arXiv subjects

Nishal Rai

Publications and source records attributed to Nishal Rai.

8 recordsLinked to original sources

arXiv2026

Anomalous Transport and Explicit Symmetry Breaking in Holography

We consider a holographic Einstein-Maxwell model in five dimensions with pure gauge and mixed gauge-gravitational Chern-Simons terms to study anomaly-induced transport in the presence of explicit symmetry breaking. We include the full backreaction of the scalar field and gauge fields on the metric and compute the anomalous transport coefficients using Kubo formulae involving charge and energy current correlators. Our findings reveal that, in the presence of explicit symmetry breaking, anomaly-induced transport phenomena can extend beyond anomalous currents and affect the non-anomalous sector as well. The transport coefficients exhibit a clear dependence on the symmetry-breaking mass parameter, highlighting the interplay between quantum anomalies and explicit symmetry breaking in holographic systems.

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arXiv2026

Anomaly induced transport from symmetry breaking in holography

We study the transport properties of relativistic fluids induced by quantum anomalies in presence of explicit symmetry breaking. To this end we consider a holographic Einstein-Maxwell model in 5 dimensions with pure gauge and a mixed gauge-gravitational Chern-Simons terms, coupled with a scalar field. To study the chiral vortical effects and the energy transport sector, apart from the chiral magnetic effects, we have considered the full backreaction of the gauge field on the metric. We have studied the anomalous effects by using Kubo formulae involving correlators of the charged currents and the energy current. Our findings reveal that, in the presence of explicit symmetry breaking, anomaly-induced transport phenomena can extend beyond anomalous currents and affect non-anomalous sectors as well. In particular, we find that all the conductivities display a distinct sensitivity to the mass parameter controlling the symmetry breaking, thus reflecting the interplay between anomaly coefficients and explicit symmetry breaking terms. These findings highlight the role played by pure gauge and mixed gauge-gravitational anomalies in holographic transport, and their importance for strongly coupled systems with broken symmetries.

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arXiv2024

Hydrodynamic Modes of Holographic Weyl Semimetals

We study the quasinormal modes of a holographic model of a Weyl semimetal. The model features quantum phase transition between a topological phase and a trivial phase. We put particular emphasis on the hydrodynamic modes and show that a hydrodynamic mode is present only in the topological Weyl semimetal phase.

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arXiv2024

Holographic approach to anomalous transport in a massive $U(1)$ gauge theory

In this study, we explore a massive (U(1)) gauge holographic model with pure gauge and mixed gauge-gravitational Chern-Simons terms. By considering the full backreaction of the gauge field on the metric tensor, we explore the vortical and energy transport sectors. Our findings for the chiral vortical conductivity, $σ_V$, and the chiral magnetic/vortical conductivity of energy current show that $σ^\varepsilon_B = σ^\varepsilon_V$. Notably, we highlight a contribution to (σ_V) induced by the mixed term in the massive theory, which is absent in the massless case.

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arXiv2023

Anomalous conductivities in the holographic Stuckelberg model

We have studied a massive U(1) gauge holographic model with pure gauge and mixed gauge-gravitational Chern-Simons terms. The full backreaction of the gauge field on the metric tensor has been considered in order to explore the vortical and energy transport sector. The background solution has been computed numerically. On this background, we have considered the fluctuation of the fields and evaluated the different correlators. We have found that all the correlators depend on the mass of the gauge field. Correlators such as the current-current one, $\langle J_xJ_x\rangle$, which were completely absent in the massless case, in the presence of a finite gauge boson mass start picking up some finite value even at zero chemical potential. Similarly, the energy-current correlator, $\langle T_{0x}J_x\rangle$, which was also absent in the massless theory, has now a non-vanishing value but for finite values of the chemical potential. Our findings for the chiral vortical conductivity, $σ_V$, and the chiral magnetic/vortical conductivity of energy current, $σ^\varepsilon_B = σ^\varepsilon_V$, are completely new results. In addition to this, we have found that these anomalous transport coefficients depend linearly both on the pure Chern-Simon coupling, $κ$, and on the mixed gauge-gravity Chern-Simon coupling, $λ$. One of the results that we would like to highlight is that its not just $κ$ that contributes to the $σ_B$ but there is an additional contribution from $λ$ as well unlike the previous studies.

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arXiv2021

Holographic Fermi surfaces in charge density wave from D2-D8

D2-D8 model admits a numerical solution that corresponds to a charge density wave and a spin density wave. Considering that as the background, we numerically solve the Dirac equation for probe fermions. From the solution, we obtain the Green's function and study the behaviour of the spectral density. We begin with generic fermions and have studied the formation of the Fermi surface and where it develops a gap. In addition, we have incorporated an ionic lattice and study its effect on the Fermi surface. Then we analysed the worldvolume fermions. In this particular model we do not find Fermi surface for the dual operators.

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arXiv2020

Holographic charge density wave from D2-D8

We have considered D2-D8 model and obtain a numerical solution that exhibits spatially modulated phases corresponding to a charge density wave and a spin density wave. We have analysed behavior of the free energy density for different values of the chemical potential and the magnetic field.

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arXiv2019

Fermionic spectrum from a domain wall in five dimensions

We study fermions in a domain wall backgrounds in five dimensional supergravity, which is similar to zero temperature limit of holographic superconductor. We find the fermionic operators for small charges in the dual four dimensional theory have gapped spectrum.

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