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Soumangsu Chakraborty

Publications and source records attributed to Soumangsu Chakraborty.

At least 19 recordsLinked to original sources
arXiv2026

Generating Rotation in a Snap

We build a technique to generate rotation from arbitrary static solutions that asymptote to four- or five-dimensional Minkowski spacetime based on Clément's approach [1]. The method is purely algebraic and does not require solving Einstein equations. It proceeds by transforming the static solution to AdS$\times$S asymptotics, performing a coordinate shift to a uniformly rotating frame, and then transforming the solution back to asymptotically flat spacetime. We implement this construction in five-dimensional minimal supergravity, although it applies more broadly to any framework admitting AdS$\times$S geometries and relevant sigma-model transformations. As a first application, we recover simply the Kerr and Myers-Perry black holes directly from Schwarzschild black holes. We then apply the method to the linear class of static Weyl solutions and obtain the first linear ansatz describing an arbitrary number of non-extremal rotating and charged sources. This approach provides a systematic and simple route to constructing non-extremal rotating geometries in four and five dimensions.

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arXiv2025

Microstates of Non-extremal Black Holes: A New Hope

We provide a new roadmap for constructing microstates of non-extremal black holes in supergravity. First, we review the non-linear sigma model of five-dimensional supergravity governing stationary solutions with a U(1) isometry and present the first generalized Ernst formulation of this model. We then revisit solution-generating techniques associated to the coset model symmetry, Ernst formalism and inverse scattering method. While some of these techniques have been extensively used to generate non-extremal black holes and black rings in supergravity, we demonstrate how they can be adapted to construct systematically non-BPS smooth horizonless geometries that have the same mass and charges as non-extremal black holes. To illustrate these methods, we construct novel static solutions of this type, including a non-BPS generalization of the $\frac{1}{2}$-BPS Gibbons-Hawking center, which has served as the fundamental building block of multicenter microstates of BPS black holes.

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arXiv2025

Extremal curves in single-trace $T\bar{T}$-holography

In this paper, we continue the study of single-trace $T\bar{T}$-holography where the boundary field theory can be realized as a CFT$_2$ deformed by a single-trace irrelevant operator of dimension $(2,2)$ and dual spacetime geometry is $AdS_3$ smoothly glued to flat spacetime with a linear dilaton near the boundary. In this non-AdS holographic framework, we propose that the length of real extremal curves connecting the two boundaries of an eternal black hole at fixed boundary time captures the time-evolved entanglement entropy of an entangled, quenched boundary system. At late times, we find two analytic extremal solutions in the complexified geometry, which become real in complementary temperature regimes. Focusing only on the real solutions leads to a non-analyticity at a critical temperature $T_c$, which we interpret as a second-order phase transition separating a local (CFT$_2$) phase from a non-local (Little String Theory) phase.

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arXiv2025

On string theory on (deformed) $AdS_3\times \mathbb{T}^3$

We revisit the fermionic string theory on $AdS_3\times \mathcal{N}$ with $k=1$, and its single-trace $T\bar T$ deformation, with a focus on the $(2,2)$ superstring on (deformed) $AdS_3\times \mathbb{T}^3$. In a certain limit, it is dual to the symmetric product of the ($T\bar T$-deformed) SCFT$_2$ on $\mathbb{R}\times \mathbb{T}^3$. We present the winding-one delta-function normalizable worldsheet operators which, in the $k=1$ decoupling limit, correspond to those of $\mathbb{R}\times \mathbb{T}^3$ in spacetime. We then demonstrate how their properties in string theory reproduce those of $\mathbb{R}\times\mathbb{T}^3$, or more generally, of a ($T\bar{T}$-deformed) $\mathbb{R}\times\mathcal{N}$ seed of the boundary theory.

