HEP Seminars – Spring 2024

APRIL 24 – *Note time change to 1:00 pm*

Topological Interfaces and Gauging Generalized Symmetries”

YIFAN WANG – New York University


We’ll describe gauging generalized symmetries in two-dimensional quantum field theory in terms of topological interfaces. We will see that familiar properties one encounters in gauging conventional invertible symmetries generalize naturally to non-invertible symmetries in this physical perspective. We will discuss a bootstrap approach to classify such topological interfaces, and correspondingly the different ways of gauging. We illustrate this general procedure for concrete generalized symmetries realized by concrete 2d CFTs and explain the physical consequences.



“Open-Closed String Duality and Topological Recursion”

ASHTON LOWENSTEIN – USC, Physics and Astronomy


A single family of differential equations, called string equations, has the ability to describe two classes of matrix models dual to non-supersymmetric and supersymmetric two-dimensional string theories. The string equations naturally contain information about both the open and closed string sectors of the theories, making them a useful tool to study open-closed duality. The perturbative solutions to these differential equations can be used to calculate all observables in the models, including asymptotic boundary partition functions and FZZT brane quantities. I will provide several examples of the utility of open-closed duality, including calculating the trumpet path integral and Weil-Petersson volumes in arbitrary topological gravity backgrounds, with and without supersymmetry.



“Non-Perturbative Effects in 2D Conformal Field Theories via Resurgence”

VIRAJ MERULIYA – McGill University


In this talk, I will consider two-dimensional Conformal Field Theories (CFTs) in the semi-classical limit of large central charge-c. Observables within this regime are amenable to analysis via a 1/c expansion, revealing an asymptotic series that demands the inclusion of non-perturbative effects. Using techniques like Borel resummation, we can systematically study these effects. These ideas will be concretely applied to study the structure constants in Liouville theory using the DOZZ formula. We demonstrate how non-perturbative effects in this context correspond to complex solutions to the Liouville equation. Along the way, we show that the Borel transform has a much simpler expression than the original DOZZ formula. This can provide a better understanding of its analytic structure and applications.



“A Synergy of Shockwaves, Edge Modes, and Infrared Physics”

TEMPLE HE – Caltech


In this talk, I will focus on two interesting directions of research in the infrared sector of gauge theories and gravity. First, we study the relationship between shockwave geometries and the gravitational memory effect in four-dimensional asymptotically flat spacetime. In particular, we show the ‘t Hooft commutation relations of shockwave operators are equivalent to the commutation relation between soft and Goldstone modes parametrizing a sector of the gravitational phase space. Second, we present a concrete connection between soft modes on the celestial sphere and entanglement edge modes in abelian gauge theory, paving the way to study entanglement properties of soft modes.



“Unoriented Perturbative JT Gravity and Matrix Models”



We will explore the perturbative expansion of Jackiw-Teitelboim (JT) gravity on oriented surfaces in terms of multicritical matrix models. Expanding our horizons, we will see that to incorporate unoriented surfaces in the perturbative expansion, we need the double scaling limit of the multicritical matrix models in the $$\beta=1$$ Dyson-Wigner class. They capture the physics of 2D quantum gravity coupled to minimal matter on unorientable surfaces, otherwise called unoriented minimal strings. Through a similar framework as oriented JT gravity, we will derive a formula for the density of states valid to all orders in perturbation theory, show how to define an interpolation between the multicritical models and that a certain interpolation among an infinite number of them provides an alternative definition of unoriented JT gravity.



“Bootstrap Meets Experimental Data”

NING SU – Caltech


The bootstrap method explores fundamental consistency conditions to constrain physical observations. The consistency conditions often translate into highly non-trivial numerical problems. In this talk, I will show that, with advanced numerical techniques, formal constraints such as unitarity and crossing symmetries lead to precise predictions for experimental phenomena in condensed matter and particle physics. I will discuss two experiments: the He4 superfluid phase transition and pion scattering. In both cases, bootstrap results provide insights into the experimental analysis. 



