High Energy Physics

Gravity is exciting from both theoretical and observational perspectives. In this talk, I will discuss how gravitational observables, such as waveforms, can be determined from scattering amplitudes in quantum field theory. We can therefore use the full arsenal of theoretical collider physics to compute gravitational waveforms. As an example, I will describe the waveform generated in a scattering process at next-to-leading order. I will finish by discussing how amplitudes can further be used to understand non-radiative aspects of gravity, including the curvature of the Kerr metric itself. This leads to a network of “double copy” relations between classical solutions of the Maxwell and Einstein equations.

Zoom link:  https://pitp.zoom.us/j/92038383246?pwd=RjQwVHo1VWR6VDl0a3VPZEU0ZXFyUT09

We study the low-energy effective action for relativistic superfluids obtained by integrating out the heavy fields of a UV theory. A careful renormalization procedure is required if one is interested in deriving the EFT to all orders in the light fields (at a fixed order of derivatives per field). The result suggests a general relation between finite density and spontaneous symmetry breaking for QFTs of interacting scalars with an internal global symmetry. The ground state at finite chemical potential of these systems is usually associated with a superfluid phase, in which the global symmetry is spontaneously broken along with Lorentz boosts and time translations. We show that this expectation is always realized at one loop for complex scalar fields with arbitrary UV potential in d > 2 spacetime dimensions. The physically distinct phenomena of finite charge density and spontaneous symmetry breaking occur simultaneously. We quantify this result by deriving universal scaling relations for the symmetry breaking scale as a function of the charge density, at low and high density. Moreover, we show that the critical value of μ coincides with the pole mass. The same conclusions hold non-perturbatively for an O(N) theory with quartic interactions in d = 3, at leading order in the 1/N expansion. In order to do this we compute analytically the one-loop effective potential at finite μ and zero temperature. As an application we derive in closed form the one-loop EFT for superfluid phonons for arbitrary UV scalar potentials in d > 2. From this we obtain analytically the one-loop scaling dimension of the lightest charge n operator in the $\phi^6$ conformal superfluid in d=3, at leading order in 1/n, reproducing a numerical result of Badel et al. 

Zoom Link:  https://pitp.zoom.us/j/97727675289?pwd=TWJyNzRucEhkM0JNM0NWeEdMM0xTQT09

A new approach for the first quantization of superstrings, called B-RNS-GSS formalism, is being constructed. It consists of quantizing embeddings of super surfaces into superspaces. As in the classical theory of super-embeddings, it has twistor-like variables. In this talk, besides motivating the need for such a formalism, I will review the work done in hep-th: 2211.06899, where the hetetoric supergravity equations of motion were derived from BRST nilpotency.

Zoom link:  https://pitp.zoom.us/j/98656433153?pwd=NjlpcUtITDAwWlgycUtUZUVsZ3QrQT09

Taking string theory off shell requires breaking Weyl invariance on the worldsheet, i.e. the worldsheet theory is now a QFT instead of a CFT. I will explain Tseytlin’s first-quantized approach to taking the worldsheet theory off-shell in a consistent manner, with a particular emphasis on the subtleties involved in calculating the sphere amplitude. This approach allows for the derivation of a classical string action which gives rise to the correct equations of motion and S-matrix, to all orders in perturbation theory. 

I'll also explain the underlying conceptual structure of the Susskind and Uglum black hole entropy argument. There I will show explicitly how the classical (tree-level) effective action and entropy S = A/4G_N may be calculated from the sphere diagrams. 

Time permitting, I will discuss ongoing efforts to derive the Ryu-Takayanagi formula in string theory.

Based on arXiv:2211.08607 and arXiv:2211.16448. 

Zoom link:  https://pitp.zoom.us/j/93668017324?pwd=K2pxZEhjalRTWkVVbVRESCtRVDFmUT09