Okay, let's begin. Hi, everybody, and welcome to this PSM two session. Today
we're going to be talking about dark sectors. And our first talk is from Brian,
who will give us the theoretical background to this, all of the talks today
will be 15 minutes, they'll have a three minute time for questions afterwards. And
if we have a little time left over at the end, we can discuss with all the panelists
then. So I'm fine, feel free to get started.
Thanks very much for inviting me. And thanks to the organizers for organizing
this wonderful online meeting. So I have the tall task of giving an overview of
hidden sector theory in 15 minutes. So let's get started. So the reason why we
believe in the existence of hidden sectors and why all of the impressive searches
that you're seeing presented this conference are taking place is because of
a bunch of things that we don't understand, that can't be explained by the
standard model. These are of course, questions of dark matter. The origins of
the matter antimatter asymmetry, and also neutrino oscillations. And in each of
these cases, the evidence is pointing towards new particles and interactions
that are very weakly coupled with the standard model. And also where the new
particles and forces responsible for this phenomena could happen at really any mass
scale ranging from Evie up to maybe the guts scale and beyond for some of these
interactions. And so it gives us a rich array of kinds of theories that we should
be trying to study in whatever experiments we have. And as I'm sure you're all aware,
there's a proliferation of theories of hidden sectors and what they could do. So
one of the pictures I tried to keep in mind when trying to make sense of this
really extensive set of interactions that could be out there is to try and think
about terms of the signatures, how can I organize them and maybe group them into
categories and I think tried to do that here by adopting, perhaps an organization
scheme that we've seen before and for instance, tried to tackle Susie or there
is a strong dynamics in terms of trying to come up with what are the irreducible non
logical features of the theory? And how can we look for those. And the simplest
place to start is a theory with a single particle and some relatively well
prescribed set of interactions. And these are the things that have become sort of
the canonical example so far kinetically, mixed dark photon, singlet scalar that
mixes the Higgs sterile neutrino and so on.
And for the most part, we have a pretty good understanding of what these look like
how we can look for them. And there's a robust search program to look for those,
we can then move beyond this single particle and imagine what happens if I
have say, two particles that I connect and suddenly the array of signatures becomes
much more vast because I have for instance, a different possible production
mechanism. From decay mechanism so for instance, I could make dark Higgs is from
the decay of a vector and then you know, the the decay comes through the scalar
mixing or vice versa. And so suddenly we have a different range of production,
cross sections, decay mechanisms, lifetimes, and so on. And in many cases,
more becomes a very different. So it's not just like, Oh, I got different, a few
different signatures, all of which will look similar to the single particle cases.
But in many cases, the single particle signatures go away and I got some new
ones. And this goes all the way up to a more complicated code complete model,
which could have, you know, a set of 10s or hundreds of particles. And this could
lead to very sophisticated things like showers and things that reproduce features
from the standard model. And so I think what we want to do is March from the
simpler examples that we've been looking at towards these more complicated ones.
And of course, There are many ways that we can move forward. And I hope to talk about
just three of these today, or at least you touch on what I think some of the
interesting directions are. And then hopefully, those of you who are
experimentalists looking for something to do. If you're bored, you can follow some
of the references or Google some of these ideas and see what, what more we could be
doing. And I've kind of grouped these roughly under sort of non minimal
couplings meaning coupling patterns that deviate from the canonical examples of
dark photon dark Higgs, etc. Non thermodynamics So, this specifically is
interesting from the point of view of dark matter, but, you know, we have a well
prescribed Dark Matter program at the Elysee. And this is of course, predicated
on a specific thermal history in a specific way that those particles are
making dark matter and if you change those, then you change maybe the
phenomenological signatures and coupling ranges that are of interest. And then
finally, what happens if we move to words Non perturbative are many body signatures,
right? Got lots of new states showing up like confining sectors and dark showers.
So let's start with the non minimal couplings and your sense of what I mean.
So if you think about dark photons, or dark scalars, these couple, the same way
as regular photons are the standard model takes just time some small overall mixing
factor. And as we will see some of the talks to come. There's really impressive
coverage that's beginning to take shape for many of these signatures. And we
haven't seen any evidence yet, so we're just piling up more and more constraints.
