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.

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Wednesday 29th January, 2:30 - 3:30

3481 Randall Lab

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.

]]>Ultracold atoms are amongst the excellent test beds to study coherent quantum chemistry due to capabilities of controlling quantum states of the atoms with precision. In my talk, I will discuss how to control quantum pathway interferences in an ultracold molecule formation that is induced by a laser light, a process known as photoassociation (PA). We utilize a Rb-87 Bose-Einstein condensate (BEC) apparatus where all-optically-trapped condensates are prepared in superposition of different spin states in the F=1 hyperfine level. By controlling the cumulative phase of the reactants taking different scattering channels, we interferometrically control the normalized PA rate with perfect visibility. To control the relative phase between the two quantum pathways (scattering channels of spin 0 pairs and spin +1/-1 pairs), we exploit the inherent quadratic energy shift at low magnetic bias field strengths and a free evolution time after a spin population transfer with an RF pulse. Our method also serves as a robust measurement technique to determine quadratic Zeeman energy splitting.

Short bio:

Dr. Hasan Esat Kondakci received his Ph.D. in 2015 from CREOL, the College of Optics & Photonics at the University of Central Florida, where he studied photon statistics in disordered lattices under the supervision of Prof. Bahaa Saleh (primary) and Prof. Ayman Abouraddy. Following his Ph.D., he worked on diffraction-free space-time light sheets and coherence phenomena in Prof. Ayman Abouraddy's lab at CREOL. Currently, he is a postdoctoral researcher in Prof. Yong Chen's lab at the Department of Physics and Astronomy at Purdue University. His current research interests include spin-orbit-coupled Bose-Einstein condensates, photo-association of ultracold atoms, and deterministic state rotations in d-dimensional Hilbert space.

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.

]]>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.

]]>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.

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