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arXiv2025

Effective $AdS_3/CFT_2$

In arXiv:2109.00065, it was pointed out that superstring theory on $AdS_3$ with $(NS,NS)$ $B$-field background and $R_{AdS}/l_s=\sqrt k<1$ is dual to a symmetric product CFT deformed by an operator in the $\mathbb{Z}_2$ twisted sector. We generalize the analysis of arXiv:2109.00065 to $k>1$, and show that the resulting picture matches that discussed in the bosonic case in arXiv:2110.07535. We argue that in the critical case, $k=1$ hep-th/0503121, the $\mathbb{Z}_2$ twisted deformation remains non-trivial. This resolves some confusions in the literature.

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arXiv2025

Path integral of free fields and the determinant of Laplacian in warped space-time

We revisit the problem of computing the determinant of Klein-Gordon operator $Δ= -\nabla^2 + M^2$ on Euclideanized $AdS_3$ with the Euclideanized time coordinate compactified with period $β$, $H_3/Z$, by explicitly computing its eigenvalues and computing their product. Upon assuming that eigenfunctions are normalizable on $H_3/Z$, we found that there are no such eigenfunctions. Upon closer examination, we discover that the intuition that $H_3/Z$ is like a box with normalizable eigenfunctions was false, and that there is, instead, a set of eigenfunctions which forms a continuum. Somewhat to our surprise, we find that there is a different operator $\tilde Δ= r^2 Δ$, which has the property that (1) the determinant of $Δ$ and the determinant of $r^2 Δ$ have the same dependence on $β$, and that (2) the Green's function of $Δ$ can be spectrally decomposed into eigenfunctions of $\tilde Δ$. We identify the $\tilde Δ$ operator as the ``weighted Laplacian'' in the context of warped compactifications, and comment on possible applications.

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arXiv2024

The M2-M5 Mohawk

We show that the near-brane back-reaction of M2 branes ending on M5 branes has a rich "spike structure" that is determined by partitioning the numbers of M2 branes that are terminating on groups of M5 branes. The near-brane limit of the metric describing these branes has an AdS$_3$ factor, implying the existence of a dual CFT. Each partition of the M2 and M5 charges among spikes gives rise to a different "mohawk" revealing a new layer of brane fractionation. We conjecture that all these mohawks are dual to ground states of near-brane-intersection CFT's. We show that the supergravity solutions describing these mohawks are part of the large families of AdS$_3$ $\times S^3 \times S^3$ solutions described in [arXiv:1312.5477]. We identify precisely which of these families are relevant to brane intersections and show that the AdS$_3$ invariance emerges from the self-similarity of the spikes.

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arXiv2024

Thermal partition function of $J_3 \bar{J}_3$ deformed $AdS_3$

We derive a compact formula for the one-loop, bosonic string partition function of Euclideanized $J_3 \bar J_3$ deformed $AdS_3$ with periodic Euclidean time as an integral transform of the partition function of the undeformed Euclideanized $AdS_3$. Such a deformation is interpretable as an irrelevant "single-trace $T \bar T$ deformation" of the boundary. We will do this by first establishing a formal procedure to compute a worldsheet torus zero point function for an exactly marginal $J \bar J$ deformation of a sigma model with $U(1)_L \times U(1)_R$ global symmetry. We then describe how this procedure is implemented on $SL(2,R)$ sigma model and its Euclidean continuation. Finally, we describe the embedding of the deformed $SL(2,R)$ torus amplitude into critical string theory and interpret the result as the leading perturbative contribution to the thermal partition function of the deformed theory.

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arXiv2024

On string theory on deformed BTZ and $T\bar T$

Aspects of superstring theory on deformed BTZ black holes, formed near $k$~NS5 branes by $p$~fundamental strings, and single-trace $T\bar T$ holography, are presented. The excitation energy of a singly wound long string plus its contribution to the energy of the black hole, $1/p$ fraction of the black-hole energy, is the same as that in $T\bar T$ deformed $CFT_2$ with $c=6k$. This supports the claim that the black hole can be thought of as a state in a symmetric product of $p$~$CFT_2$'s of central charge~$6k$, where the black-hole energy is split equally among all $p$ factors. A comment on superstring theory on deformed global $AdS_3$ is also presented.

