanna point out is first of all, in principle, for a kilogram year of exposure, which is not a lot by experimental, at least with what we're talking about in direct detection experiments these days, it's not a huge amount. So are there models that actually satisfy all the constraints that live there? And so just to show proof of principle, let's just take a simple model with a dark matter particle talking to the standard model electrons through a kinetically mixed U1. And you have to put in all the constraints, dark matter, self-scattering, stellar cooling, terrestrial experiments, decoupling at the CNB app, all these things enter into these direct detection constraints and I'm running out of time so I'm just gonna rush through these very quickly. The point is that I need to make sure that the self-scattering isn't too large. And the reason why is that if there was large self-scattering that would tend to randomize the direction of the dark matter, it would make the halo-spherical. And that puts some constraint on a dark matter coupling to a mediator. I have to make sure that I don't produce too many of these in the center of a star. Very light dark matter below the temperature of the star can be produced. That puts a constraint. I mentioned earlier these terrestrial constraints that are being designed. It's potentially can also be complementary to these direct detection experiments. And then I also have to check that my dark matter is actually decoupled from the baryons at the CNB epoch. So I didn't have time to go through any of those in details. But when you put it all together, so here was just the simplest sort of stupidest model that I could write down. It satisfies everything. It satisfies all these constraints. And so I can take a family of curves. So these are families of curves that satisfy all these constraints for the light mediator and the massive mediator case as a function of the dark matter mass. You can see now, we start at one GEV. The current experiments stop at 10 GEV. CDMS is gonna get all the way down. Super CDMS is gonna get down here to the 0.1 GEV level. You can see what the Xenon-10 experiment has done already. And here we have projections for a superconducting experiment with a one milli-EV or 10 milli-EV threshold. And you can see that for these models that satisfy all these constraints, you certainly can have very large signals in these experiments. And you can see how many orders of magnitude we actually span in this direct detection plane. Okay, so I think I'm out of time pretty much. So let me conclude. So I think we're at a time now where sort of a number of factors coalescing are really pushing us to move beyond the whip. And I think this is going to happen, especially as we're moving beyond the weak scale. So, so far LHC has produced a Higgs boson, which is an enormous triumph. On the other hand, we don't know that we're gonna find anything else. And even if we do find something else, it's still not proof that we have actually detected all of the dark matter. So even if we see a signal missing energy at the LHC, we still have a long way to go to show that that is actually what's composing all of the dark matter. And I think we also are in a unique place in the sense that there's all this technology. Since people started looking for dark matter 30 years ago, this technology has gotten so much better. And superconductors is one example of a technology that has gotten so good. So for example, this TES technology is what's used for CMB experiments. And we can leverage that technology to start to look for new types of dark matter candidates. In one natural place to go, I'm not saying this is the only place, one natural place to go because of asymmetric dark matter, because of hidden sector dark matter, or two examples that I gave, is to lighter dark matter. Whenever you write down these models, astrophysics and cosmology have to be your constant companion. Because those are the things you have to make sure that you're satisfying all the bounds and that what you're looking for makes sense. On the other hand, there really is very little that has been explored in terms of dark matter models in the literature so far. So I think there's a lot of work to be done. And one way that you can look at that is that sort of our leading order of approximations. First of all, we found out it needed to be particle dark matter. Then we said, okay, it's a wimp or an axion. Now we sort of moved on to the next level and said it's a wimp or an axion or asymmetric dark matter or hidden sector dark matter. So now we're in this process of iterating down, okay? And trying, just because our first order things didn't work or are not working so far, it doesn't, you know, dark matter exists. It seems very likely that it's physics beyond the standard model. And so now we really need to use all the possible tools at our disposal to try to understand what it is and to characterize it. So if dark matter is discovered in the sense that we have some signal in some type of an experiment, it's really the beginning of a new field. So I'll stop there. Thank you. We have time for some questions. For those of us that don't know, can you sing a little bit more of what this TES technology is? What does it stand for first and what does it do in terms of readout? Yeah, so it's a transition edge sensor, okay? And it's also another superconductor that's basically doped to have a superconducting transition right at the energy that you're interested in. So basically what you do is you build one of these devices so that there's a superconducting transition at milli-EV, and you just sit there and as soon as it detects, say, a milli-EV of energy, basically you have this transition from zero conductivity up to high conductivity. That's essentially the way that they work. So these have been used very successfully in CNB experiments. So for example, the polar bear experiment, what they use to... So when you introduce this asymmetric dark matter, you introduce a supersymmetry, it's an arbitrary evaluating kind of a structure. And so is it necessary to have a supersymmetric to have a asymmetric dark matter? Is that just an example? No, it's not at all necessary. So in fact, I can write these things down just without supersymmetry, and it's perfectly fine. I just decided to use that structure, first of all, because you can use the r-parity to stabilize the dark matter if you want. And secondly, to emphasize the point that should you choose to keep a principle of naturalness, it's very compatible with these models. All you're doing is extending supersymmetry effectively by the dark matter, plus you typically need some force in the dark matter sector. I personally don't feel like I need to hold onto minimal dark matter sectors. I mean, if you just look at the standard model, it's not minimal, okay? But if you want to hold onto that principle, it's very easy to accommodate within these models. As far as I understood, you are suggesting some methods to probe dark matter coupling to electron. If we have this light dark matter, but mainly it's coupled to quarks rather than electron, is there any chance to detect them by directly? So it's certainly what supersede-MS is doing. As I said, it's a Q-squared on M-nucleon in that case. So in terms of the deposit and energy, you're paying a factor of 10 to the three, which ends up as a ratio of square root 10 to the three in terms of sensitivity to dark matter mass. So certainly you can do that. But if you want to go to really light dark matter, right now, the ideas on the table are using scattering off of an electron. Any more questions? Okay, let's thank Professor Zurek again.