Quantum Fields and Strings

The holographic duality between strongly coupled quantum field theories and weakly coupled gravitational theories in one higher dimension holds, in principle, the promise of understanding strongly coupled systems that occur in condensed matter physics, such as the "strange" metals that appear in materials such as high-Tc cuprates. Unfortunately, the holographic models of metals that have previously been studied have not been successful in capturing even the most basic physics that any realistic model of a metal should obey. In this talk, I will review the essential properties that any metal (strongly coupled or not) must satisfy, and propose a new holographic model that is consistent with these requirements. The new model is based on a radically different approach compared with previous holographic models of metals, and crucially relies on recent work that formulates in a precise way the conditions for an IR effective field theory to be "emergeable" from a UV theory at nonzero charge density. In particular, the holographic model I study is dual to a quantum field theory with a global symmetry group LU(1) -- the "loop group" whose elements are smooth functions from the circle into U(1). I present the results of a solution of the model and argue that its properties are qualitatively consistent with what one should expect to find in a strongly coupled metal.

Zoom Link: TBD

It has long been known in studies of Pion physics, non-linear sigma models and cosmology that thinking in terms of field space metrics can be useful. Such an approach can help identify and define field redefinition invariant physics in observables. This approach is reemerging recently an a key organizing principle and calculational tool for interpreting collider physics data to study Higgs properties. I will review some known results and discuss outstanding issues being worked on in this area. 

Zoom Link: https://pitp.zoom.us/j/96662488113?pwd=cGs0THQwWXRkcm9pVzcwVytnNjZ5Zz09

For a theory whose half-BPS sector can be described by N=4 quiver quantum mechanics, its BPS algebra (à la Harvey-Moore) is given by the quiver Yangian. I will first review the construction of the BPS quiver Yangians and then discuss their applications, such as on BPS counting, Gauge/Bethe correspondence, and knot-quiver correspondence. 

Zoom Link: TBD

I review a class of quantum error correcting codes that directly takes into account the large-N aspects of holographic theories. I will discuss some aspects of the vacuum sector of these codes and use them to show the equivalence between two different approaches to entanglement wedge reconstruction.

Zoom link:  https://pitp.zoom.us/j/96318197584?pwd=YXJEdkJrVktXVmI3SWVlRmlaK3A4Zz09

Universal properties of two-dimensional conformal interfaces are encoded by the flux of energy transmitted and reflected during a scattering process.

In this talk, I will develop a method that allows me to extend previous results based on thin-brane holographic models to smooth domain-wall solutions of 3-dimensional gravity.

As an application, I will compute the transmission coefficient of a Janus interface in terms of its deformation parameter.

Zoom link:  https://pitp.zoom.us/j/98684574364?pwd=WGdrQXhRcHRJZUZMYmNObUVZT1ZCZz09

We construct two-dimensional quantum states associated to four-dimensional linearized rotating self-dual black holes in (2,2) signature Klein space. The states are comprised of global conformal primaries circulating on the celestial torus, the Kleinian analog of the celestial sphere. By introducing a generalized tower of Goldstone operators we identify the states as coherent exponentiations carrying an infinite tower of w1+inf charges or soft hair. We relate our results to recent approaches to black hole scattering, including a connection to Wilson lines, S-matrix results, and celestial holography in curved backgrounds.

Zoom link:  https://pitp.zoom.us/j/94163164577?pwd=RHFVZU5XUEN0T3c3Zm1VR3VhZnNsZz09

We develop the bulk geometric description of correlation functions of operators whose scaling dimensions are of order the central charge in AdS/CFT. We follow a bottom-up approach, discussing solutions to Einstein gravity that are closely related to familiar black holes in AdS. In order to reproduce the correct dependence of a conformal correlation function on the location of operator insertions, we must introduce a novel Gibbons-Hawking-York boundary term associated with the stretched horizon of each black hole. We discuss the bulk dual of two point functions in CFT’s living in arbitrary dimensions. Specializing to AdS3 allows us to discuss higher point functions, where we find that the dual geometries are sometimes multi-boundary wormholes, whose holographic interpretation has been the focus of much recent activity.

Zoom Link: TBD

I will construct a top-down example of celestial holography, based on recent work with Costello and Paquette. Our duality relates certain models of self-dual gauge theory and conformal gravity, placed on an asymptotically flat four dimensional spacetime called Burns space, to a two dimensional chiral algebra living on D1-branes in a topological string theory on twistor space.

Zoom link:  https://pitp.zoom.us/j/92898535744?pwd=T2w2SUp0VnU5NWtPSm50VENvWlRYQT09

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

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