arXiv subjects

Hare Krishna

Publications and source records attributed to Hare Krishna.

14 recordsLinked to original sources

arXiv2026

Aspects of Carrollian field theory from holography

We study holography for three-dimensional asymptotically flat spacetimes in which the bulk gravitational dynamics is conjectured to be dual to a two-dimensional Carrollian (equivalently BMS) conformal field theory. Such theories are known to arise as ultrarelativistic ($c\rightarrow0$) contractions of relativistic 2d conformal field theories. Under this contraction, the Virasoro algebra becomes the conformal Carrollian algebra and the Brown-Henneaux central charges become $c_L=0$, $c_M=\frac{3}{G}$. In this article, we recover these central charges directly from holography. We first construct the holographic quasilocal stress tensor for asymptotically flat spacetimes carrying Bondi mass and angular momentum. Under BMS$_3$ transformations, the stress tensor acquires an inhomogeneous term, the ``BMS Schwarzian", and extracting the central charges from it reproduces the algebraic result exactly. We then obtain the action for the boundary BMS Schwarzian modes. Finally, we show that the holographic stress-tensor correlators satisfy the expected Ward identity, while stress-tensor conservation obeys flux-balance laws.

hep-th↗

arXiv2026

Holographic entanglement entropy with conformal boundary conditions

We study holographic entanglement entropy in 3-dimensional AdS gravity with conformal boundary conditions which fix the conformal class of the boundary metric and its extrinsic curvature, $K$, while leaving the Weyl mode dynamical. Extending Lewkowycz-Maldacena-Dong's replica construction, we derive the corresponding holographic entanglement entropy formula. We show that the fluctuating Weyl mode does not contribute additional entropy. The entropy of the full boundary is therefore the Bekenstein-Hawking entropy, and the entropy of a boundary subregion continues to obey the Ryu-Takayanagi prescription, namely, the area of a minimal surface divided by $4G_N$. We carry out explicit calculations for global AdS, rotating and non-rotating BTZ geometries. For an interval in AdS$_3$ we find that the $K$-dependent holographic entanglement entropy is governed by $c_m=\frac{3 \ell}{2 G_N}.$ For a thermal state at high conformal temperatures we find that, the entropy is governed by $c_{\rm eff}=\frac{3 \ell}{2 G_N} \frac{K \ell- \sqrt{K^2 \ell^2-4}}{2}$, the same effective central charge that governs the Cardy-like density of states, in agreement with previous results in the literature. Finally, we also compute the entanglement entropy directly from the conjectured dual boundary theory - a holographic CFT coupled with time-like Liouville theory and deformed by a marginal $T \bar{T}$ like operator - and find $S_{EE} =\frac{c_{\rm eff}}{3} \ln\!\left(\frac{2 R \sin\phi_0}{\epsilon}\right) .$ This result for the state with no operator insertions (vacuum state ), provides an independent boundary realization of $c_{\mathrm{eff}}$ while clarifying that this state is not the state dual to global AdS.

hep-th↗

arXiv2025

Seeing double: shock waves and the de Sitter horizon

We consider a de Sitter observer in his rest frame at late times who observes a particle slightly displaced from unstable equilibrium. Initially, the observer notices an axisymmetric and parity-violating deformation along the trajectory of the displaced particle of his cosmological horizon. On a time scale of order $\ell$, the de Sitter radius, the particle is nearly absorbed by the cosmological horizon and has been accelerated to an ultra-relativistic speed and thus is well approximated as a shock wave. In the shock wave limit, the observer sees an axisymmetric deformation of his horizon with parity restored, which we interpret as arising due to a particle from the complementary static patch. We comment on the holographic implications of this result and note that there is no need to extend the holographic screen of de Sitter spacetime beyond the empty static patch to account for this signal.

hep-th↗

arXiv2025

On thermal holographic RG flows

Holographic Renormalization Group (RG) flows, described by Einstein gravity coupled to matter fields, have been thoroughly explored in the context of vacuum states. In this work, we shift the focus to thermal states. Using the Hamilton-Jacobi formalism for the coupled system, we derive the Ward identity associated with broken dilatation symmetry in thermal correlators and obtain the modified Callan-Symanzik equation for the dual thermal CFT. We then employ the Hamiltonian approach to analyze the black hole interior and comment on the near-singularity behavior from this perspective.

