arXiv subjects

Avik Chakraborty

Publications and source records attributed to Avik Chakraborty.

15 recordsLinked to original sources

arXiv2026

Quasiparticle tunnelling in two coupled chiral SYK model

The chiral SYK model is a 1+1 dimensional generalisation of the Sachdev-Ye-Kitaev model with chiral Majorana fermions and homogeneous random interactions. In the large-N limit, the model admits an exact solution of the two-point function due to its scaling symmetry and exhibits a quantised thermal Hall conductance consistent with that of a 2+1-dimensional gapped topological system. We study two chiral SYK systems coupled by a relevant quadratic interaction that explicitly breaks scaling and time-reversal symmetry. Working in the regime of weak intersystem coupling, we solve the Dyson-Schwinger equations perturbatively and obtain analytic expressions for two-point functions at finite temperature. Unlike the coupled SYK model in 0+1 dimensions, the 1+1-dimensional chiral system does not develop a mass gap, and no thermal phase transition is observed. We show that the leading correction to the thermodynamic free energy is temperature independent, implying that the entropy density remains identical to that of two uncoupled chiral SYK systems. A real-time analysis of the retarded correlator reveals the emergence of massless collective bosonic modes propagating between the two subsystems at zero temperature, signalling quasiparticle tunnelling without gap generation. Our results demonstrate a sharp qualitative distinction between relevant deformations of SYK models in zero and one spatial dimensions, and highlight the robustness of gapless chiral edge dynamics against explicit scaling symmetry-breaking interactions.

hep-th↗

arXiv2026

Junctions, strings, clocks and gravitational memory in three dimensional dS space

We show that non-trivial stringy excitations in Lorentzian three dimensional de Sitter spacetime can be created self-consistently from gravitational memory in the infinite past. In addition to demonstrating that the Nambu-Goto equations for the string emerge from the two-way gravitational junction conditions, we establish the existence of well-behaved solutions corresponding to transient fluctuations of a closed string about the equator which are both borne out of and dissolve to distinct gravitational memory in the infinite past and future, respectively. The memory at infinite past, which uniquely characterizes such a solution, is a single function giving the relative angular shift at the junction gluing two two-dimensional hemispheres. This reveals that a clock dynamically emerges in the presence of a gravitational junction without the need of any external observer. We also show that our results generalize to the $n$-way gravitational junctions with $n\geq 3$, which are captured by Nambu-Goto-Monge-Ampère equations for coupled $n-1$ strings -- these degrees of freedom exist even in the tensionless limit. Furthermore, for $n\geq 3$, $n-1$ correlated clocks dynamically emerge without the need of external observers in the tensionless limit, revealing a novel feature of pure three-dimensional gravity.

hep-th↗

arXiv2026

Decoding the string in terms of holographic quantum maps

It has recently been shown that the Nambu-Goto equation for a string emerges from the junction conditions in three-dimensional gravity. Holographically, gravitational junctions are dual to interfaces in conformal field theory. We demonstrate at the level of linearized gravitational perturbations that each stringy mode of the junction corresponds to a $\mathcal{H}_{in}\rightarrow \mathcal{H}_{out}$ quantum map which can be factorized into a scattering matrix involving reflection/transmission and a relative automorphism of the Virasoro algebra, and also a $\mathcal{H}_{L}\rightarrow \mathcal{H}_{R}$ map of similar nature. These maps preserve the conformal boundary condition, are independent of the background conformal frame, as in the case of conformal interfaces studied in the literature, and realize a tunable energy transmitter.

hep-th↗

arXiv2026

The degrees of freedom of multiway junctions in three dimensional gravity

We demonstrate that $n$-way junctions in three dimensional gravity correspond to coupled $n-1$ strings each satisfying the Nambu-Goto equation in the smoothened background, and with sources consisting of Monge-Ampère like terms which couple the strings. For $n\geq 3$, these $n-1$ degrees of freedom survive the tensionless limit implying that matter-like behavior can arise out of \textit{pure} gravity. We interpret these stringy degrees of freedom of gravitational junctions holographically in terms of wavepackets which collectively undergo perfect reflection at the multi-interface in the dual conformal field theory.

hep-th↗

arXiv2026

Decoding multiway gravitational junctions in AdS in terms of holographic quantum maps

