Tony Gherghetta (Minnesota): Partially Composite Supersymmetry | 9/4/20
Partial compositeness can be used to explain the Standard Model fermion mass hierarchy and predict the sfermion mass spectrum in a supersymmetric model. It assumes that the Higgs and third-generation matter superfields are elementary, while the first two matter generations are composite, with a linear mixing between elementary superfields and supersymmetric operators with large anomalous dimensions. This gives rise to a split-like, supersymmetric model that intricately connects the sector responsible for the generation of flavor with supersymmetry breaking to produce a unique sparticle spectrum. The inverted sfermion mass spectrum can be probed at future flavor violation experiments such as Mu2e or searches for the electron and neutron electric dipole moment.
Abhijit Gadde (Tata Institute of Fundamental Research, Mumbai): Modularity of supersymmetric partition functions | 9/25/20
In this talk, I will present a novel modular property of 4d N=1 supersymmetric partition functions of supersymmetric theories with R-symmetry. It is a generalization of the modular invariance of the supersymmetric partition function of two-dimensional supersymmetric theories on a torus i.e. of the elliptic genus. It comes from requiring consistency of partition functions under gluing and, among other things, can be used to rederive the supersymmetric Cardy formula for four-dimensional gauge theories that has played a key role in computing the entropy of supersymmetric black holes.
Andrea Puhm (Institute Polytechnique de Paris): A Double Copy for Celestial Amplitudes | 10/9/20
Celestial amplitudes which use conformal primary wavefunctions rather than plane waves as external states offer a novel opportunity to study properties of amplitudes with manifest conformal covariance and give insight into a potential holographic celestial CFT at the null boundary of asymptotically flat space. With the notion of energy traded for the conformal dimension under the Lorentz group acting on the celestial sphere, energetically soft theorems of QFT scattering amplitudes are replaced by "conformally soft" theorems. Moreover, since translation invariance is obscured in the conformal basis, features of amplitudes that heavily rely on it, such as the remarkable relations between gauge theory and gravity amplitudes known as the double copy, appear to be lost. My main focus in this talk is to show that there exists nevertheless a well-defined procedure for a celestial double copy. This requires a generalization of the usual squaring of numerators to first promoting them to generalized differential operators acting on external wavefunctions, and then squaring them. I will end with recent results on how to obtain celestial loop amplitudes from tree level ones.
Jim Halverson (Northeastern): Neural Networks and Quantum Field Theory | 10/16/20
We propose a theoretical understanding of neural networks in terms of Wilsonian effective field theory. The correspondence relies on the fact that many asymptotic neural networks are drawn from Gaussian processes, the analog of non-interacting field theories. Moving away from the asymptotic limit yields a non-Gaussian process and corresponds to turning on particle interactions, allowing for the computation of correlation functions of neural network outputs with Feynman diagrams. Minimal non-Gaussian process likelihoods are determined by the most relevant non-Gaussian terms, according to the flow in their coefficients induced by the Wilsonian renormalization group. This yields a direct connection between overparameterization and simplicity of neural network likelihoods. Whether the coefficients are constants or functions may be understood in terms of GP limit symmetries, as expected from 't Hooft's technical naturalness. General theoretical calculations are matched to neural network experiments in the simplest class of models allowing the correspondence. Our formalism is valid for any of the many architectures that becomes a GP in an asymptotic limit, a property preserved under certain types of training.
Sebastian Mizera (IAS): Feynman Integrals and Intersection Theory | 10/23/20
Singularity structure of scattering amplitudes is as intricate as it is inscrutable. Work in this area over the recent years has been hinting at an existence of a “scalar product” between Feynman integrals, which would tell us how to characterize their analytic behavior. In this talk I will explain how to formulate this notion using the tools of intersection theory as well as review its theoretical and practical applications.
Robert McGehee (UM): Direct Detection Signals from Absorption of Fermionic Dark Matter | 11/6/20
Absorption of fermionic dark matter leads to a range of distinct and novel signatures at dark matter direct detection and neutrino experiments. We study the possible signals from fermionic absorption by nuclear or electron targets, which we divide into two classes of four Fermi operators: neutral and charged current. In the neutral current signal, dark matter is absorbed by a target nucleus or electron and a neutrino is emitted. For nuclear targets, this results in a characteristically different nuclear recoil energy spectrum from that of elastic scattering. For electron targets, we calculate electron recoil spectra in xenon-based detectors for sub-MeV dark matter. The charged current channel is specific to nuclear targets and leads to induced beta decays in isotopes which are stable in vacuum as well as shifts of the kinematic endpoint of beta spectra in unstable isotopes. Last, we present UV completions of the four Fermi operators which give rise to these signals and study the prospects of seeing an absorption signal in light of other constraints, such as dark matter decays and mediator searches.