And these usually come from the coupling of the dark photons that are scalars to
standard model particles that are easy to access and experiments like coupling to
electrons or coupling the top quarks. At the same time as we continue to improve
our exclusions there are anomalies and hints of new things that continue to
accrue. So for instance, new on G minus two is a persistent discrepancy with the
standard model. There are, of course, the anomalies in electronic similar time. BDK
is possible upon flavor stuff going on there. The Koto anomaly is a new thing of
the past year, and so on. And if we want to try and accommodate one or more of
these within the standard framework, this is often excluded in the minimal case. And
so the workaround for this is to just say, well, let's just shut off this most
important coupling that's often used to constrain these new particles. And this
can weaken the constraints on the models and potentially open up the viability in
terms of explaining some of these examples. And we'll talk about one
scenario, which is something that I've worked on in terms of searches with a bar
experiment, which is what I call electrophilic scalar. So it's a scalar.
The couple's masks unfortunately, just like the Higgs, but a couple's
predominantly to leptons, as opposed to
And this was shown recently that it could potentially, for instance, simultaneously
explain the new g minus two and the Koto anomaly. But if we look at this plot on
the lower right, if you ignore the green curve, which is what the experiment just
recently did, actually, most of them laundry minus two parameter space was open
and really uncovered. And so what we did was we did a search where the dominant
production mode of this is not going to be directly off of the electrons but off of
final state radiation from towers, which which it has the largest coupling and then
it will decay and to save your lines or electrons. And this requires doing a
search at finite lifetime. So, we're sort of having to bring in a lot of different
interesting modules initially of hidden sectors. And the short version is we
didn't see anything, and we exclude this whole green region which greatly
eliminates the view on T minus two parameter space below the top shot. And
this is interesting both because it shows the power that a single search can have to
improve our sensitivity. But also the fact that, you know, the sensitivity dies off
as soon as the thing starts decaying into Taos as well. And so if we have a
completely tau philic scalar, there's a lot of open parameter space. So this might
be a zooming in for our attention, as you know, are there ways that we can try and
access this parameter space? So what are some things that I think are open
opportunities with respect to these non mental couplings? Like I said, I think
Catholic forces things a couple probably to nuance as opposed to electrons are a
major gap and possible explanation and being rungy minus two particularly below
the diamond threshold and at high masses. So in the Atlas CMS range of interest, and
also accent like particles, which are particles that coupled predominantly to
pairs of gauge bosons and photons, electric boat, those odds include bonds
and so you know, While we should continue to press ahead on these minimal scenarios,
we should also see if there's something hiding in some of these other cases. What
about if we changed the dynamics in the early universe are we consider different
types of ways of explaining Dark Matter abundance. Until recently thermal freeze
out which is the mechanism for explaining the dark matter, abundance and rent models
was the major way of thinking about how we come about dark matter abundance. But as
we know, we have not seen any positive signals in wimps searches nor in you know,
some searches for lighter versions of thermal dark matter and indirect detection
and direct detection, so on.
And so we can wonder, well, is this the actual way the dark matter is determined
and the answer is maybe not. So as soon as we have multiple component hidden sectors
with mediators and dark matter particles with different masses and couplings, we
can actually get a very wide range of subjects very creatively named, dark
matter things. So there were so many references here, I couldn't fit them on
the slide. But if you just Google any of these, I guarantee that things will pop
up. But it's probably the easiest way. So if you're ever bored and depressed, that
we haven't found dark matter, just look up some of these and get some sense of how
rich, docile Dark Matter dynamics can be. I'm going to talk about a variant which is
pretty simple, but it's called freezin. And it's a scenario where the dark matter
is so weakly coupled, that it never comes into equilibrium is never abundantly
produced in the early universe. And in these cases, dark matter is just produced
from the decay of some scalar that carries Standard Model charge, for instance, and
you just accumulate Dark Matter slowly over time. And as the temperature of the
universe evolves, and as we go through time, you make it and then at some point,
you stop making it it just happened amount, and you can calculate how much
that amount is and it's roughly this given by the bottom of screen and you can see
that for kind of reasonable masses, you get very tiny couplings or 10 to the minus
eight. So this can be interesting predictions along with particle
signatures. And this is kind of come back into vogue recently because it's
relatively untested type of dark matter scenario. I've become interested in AI
recently because it turns out that this same interaction, if you have two or more
dark matter particles, can also give you the matter antimatter asymmetry almost for
free with similar kinds of couplings. But over a much more constrained parameter
space, it's actually quite testable. So over here on the left shows the mass of
this scalar, which carries Standard Model charges and the lifetime and you can see
that in order to get the bearings and do the work, which is in these shaded
regions, you actually have to have the scalar be within kinematic range vhc. And
in the lifetime range, it's also an interest for different sector searches.
