We generalize previous work on the signatures of bulk signals detected by brane-based observers in a spacetime with a compactified dimension. When such braneworlds move with constant velocities or constant proper accelerations in the extra dimension, the observers may witness apparent superluminal signaling. Our analysis includes tilted branes that are partially wrapped along the compact dimension. We identify parameters that help characterize various scenarios, and verify that anisotropies arising in the propagation of signals through the bulk ensure that causality is not violated, despite the apparent superluminal signaling effects. Some of the effects studied here could be the basis for alternative cosmological models, as well as observable signatures of braneworld scenarios.

United States

Ryan Debolt

David Kagan

Braneworlds in constant and accelerated motion and their causal characteristics

We analyze the nonabelian surface holonomy on a bipartite hypercubic lattice following a proposal in arXiv:1002.4636 [hep-th]. The bipartite structure of the lattice enables us to introduce spike string configurations. These spikes play a crucial role for the time evolution of the string when the total number of color indices changes.

South Korea

Andreas Gustavsson

A nonabelian Wilson surface on a lattice

I provide multiple examples of conformal field theories (CFTs) on the world-sheet that describe string propagation in target space wormholes connecting two disjoint asymptotic manifolds. The worldsheet approach goes beyond the framework of supergravity by incorporating wormholes for which the size of the throat is comparable to the string scale. Typically, strongly coupled CFTs describe these stringy wormholes, which include Euclidean wormholes, double cones, and Einstein-Rosen bridges. Finally, I interpret a certain conformal manifold that contains an SU(2) × $\textit{U}$ (1) Wess-Zumino-Witten model as mediating a transition between a closed Universe and a wormhole.

Israel

Yoav Zigdon

Bridging worldsheet CFTs and wormholes

In this paper, we study thermal partition functions of free exotic conformal field theories, focusing on conformal higher-derivative and conformal higher-spin fields, in the semi-universal limit |$\textit{ω}$ | → 1. It was recently conjectured in [1] that, in this limit, the thermal partition function develops universal poles in (1 – |$\textit{ω}$ |), while the corresponding residue functions are theory-dependent. We analyze conformal higher-derivative scalar, fermionic, and vector fields in the semi-universal limit. We then extend the study to the Weyl graviton, the Weyl gravitino, and conformal higher-spin fields (CHS) on $$ {S}_{\beta}^1\times {S}^3 $$ , using both spectral mode-sum and operator-counting methods. In all cases, we find the expected pole structure, with residue functions whose behavior depends on the presence or absence of negative-twist states. For four-dimensional conformal higher-spin fields, we further reproduce the same residue-pole structure from the one-loop partition function of massless higher-spin fields in thermal AdS . Finally, we show that the semi-universal limit provides a useful diagnostic of negative-twist states, which indicate violations of ANEC-type bounds in these theories, whereas the traditional high-temperature expansion is insensitive to them.

India

Jyotirmoy Mukherjee

Pabitra Ray

Semi-universality of conformal higher-derivative and conformal higher-spin fields

We compute the first-order hydrodynamic transport coefficients (shear viscosity $\textit{η}$, bulk viscosity $\textit{ζ}$, and charge conductivity $\textit{σ}$) for a broad class of strongly coupled, four-dimensional charged relativistic gauge theory plasma with holographic gravitational duals containing higher-derivative corrections. The landscape of our holographic models captures non-conformal gauge theories with an arbitrary number of relevant coupling constants and a general scalar potential in the gravitational dual (albeit without higher-derivative scalar gradient couplings), allowing for a systematic exploration of charged transport along generic holographic RG flows. The leading-order higher-derivative corrections probe gauge theories with unequal central charges $\textit{c}$ ≠ $\textit{a}$ at the ultraviolet fixed point, and enable the engineering of diverse temperature and charge density profiles for the viscosities and the conductivity. Our results establish the $\textit{membrane paradigm}$ in higher-derivative holographic models: the transport coefficients are extracted from black brane horizon data, including the horizon values of the bulk scalars and of the functions defining the gravitational dual. For the bulk viscosity and the conductivity, this horizon data also includes the corresponding zero-frequency diffeomorphism-invariant scalar and gauge-field fluctuations.

Canada

Alex Buchel

Sera Cremonini

Mohammad Moezzi

George Tringas

Holographic charged transport with higher derivatives

An effective field theory framework is developed to study the interaction of heavy quarks in strongly coupled quark-gluon plasma (QGP). The latter is treated as a relativistic non-dissipative colorless fluid which can be studied using a derivatively coupled effective field theory based on previous work. Coupling this to heavy quarks provides a systematic way to obtain the interaction between the heavy quark and phonons, excitations of the fluid. In particular we calculate the quasiparticle width of heavy quark to phonon and phonon-heavy quark scattering in a thermal medium.