hep-th↗

arXiv2024

There is more to the de Sitter horizon than just the area

It is well known that the area of the de Sitter cosmological horizon is related to the entropy of the bulk spacetime. Recent work has however shown that the horizon encodes more information about the bulk spacetime than just the entropy. In this work, we show that the horizon contains all of the gauge invariant (diffeomorphism and $U(1)$) information about (static albeit unstable) configurations of charged and rotating objects placed deep inside the de Sitter spacetime. We study highly symmetric objects, such as dipoles and cubes, built of objects with electric charge and angular momentum at their vertices. We show how these configurations affect the geometry of the cosmological horizon and imprint detailed information about the objects in the bulk onto the cosmological horizon.

hep-th↗

arXiv2024

A stress tensor for asymptotically flat spacetime

In this article, we propose a procedure for calculating the boundary stress tensor of a gravitational theory in asymptotic flat spacetime. As a case study, the stress tensor correctly reproduces the Brown-York charges for the Kerr blackhole i.e. mass and angular momentum. In asymptotic flat spacetime, there are asymptotic symmetries called BMS symmetries. We also compute the charges associated with these symmetries with the proposed stress tensor. The asymptotic charges can be compared with the Wald-Zoupas method. Our result for the stress tensor can be interpreted as the expectation value for the boundary stress tensor.

hep-th↗

arXiv2024

Topologically charged BPS microstates in AdS$_3$/CFT$_2$

In the standard $\mathcal{N}=(4,4)$ AdS$_3$/CFT$_2$ with $\mathrm{sym}^N(T^4)$, as well as the $\mathcal{N}=(2,2)$ Datta-Eberhardt-Gaberdiel variant with $\mathrm{sym}^N(T^4/\mathbb{Z}_2)$, supersymmetric index techniques have not been applied so far to the CFT states with target-space momentum or winding. We clarify that the difficulty lies in a central extension of the SUSY algebra in the momentum and winding sectors, analogous to the central extension on the Coulomb branch of 4d $\mathcal{N}=2$ gauge theories. We define modified helicity-trace indices tailored to the momentum and winding sectors, and use them for microstate counting of the corresponding bulk black holes. In the $\mathcal{N}=(4,4)$ case we reproduce the microstate matching of Larsen and Martinec. In the $\mathcal{N}=(2,2)$ case we resolve a previous mismatch with the Bekenstein-Hawking formula encountered in the topologically trivial sector by going to certain winding sectors.

hep-th↗

arXiv2023

Celestial gluon and graviton OPE at loop level

In this paper, we analyze the loop corrections to celestial OPE for gluons and gravitons. Even at the loop level, the soft gluons and gravitons have conformal dimensions $\Delta=1-\mathbb Z_{\geq 0}$. The only novelty is the presence of higher poles. At one loop level, there are two types of conformal soft gluons with a single pole and a double pole in the $\Delta$ plane. The celestial OPEs are obtained using the collinear splitting functions. In the case of gluons, the splitting functions receive loop corrections. After taking the holomorphic soft limit, we find the OPE of conformal soft gluons. We find a novel mixing of simple and double poles soft gluon operators in the OPE. In the case of gravitons, where splitting functions are known to be all loop exact, we still find a wedge algebra of $w_{\infty}$ which is in addition to the wedge algebra of $w_{1+\infty}$ already found by Strominger.

hep-th↗

arXiv2023

Universality of Loop Corrected Soft Theorems in 4d

In \cite{1808.03288}, logarithmic correction to subleading soft photon and soft graviton theorems have been derived in four spacetime dimensions from the ratio of IR-finite S-matrices. This has been achieved after factoring out IR-divergent components from the traditional electromagnetic and gravitational S-matrices using Grammer-Yennie prescription. Although the loop corrected subleading soft theorems are derived from one-loop scattering amplitudes involving scalar particles in a minimally coupled theory with scalar contact interaction, it has been conjectured that the soft factors are universal (theory independent) and one-loop exact (don't receive corrections from higher loops). This paper extends the analysis conducted in \cite{1808.03288} to encompass general spinning particle scattering with non-minimal couplings permitted by gauge invariance and general coordinate invariance. By re-deriving the $\ln\omega$ soft factors in this generic setup, we establish their universal nature. Furthermore, we summarize the results of loop corrected soft photon and graviton theorems up to sub-subleading order, which follows from the analysis of one and two loop QED and quantum gravity S-matrices. While the classical versions of these soft factors have already been derived in the literature, we put forth conjectures regarding the quantum soft factors and outline potential strategies for their derivation.