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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

A 4d non-BPS NS-NS microstate

We construct a two-parameter four-dimensional non-BPS NS-NS smooth microstate solution that asymptotes to flat spacetime with a linear dilaton in type II superstring theory. From the microscopic point of view, the background is made out of a certain number of decoupled (i.e. $g_s\to 0$) NS5 branes wrapping $T^3\times S^1\times S^1$ with fundamental strings wrapping non-contractable cycles of $S^1\times S^1$ with integer momentum modes along them. We show that perturbative worldsheet theory in this background is given by a null-gauged WZW model. We also show that the consistency of the worldsheet theory imposes non-trivial constraints on the supergravity background.

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arXiv2023

Comments on Single-Trace $T\bar T$ Holography

We explore the holographic duality between string theory in backgrounds that interpolate between asymptotically linear dilaton spacetime in the UV and $AdS_3$ in the IR, and single-trace $T\bar T$ deformed CFT. In particular, we explain how the deformation of states in the boundary theory is reflected in the bulk geometry, and show that the coupling above which the deformed energy of the $SL(2,\mathbb{R})$ invariant ground state of the IR CFT becomes complex is a maximal coupling.

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arXiv2023

Linear response of entanglement entropy to $T\bar{T}$ in massive QFTs

We compute the leading correction to entanglement entropy in $T\bar{T}$ deformed massive QFTs. We show that both for massive scalar and Dirac fermion, the leading order correction to the entanglement entropy of half-space comes from the boundary of the entangling surface. For the case of massive scalar, the boundary term is finite while for massive fermion, it diverges logarithmically giving rise to an additional log-square divergence in the entanglement entropy.

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arXiv2022

Solvable time-like cosets and holography beyond $AdS$

We build a novel time-like coset sigma-model describing type-II superstring theory in a charged rotating black-brane background that interpolates between a locally $AdS_3$ in the IR and a linear-dilaton geometry in the UV. This allows one to perform a systematic study of holography in non-AdS backgrounds which are smoothly connected to $AdS_3$. We construct massless closed string states vertex operators in the NS-NS sector, calculate the corresponding two-point correlation functions, and discuss holographic interpretation of our results from 4+1 dimensional boundary field theory point of view. Compactifying the theory on $\mathbb{T}^4$, we show that the spectrum of a single long string with unit winding agrees with the spectrum of a CFT$_2$ deformed by $T\bar{T}$. We also calculate correlation functions of operators of the dual 1+1 dimensional non-conformal boundary field theory using world-sheet techniques.

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arXiv2022

Weighed average over Narain moduli space as $T \bar T$ deformation of CFT target space

We consider the weighted average of a two dimensional CFT, whose target space is $T^2$, over its Narain moduli space. We take as the weighing function the integral kernel which gives rise to $T \bar T$ deformation when applied to the world sheet moduli data of the partition function viewed as vacuum amplitude when the world sheet is a torus. We compute the smeared partition function where this kernel is applied to the target space moduli. Smearing the partition function over the parameter space of a field theory generally leads to the breakdown in the ability to write the partition function as a sum over Boltzmann factor with unit coefficients. The weight function inspired by the $T \bar T$ deformation appears to be an exception to this general expectation. We show that this smearing leads to a marginal deformation corresponding to the overall rescaling of the target space $T^2$.

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arXiv2022

Comments on the negative specific heat of the $T \bar T$ deformed symmetric product CFT

We show that the $T \bar T$ deformation of conformal field theories whose entropy grows as $S(E) \sim E^γ$ for $γ> 1/2$ exhibits negative specific heat in its microcanonical thermodynamic function $S({\cal E})$. We analyze the large $N$ symmetric product CFT as a concrete example of a CFT with this property and compute the thermodynamic functions such as $S({\cal E})$ and ${\cal E}(T)$. The negative specific heat in the microcanonical data is interpreted as signaling the first order phase transition when the system is coupled to a heat bath.

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arXiv2021

Long-range fermions and critical dualities

We construct long-range fermionic models with the Gross-Neveu and Gross-Neveu-Yukawa interaction, and argue that their critical regimes are equivalent. To this end, we calculate various CFT data in $ε$- and $1/N$- expansion, and demonstrate their agreement in the overlapping regimes of validity.

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