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Fall 2018

Seminars take place Fridays 3-4pm in West Hall Room #335
Organizer: Ben Safdi, Ratindranath Akhoury

Dan Hooper (FNAL): Might the Dark Matter also be the Inflaton? | 9/14/18

Dark matter and inflation represent two of the biggest open question in cosmology. Although they are generally thought of as distinct and unrelated phenomena, here I will ask whether they might be closely connected. In particular, I will describe a class of models in which a stable inflaton is produced as a thermal relic in the early universe and constitutes the dark matter. I will show that the annihilations of these inflatons can efficiently reheat the universe, and I will identify several examples of inflationary potentials within this scenario which can accommodate all cosmic microwave background observables. As a simple example, I will discuss a model in which inflaton annihilations that take place through a Higgs portal interaction, leading to encouraging prospects for future direct detection experiments.

 

Jun Nian (UM) : Supersymmetric Localization: Review and Recent| 9/21/18

 ProgressSupersymmetric localization is a powerful tool that can provide us with some exact non-perturbative results of quantum field theories. In the first half of this talk we will review its basic idea and some important applications. The results of localization can be used to test some conjectured dualities, for instance the Seiberg-like dualities in various dimensions, and also to help set up new dualities. We will demonstrate these aspects with some examples. In the second half of this talk, we will discuss some recent progress on the localization of 4d N=1 gauge theories. We consider 4d N=1 gauge theories on S2*R2 and compute their partition functions. The results are related to the partition functions of 4d N=1 gauge theories on the Omega background with two epsilon parameters, which can be viewed as building blocks of the Nekrasov partition functions of the 4d N=2 theories on the Omega background. As an application, we use the N=1 partition functions to test various dualities such as the 4d Seiberg duality. Further applications to the 4d Argyres-Douglas theories and the generalized AGT relation will also be discussed. This talk is based on a few papers 1309.3266, 1411.4694, 1505.06207, 1705.01896 and some work in progress.

 

Andrew Long (UM): Black Holes, Nuggets, & Blobs.  Oh my! | 9/28/18

The past few years have seen a growing interest to explore dark matter candidates that are outside of the standard WIMP / axion paradigms.  A resurgence of macroscopic dark matter candidates have brought with it a mix of whimsical names — primordial black holes, asymmetric dark matter nuggets, and dark blobs — to name a few.  In general the difficulty with macro dark matter is not the observational constraints, which are typically quite sparse and weak, but rather the challenge is finding a well-motivated mechanism for producing gram-sized dark matter objects.  In this talk, I will argue that “dark quark nuggets” are a generic prediction of confining, hidden-sector gauge theories.  I will discuss the phenomenology of these theories, the cosmological production of dark quark nuggets, and their observational probes.  

10/5/18 No talk scheduled

Nausheen Shah (Wayne State) :Higgs and Dark Matter: Absence of Evidence != Evidence of Absence? | 10/12/18

Since the Higgs discovery in 2012, the LHC has not found any conclusive evidence for the presence of New Physics (NP) at the weak scale. While there are stringent limits on strongly interacting NP, the weakly interacting sector is minimally constrained. In addition, dark matter direct detection experiments have been putting increasingly stringent bounds on the cross sections of dark matter particles scattering off nuclei. This has led to wide spread pessimism regarding the WIMP paradigm and most well studied SUSY models such as the MSSM or the NMSSM. I take a different view point. What if the lack of evidence, instead of being due to absence of NP at the weak scale, is actually telling us where NP could be hiding? In that spirit I will discuss the implications for an extended Higgs sector of a SM-like Higgs in generic 2HDMs+, using the NMSSM as motivation. Next I will talk about the possible connections of 2HDMs with dark matter using an EFT formulation, particularly focusing on the connotations of null signals in direct detection experiments. Finally, I will discuss some tantalizing recent results from electroweakino searches at the LHC, showing how these may be consistent with astrophysical observations, and fit naturally in the MSSM/NMSSM setup. 

 

 Jim Halverson (Northeastern): Complexity of Vacua and Near-Vacua |10/19/18

In this talk I will study the computational complexity of vacua and near-vacua in field theory and string theory. From analogy to protein folding, it is natural to expect that finding stable vacua is computationally hard, in the sense of complexity theory. However, I will demonstrate that this is the case even for metastable vacua. The problem is exacerbated in string theory, since setting up the hard problem of finding string vacua requires actually computing the scalar potential in a controlled regime. Such computations involve solving instances of computationally hard problems. Cosmological implications will be discussed in light of a recently proposed measure that utilizes computational complexity.

 

Tim Cohen  (U Oregon): Hunting for Heavy Winos |10/26/18

I will discuss recent progress in calculating a precision photon spectrum for heavy wino annihilation to photons, along with implications for indirect detection experiments.  I will review arguments that the 3 TeV mass wino is one of the simplest WIMP dark matter candidates.  Then I will discuss how the large separation of scales from 3 TeV to the weak scale leads to a breakdown of perturbation theory.  I will demonstrate how one can rely on modern effective field theory techniques to restore the convergence of the perturbative expansion, and will discuss our precision prediction for the wino annihilation spectrum.  I will review the status of searching for these photons using a ground based air Cherenkov telescope array (the H.E.S.S. experiment), along with the impact of our calculation on the interpretation of these limits.

 

Savdeep Sethi (UChicago) : The Status of the String Landscape | 11/2/18

Whether string theory admits a multiverse of de Sitter solutions that look approximately like our universe is a hotly debated current topic. I will overview the basics of landscape constructions and explain my view on this question. 

 

 Jesse Thaler (MIT): Deep Sets for Particle Jets| 11/9/18

One of most basic facts about quantum mechanics is that identical particles are indistinguishable.  One of most basic facts about quantum field theory is that only infrared-and-collinear-safe observables can be calculated in a fixed-order expansion.  In this talk, I show how to incorporate both of these facts into a novel machine learning architecture called Energy Flow Networks (EFNs).  EFNs are a special case of a more general architecture called Deep Sets, with the nice feature that one can "open the box" of an EFN to gain insight into what the network has learned.  Using the example of quark/gluon jet tagging at the LHC, I highlight the excellent performance of EFNs and their intuitive visualization.

 

No Talk Scheduled| 11/16/18

 

Thanksgiving, No Talk| 11/23/18

 

Asimina Arvanitaki (Perimeter   Institute): Particle Physics Beyond Colliders| 11/30/18

Recently there have been several proposals of low-energy precision experiments that can search for new particles, new forces, and the Dark Matter of the Universe in a way that is complementary to collider searches. In this talk, I will present some examples involving atomic clocks, nuclear magnetic resonance, molecules, and astrophysical black holes accessible to LIGO.