I will present a classification of all unitary, rational conformal field theories with two primaries, central charge c < 25, and arbitrary Wronskian index. These are shown to be either certain level-1 WZW models or cosets of meromorphic theories by such models. By leveraging the existing classification of  meromorphic CFTs of central charge c ≤ 24, all the relevant cosets are enumerated and their characters computed. This leads to 123 theories, most of which are new. It will be emphasised that this is a classification of RCFTs and not just consistent characters. Work in collaboration with Brandon Rayhaun.

This is a joint Theory Seminar/Strings Seminar

It has long been known that smooth crossovers between “Higgs” regimes and “confining” regimes are possible in some gauge theories with fundamental representation matter, leading to a notion of Higgs/confinement “complementarity”.  But the validity, or otherwise, of such complementarity can be subtle, especially in massless phases with Goldstone bosons.  This talk will examine the presence or absence of Higgs/confinement phase transitions, when there are no distinguishing local order parameters, in both instructive models and in dense QCD.

Abstract: The Deep Underground Neutrino Experiment (DUNE) will be the leading next-generation particle project in the US.  It aims to measure CP violation in the neutrino sector and determine the mass ordering of neutrinos.  These measurements are straightforward conceptually but challenging practically.  One outstanding issue is the modeling of GeV neutrino-nucleus interaction.  With a lack of a proper theoretical framework, it is not only difficult to simulate neutrino events in the detector accurately but also difficult to assess its impact on the physics measurements.  I will discuss our attempts at understanding how cross-section uncertainties impact oscillation measurements and new physics searches.

Abstract: The Deep Underground Neutrino Experiment (DUNE) will be the leading next-generation particle project in the US.  It aims to measure CP violation in the neutrino sector and determine the mass ordering of neutrinos.  These measurements are straightforward conceptually but challenging practically.  One outstanding issue is the modeling of GeV neutrino-nucleus interaction.  With a lack of a proper theoretical framework, it is not only difficult to simulate neutrino events in the detector accurately but also difficult to assess its impact on the physics measurements.  I will discuss our attempts at understanding how cross-section uncertainties impact oscillation measurements and new physics searches.

String Theory modifies general relativity with Chern-Simons terms.  In this talk we show how this theory naturally encodes a graviaxion dark matter particle, baryogenesis during cosmic inflation, and leaves imprints on gravitational wave signals in compact binary systems.

After introducing the Taylor expansion method for lattice QCD calculations at non-vanishing baryon chemical potential, I will scrutinize the limitations of the method arising from the presence of Yang-Lee edge singularities in the QCD phase diagram. I will discuss a newly introduced resummation scheme for the Taylor expansion to overcome this limitation and show the efficacy of this scheme using a simple solvable model. I will present some results from realistic lattice QCD calculations utilizing this resummation scheme. I will conclude by introducing a generalized version of the scheme that can resum the recently proposed multi-parameter Taylor expansion. 

Scattering amplitudes are the arena where quantum field theory directly meets collider experiments. An excellent model for scattering in QCD is provided by N=4 super-Yang-Mills theory, particularly in the planar limit of a large number of colors, where the theory becomes integrable, and amplitudes become dual to light-like polygonal Wilson-loop expectation values. The first nontrivial case is the 6-gluon amplitude (hexagonal Wilson loop), which can be computed to 7 loops using a bootstrap which is based on the rigidity of the function space of multiple polylogarithms, together with a few other conditions. It is also possible to bootstrap a particular form factor for the chiral stress-tensor operator to produce 3 gluons, through 8 loops. Remarkably, the two sets of results are related by a mysterious “antipodal” duality, which exchanges the role of branch cuts and derivatives. I will describe how the bootstrapping works and what we know about this new duality.

I’ll review a new, simpler explanation for the large scale geometry of spacetime, presented in our recent preprint arXiv:2201.07279. The basic ingredients are elementary and well-known, namely Einstein’s theory of gravity and Hawking’s method of computing gravitational entropy. The new twist is provided by the boundary conditions we proposed for big bang-type singularities, allowing conformal zeros but imposing CPT symmetry and analyticity at the bang. These boundary conditions allow gravitational instantons for universes with positive Lambda, massless radiation and positive or negative space curvature. Using them, we are able to infer the gravitational entropy for a complete set of quasi-realistic, four-dimensional cosmologies. If the total entropy in radiation exceeds that of Einstein’s static universe, the gravitational entropy exceeds the de Sitter entropy. As the total entropy is increased,  the most probable large-scale geometry for the universe becomes increasingly flat, homogeneous and isotropic. I’ll briefly summarize recent progress towards elaborating this picture into a fully predictive cosmological theory.

Electroweak interactions assign a central role to the gauge group 𝑆𝑈(2)𝐿×𝑈(1)𝑌 , which is either realized linearly (SMEFT) or nonlinearly (e.g., HEFT) in the effective theory obtained when new physics above the electroweak scale is integrated out. Although the discovery of the Higgs boson has made SMEFT the default assumption, nonlinear realization remains possible.