Josh Foster (MIT) : Lumped Element Axion Detection at All Frequencies | 1/18/2023
Lumped element detectors utilizing inductive couplings to an axion effective current represent a promising detection concept for light (neV-ueV) axion dark matter. Lumped element detectors that have been realized thus far have operated in a geometrically small limit that admits a magnetoquasistatic approximation for sensitivity calculations, but their sensitivities at higher frequencies have remained poorly understood. In this talk, I will present new work studying the sensitivity of lumped element detectors in the high-frequency limit, revealing new challenges and opportunities for the rapidly developing experimental paradigm.
Finn Larsen (UMICH) : Introduction to Holographic Complexity | 1/25/2023
Jose De La Cruz Moreno (LCTP) : Detecting knot topology from Chern-Simons theory | 2/15/2023
The topological knot invariants can be studied in the context of Chern-Simons theory both in the non-perturbative and the perturbative regimes. In the former case polynomial knot invariants can be obtained while in the latter case the so called Vassiliev knot invariants arise. Recent work in the non-perturbative regime has been done with the incorporation of entanglement entropy computations associated with knot states, while in the perturbative regime the Vassiliev invariants have been extended to include information of a vector field in the theory.
Grant Remmen (KITB, UCSB) : Veneziano Variations: How Unique are String Amplitudes? | 3/08/2023
String theory offers an elegant and concrete realization of how to consistently couple states of arbitrarily high spin. But how unique is this construction? In this talk, I will derive a novel, multi-parameter family of four-point scattering amplitudes exhibiting i) polynomially bounded high-energy behavior and ii) exchange of an infinite tower of high-spin modes, albeit with a finite number of states at each resonance. These amplitudes take an infinite-product form and, depending on parameters, exhibit mass spectra that are either unbounded or bouended, thus corresponding to generalizations of the Veneziano and Coon amplitudes, respectively. For the bounded case, masses converge to an accumulation point, a peculiar feature seen in the Coon amplitude but more recently understood to arise naturally in string theory. Importantly, our amplitudes contain free parameters allowing for the customization of the slope and offset of the spin-dependence in the Regge trajectory. We compute all partial waves for this multi-parameter class of amplitudes and identify unitary regions of parameter space. For the unbounded case, we apply similar methods to derive new deformations of the Veneziano and Virasoro-Shapiro amplitudes.
Tim Cohen (Oregon/CERN) : Large Deviations in the Early Universe | 3/17/2023
Fluctuations play a critical role in cosmology. They are relevant across a range of phenomena from the dynamics of inflation to the formation of structure. In many cases, these it is a good approximation to coarse grain these fluctuations (in the sense of a Renormalization Group flow), and they follow a Gaussian distribution as a consequence of the Central Limit Theorem. Yet, some classes of observables are dominated by rare fluctuations and are sensitive to the details of the underlying microphysics. In this talk, I will introduce the Large Deviation Principle, and will explain how it can be used to diagnose when effective approaches fail and one must instead to appeal to the microscopic description. I will illustrate this phenomenon in the context of determining the phase transition to eternal inflation, the distribution of scalar field fluctuations in de Sitter, and the production of primordial black holes.
Shreya Vardhan (Stanford) : Non-isometric codes and the black hole interior | 3/22/2023
At late times, any holographic map from the large semiclassical Hilbert space in the interior of a black hole to the smaller Hilbert space in the boundary must be non-isometric. This implies that a large set of states in the bulk description do not exist in the fundamental description of the system. Despite this, I will show using a simple model that bulk states and operators whose complexity is sub-exponential in the black hole entropy can be represented in the boundary. I will also discuss the validity of the quantum extremal surface formula and entanglement wedge reconstruction for this non-isometric map.
Sam Hollier (Harvard) : Models of Higgsed CP and their Cosmology | 3/29/2023
Nelson-Barr models, which assume that CP is a spontaneously broken symmetry of nature, are a well-known solution to the strong CP problem with no new light degrees of freedom. Nevertheless, the spontaneous breaking of CP can have dramatic implications in cosmology. It was recently shown that domain walls which form from this spontaneous breaking are exactly stable, and therefore must be inflated away. Combined with the "Nelson-Barr quality problem", which sets an upper bound on the breaking scale to avoid the effects of dangerous irrelevant operators, this puts an upper bound on the scale of inflation and the subsequent reheating temperature. In this talk, I will briefly review the Nelson-Barr solution to the strong CP problem, its quality problem, and demonstrate that minimal Nelson-Barr models are in tension with simple models of inflation and thermal leptogenesis. I will also show one possibility for ameliorating this tension by introducing a new, chiral symmetry which forbids the most dangerous dimension-5 operators.
Scott Collier (Princeton) : 3d gravity and Teichmuller TQFT | 4/05/2023
I will describe a proposal that relates AdS_3 quantum gravity to a topological quantum field theory known as ``Teichmuller TQFT.’’ This proposal makes precise the idea that pure AdS_3 quantum gravity is related to two copies of SL(2,R) Chern-Simons theory and resolves some well-known issues with this lore. I will argue that moreover this proposal provides a systematic and practical tool for the computation of partition functions of 3d gravity, and will describe how it elucidates the recent ensemble interpretation of semiclassical 3d gravity. (Based on work in progress with Lorenz Eberhardt and Mengyang Zhang.)