And so we got, for instance, cares of lung lip particles, each of which decays to a
single standard model particle plus mad. And so this is, could be a clear signature
of both the dark matter production as well as a matter antimatter asymmetry coming in
one bundle. And this is the only way the freezing could happen. For instance,
instead of having a TV scale Meteor, we could have a low mass and the leader like
a dark photon, there's recently been a lot of theoretical work that's been going into
calculating what's going on in the early universe plasma effects that are relevant
at those scales. And this has been opening up some parameter space for Dark Matter
also in the kind of K 10s of k v to hundreds of k v scale, the producer very
different mechanism, predicting new signals inferences, direct detection
experiments, astrophysical probes, cosmology and so on. So by tricking our
our prejudice or our views of what Dark Matter could be and how its produced we
also expand our range of phenomenological probes. Within the last couple of minutes,
I want to touch briefly on the non perturbative in many body signatures,
which is Not gonna be super extensive because this is still a relatively
emerging field. But in these scenarios, you might consider our hidden sectors
where the dark matter carries some charge under a dark confining force, and so it
undergoes apart on shower, and then hunter ization much like you see. And in these
scenarios, the dark hadrons can decay properly or long lived. And because we
don't know anything about this dark, confining forest, the shower properties
are unknown. And they could range anywhere between the jet like features like we see
in the bottom left, or we could end up with something that's very kind of
isotopic radiation patterns that you see on the right. Then, of course, there's an
open question about well, if I change the knobs of the theory, do I move smoothly
from the picture on the left to the right, you know, do it go through some
interesting intermediate phase? And this is hard to answer theoretically because of
the non perturbative nature. So, you know, this is a new area of experimental study.
There's, as far as I'm aware, one public was often seen So we know that Atlas is
working on
a search for similar kinds of models, these so called a virgin jets with long
lift, two K's of these dark hadron. So this shows that it is feasible. And it's
interesting and that we need to do better to understand it for theoretically and in
terms of experimental sensitivity. And just in the past month, there's been
several papers that have come out that have investigated for instance, new events
shape variables that are kind of like thrust, or they're based on something
called the energy movers distance that can distinguish a digest sample from isotropic
distributions that have different numbers of particles per events ranging from 10 to
50. And you see that they're all separated from one another, as well as new
applications of jet substructure variables like energy correlation functions that can
be used to distinguish QED showers from these dark showers. This is very much an
early stages and so it's a great opportunity for new theory and
experimental development. So I'm out of time So we'll leave it here. I think that
to the sector's there's been a really impressive development and search program
for them. And we still have a lot of interesting things to look at the LFC has
a really important role to play and testing, particularly sort of Hidden
Valley scenarios or scenarios where you have a heavier mediator relative to other
lower energy experiments. And stay tuned because we have three great talks that are
going to show just some of the exciting results from these efforts.
Thanks a lot, Brian. That was both a fascinating talk and on time to within
plus or minus one second. So I have any questions from the attendees, the other
speakers, use the raise your hand option zoom will be able to unmute you.
Go ahead, Mary.
was wondering if you could say a few more words about the energy movers distance and
what it is exactly. This new variable?
Yeah, so I was not involved in this. So I've only kind of glanced at the paper.
But I think the rough idea is, so it's based on something called the Earthmovers
distance, which is a problem in computer science, which is that if I have two
distributions of masses in space, and you can ask what's the minimal way that I can
rearrange math so that I moved from pattern age to pattern B. What this
variable does is it compares a particular event which has some distribution in phi
and pseudo rapidity. And then it asks if this were a purely isotopic event, I can
compare those two pictures and what's the minimum amount of energy that I have to
expend to change one to the other. And the paper goes into great detail of how they
define exactly the waiting and the metric of this but the rough idea is that if it's
already isotopic, you don't have to rearrange the events at all. And so it has
a very small energy movers distance whereas if it's a diner Like then you have
to expend a lot of this normalized.
interest, just for my understanding on this plot as well. I was curious about it
to the end in this case is the number of initial particles you have creating the
energy distributions you're looking at, or?
Yeah, so this was a, I picked this one because it kind of showed the the most
distinguishing power even though it's perhaps a little bit of an artificial
setup, we're basically out there saying, I'm not going to go into the details of
the model, I'm just going to generate events that have kind of isotropic ish
distributions of say, 50 particles compared to say QC D digest events. And
the remarkable thing is that so if for instance, you showed the corresponding
plot for thrust, which if you look at the paper, it's there or some other events,
shape variables, it's hard to distinguish the 1025 and 50. You can distinguish maybe
the From QC dB, you can't tell them apart. Whereas this is really sensitive to like
how many particles Do I need to rearrange?
testing? we maybe have time for one more question for Brian. What else hustler?
Okay, in that case, thanks again. This was very interesting. And let's move on to our
next speaker, which I believe is Constantine