arXiv subjects

Ritabrata Bhattacharya

Publications and source records attributed to Ritabrata Bhattacharya.

12 recordsLinked to original sources

arXiv2026

Maximal $D=5$ trombone supergravity from M5-branes and $\mathrm{SU}(2)$-flavoured $\mathcal{N}=1$ class $\mathcal{S}$ operator spectra

We recently presented a new $D=5$ $\mathcal{N}=8$ gauged supergravity involving the local trombone scaling symmetry. It arises by consistent truncation of M-theory on the internal space of the Maldacena-Núñez AdS$_5$ solution dual to the $\mathcal{N}=2$ four-dimensional superconformal field theory (SCFT) of class $\mathcal{S}$ associated to M5-branes wrapped on an unpunctured Riemann surface. Using exceptional generalised geometry/field theory, we extend that construction to show that the same $D=5$ $\mathcal{N}=8$ supergravity also arises by consistent truncation of $D=11$ supergravity on the family of $\mathcal{N}=1$ M5-brane-wrapped solutions of Bah-Beem-Bobev-Wecht, including the $\mathcal{N}=1$ Maldacena-Núñez (MN1) configuration. Then, using recently derived mass matrices, we compute universal sectors of the Kaluza-Klein spectrum on the MN1 solution. In general, this universal spectrum is only locally defined, and we give a prescription for extracting globally defined subsectors thereof. This globally defined universal Kaluza-Klein spectrum is dual to a universal sector of the light operator spectrum of the SU(2)-flavoured $\mathcal{N}=1$ class $\mathcal{S}$ SCFT dual to MN1.

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arXiv2026

Large-$N$ Torus Knots in Lens Spaces and Their Quiver Structure

We study torus knot invariants in the lens space $S^{3}/\mathbb{Z}_{p}$ within Chern--Simons theory. Using the surgery and modular description of lens spaces, we derive a general expression for the invariant of an $(α,β)$ torus knot in this background. In the large-$N$ limit these invariants simplify and acquire a universal form: the invariant of an $(α,β)$ torus knot in $S^{3}/\mathbb{Z}_{p}$ can be expressed in terms of the invariant of the $(α,α+pβ)$ torus knot in $S^{3}$. After an appropriate redefinition of knot variables, the generating functions of these invariants exhibit a structure analogous to quiver partition functions. Since the associated quiver is independent of the rank $N$ and level $k$ of Chern--Simons theory, the large-$N$ result provides a direct way to identify the underlying quiver, allowing us to determine the quiver structure associated with torus knots in $S^{3}/\mathbb{Z}_{p}$.

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arXiv2025

Crossing symmetry including non planar diagrams in perturbative QFT

We venture a proof of crossing symmetry for non-planar diagrams in perturbative QFT. For the planar diagrams a proof of crossing is available in the literature and our method closely follows the one depicted in that case. We classify the non-planar diagrams broadly into two types. For one of these types the proof is pretty straightforward and hence the result extends to all point all loop on-shell amplitudes. These are called the "trivial" cases while for the other type we find certain cases called the "non trivial" cases for which the proof is much more subtle. We present an explicit example of such a "non trivial" case at 3-loop order and argue how the proof of crossing symmetry holds true when all subtleties are taken into consideration. Based on this simple example we argue how the proof works out in general for these "non-trivial" cases at higher loop and with arbitrary number of non-planar edges.

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arXiv2025

Class $\mathcal{S}$ superconformal indices from maximal supergravity

We present a new gauging of maximal supergravity in five spacetime dimensions with gauge group containing ISO(5), involving the local scaling symmetry of the metric, and admitting a supersymmetric anti-de Sitter vacuum. We show this maximal supergravity to arise by consistent truncation of M-theory on the (non-spherical, non-parallelisable) six-dimensional geometry associated to a stack of $N$ M5-branes wrapped on a smooth Riemann surface. The existence of this truncation allows us to holographically determine the complete, universal spectrum of light operators of the dual four-dimensional $\mathcal{N}=2$ theory of class $\mathcal{S}$. We then compute holographically the superconformal index of the dual field theory at large-$N$, finding perfect agreement with previously known field theory results in specific limits.

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arXiv2023

Two loop mass renormalisation in heterotic string theory: NS states

In this work computation of the renormalised mass at two loop order for the NS sector of heterotic string theory is attempted. We first implement the vertical integration prescription for choosing a section avoiding the spurious poles due to the presence of a required number of picture changing operators. As a result the relevant amplitude on genus 2 Riemann surface can be written as a boundary term. We then identify the 1PI region of the moduli space having chosen a gluing compatible local coordinates around the external punctures. We also identify the relevant integrands and the relevant region of integration for the modular parameters at the boundary.

