arXiv subjects

Subhroneel Chakrabarti

Publications and source records attributed to Subhroneel Chakrabarti.

18 recordsLinked to original sources

arXiv2026

Generalised Symmetries and Manifest Duality I: Flat Spacetime

We present a novel, manifestly Lorentz-invariant, local, polynomial, and straightforwardly quantisable action for duality-symmetric gauge theories formulated using gauge potentials and fluxes. This new action possesses a novel higher-form gauge symmetry that we dub $h$-gauge symmetry, which on gauge fixing can lead to Sen's formalism or to a solely potential-based description. Unlike Sen's flux-based formalism, the potential-based action admits a simple minimal coupling to matter, thereby allowing us perform a number of consistency checks, including incorporating dynamical matter and establishing the Witten effect. The new action admits remarkably simple supersymmetrisation. We demonstrate the formalism explicitly for quantum electro-magnetodynamics in $D=4$. We also present a proof of charge quantisation that applies equally to our and Sen's formalisms.

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arXiv2026

Generalised Symmetries and Manifest Duality II: Curved Spacetime

We extend the potential-based formulation of self-dual and duality-symmetric gauge theories developed in \cite{Chakrabarti:2025gyt} to curved spacetime. The gravitational coupling is encoded by the same metric-dependent linear map of Sen's formalism. The parent new action retains the higher-form $h$-gauge symmetry, and different gauge choices reproduce either Sen's flux-based formulation or a potential-based description in which the shadow sector decouples directly at the level of the action. We also derive explicit form of the gravitational map for the toroidally reduced theory in $D=4n$ and for a polyform formulation in arbitrary dimension, both of which apply equally to ours as well as Sen's formalism. As non-trivial checks, we reproduce the Álvarez-Gaumé-Witten gravitational anomalies of the two-dimensional chiral boson without fermionisation, and of the ten-dimensional self-dual five-form. Finally, on $\mathrm{AdS}_5\times S^5$ the physical on-shell action yields the non-vanishing boundary contribution required by holography without adding a boundary term by hand. We also establish a local on-shell identification with the textbook supergravity RR four-form potential.

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arXiv2026

One loop in $D=11$ vs $D=10$: 4-point check

The one-loop correction to eleven-dimensional supergravity involves a cubically divergent term $t_8t_8R^4$, with four Riemann tensors. A similar term (with finite coefficient) has been argued to be present in the M-theory effective action. It is expected to reduce to a similar one-loop term present in the type IIA effective action. This has previously been verified in the NSNS sector at the 4-point level. Here we extend this result to couplings of NSNS and RR fields, which have been computed using the pure spinor formalism. In particular, we check all couplings of RR fields to the dilaton as well as all couplings involving the metric and RR three-form. Correcting some minor mistakes in the literature we find complete agreement. We also give a complete analysis of 4-point terms in eleven dimensions computed previously from superparticle amplitudes and present a very simple form for these.

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arXiv2025

Perturbative Unitarity Calls for An Action

In this work, we investigate the consistency of a perturbative definition of the S-matrix in a particular class of non-Lagrangian theories. We focus on the $p$-form theories proposed in \cite{Broccoli:2021pvv}, which are fully defined by "third-way" consistent equations of motion. Using the perturbiner method, we show that the unitarity is absent even at the tree level. We then pin down a unique modification of the equations of motion that restores unitarity. The trade-off is the reinstatement of an underlying Lagrangian, which we recognize as the higher-dimensional generalization of the Freedman-Townsend (FT) model. Finally, we discuss conserved currents in third-way theories and show they all follow from parent currents in the FT model. In particular, we point out the existence of a higher-ranked global symmetry, which signals that the FT model is compatible with the existence of brane-like charged objects in higher dimensions.

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arXiv2025

Monopoles, Clarified

We propose a manifestly duality-invariant, Lorentz-invariant, and local action to describe quantum electrodynamics theory in the presence of magnetic monopoles that derives from Sen's formalism. By employing field strengths as the dynamical variables, rather than potentials, this formalism resolves longstanding ambiguities in prior frameworks. Our analysis finds consistent outcomes at both tree and loop levels using the established principles of quantum field theory, obviating the need for external assumptions or amendments. We clarify the mechanisms of charge renormalisation and demonstrate the renormalisation group invariance of the charge quantisation condition. Our approach can be useful for phenomenological studies and in quantum field theories with strong-weak dualities.

