arXiv subjects

Silvia Georgescu

Publications and source records attributed to Silvia Georgescu.

7 recordsLinked to original sources

arXiv2026

Gravitational index of the D1-D5-P black string

We present saddle-points of the Euclidean Gravitational Path Integral (GPI) corresponding to the supersymmetric index of the D1-D5-P black string. These saddles are complex, supersymmetric, non-extremal solutions of 10-dimensional IIB supergravity theory with arbitrary inverse temperature $\beta$. The solutions carry fixed monopole charges $Q_1$, $Q_5$, $Q_n$, and angular momentum $J_L$ equal to the extremal supersymmetric black string. Crucially, the solutions have fixed angular velocity $\Omega_{R} = - 2 \pi i /\beta$, which is the chemical potential dual to $J_R$. This implements the insertion of $(-1)^{F}$ in the GPI. The Gibbons-Hawking on-shell action is temperature-independent and agrees with the supersymmetric index of the extremal black string carrying the same monopole charges. Upon taking a finite-temperature near-horizon decoupling limit, we obtain solutions of the form $S^3$ fibered over BTZ. Although these near-horizon solutions have finite holomorphic and anti-holomorphic modular parameters, their on-shell action reproduces the Cardy formula of the holomorphic elliptic genus of the dual D1-D5 SCFT$_2$.

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arXiv2026

The Stretched Horizon Limit

We consider four-dimensional general relativity with a positive cosmological constant, $Λ$, in the presence of a boundary, $Γ$, of finite spatial size. The boundary is located near a cosmological event horizon, and is subject to boundary conditions that fix the conformal class of the induced metric, and, $K$, the trace of the extrinsic curvature along $Γ$. The proximity of $Γ$ to the horizon is controlled by the dimensionless parameter ${K}{Λ^{-\frac{1}{2}}}$. We provide an exhaustive analysis of linearised gravitational perturbations for the setup. This is performed both for a $Γ$ encasing a portion of the static patch that ends just before the cosmological horizon (pole patch), as well as a $Γ$ containing only the region near the cosmological horizon (cosmic patch). In the pole patch, we uncover a layered hierarchy of modes: ordinary normal modes, a novel type of boundary gapless mode, and boundary soft modes of frequency $ω\approx \pm 2πi T_{\text{dS}}$, with $T_{\text{dS}}$ the horizon temperature. Minkowskian behaviour is recovered only for angular momenta $l \gtrsim {K}{Λ^{-\frac{1}{2}}}$ which can be made parametrically large, thus attenuating previously found growing modes. In the cosmic patch, we uncover sound and shear fluid-dynamical modes that we interpret in terms of a conformal fluid with shear viscosity over entropy density ratio $\tfracη{s} = \tfrac{1}{4π}$ and vanishing bulk viscosity $ζ=0$. The fluid dynamical sector is shown to admit a non-linear treatment. We describe a scaling regime in which the stretched horizon gravitational dynamics is dictated by a universal Rindler geometry, independent to the details of the infilling horizon. We briefly discuss quantitative features that distinguish cosmological and black hole horizons away from the Rindler regime.

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arXiv2025

Non-linear asymptotic symmetries in warped AdS$_3$ holography

Warped AdS$_3$ backgrounds provide set-ups to study holography beyond AdS and, in particular, holography for near-extremal Kerr black holes. A certain $U(1)$ charged warped BTZ background supported by pure NS-NS flux was constructed in string theory in arXiv:2111.02243. While older works found, in absence of $U(1)$ charges, that the warped black holes' thermal entropy obeys a Cardy formula, the addition of $U(1)$ charges in arXiv:2111.02243 leads to the universal entropy formula in a $J\bar{T}$-deformed CFT and not to the charged Cardy formula. In this article, we explore further the implications of this result for warped AdS$_3$ holography. We compute the asymptotic symmetries of the warped BTZ background of arXiv:2111.02243 and obtain an infinite-dimensional non-linear Poisson algebra that can be linearized, after a non-linear redefinition of generators, to two commuting copies of the $(Virasoro\times U(1)Kac-Moody)$ algebra. The algebra matches the symmetry algebra of a symmetric product orbifold of $J\bar{T}$-deformed CFTs. We contrast the results with those for a similar warped BTZ background supported by both NS-NS and RR flux.

