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Suresh Nampuri

Publications and source records attributed to Suresh Nampuri.

At least 19 recordsLinked to original sources
arXiv2026

Holography from number theory: Emergent holographic AdS$_2$ space-time from exact BPS black hole microstate counting

In this note, starting from the exact counting formulae for 4D BPS black hole degeneracies in the cases of 1/2 BPS $\mathcal{N}=4$ and 1/8 BPS $\mathcal{N}=8$ solutions, expressed as Rademacher expansions for coefficients of modular and Jacobi forms respectively, we explicitly show how the number theoretic data in each Rademacher summand is encoded by a Segal-Bargmann heat kernel calculation in the de Alfaro-Fubini-Furlan (DFF) model of conformal quantum mechanics, thus demonstrating the holographic origin of the BPS Bekenstein-Hawking entropy, and all logarithmic and power law suppressed corrections to it. We then derive the 2D holographically dual bulk space-time for this CQM and show that it is an AdS$_2$ space-time with radial length scale correlated to the energy scale of the DFF model. We further show how the Bekenstein-Hawking entropy emerges from an entanglement entropy computation in this bulk space-time. Hence, for the two classes of 4D BPS black holes under consideration, we have inferred the holographic CQM relevant for microscopic state counting from the exact number-theoretic degeneracy formulae and demonstrated the emergence of the near-horizon AdS$_2$ attractor geometry that is holographically dual to it.

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arXiv2025

Exact BPS black hole microstate counting from holographic conformal quantum mechanics

In this note, we develop a prescription for describing BPS black hole microstates in terms of a holographic conformal quantum mechanics (CQM) model dual to the near-horizon $AdS_2$ geometry of the black hole. We use 1/2 BPS small black holes in a 4D ${\cal N}=4$ toroidal heterotic compactification as well as 1/8 BPS large black holes in a 4D ${\cal N}=8$ Type II toroidal compactification as test cases for our approach. In each case, the $SL(2,\mathbb{Z})$ modular symmetries of the known generating function of the exact microstate degeneracies enables the latter to be expressed as a Rademacher series expansion, with each summand consisting of phases and a modified Bessel function of the first kind. We make a motivated ansatz that the de Alfaro-Fubini-Furlan model (DFF) coupled to a simple harmonic oscillator is a universal sector of the holographic CQM dual to the BPS black hole's near-horizon $AdS_2$ geometry, and demonstrate how in both cases, the two parameters of this putative CQM, the DFF coupling as well as the oscillator frequency, exactly encode both the index and the argument of the Bessel function. Consequently, we extract the leading, logarithmic and all sub-leading power law black hole entropy contributions from calculations in the CQM. In the ${\cal N}=4$ case, the DFF ansatz is sufficient to successfully reproduce the exact microscopic generating function from the CQM.

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arXiv2025

Bulk-boundary entanglement correspondence and the Ryu-Takayanagi conjecture in an $AdS_2/CFT_1$ setup

Using recent developments in expressing one-loop partition functions in Euclidean $AdS_2$ space-times in terms of character integrals, we relate the one-loop effective action for a free field theory in $AdS_2$ (comprised of a massless scalar field and a massless Majorana fermion field) to the partition function of the de Alfaro-Fubini-Furlan (DFF) conformal quantum mechanics (CQM) models on the two global $AdS_2$ boundaries. The equal number of bosonic and fermionic degrees in the field theory guarantee that the one-loop calculation is free of all UV divergences except a logarithmic one consistent with the expected entanglement entropy behaviour in a CQM. Via a thermofield double representation, we compute the entanglement entropy between two copies of the $CFT_1$ (CQM), each living near one of the two boundaries of global $AdS_2$, in a state at global time $τ\rightarrow - \infty$. This entanglement entropy is expressed in terms of the logarithm of the regularised length of a closed particle trajectory infinitesimally near the rim of the Euclidean $AdS_2$ disc. We view this relation between boundary quantum entanglement and a bulk geometrical quantity as the $AdS_2/CFT_1$ version of the Ryu-Takayanagi conjecture in our setup. The boundary entanglement entropy is equal to 4 times the thermodynamic entropy read off from the regularised one-loop effective action in $AdS_2$. Further, we compute the bulk entanglement entropy associated with black hole horizons in Lorentzian $AdS_2$ and show that it precisely matches the boundary entanglement entropy.