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arXiv2023

Exploring T-Duality for Self-Dual Fields

We study avatars of T-duality within Sen's formalism for self-dual field strengths in various dimensions. This formalism is shown to naturally accommodate the T-duality relation between Type IIA/IIB theories when compactified on a circle without the need for imposing the self-duality constraint by hand, as is usually done. We also continue our study of this formalism on two-dimensional target spacetimes and initiate its study as a worldsheet theory. In particular, we show that Sen's action provides a natural worldsheet-based understanding of twisted and asymmetrically twisted strings. Finally, we show that the $\mathrm{T}\bar{\mathrm{T}}$-deformed theory of left- and right-chiral bosons described in Sen's formalism possesses a scaling limit that is related via field-theoretic T-duality to a recently studied integrable deformation of quantum mechanics.

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arXiv2022

On-Shell Action for Type IIB Supergravity and Superstrings on $AdS_5 \times S^5$

AdS/CFT predicts that the value of the on-shell action for type IIB Supergravity (SUGRA) on $AdS_5 \times S^5$ background must be a non-zero number completely determined from the boundary theory. We examine this statement within Sen's formalism for type IIB SUGRA and find that consistency with AdS/CFT requires us to add a specific boundary term to the action. We contrast our resolution with two other resolutions recently proposed in the literature in the context of different approaches to type IIB SUGRA. We explain how our resolution presents a strong benchmark for the possible boundary term of the complete spacetime action for type IIB superstring and how it may possibly lead to a piece of evidence for the strongest form of AdS/CFT conjecture in $AdS_5 \times S^5$. We also comment on the fate of the on-shell action for general self-dual $p$-form fields in Sen's formalism in any curved backgrounds.

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arXiv2022

Renormalisation in $\text{T}\bar{\text{T}}$-Deformed (Non-)Integrable Theories

That the exact quantum S-matrix of $\text{T}\bar{\text{T}}$-deformed field theories is known has interesting consequences for their perturbative renormalisation. Recent investigations into the interplay between renormalisation and integrable deformations have focused on those cases where the (undeformed) seed theories are integrable. In this paper, we study the perturbative renormalisation of non-integrable $\text{T}\bar{\text{T}}$-deformed field theories, focusing on a theory of scalars with a quartic interaction. We show that in this theory, the 4-point 1-loop S-matrix exhibits features similar to its integrable cousins. We also carry out a similar analysis for the case of an integrable quantum field theory comprising a pair of chiral bosons. Our discussion of this latter theory supplies the first explicit example of a perturbative field theory computation in the formalism due to Sen.

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arXiv2022

Black Hole Hair Removal For N=4 CHL Models

Although BMPV black holes in flat space and in Taub-NUT space have identical near-horizon geometries, they have different indices from the microscopic analysis. For K3 compactification of type IIB theory, Sen et al in a series of papers identified that the key to resolving this puzzle is the black hole hair modes: smooth, normalisable, bosonic and fermionic degrees of freedom living outside the horizon. In this paper, we extend their study to N = 4 CHL orbifold models. For these models, the puzzle is more challenging due to the presence of the twisted sectors. We identify hair modes in the untwisted as well as twisted sectors. We show that after removing the contributions of the hair modes from the microscopic partition functions, the 4d and 5d horizon partition functions agree. Special care is taken to present details on the smoothness analysis of hair modes for rotating black holes, thereby filling an essential gap in the literature.

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arXiv2020

Irrelevant Deformations of Chiral Bosons

We study $ \text{T}\overline{\text{T}} $ deformations of chiral bosons using the formalism due to Sen. For arbitrary numbers of left- and right-chiral bosons, we find that the $ \text{T}\overline{\text{T}} $-deformed Lagrangian can be computed in closed form, giving rise to a novel non-local action in Sen's formalism. We establish that at the limit of infinite $ \text{T}\overline{\text{T}} $ coupling, the equations of motion of deformed theory exhibits chiral decoupling. We then turn to a discussion of $ \text{T}\overline{\text{T}} $-deformed chiral fermions, and point out that the stress tensor of the $ \text{T}\overline{\text{T}} $-deformed free fermion coincides with the undeformed seed theory. We explain this behaviour of the stress tensor by noting that the deformation term in the action is purely topological in nature and closely resembles the fermionic Wess-Zumino term in the Green-Schwarz formalism. In turn, this observation also explains a puzzle in the literature, viz. why the $ \text{T}\overline{\text{T}} $ deformation of multiple free fermions truncate at linear order. We conclude by discussing the possibility of an interplay between $ \text{T}\overline{\text{T}} $ deformations and bosonisation.

