Finn Larsen (UM) : A nAttractor Mechanism for nAdS(2)/nCFT(1) | 1/18/19
Michael Baker (U Zurich) : Dark Matter Production: Finite Temperature Effects in the Early Universe | 1/25/19
In the early universe, the Standard Model particles formed a hot thermal bath. We highlight the importance of finite temperature corrections in these conditions on various production mechanisms of dark matter, primarily through temperature dependent masses and scalar vevs. We first consider a variation on standard freeze-out, where kinematic thresholds determine the relic abundance. We then consider a freeze-in model where the production rate is dramatically increased when a kinematic threshold opens. Finally, we present a qualitatively new production mechanism for dark matter, where dark matter decay is allowed for a limited amount of time just before the electroweak phase transition.
Thomas Dumitrescu : From Seiberg-Witten Theory to Adjoint QCD | 2/1/19 ( Cancelled due to unforeseen circumstances)
Ben Safdi (UM) : The Search for Axion Dark Matter | 2/8/19
Dark matter is the dominant source of matter in our Universe. However, while dark matter dictates the evolution of large-scale astrophysical systems through its gravitational effects, the particle nature of dark matter is unknown. This is despite the significant effort that has gone into the search for particle dark matter over the past decades. In this talk I will review the current status of the search for particle dark matter. I will focus specifically on a dark matter particle candidate called the axion, which is both well-motivated theoretically and also relatively unexplored experimentally. I will outline the near-term program for searching for axion dark matter and show that if this theory is correct, then we will probably know soon.
Daniel Kabat (CUNY) : Building bulk observables in AdS/CFT | 2/15/19
The AdS/CFT correspondence relates a theory of gravity in anti-de Sitter space to a CFT on the boundary. A natural question is how local fields in AdS can be expressed in terms of the CFT. In the 1/N expansion this can be done by (i) identifying suitable building blocks - free bulk fields - in the CFT, (ii) assembling the building blocks to make interacting bulk fields. I'll present an approach where the first step is carried out using modular flow in the CFT and the second step is driven by requiring bulk causality.
Sean Tulin (York University) : New directions in self-interacting dark matter, from astrophysics to the lattice | 3/15/19
Dark matter may have its own dark forces and interactions that are distinct from the Standard Model and unrelated the weak scale. To test this idea, galaxies and clusters of galaxies serve as cosmic colliders for measuring self-scattering among dark matter particles. Present constraints imply that if self-interactions are to solve the infamous core-cusp problem in dwarf galaxies, the scattering cross section must fall with energy/velocity to avoid cluster limits. To test this velocity dependence, I present new constraints on dark matter self-interactions at an intermediate scale with groups of galaxies. I also describe using mock observations from N-body simulations of self-interacting dark matter with baryons as a test of our methods. Lastly, I describe some recent work toward strongly-coupled theories of self-interacting dark matter, using tools borrowed from lattice QCD to compute its properties nonperturbatively.
Jessie Shelton (UIUC) : Dark Matter In and Out of Equilibrium | 3/29/19
One generic scenario for the dark matter of our universe is that it resides in a hidden sector: it talks to other dark fields more strongly than it talks to the Standard Model. I'll discuss some simple, WIMP-y models of this kind of hidden sector dark matter, paying particular attention to what we can learn from the cosmic history of the dark sector. In particular, the need to populate the dark sector in the early universe can control the observability of dark matter today. Some results of interest include new cosmological lower bounds on direct detection cross-sections and simple models of dark matter with parametrically novel behavior.
Sera Cremonini (Lehigh) : Intertwined orders and fermions in holography | 4/5/19
Behind the unconventional behavior of many strongly interacting quantum systems is an intrinsically complex phase diagram exhibiting a variety of orders. These may not only compete but also cooperate with each other, describing phases with a common origin that are intertwined. Holographic techniques provide a theoretical laboratory to probe such strongly correlated systems, offering a new window into their dynamics. In this talk I will discuss a holographic model of a striped superconductor, which provides a concrete realization of intertwined orders. I will also examine the formation and structure of Fermi surfaces in various holographic systems with broken translational invariance. In particular, we will see that sufficiently strong lattice effects generically cause the Fermi surface to dissolve, leaving behind disconnected segments. This segmentation process is reminiscent of the puzzling Fermi arc phenomenon observed in the high temperature superconductors.
David Curtin (U toronto) : Cosmology and Astrophysics of the Twin Higgs | 4/12/19
The Twin Higgs model is an attractive solution to the little Hierarchy problem with top partners that are neutral under SM gauge charges. The framework is consistent with the null result of LHC colored top partner searches while offering many alternative discovery channels. Depending on model details, the phenomenology looks very different: either spectacular long-lived particle signals at colliders, or a plethora of unusual cosmological and astrophysical signatures via the existence of a predictive hidden sector. I will examine the latter possibility, and describe how the asymmetrically reheated Mirror Twin Higgs provides a predictive framework for a highly motivated and highly non-trivial interacting dark sector, with correlated signals in the CMB, Large Scale Structure, and direct detection searches, as well as higgs precision measurements at colliders. This provides a vivid example of the collider-cosmology complementarity, and motivates a variety of new astrophysical searches, including the search for X-ray point sources from Mirror Stars, that are motivated by the hierarchy problem.
