Paulo Glorioso (UChicago): " Effective field theory near and far from equilibrium" | 1/15/20
I will discuss effective field theories for two classes of non-equilibrium systems, one far and one near equilibrium. In the first part I will present an effective response theory for topological driven (Floquet) systems, which are inherently far from equilibrium. As an example, I will discuss a topological chiral Floquet drive coupled to a background $U(1)$ field, which gives rise to a theta term in the effective action. In the second part, I will discuss an ongoing project using effective field theories for hydrodynamics. I will show that chiral diffusion for interacting systems in 1+1 dimensions, which may be relevant to edge transport in quantum Hall systems, has an infrared instability. I will then discuss the fate of this instability.
Siddharth Mishra-Sharma (NYU) : "Statistical inference of dark matter substructure with weak and strong gravitational lensing" | 1/29/20
The Dark matter structures are expected to exist over a large range of scales, and their properties and distribution can strongly correlate with the underlying particle physics. In this talk, I will describe two separate methods to statistically infer the properties of dark matter substructure using (astrometric)-weak and strong lensing observations, respectively. In the first part of the talk, I will describe how the motion of subhalos in the Milky Way induces a correlated pattern of motions in background celestial objects---known as astrometric weak lensing---and how global signatures of these correlations can be measured using the vector spherical harmonic decomposition formalism. These measurement can be used to statistically infer the nature of substructure, and I will show how this can be practically achieved with future astrometric surveys and/or radio telescopes such as WFIRST and the Square Kilometer Array. Next, I will describe a novel method to disentangle the collective imprint of dark matter substructure on extended arcs in galaxy-galaxy strong lensing systems using likelihood-free (or simulation-based) inference techniques. This method uses neural networks to directly estimate the likelihood ratios associated with population-level parameters characterizing substructure within lensing systems. I will show how this method can provide an efficient and principled way to mine the large sample of strong lenses that will be imaged by future surveys like LSST and Euclid to look for signatures of dark matter substructure. I will emphasize how the statistical inference of substructure using these techniques can be used to stress-test the Cold Dark Matter paradigm and probe alternative scenarios such as scalar field dark matter and enhanced primordial fluctuations.
Martin Fluder (Caltech): "The supersymmetric Cardy formula from effective actions" | 2/5/20
In this talk I will discuss supersymmetric Cardy formulae in d=4 and d=6. These formulae govern the universal behavior in the high-temperature regime of supersymmetric partition functions — or, in the case of the superconformal index, they govern the high-energy asymptotics of SUSY operators at large energy. I will outline the proof of the Cardy formulae for theories with moduli spaces of vacua, which relies on an effective supersymmetric Chern-Simons action in d-1 dimensions. I will argue that this effective action is universal and intimately related to perturbative as well as global gravitational anomalies. Finally, I will discuss some immediate consequences of our results and briefly compare and distinguish our results to other proposed Cardy formulas.
Ken Van Tilburg (UCSB): "The Large-Misalignment Mechanism for Compact Axion Structures" | 2/12/20
Axions are some of the best motivated particles beyond the Standard Model. I will show how the attractive self-interactions of dark matter (DM) axions over a broad range of masses, from 10^−22 eV to 10^7 GeV, can lead to nongravitational growth of density fluctuations and the formation of bound objects. This structure formation enhancement is driven by parametric resonance when the initial field misalignment is large, and it affects axion density perturbations on length scales of order the Hubble horizon when the axion field starts oscillating, deep inside the radiation-dominated era. This effect can turn an otherwise nearly scale-invariant spectrum of adiabatic perturbations into one that has a spike at the aforementioned scales, producing objects ranging from dense DM halos to scalar-field configurations such as solitons and oscillons. This "large-misalignment mechanism" leads to various observational consequences in gravitational lensing and interactions, baryonic structures and star formation, direct detection (including for the QCD axion), and stochastic gravitational waves.
Cheng Peng (UC Davis): "SYK, Chaos, and higher-spin" | 2/19/20
I will discuss two related topics in the talk. In the first part, I will discuss a 2-dimensional SYK-like model whose moduli space consists of both a chaotic regime and corners with emergent higher-spin symmetry. This model provides a manifest realization of the widely believed connection between SYK-like models and higher-spin theories. In the second part, I will discuss a general class of coupled quantum systems that share a somewhat surprising property: their ground states approximate the thermofield double state to very good accuracy. This provides a practical way to prepare the thermofield double state.
Mikhail Solon (Caltech): “Binary Black Holes and Scattering Amplitudes” | 2/26/20
We develop a systematic framework for describing binary dynamics using modern tools from quantum field theory. Our approach combines onshell methods such as generalized unitarity and the double-copy construction with effective field theory methods for integration and matching. As a first application, we derive a new result in general relativity: the third post-Minkowskian correction to the conservative two-body Hamiltonian for spinless black holes. Prospects and challenges for applying quantum field theory for the gravitational wave physics program are discussed.
Cancelled talks due to COVID 19
Natalie Paquette (Caltech) 3/11/20
Fabrizio Rompineve (Tufts) 3/18/20
Joaquin Turiaci (UCSB) 3/25/20
Lena Funcke (Perimeter) 4/1/20
Joonho Kim (IAS Princeton) 4/8/20
Djuna Croon (TRIUMF) 4/15/20