hep-th↗

arXiv2023

Celestial holography from Chiral strings

In this paper, we studied the relationship between celestial holography and chiral strings. Chiral strings differ from the usual string theory by a change of boundary conditions on the string propagators. It is shown that chiral strings would reproduce graviton amplitudes and could serve as an alternative description of Einstein's gravity. Celestial holography is a proposed duality between gravity in asymptotically flat space-time and a CFT living on its conformal boundary. Since both are CFT descriptions of gravity, we investigate the potential connection between these two formalisms. In this paper, we find that both the energetic as well as conformal soft theorems could be derived from the OPEs of vertex operators of chiral strings. All operators in the CCFT can be described by Mellin transforming the vertex operators in the chiral string theories, and the OPE coefficients of CCFT can also be obtained from the world-sheet description.

hep-th↗

arXiv2023

Modified supersymmetric indices in AdS$_3$/CFT$_2$

We consider the $\mathcal{N}=(2,2)$ AdS$_3$/CFT$_2$ dualities proposed by Eberhardt, where the bulk geometry is AdS$_3\times(S^3\times T^4)/\mathbb{Z}_k$, and the CFT is a deformation of the symmetric orbifold of the supersymmetric sigma model $T^4/\mathbb{Z}_k$ (with $k=2,\ 3,\ 4,\ 6$). The elliptic genera of the two sides vanish due to fermionic zero modes, so for microstate counting applications one must consider modified supersymmetric indices. In an analysis similar to that of Maldacena, Moore, and Strominger for the standard $\mathcal{N}=(4,4)$ case of $T^4$, we study the appropriate helicity-trace index of the boundary CFTs. We encounter a strange phenomenon where a saddle-point analysis of our indices reproduces only a fraction (respectively $\frac{1}{2},\ \frac{2}{3},\ \frac{3}{4},\ \frac{5}{6}$) of the Bekenstein-Hawking entropy of the associated macroscopic black branes.

hep-th↗

arXiv2021

Holographic thermal correlators revisited

We study 2-point correlation functions for scalar operators in position space through holography including bulk cubic couplings as well as higher curvature couplings to the square of the Weyl tensor. We focus on scalar operators with large conformal dimensions. This allows us to use the geodesic approximation for propagators. In addition to the leading order contribution, captured by geodesics anchored at the insertion points of the operators on the boundary and probing the bulk geometry thoroughly studied in the literature, the first correction is given by a Witten diagram involving both the bulk cubic coupling and the higher curvature couplings. As a result, this correction is proportional to the VEV of a neutral operator $O_k$ and thus probes the interior of the black hole exactly as in the case studied by Grinberg and Maldacena [13]. The form of the correction matches the general expectations in CFT and allows to identify the contributions of $T^nO_k$ (being $T^n$ the general contraction of n energy-momentum tensors) to the 2-point function. This correction is actually the leading term for off-diagonal correlators (i.e. correlators for operators of different conformal dimension), which can then be computed holographically in this way.

hep-th↗

arXiv2018

Light-Cone Reduction vs. TsT transformations : A Fluid Dynamics Perspective

We compute constitutive relations for a charged $(2+1)$ dimensional Schrödinger fluid up to first order in derivative expansion, using holographic techniques. Starting with a locally boosted, asymptotically $AdS$, $4+1$ dimensional charged black brane geometry, we uplift that to ten dimensions and perform $TsT$ transformations to obtain an effective five dimensional local black brane solution with asymptotically Schrödinger isometries. By suitably implementing the holographic techniques, we compute the constitutive relations for the effective fluid living on the boundary of this space-time and extract first order transport coefficients from these relations. Schrödinger fluid can also be obtained by reducing a charged relativistic conformal fluid over light-cone. It turns out that both the approaches result the same system at the end. Fluid obtained by light-cone reduction satisfies a restricted class of thermodynamics. Here, we see that the charged fluid obtained holographically also belongs to the same restricted class.

hep-th↗

arXiv2006

A compound figure of merit for photonic applications of metal nanocomposites

Selecting nanocomposites for photonic switching applications requires optimizing their thermal, nonlinear and two-photon absorption characteristics. We simplify this step by defining a compound figure of merit (FOM_{C}) for nanocomposites of noble metals in dielectric based on criteria that limit these structures in photonic applications, i.e. thermal heating and two-photon absorption. The device independent results predict extremely large values of FOM_{C} for a specific combination of the metal and insulator dielectric constant given by ε_{h}=\frac{ε_{1}-ε_{2}}{2}, where ε_{h} is the dielectric constant of the host and ε_{1} and ε_{2} are the real and imaginary parts for the metal.

cond-mat.mtrl-sci↗