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Madhusudhan Raman

Publications and source records attributed to Madhusudhan Raman.

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.

hep-th↗
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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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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arXiv2024

Trace Relations in Deformed Gauge Theories

We compute trace relations governing chiral ring elements of fully $Ω$-deformed N = 2* gauge theories with SU(N) gauge groups by demanding the regularity of the fundamental qq-character.

hep-th↗
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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arXiv2023

Effective Gravitational Couplings of Kaluza-Klein Gauge Theories

We study the effective gravitational couplings of four-dimensional Kaluza-Klein compactified gauge theories with eight supercharges. The class of theories we consider are the pure SU(N) Yang-Mills theories at admissible Chern-Simons levels and the conformal gauge theories with 2N fundamental flavours. The resolvent of the gauge theory plays a crucial role in the calculation of these gravitational couplings. The results obtained from the Seiberg-Witten geometry are matched against independent computations using localisation.

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arXiv2022

Effective Gravitational Couplings of Higher-Rank Supersymmetric Gauge Theories

When placed on four-manifolds, $ \mathcal{N} = 2 $ gauge theories couple to topological invariants of the background via two functions $ A $ and $ B $. General considerations allow for these functions to be fixed in terms of the Coulomb moduli and other parameters in the theory, but only up to multiplicative factors about which little is known. We extend earlier work on the microscopic study of these functions in the $ Ω$-background to $ \mathcal{N} = 2 ^{\star } $ gauge theories with higher-rank $ \mathrm{U}(N) $ gauge groups. We complement this analysis by carrying out a perturbative study of these functions. This allows us to determine the manner in which these multiplicative factors scale with the rank of the gauge group and the mass of the adjoint hypermultiplet.

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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

Replicas for Random Matrices

We discuss the use of the replica ansatz in computing free energies in random matrix theory, and confirm a conjectured condition on analytic continuation in the replica index at large-N.

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arXiv2021

Triangle Groups: Automorphic Forms and Nonlinear Differential Equations

We study the relations governing the ring of quasiautomorphic forms associated to triangle groups with a single cusp, thereby extending our earlier results on Hecke groups. The Eisenstein series associated to these triangle groups are shown to satisfy Ramanujan-like identities. These identities in turn allow us to associate a nonlinear differential equation to each triangle group. We show that they are solved by the quasiautomorphic weight-2 Eisenstein series associated to the triangle group and its orbit under the group action. We conclude by discussing the Painlevé property of these nonlinear differential equations.

nlin.SI↗
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

Virasoro blocks and quasimodular forms

We analyse Virasoro conformal blocks in the regime of heavy intermediate exchange $(h_p \rightarrow \infty)$. For the 1-point block on the torus and the 4-point block on the sphere, we show that each order in the large-$h_p$ expansion can be written in closed form as polynomials in the Eisenstein series. The appearance of this structure is explained using the fusion kernel and, more markedly, by invoking the modular anomaly equations via the 2d/4d correspondence. We observe that the existence of these constraints allows us to develop a faster algorithm to recursively construct the blocks in this regime. We then apply our results to find corrections to averaged heavy-heavy-light OPE coefficients.

hep-th↗
arXiv2020

On Chebyshev Wells: Periods, Deformations, and Resurgence

We study the geometry and mechanics (both classical and quantum) of potential wells described by squares of Chebyshev polynomials. We show that in a small neighbourhood of the locus cut out by them in the space of hyperelliptic curves, these systems exhibit low-orders/low-orders resurgence, where perturbative fluctuations about the vacuum determine perturbative fluctuations about non-perturbative saddles.

hep-th↗
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.

hep-th↗
arXiv2020

Aspects of Hecke Symmetry: Anomalies, Curves, and Chazy Equations

We study various relations governing quasi-automorphic forms associated to discrete subgroups of ${\rm SL}(2,\mathbb{R}) $ called Hecke groups. We show that the Eisenstein series associated to a Hecke group ${\rm H}(m)$ satisfy a set of $m$ coupled linear differential equations, which are natural analogues of the well-known Ramanujan identities for quasi-modular forms of ${\rm SL}(2,\mathbb{Z})$. Each Hecke group is then associated to a (hyper-)elliptic curve, whose coefficients are determined by an anomaly equation. For the $m=3$ and $4$ cases, the Ramanujan identities admit a natural geometric interpretation as a Gauss-Manin connection on the parameter space of the elliptic curve. The Ramanujan identities also allow us to associate a nonlinear differential equation of order $ m $ to each Hecke group. These equations are higher-order analogues of the Chazy equation, and we show that they are solved by the quasi-automorphic Eisenstein series $E_2^{(m)}$ associated to ${\rm H}(m) $ and its orbit under the Hecke group. We conclude by demonstrating that these nonlinear equations possess the Painlevé property.

hep-th↗
arXiv2017

Horizon Tunneling Revisited: The Case of Higher Dimensional Black Holes

We study the tunneling of massless scalars across black hole horizons in any number of spacetime dimensions greater than three. Our analysis finds that corrections due to backreaction and the inverse dimensional expansion are naturally concomitant, and furnishes a simple proof of the classic relation between entropy and area in all spacetime dimensions, finite or infinite. We conclude with a discussion of the limit in which the the number of spacetime dimensions is taken to infinity, where we find that thermodynamic quantities are related to the "thickness" of the membrane on which all the curvature is localized.

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arXiv2016

Exact WKB Analysis of N = 2 Gauge Theories

We study N = 2 supersymmetric gauge theories with gauge group SU(2) coupled to fundamental flavours, covering all asymptotically free and conformal cases. We re-derive, from the conformal field theory perspective, the differential equations satisfied by omega deformed instanton partition functions. We confirm their validity at leading order in one of the deformation parameters via a saddle-point analysis of the partition function. In the semi-classical limit we show that these differential equations take a form amenable to exact WKB analysis. We compute the monodromy group associated to the differential equations in terms of deformed and Borel resummed Seiberg-Witten data. For each case, we study pairs of Stokes graphs that are related by flips and pops, and show that the monodromy groups allow one to confirm the Stokes automorphisms that arise as the phase of the deformation parameter is varied. Finally, we relate the Borel resummed monodromies with the traditional Seiberg-Witten variables in the semi-classical limit.

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