It has been shown that multiway junctions gluing $n$ copies of locally AdS$_3$ spacetimes ($n\geq 2$) can be described by $n-1$ strings obeying non-linear Nambu-Goto equations coupled by Monge-Amp\`{e}re like terms. Here we study how such junctions along with their stringy degrees of freedom can be interpreted in terms of an interface between $n$ identical holographic conformal theories each defined on a semi-infinite line (wire). We study the gravitational scattering problem at the multiway junction, and show that at the linearized order the dual interfaces correspond to quantum maps which factorize into a product of a scattering matrix determined only by the tension of the dual junction and relative automorphisms of the Virasoro algebra governed by the $n-1$ stringy modes. Both of these are universal in the sense that they are independent of linear modifications of the background state. These generalize earlier results for the 2-way junctions implying that the dual interface is a tunable energy transmitter. We comment on understanding the quantum map corresponding to the full non-linear gravitational problem, and study Ward identities and unitarity bounds.

hep-th↗

arXiv2026

Renormalization of Einstein-Gauss-Bonnet AdS gravity

The asymptotic analysis for the metric of a generic solution of Einstein-Gauss-Bonnet AdS theory is provided by solving the field equations in the Fefferman-Graham frame. Using standard holographic renormalization, the counterterms that render the action finite are found up to seven spacetime dimensions. In the case of 6D, an equivalent formulation that permits a fully covariant determination of the counterterms is introduced, based on the finiteness of conformal invariants. It is shown that both schemes end up in the same holographic stress-energy tensor. Physical properties of six-dimensional topological Boulware-Deser black holes in Einstein-Gauss-Bonnet-AdS$_6$ gravity, whose boundary has nontrivial conformal features, are worked out in detail. Employing both renormalization prescriptions, finite asymptotic charges are found, and the correct black hole thermodynamics is recovered.

hep-th↗

arXiv2023

Weyl-invariant scalar-tensor gravities from purely metric theories

We describe a method to generate scalar-tensor theories with Weyl symmetry, starting from arbitrary purely metric higher derivative gravity theories. The method consists in the definition of a conformally-invariant metric $\hat{g}_{μν}$, that is a rank (0,2)-tensor constructed out of the metric tensor and the scalar field. This new object has zero conformal weight and is given by $ϕ^{2/Δ}g_{μν}$, where ($-Δ$) is the conformal dimension of the scalar. As $g_{μν}$ has conformal dimension of 2, the resulting tensor is trivially a conformal invariant. Then, the generated scalar-tensor theory, which we call the Weyl uplift of the original purely metric theory, is obtained by replacing the metric by $\hat{g}_{μν}$ in the action that defines the original theory. This prescription allowed us to define the Weyl uplift of theories with terms of higher order in the Riemannian curvature. Furthermore, the prescription for scalar-tensor theories coming from terms that have explicit covariant derivatives in the Lagrangian is discussed. The same mechanism can also be used for the derivation of the equations of motion of the scalar-tensor theory from the original field equations in the Einstein frame. Applying this method of Weyl uplift allowed us to reproduce the known result for the conformal scalar coupling to Lovelock gravity and to derive that of Einsteinian cubic gravity. Finally, we show that the renormalization of the theory given by the conformal scalar coupling to Einstein-Anti-de Sitter gravity originates from the Weyl uplift of the original renormalized theory, which is relevant in the framework of conformal renormalization.

hep-th↗

arXiv2021

Reconstructing the Bulk Dual of ABJM from Holographic Entanglement Entropy

Recent work has shown that entanglement and the structure of spacetime are intimately related. One way to investigate this is to begin with an entanglement entropy in a conformal field theory (CFT) and use the AdS/CFT correspondence to calculate the bulk metric. We perform this calculation for ABJM, a particular 3-dimensional supersymmetric CFT (SCFT), in its ground state. In particular we are able to reconstruct the pure AdS4 metric from the holographic entanglement entropy of the boundary ABJM theory in its ground state. Moreover, we are able to predict the correct AdS radius purely from entanglement. We also address the general philosophy of relating entanglement and spacetime through the Holographic Principle, as well as some of the philosophy behind our calculations.

hep-th↗

arXiv2020

Testability of Reversible Iterative Logic Arrays

Iterative Logic Arrays (ILAs) are ideal as VLSI sub-systems because of their regular structure and its close resemblance with FPGAs (Field Programmable Gate Arrays). Reversible circuits are of interest in the design of very low power circuits where energy loss implied by high frequency switching is not of much consideration. Reversibility is essential for Quantum Computing. This paper examines the testability of Reversible Iterative Logic Arrays (ILAs) composed of reversible k-CNOT gates. For certain ILAs it is possible to find a test set whose size remains constant irrespective of the size of the ILA, while for others it varies with array size. Former type of ILAs is known as Constant-Testable, i.e. C-Testable. It has been shown that Reversible Logic Arrays are C-Testable and size of test set is equal to number of entries in cells truth table implying that the reversible ILAs are also Optimal-Testable, i.e. O-Testable. Uniform-Testability, i.e. U-Testability has been defined and Reversible Heterogeneous ILAs have been characterized as U-Testable. The test generation problem has been shown to be related to certain properties of cycles in a set of graphs derived from cell truth table. By careful analysis of these cycles an efficient test generation technique that can be easily converted to an ATPG program has been presented for both 1-D and 2D ILAs. The same algorithms can be easily extended for n-Dimensional Reversible ILAs.