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arXiv2024

Classical $J\bar T$ symmetries -- three ways -- and a precision holography check

The $J\bar T$ deformation is a fully tractable irrelevant deformation of two-dimensional CFTs, which yields a UV-complete QFT that is local and conformal along one lightlike direction and non-local along the remaining one. Such QFTs are interesting, in particular, as toy models for the holographic dual to (near)-extremal black holes. Despite its non-locality, the deformed theory has been shown to posess a (Virasoro-Kac-Moody)$^2$ symmetry algebra, whose action on the non-local side is non-standard. In this article we present, in a unified way, three different perspectives on the classical symmetries of $J\bar T$ - deformed CFTs: Hamiltonian, Lagrangian and holographic, showing how the peculiar action of the symmetries can be recovered in each of them. The perfect match we obtain between the Lagrangian and holographic results constitutes a precision check of the holographic dictionary proposed in [1], which we slightly generalize and improve. We also comment on the interpretation of the Compère-Song-Strominger boundary conditions from the $J\bar T$ viewpoint.

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arXiv2024

Ascending the attractor flow in the D1-D5 system

We study maximally supersymmetric irrelevant deformations of the D1-D5 CFT that correspond to following the attractor flow in reverse in the dual half-BPS black string solutions of type IIB supergravity on K3. When a single, quadratic condition is imposed on the parameters of the 22 such irrelevant deformations, the asymptotics of the solution degenerate to a linear dilaton like spacetime. We identify each such degeneration limit with a known decoupling limit of string theory, which yields little string theory or deformations thereof (the so-called open brane LST, or ODp theories), compactified to two dimensions. This suggests that a 21-parameter family of the above deformations leads to UV-complete theories, which are string theories decoupled from gravity that are continuously connected to each other. All these theories have been argued to display Hagedorn behaviour; we show that including the F1 strings leads to an additional Cardy term. The resulting entropy formula closely resembles that of single-trace $T\bar T$-deformed CFTs, whose generalisations could provide possibly tractable effective two-dimensional descriptions of the above web of theories. We also consider the asymptotically flat black strings. At fixed temperature, the partition function is dominated by thermodynamically stable, small black string solutions, similar to the ones in the decoupled backgrounds. We show that certain asymptotic symmetries of these black strings bear a striking resemblance with the state-dependent symmetries of single-trace $T\bar T$, and break down precisely when the background solution reaches the large black string threshold. This suggests that small, asymptotically flat black strings may also admit a $T\bar T$ - like effective description.

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arXiv2023

States, symmetries and correlators of $T\bar{T}$ and $ J\bar{T} $ symmetric orbifolds

We derive various properties of symmetric product orbifolds of $T\bar{T}$ and $J\bar{T}$ - deformed CFTs from a field-theoretical perspective. First, we generalise the known formula for the torus partition function of a symmetric orbifold theory in terms of the one of the seed to non-conformal two-dimensional QFTs; specialising this to seed $T\bar{T}$ and $J\bar{T}$ - deformed CFTs reproduces previous results in the literature. Second, we show that the single-trace $T\bar{T}$ and $J\bar{T}$ deformations preserve the Virasoro and Kac-Moody symmetries of the undeformed symmetric product orbifold CFT, including their fractional counterparts, as well as the KdV charges. Finally, we discuss correlation functions in these theories. By extending a previously-proposed basis of operators for $J\bar{T}$ - deformed CFTs to the single-trace case, we explicitly compute the correlation functions of both untwisted and twisted-sector operators and compare them to an appropriate set of holographic correlators. Our derivations are based mainly on Hilbert space techniques and completely avoid the use of conformal invariance, which is not present in these models.

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arXiv2023

Infinite $\mathrm{T\bar T}$-like symmetries of compactified LST

We show that the three-dimensional asymptotically linear dilaton background that arises in the near-horizon decoupling region of NS5-branes compactified on $T^4$ admits boundary conditions that lead to an infinite set of symmetries. The associated conserved charges, which implement field-dependent coordinate transformations, are found to be identical to the corresponding generators in a symmetric product orbifold of $T\bar T$ - deformed CFTs. Their algebra is a non-linear modification of the $\mathrm{Virasoro \times Virasoro}$ algebra, which precisely coincides with the algebra of the "unrescaled" symmetry generators in $T\bar T$-deformed CFTs. This further strengthens a previously proposed link between the single-trace $T\bar T$ deformation and compactified little string theory.

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