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arXiv2020

Chiral Decoupling from Irrelevant Deformations

We show that at the level of the equations of motion (i.e. classically), in the limit in which the $ \text{T}\overline{\text{T}} $ deformation parameter is sent to infinity, the left- and right-chiral sectors of $ \text{T}\overline{\text{T}} $-deformed free theories decouple.

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arXiv2019

Generalised Garfinkle-Vachaspati Transform With Dilaton

The generalised Garfinkle-Vachaspati transform (GGV) introduced in our previous work (arXiv:1808.04981) is a powerful technique to add hair modes to a class of known D1-D5 solutions. The richest and most interesting examples of D1-D5 geometries involve the dilaton and this calls for an extension of the procedure to accommodate for the presence of the dilaton field. In this paper we present such extended version of the GGV transform. We explore this generalisation in ten-dimensions with R-R or NS-NS 2-form field and relate the two set-ups via S-duality. In the context of the D1-D5 system, this generalisation allows us to add travelling wave deformations on solutions beyond minimal six-dimensional supergravity lifted to IIB supergravity. We work out travelling wave deformations involving the torus directions on a class of supersymmetric D1-D5-P geometries. We also explore applications of our technique to the F1-P system.

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arXiv2018

Integrated Massive Vertex Operator in Pure Spinor Formalism

We construct the integrated vertex operator for the first massive states of open superstrings with $(mass)^2=1/α'$ in the pure spinor formalism of the superstring theory. This vertex operator is expressed in terms of the ten dimensional $\mathcal{N}=1$ superfields describing the massive supermultiplet which appear in the unintegrated vertex operator of the same states.

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arXiv2018

Amplitudes Involving Massive States Using Pure Spinor Formalism

Same amplitudes evaluated independently using RNS and pure spinor formalism are expected to agree. While for massless states, this fact has been firmly established, for massive states such an explicit check has been lacking so far. We compute all massless-massless-massive 3-point functions in open supertrings in pure spinor formalism for the first massive states and compare them with the corresponding RNS results. We fix the normalization of the vertex operators of the massive states by comparing same set of 3-point functions for a fixed ordering in the two formalisms. Once fixed, the subsequent 3-point functions for each inequivalent ordering match exactly. This extends the explicit demonstration of equivalence of pure spinor and RNS formalism from massless states to first massive states.

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arXiv2017

Testing Subleading Multiple Soft Graviton Theorem for CHY Prescription

In arXiv:1707.06803 we derived the subleading multiple soft graviton theorem in a generic quantum theory of gravity for arbitrary number of soft external gravitons and arbitrary number of finite energy external states carrying arbitrary mass and spin. In this paper we verify this explicitly using the CHY formula for tree level scattering amplitudes of arbitrary number of gravitons in Einstein gravity. We pay special care to fix the signs of the amplitudes and resolve an apparent discrepancy between our general results in arXiv:1707.06803 and previous results on soft graviton theorem from CHY formula.

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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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arXiv2017

Subleading Soft Theorem for Multiple Soft Gravitons

We derive the subleading soft graviton theorem in a generic quantum theory of gravity for arbitrary number of soft external gravitons and arbitrary number of finite energy external states carrying arbitrary mass and spin. Our results are valid to all orders in perturbation theory when the number of non-compact space-time dimensions is six or more, but only for tree amplitudes for five or less non-compact space-time dimensions due to enhanced contribution to loop amplitudes from the infrared region.

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arXiv2017

Theta Expansion of First Massive Vertex Operator in Pure Spinor

We provide the covariant superspace equations that are sufficient to determine the complete $θ$ expansion of the vertex operator of the open string massive states with $(mass)^2=1/α'$ in pure spinor formalism of superstring theory. These equations get rid of the redundant degrees of freedom in superfields and are consistent with the BRST conditions derived in [1]. Further, we give the explicit $θ$ expansion of the superfields appearing in the unintegrated vertex to $O(θ^3)$. Finally, we compute the contribution to a 3-point tree amplitude with the resulting vertex operator upto $O(θ^3)$ and find its kinematic structure to be identical to the corresponding RNS computation.

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