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arXiv2021

Analyticity Domain for Off-shell Five-point Superstring Loop Amplitudes

In an earlier work arXiv:2009.0337, we showed that for arbitrary Feynman loop diagrams (with no massless internal propagators) in closed superstring field theory, a known domain can be analytically extended by simply adjoining convex combinations of points drawn from it. Such extension yielded 350 of the well-known 370 primitive tubes for 5-point functions. In this paper, we consider the remaining 20 primitive tubes. We show that different types of convex combinations cover different sections of these tubes. We use a specific algorithm to analytically obtain 129 types of convex combinations along with their region of validity. Then, we use numerical techniques to locate points from those tubes that are not covered by them. This does not rule out the possibility of the leftover points being represented as desirable convex combinations. Indeed we give ways to improve our algorithm indicating that the leftover points can be covered.

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arXiv2021

Supercritical linear dilaton capping state using Interpolating functions

We consider time dependent backgrounds with a time-like linear dilaton which leads to a weakly coupled theory at asymptotic future known as the Supercritical Linear Dilaton (SCLD) phase. Even after projecting out the tachyon there are naive divergences in the partition function due to the spectrum of relevant deformations. Although the partition function seems divergent, the background is actually well defined in the far future due to vanishing backreactions, provided we start from an appropriate initial state called the "capping" state. We use the technique of interpolating functions to construct this state by embedding the SCLD phase in a strong coupling completion of string theory. Although we are unable construct a specific example, we do provide the general strategy in cases where S-duality may provide the completion.

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arXiv2021

Chaotic Correlation Functions with Complex Fermions

We study correlation functions in the complex fermion SYK model. We focus, specifically, on the h = 2 mode which explicitly breaks conformal invariance and exhibits the chaotic behaviour. We explicitly compute fermion six-point function and extract the corresponding six-point OTOC which exhibits an exponential growth with maximal chaos. Following the program of Gross-Rosenhaus, this correlator contains information of the bulk cubic coupling, at the conformal point as well as perturbatively away from it. Unlike the conformal modes with high values of h, the h = 2 mode has contact interaction dominating over the planar in the large q limit.

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arXiv2020

Analyticity of Off-shell Green's Functions in Superstring Field Theory

We consider the off-shell momentum space Green's functions in closed superstring field theory. Recently in arXiv:1810.07197, the off-shell Green's functions -- after explicitly removing contributions of massless states -- have been shown to be analytic on a domain (to be called the LES domain) in complex external momenta variables. Analyticity of off-shell Green's functions in local QFTs without massless states in the primitive domain is a well-known result. Using complex Lorentz transformations and Bochner's theorem allow to extend the LES domain to a larger subset of the primitive domain. For the 2-, 3- and 4-point functions, the full primitive domain is recovered. For the 5-point function, we are not able to obtain the full primitive domain analytically, only a large part of it is recovered. While this problem arises also for higher-point functions, it is expected to be only a technical issue.

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arXiv2020

Cosmological singularities and 2-dimensional dilaton gravity

We study Big-Bang or -Crunch cosmological singularities in 2-dimensional dilaton-gravity-scalar theories, in general obtained by dimensional reduction of higher dimensional theories. The dilaton potential encodes information about the asymptotic data defining the theories, and encompasses various families such as flat space, $AdS$, conformally $AdS$ as arising from nonconformal branes, and more general nonrelativistic theories. We find a kind of universal near singularity behaviour independent of the dilaton potential, giving universal interrelations between the exponents defining the time behaviour near the cosmological singularity. More detailed analysis using a scaling ansatz enables finding various classes of cosmological backgrounds, recovering known examples such as the $AdS$ Kasner singularity as well finding as new ones. We give some comments on the dual field theory from this point of view.

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arXiv2020

Quantum Quenches and Thermalization in SYK models

We study non-equilibrium dynamics in SYK models using quantum quench. We consider models with two, four, and higher fermion interactions ($q=2, 4$, and higher) and use two different types of quench protocol, which we call step and bump quenches. We analyse evolution of fermion two-point functions without long time averaging. We observe that in $q=2$ theory the two-point functions do not thermalize. We find thermalization in $q=4$ and higher theories without long time averaging. We calculate two different exponents of which one is equal to the coupling and the other is proportional to the final temperature. This result is more robust than thermalization obtained from long time averaging as proposed by the eigenstate thermalization hypothesis(ETH). Thermalization achieved without long time averaging is more akin to mixing than ergodicity.

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arXiv2017

SYK Model, Chaos and Conserved Charge

We study the SYK model with complex fermions, in the presence of an all-to-all $q$-body interaction, with a non-vanishing chemical potential. We find that, in the large $q$ limit, this model can be solved exactly and the corresponding Lyapunov exponent can be obtained semi-analytically. The resulting Lyapunov exponent is a sensitive function of the chemical potential $μ$. Even when the coupling $J$, which corresponds to the disorder averaged values of the all to all fermion interaction, is large, values of $μ$ which are exponentially small compared to $J$ lead to suppression of the Lyapunov exponent.

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