arXiv subjects

Hemant Rathi

Publications and source records attributed to Hemant Rathi.

13 recordsLinked to original sources

arXiv2026

Hall transports from Taub-NUT AdS black holes

We compute Hall transport coefficients associated with Taub-NUT AdS black holes in four space-time dimensions using the probe D-brane approach. In particular, we examine the effects due to the NUT parameter ($n$), or equivalently, the novel frame-dragging on the holographic charge transport properties. In our analysis, we treat the external electric field as a constant background, while varying the magnetic field ($B$) from small to finite. Within this framework, we analyze conductivities in both low and high temperature regions, focusing on locations that are both near and far from the Misner string. Our calculations show that frame-dragging effects are significant primarily at lower temperatures and near the Misner string, while a small magnetic field is maintained. However, these effects become negligibly small at a ``finite" magnetic field and even at lower temperatures. Our analysis reveals the existence of finite Hall transport, that has its origin in the novel frame-dragging.

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arXiv2026

Probing sine dilaton gravity with flow central charge

We construct a holographic c-function for sine dilaton gravity (sDG) in the domain wall gauge. We show the equivalence between sDG and the two copies of Liouville conformal field theory (LCFT) and compute the associated central charge. We reproduce the central charge of LCFT from the holographic c-function of sDG corresponding to the UV limit. In contrast, in the deep IR limit, the c-function flows to the pure JT gravity, where the central charge becomes identically zero.

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arXiv2025

Metallic transports from Taub-NUT AdS black holes

We compute holographic DC conductivity associated with the Taub-NUT-$AdS_4$ black holes following the probe D-brane approach. In particular, we examine the effects of frame dragging on charge transport in both low and high temperature regimes. Our analysis reveals that in the low temperature regime, the conductivity is sensitive to the presence of the Misner string that causes frame dragging. Notably, the increase in the conductivity near the Misner string is sharper as compared to points farther away from it. On the other hand, in the high temperature regime, the effects due to frame dragging are significantly suppressed, and the thermal contribution to the charge transport takes over that due to the U(1) charge carriers.

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arXiv2025

Holographic central charge for sine dilaton gravity

In this paper, we calculate the holographic central charge ($c_{sDG}$) associated with sine dilaton gravity (sDG) in the semiclassical limit. In the low energy limit, the sDG flows into the ordinary JT gravity which is a conjectured dual of ordinary Schwarzian quantum mechanics at strong coupling. We compute the associated central charge ($c_{JT}$), which reveals $c_{sDG}>c_{JT}$. We identify this as an artifact of the UV completion of JT gravity in terms of sine dilaton gravity.

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arXiv2024

Topology of black hole phase transition in JT gravity

We present a JT gravity setup coupled with $U(1)$ and $SU(2)$ Yang-Mills fields in two dimensions that reveals the onset of a small black hole to large black hole phase transition at finite chemical potential(s). We identify these black hole solutions as topological defects in the thermodynamic phase space and calculate the associated topological numbers following the standard procedure. We confirm the robustness of our model by estimating perturbative corrections to the bulk free energy at an arbitrary order in the Yang-Mills coupling. We also construct the Schwarzian for the boundary theory using the 2D gravitational action in the bulk and comment on the dual SYK like model where similar observations can be made.

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arXiv2024

AdS_2/CFT_1 at finite density and holographic aspects of 2D black holes

In the present thesis, we study various models of 2D dilaton gravity known as JT gravity coupled with non-trivial gauge interactions (for instance $SU(2)$ Yang-Mills, quartic interactions between $U(1)$ gauge fields and Modmax interactions etc.). In particular, we investigate the effects of the non-trivial gauge couplings on the thermal properties of black holes and wormholes in two dimensions and compute various physical observables like entropy, free energy, etc. Further, we examine the possibilities of the Hawking-Page transition and wormhole to black hole phase transition in two dimensions. In addition, we also study the transformation properties of boundary stress-energy tensor under the diffeomorphism and $U(1)$ gauge transformation and hence compute the central charge associated with the 1D boundary theory.

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arXiv2024

Carrollian expansion of Born-Infeld Electrodynamics

In this paper, we carry out a detailed investigation of Born-Infeld Electrodynamics in the Carrollian limit. We explore these theories by looking at expansion in a small c limit at the level of Lagrangian. Particularly, we study the symmetries and correlation functions in the presence of non-linear interactions.

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arXiv2023

Yang-Baxter deformed wedge holography

In this paper, we construct the wedge holography in the presence of homogeneous Yang-Baxter deformation. We observe that the DGP term is the reason for the existence of non-zero tension of the Karch-Randall branes in Yang-Baxter deformed wedge holography. The homogeneous Yang-Baxter deformation introduce non-trivial island surfaces inside the black hole horizon whose entanglement entropy is lower than the twice of thermal entropy of the black hole. Therefore, we obtain the Page curve even without the DGP term on the Karch-Randall branes due to the homogeneous Yang-Baxter deformation in the context of wedge holography. Finally, we compute the the holographic complexity in homogeneous Yang-Baxter deformed $AdS_2$ background.