“Holography and Regge Phases at Large U(1) Charge”

GIULIA FARDELLI – Boston University


 A single Conformal Field Theory (CFT) can have a rich phase diagram with qualitatively different emergent behaviors in a range of different regimes parameterized by the conserved charges of the theory. In this talk, I will consider a CFT with a global U(1) current and explore the phase diagram as a function of the U(1) charge Q and angular momentum J, particularly at large J and Q. By taking the large J limit first, we are able to employ a dual holographic interpretation in AdS_{d+1} to predict the energy spectrum of Q-particle states. This limit has been studied in detail for Q=2, yielding very general results applicable to unitary CFTs in d>2. When Q is also taken to be large, the description is more complicated; nevertheless, we can draw interesting conclusions about the energy spectrum under certain assumptions. I will conclude with a concrete example, the O(2) model in 3d, highlighting interesting connections with recent (and less recent) results in this context.



“Tauberian Theorems and High Energy Asymptotic Data in CFT”

SRIDIP PAL – Caltech


In this talk, I will introduce Tauberian techniques, a widely used tool in analytical number theory, to expound on the universality in the \textit{averaged} asymptotic data of 2D CFT, specifically to probe the granularity of the averaging process and learn about the asymptotic spacing of Virasoro primaries. In particular, we show that for a unitary modular invariant 2D CFT with fixed central charge $c>1$, having a nonzero twist gap in the spectrum of Virasoro primaries, for sufficiently large spin $J$, there always exist spin $J$ operators with twist falling in a vanishingly small interval $\left(\frac{c-1}{12} – \varepsilon , \frac{c-1}{12} + \varepsilon \right)$ with $\varepsilon=O(J^{-1/2}\log J)$ i.e the twist spectra is dense. We establish that the number of Virasoro primary operators in such a window has a Cardy-like i.e., $\exp\left[2\pi \sqrt{\frac{(c-1) J}{6}}\right]$ growth. A similar result is then proven for a family of holographic CFTs with the twist gap growing linearly in c and a uniform boundedness condition, in the regime $J>\!\!\!>c^3>\!\!\!>1$. Our result sheds light on the validity regime of Schwarzian approximation in describing the near-extremal rotating BTZ black holes (without electric charge). We make further conjectures on potential extension of the above results to CFTs with conserved currents.



“Universal Properties in ICFTs”



Conformal interfaces are not well-studied except for special interfaces called topological interfaces. This lack of study is due to general interfaces breaking symmetry, where some powerful tools in CFT are not applicable. On this background, AdS/CFT can be a powerful tool. In this talk, we make use of AdS/CFT to understand universal properties of conformal interfaces in 2D. Interestingly, we show that the generalized holographic c-theorem can be interpreted as the upper bound on the entanglement between two (possibly different) systems. Moreover, we also show its CFT proof by using the results on the gravity side as a hint. Finally, we give the higher-dimensional generalization of our results. The key is that methods on the gravity side generally do not depend on dimensions, unlike QFT methods. This is another advantage of AdS/CFT to explore quantum many-body systems.



“AdS Bulk Locality from Dispersive CFT Functionals”



It is a long-standing conjecture that any CFT with large N and a large gap in the higher-spin single trace spectrum should have a gravity dual in the AdS whose low energy effective field theory is local at the length scale much smaller than the AdS radius (suppressed by the large gap of the CFT). I will discuss how to establish a sharp form of this conjecture using analytic conformal bootstrap. The main tool is a special class of CFT functionals called dispersive functionals. I will explain how to systematically construct them using commutativity of null-integrated operators in CFT. If time permits, I will show that the action of dispersive functionals on conformal blocks with heavy dimensions, which is an important quantity in the bootstrap method, is dominated by a saddle configuration and can be precisely related to dispersion relations of scattering amplitudes in flat spacT Functionals”e.