Andreas Kirchner

Berndt Müller

Jyotirmoy Roy

Chathuranga Sirimanna

A new effective field theory for heavy quarks in the quark-gluon plasma

In this work, we present a recurrence relation for the instanton partition function of the $$ \mathcal{N} $$ = 2 SYM $\textit{SU}$ ($\textit{N}$) gauge theory with 2$\textit{N}$ fundamental multiplets. The main difficulty lies in determining the asymptotic behaviour of the partition function in the regime of large vacuum expectation values of the Higgs field. Using the saddle point method and the $\textit{qq}$-characters technique, we demonstrate that, in this limit, the partition function is governed by the Quantum Seiberg-Witten curves, as in the Nekrasov-Shatashvili limit, up to a normalisation constant. With the asymptotic behaviour found, we are able to write the recurrence relation for the partition function and to find the effective infrared coupling constant. The resulting effective constant is an inverse of a modular function with respect to a certain triangle group, and the asymptotic itself is a product of modular functions and forms with respect to triangle groups.

Italy

Aleksei Bykov

Ekaterina Sysoeva

Zamolodchikov recurrence relation and modular properties of effective coupling in $$ \mathcal{N} $$ = 2 SQCD

Macroscopic computation of the degeneracy / index of a BPS black hole requires carrying out string theory path integral over the near horizon geometry of the black hole. It has been suggested that the path integral can be localized to a finite dimensional subspace using the unbroken supersymmetries of the near horizon geometry. We discuss several issues that need to be resolved before one can declare victory: (1) delta-function normalizable eigenmodes of the kinetic operator do not form a representation of the supersymmetry algebra since the Killing spinors grow exponentially as we approach the asymptotic boundary of the near horizon geometry, (2) the logarithmic contributions coming from various one loop determinants are sensitive to the ultraviolet cut-off and therefore without detailed knowledge of the ultraviolet cut-off one cannot determine the order one correction to the entropy that could depend on the ratios of the charges, (3) the results of index theorem indicate that there are additional flat directions of the localization action, at least at the quadratic order, than what has been considered so far. We also discuss a limited application of localization techniques to carry out the path integral over the zero modes of the metric and the gravitino, and get a finite answer. This is consistent with the results of arXiv:0905.2686 and shows that for computing BPS black hole entropy it is not necessary to regulate the path integral over these zero modes using the super-Schwartzian action.

Ashoke Sen

Revisiting localization for BPS black hole entropy

We study modular properties of conformal field theories perturbed by holomorphic fields. We prove an asymptotic formula for the modular S-transform of a generalized partition function that includes zero modes of higher spin holomorphic currents. The derivation makes use of general properties of torus correlation functions, in particular the Zhu recursion relation. The asymptotic expansion of the modular transformed partition function takes a universal form that is determined iteratively by the second order pole coefficients in the operator product expansion of the holomorphic currents. This proves and generalizes a conjecture regarding the modular transformation properties of generalized Gibbs ensembles.

Sujay Ashok

Tanmoy Sengupta

Adarsh Sudhakar

United Kingdom

Gérard Watts

Universal modular properties of generalized Gibbs ensembles and chiral deformations

We investigate the symmetry structure of the 3 + 1 D staggered fermion Hamiltonian and its implications for anomalies. Since the spin and flavor degrees of freedom of Dirac fermions are distributed over the lattice, in addition to the standard on-site mass term, the staggered fermion system also admits one-, two-, and three-link bilinear terms within a unit cube as local, charge conserving mass terms with different spin and flavor dependence. We identify the spin flavor structures of all those bilinear mass terms and determine the symmetries preserved by each of them. Among them, one of the one-link mass terms preserves a larger residual symmetry associated with conserved charges that generate the Onsager algebra. Motivated by this structure, we consider a kink profile of the one-link mass and analyze the resulting domain-wall system. In the low-energy limit, the 3 + 1 D bulk becomes gapped, while two-flavor massless Dirac fermions appear as localized modes on the 2 + 1 D domain wall. We show that the bulk conserved charges act on the wall as generators of a flavor SU(2) symmetry, and that no symmetric mass gap is allowed for the boundary theory when this SU(2) symmetry and space reflection symmetry are both imposed. This realizes the parity anomaly of the boundary theory and shows that the boundary flavor symmetry and anomaly descend from the ultraviolet staggered-fermion Hamiltonian rather than emerging only in the infrared.