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arXiv2023

$AdS_2$ holography and ModMax

We present a JT gravity set up in the presence of projected ModMax corrections in two dimensions. Our starting point is the Einstein's gravity in four dimensions accompanied by the ModMax Lagrangian. The 2D gravity action is obtained following a suitable dimensional reduction which contains a 2D image of the 4D ModMax Lagrangian. We carry out a perturbative analysis to find out the vacuum structure of the theory which asymptotes to $AdS_2$ in the absence of $U(1)$ gauge fields. We estimate the holographic central charge and obtain corrections perturbatively upto quadratic order in the ModMax and the $U(1)$ coupling. We also find out ModMax corrected 2D black hole solutions and discuss their extremal limits.

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arXiv2022

Non-chaotic dynamics for Yang-Baxter deformed $\text{AdS}_{4}\times \text{CP}^{3}$ superstrings

We explore a novel class of Yang-Baxter deformed AdS$_{4}$ $\times$ CP$^{3}$ backgrounds [Jour. High Ener. Phys. \textbf{01} (2021) 056] which exhibit a non-chaotic dynamics for (super)strings propagating over it. We explicitly use the \textit{Kovacic's algorithm} in order to establish non-chaotic dynamics of string $ \sigma $ models over these deformed backgrounds. This analysis is complemented with numerical techniques whereby we probe the classical phase space of these (semi)classical strings and calculate various chaos indicators, such as, the Poincar\'{e} sections and the Lyapunov exponents. We find compatibility between the two approaches. Nevertheless, our analysis does not ensure integrability; rather, it excludes the possibility of non-integrability for the given string embeddings.

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arXiv2021

Phases of Euclidean wormholes in JT gravity

We present a JT gravity set up that reveals the evidence of (Euclidean) wormhole to black hole phase transition at finite charge density and/or chemical potential. We identify the low temperature phase of the system as the charged wormhole solution. As the temperature of the system is increased, it undergoes a first order phase transition to a two black hole system at finite charge density. At the critical point ($T = T_0$) of the phase transition, both the Free energy (density) and the charge undergoes a discontinuous change. Finally, we conjectured that the field theory dual to this gravitational set up is a two-site (uncoupled) complex SYK model at a finite chemical potential.

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arXiv2021

Holographic JT gravity with quartic couplings

We construct the most general theory of 2D Einstein-dilaton gravity coupled with $U(1)$ gauge fields that contains all the 2-derivative and the 4-derivative interactions allowed by the diffeomorphism invariance. We renormalise the 2D action and obtain the vacuum solution as well as the black hole solution. The vacuum solution in the UV is dominated by Lifshitz$_2$ with dynamical exponent ($z=\frac{7}{3}$) while on the other hand, the spacetime curvature diverges as we move towards the deep IR limit. We calculate the holographic stress tensor and the central charge for the boundary theory. Our analysis shows that the central charge goes as the inverse power of the coupling associated to 4-derivative interactions. We also compute the Wald entropy for 2D black holes and interpret its near horizon divergence in terms of the density of states. We compare the Wald entropy with the Cardy formula and obtain the eigen value of Virasoro operator ($L_0$) for our model. Finally, we explore the near horizon structure of 2D black holes and calculate the central charge corresponding to the CFT near horizon. We further show that the near horizon CFT may be recast as a 2D Liouville theory with higher derivative corrections. We study the Weyl invariance of this generalised Liouville theory and identify the Weyl anomaly associated to it. We also comment on the classical vacuum structure of the theory.

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arXiv2020

JT gravity and the models of Hawking-Page transition for 2D black holes

We propose a top down construction for Jackiw-Teitelboim (JT) gravity using compactification of $ D=5 $ gravity theories in the presence of Abelian ($ U(1) $) as well as $ SU(2) $ Yang-Mills (YM) fields. The background solutions corresponding to $ D=2 $ model have been obtained in the perturbative regime of the theory where the corrections have been estimated over the uncharged JT solutions while treating the gauge couplings as the parameters of the expansion. Our analysis reveals the existence of two classes of solutions namely, (i) the \emph{interpolating} vacuum solution with AdS$_2$ in the IR and Lifshitz$_2$ in the UV (which serves as the thermal radiation background for our analysis) and (ii) the charged 2D black hole solution exhibiting Lifshitz$_2$ asymptotics. The analysis on thermal stability reveals the onset of a first order phase transition at $ T \sim T_0 $ such that for $ T < T_0 $ the only possible state is the thermal radiation background without any black hole. On the other hand, as the temperature is gradually increased beyond certain \emph{crossover} value $ T\sim T_2 (>T_0 )$, an emerging \emph{globally} stable black hole dominated phase has been observed which clearly indicates the onset of Hawking-Page (HP) transition in 2D gravity models.

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