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arXiv2025

Machine learning automorphic forms for black holes

Modular, Jacobi, and mock-modular forms serve as generating functions for BPS black hole degeneracies. By training feed-forward neural networks on Fourier coefficients of automorphic forms derived from the Dedekind eta function, Eisenstein series, and Jacobi theta functions, we demonstrate that machine learning techniques can accurately predict modular weights from truncated expansions. Our results reveal strong performance for negative weight modular and quasi-modular forms, particularly those arising in exact black hole counting formulae, with lower accuracy for positive weights and more complicated combinations of Jacobi theta functions. This study establishes a proof of concept for using machine learning to identify how data is organized in terms of modular symmetries in gravitational systems and suggests a pathway toward automated detection and verification of symmetries in quantum gravity.

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arXiv2024

Classical integrability in the presence of a cosmological constant: analytic and machine learning results

We study the integrability of two-dimensional theories that are obtained by a dimensional reduction of certain four-dimensional gravitational theories describing the coupling of Maxwell fields and neutral scalar fields to gravity in the presence of a potential for the neutral scalar fields. For a certain solution subspace, we demonstrate partial integrability by showing that a subset of the equations of motion in two dimensions are the compatibility conditions for a linear system. Subsequently, we study the integrability of these two-dimensional models from a complementary one-dimensional point of view, framed in terms of Liouville integrability. In this endeavour, we employ various machine learning techniques to systematise our search for numerical Lax pair matrices for these models, as well as conserved currents expressed as functions of phase space variables.

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arXiv2024

Rademacher expansion of a Siegel modular form for ${\cal N}= 4$ counting

The degeneracies of $1/4$ BPS states with unit torsion in heterotic string theory compactified on a six-torus are given in terms of the Fourier coefficients of the reciprocal of the Igusa cusp Siegel modular form $Φ_{10}$ of weight $10$. We use the symplectic symmetries of the latter to construct a fine-grained Rademacher type expansion which expresses these BPS degeneracies as a regularized sum over residues of the poles of $1/Φ_{10}$. The construction uses two distinct ${\rm SL}(2, \mathbb{Z})$ subgroups of ${\rm Sp}(2, \mathbb{Z})$ which encode multiplier systems, Kloosterman sums and Eichler integrals appearing therein. Additionally, it shows how the polar data are explicitly built from the Fourier coefficients of $1/η^{24}$ by means of a continued fraction structure.

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arXiv2023

The gravitational path integral for $ N=4$ BPS black holes from black hole microstate counting

We use the exact degeneracy formula of single-centred $\frac14$ BPS dyonic black holes with unit torsion in 4D $N=4$ toroidally compactified heterotic string theory to improve on the existing formulation of the corresponding quantum entropy function obtained using supersymmetric localization. The result takes the form of a sum over Euclidean backgrounds including orbifolds of the Euclidean $AdS_2 \times S^2$ attractor geometry. Using an $N=2$ formalism, we determine the explicit form of the Abelian gauge potentials supporting these backgrounds. We further show how a rewriting of the degeneracy formula is amenable, at a semi-classical level, to a gravitational interpretation involving 2D Euclidean wormholes. This alternative picture is useful to elucidate different aspects of the gravitational path integral capturing the microstate degeneracies. We also comment on the relation between the associated 1D holographic models.

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arXiv2022

Observations on holographic aspects of four-dimensional asymptotically flat ${\cal N}=2$ black holes

In this note, we explore holographic attributes of four-dimensional near-extremal Reissner-Nordstrom black hole solutions in ungauged ${\cal N}=2$ supergravity theories at the two-derivative level by recasting them as a specific first-order deformation in solution space, associated with an infinitesimal Harrison transformation, of black holes in an $AdS_2$ space-time. Specifically, we use this link to exhibit how bulk properties, such as mass and entropy, of four-dimensional near-extremal black holes are holographically encoded in the one-dimensional boundary theory dual to gravity in an infinitesimally deformed $AdS_2$ space-time. We do so for the case of four-dimensional near-extremal black holes that arise as deformations in solution space of BPS black holes by changing the non-extremality parameter. For these near-extremal black holes, we further show that the nAdS$_2$ attractor mechanism can be recast as a specific deformation of the BPS flow equations in four dimensions. Additionally, we also discuss time-dependent perturbations of the four-dimensional near-extremal Reissner-Nordstrom solutions from a two-dimensional point of view.