cs.OH↗

arXiv2020

On the Complexity of a $2+1$--dimensional Holographic Superconductor

We present the results of our computation of the subregion complexity and also compare it with the entanglement entropy of a $2+1$--dimensional holographic superconductor which has a fully backreacted gravity dual with a stable ground sate. We follow the "complexity equals volume" or the CV conjecture. We find that there is only a single divergence for a strip entangling surface and the complexity grows linearly with the large strip width. During the normal phase the complexity increases with decreasing temperature, but during the superconducting phase it behaves differently depending on the order of phase transition. We also show that the universal term is finite and the phase transition occurs at the same critical temperature as obtained previously from the free energy computation of the system. In one case, we observe multivaluedness in the complexity in the form of an "S" curve.

hep-th↗

arXiv2017

Benchmarking Black Hole Heat Engines, II

We extend to non-static black holes our benchmarking scheme that allows for cross-comparison of the efficiencies of asymptotically AdS black holes used as working substances in heat engines. We use a circular cycle in the p-V plane as the benchmark cycle. We study Kerr black holes in four spacetime dimensions as an example. As in the static case, we find an exact formula for the benchmark efficiency in an ideal-gas-like limit, which may serve as an upper bound for rotating black hole heat engines in a thermodynamic ensemble with fixed angular velocity. We use the benchmarking scheme to compare Kerr to static black holes charged under Maxwell and Born-Infeld sectors.

hep-th↗

arXiv2016

Benchmarking Black Hole Heat Engines

We present the results of initiating a benchmarking scheme that allows for cross-comparison of the efficiencies of black holes used as working substances in heat engines. We use a circular cycle in the p-V plane as the benchmark engine. We test it on Einstein-Maxwell, Gauss-Bonnet, and Born-Infeld black holes. Also, we derive a new and surprising exact result for the efficiency of a special `ideal gas' system to which all the black holes asymptote.

hep-th↗

arXiv2012

Attraction, with Boundaries

We study the basin of attraction of static extremal black holes, in the concrete setting of the STU model. By finding a connection to a decoupled Toda-like system and solving it exactly, we find a simple way to characterize the attraction basin via competing behaviors of certain parameters. The boundaries of attraction arise in the various limits where these parameters degenerate to zero. We find that these boundaries are generalizations of the recently introduced (extremal) subtracted geometry: the warp factors still exhibit asymptotic integer power law behaviors, but the powers can be different from one. As we cross over one of these boundaries ("generalized subttractors"), the solutions turn unstable and start blowing up at finite radius and lose their asymptotic region. Our results are fully analytic, but we also solve a simpler theory where the attraction basin is lower dimensional and easy to visualize, and present a simple picture that illustrates many of the basic ideas.

hep-th↗

arXiv2012

Subttractors

We consider extremal limits of the recently constructed "subtracted geometry". We show that extremality makes the horizon attractive against scalar perturbations, but radial evolution of such perturbations changes the asymptotics: from a conical-box to flat Minkowski. Thus these are black holes that retain their near-horizon geometry under perturbations that drastically change their asymptotics. We also show that this extremal subtracted solution ("subttractor") can arise as a boundary of the basin of attraction for flat space attractors. We demonstrate this by using a fairly minimal action (that has connections with STU model) where the equations of motion are integrable and we are able to find analytic solutions that capture the flow from the horizon to the asymptotic region. The subttractor is a boundary between two qualitatively different flows. We expect that these results have generalizations for other theories with charged dilatonic black holes.

hep-th↗

arXiv2010

Testing of Bridging Faults in AND-EXOR based Reversible Logic Circuits

Reversible circuits find applications in many areas of Computer Science including Quantum Computation. This paper examines the testability of an important subclass of reversible logic circuits that are composed of k-wire controlled NOT (k-CNOT with k >/- 1) gates. A reversible k-CNOT gate can be implemented using an irreversible k-input AND gate and an EXOR gate. A reversible k-CNOT circuit where each k-CNOT gate is realized using irreversible k-input AND and EXOR gate, has been considered. One of the most commonly used Single Bridging Fault model (both wired-AND and wired-OR) has been assumed to be type of fault for such circuits. It has been shown that an (n+p)-input AND-EXOR based reversible logic circuit with p observable outputs, can be tested for single bridging faults (SBF) using (3n + \lefthalfcap log2p \righthalfcap + 2) tests.

cs.OH↗