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arXiv2021

$R^2$ corrected AdS$_2$ holography

We approach the problem of constructing an explicit holographic dictionary for the AdS$_2$/CFT$_1$ correspondence in the context of higher derivative gravitational actions in AdS$_2$ space-times. These actions are obtained by an $S^2$ reduction of four-dimensional ${\cal N}=2$ Wilsonian effective actions with Weyl squared interactions restricted to constant scalar backgrounds. BPS black hole near-horizon space-times fall into this class of backgrounds, and by identifying the boundary operators dual to the bulk fields, we explicitly show how the Wald entropy of the BPS black hole is holographically encoded in the anomalous transformation of the operator dual to a composite bulk field. Additionally, using a 2d/3d lift, we show that the CFT holographically dual to AdS$_2$ is naturally embedded in the chiral half of the CFT$_2$ dual to the AdS$_3$ space-time, and we identify the specific operator in CFT$_1$ that encodes the chiral central charge of the CFT$_2$.

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arXiv2020

Refinement and modularity of immortal dyons

Extending recent results in ${\cal N}=2$ string compactifications, we propose that the holomorphic anomaly equation satisfied by the modular completions of the generating functions of refined BPS indices has a universal structure independent of the number ${\cal N}$ of supersymmetries. We show that this equation allows to recover all known results about modularity (under $SL(2,\mathbb{Z})$ duality group) of BPS states in ${\cal N}=4$ string theory. In particular, we reproduce the holomorphic anomaly characterizing the mock modular behavior of quarter-BPS dyons and generalize it to the case of non-trivial torsion invariant.

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arXiv2020

Comments on the double copy construction for gravitational theories

We revisit the double copy description for linearized gravity and point out various technical issues and subtleties, associated with setting up the double copy description, including the problem of matching degrees of freedom on both sides of the double copy dictionary and the related issue of the constraint between graviton and dilaton sources. We introduce and discuss possible resolutions of these issues.

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arXiv2019

Generalized Hot Attractors

Non-extremal black holes are endowed with geometric invariants related to their horizon areas. We extend earlier work on hot attractor black holes to higher dimensions and add a scalar potential. In addition to the event and Cauchy horizons, when we complexify the radial coordinate, non-extremal black holes will generically have other horizons as well. We prove that the product of all of the horizon areas is independent of variations of the asymptotic moduli further generalizing the attractor mechanism for extremal black holes. In the presence of a scalar potential, as typically appears in gauged supergravity, we find that the product of horizon areas is not necessarily the geometric mean of the extremal area, however. We outline the derivation of horizon invariants for stationary backgrounds.

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arXiv2017

Multi-centered ${\mathcal N}=2$ BPS black holes: a double copy description

We present the on-shell double copy dictionary for linearised ${\mathcal N}=2$ supergravity coupled to an arbitrary number of vector multiplets in four dimensions. Subsequently, we use it to construct a double copy description of multi-centered BPS black hole solutions in these theories in the weak-field approximation.

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arXiv2017

An SLE approach to four dimensional black hole microstate entropy

In this note, we model the Bekenstein-Hawking entropy of a four dimensional extremal black hole in terms of classifying particles moving in its near horizon AdS_2 geometry. We use the framework of SLE curves in AdS_2 to classify these particle trajectories in terms of their boundary conditions. These turn out to be related to singular vectors in two-dimensional conformal quantum gravity theory in AdS_2 and the dynamics of these particles are governed by the Hamiltonians of the integrable Calogero-like models, for these boundary conditions. We use this classification to count the leading order Bekenstein-Hawking entropy of the black hole and arrive at a first principle microscopic computation of black hole degeneracy.

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arXiv2016

The Hot Attractor Mechanism: Decoupling Without Deep Throats

Non-extremal black holes in $\mathcal{N}=2$ supergravity have two horizons, the geometric mean of whose areas recovers the horizon area of the extremal black hole obtained from taking a smooth zero temperature limit. In prior work (arxiv:1410.3478), using the attractor mechanism, we deduced the existence of several moduli independent invariant quantities obtained from averaging over a decoupled inter-horizon region. We establish that non-extremal geometries at the Reissner--Nordström point, where the scalar moduli are held fixed, can be lifted to solutions in supergravity with a near-horizon AdS$_3\times$S$^2$. These solutions have the same entropy and temperature as the original black hole and therefore allow an interpretation of the underlying gravitational degrees of freedom in terms of CFT$_2$. Symmetries of the moduli space enable us to explicate the origin of entropy in the extremal limit.

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arXiv2015

A Calogero formulation for four-dimensional black-hole micro states

We extract the leading-order entropy of a four-dimensional extremal black hole in ${\cal N}{=}2$ ungauged supergravity by formulating the CFT$_1$ that is holographically dual to its near-horizon AdS$_2$ geometry, in terms of a rational Calogero model with a known counting formula for the degeneracy of states in its Hilbert space.

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