arXiv subjects

Prasant Samantray

Publications and source records attributed to Prasant Samantray.

At least 19 recordsLinked to original sources

arXiv2026

Generation and purification of excited spacetimes using Schwarzian derivative

In this article, we use the expression of the Schwarzian derivative to set up differential equations to find answers to three fundamental questions in the context of QFT in curved spacetime, specifically in two dimensions. One of the ways in which one can derive the Unruh effect in two dimensions is to use the anomalous transformation law of the energy-momentum tensor for a CFT that involves a Schwarzian derivative (Virasoro Anomaly). We answer the following three questions. The first question is as follows: If we have a spacetime with a massless scalar field in vacuum, what are all the subsets of spacetime such that the subset has a thermal distribution of particles for the left-moving and/or right-moving sectors? We obtain a general solution to this question by setting up and solving a third-order nonlinear differential equation based on the expression of Schwarzian. Based on the general solution, we can generate various subsets of the given spacetime that have a thermal flux/density of particles, of which the Rindler spacetime is one. The second question is an inverse question in which we suppose we are given a spacetime with a thermal distribution of particles; what are the possible purifying spacetimes (the ``parent'' spacetimes with the field in vacuum state whose reduced state in the given spacetime yields the observed particle content)? We similarly obtain a general class of solutions by setting up and solving a second differential equation. In this context, we also define ``partial purification'' where we obtain a spacetime that purifies only the left-moving or right-moving sector. The third question concerns locating spacetimes with the same particle content starting from the same ``parent'' spacetime. These sibling spacetimes are generated again by obtaining the general solution of a third differential equation based on the expression of Schwarzian.

gr-qc↗

arXiv2026

Four inequivalent paths to Thermality in Minkowski spacetime

We investigate thermal behaviour in quantum fields by analysing a hierarchy of null-shifted Rindler wedges in Minkowski spacetime. Starting from the Minkowski vacuum restricted to an initial Rindler wedge, we construct several inequivalent transformation paths, including direct Minkowski-Rindler mappings, spatial translations, and sequential null displacements, and analyse the resulting particle content using Bogoliubov transformations. In the standard Unruh effect, entanglement between left- and right-moving sectors across the Rindler horizon produces Gibbsian thermality, with both sectors described by mixed thermal states. In contrast, we show that null-shifted wedge constructions lead to a selective and non-Gibbsian form of thermality: only a single chiral sector develops Bose-Einstein-distributed occupation numbers, while the complementary sector remains in the vacuum. Along composite transformation paths, the global Minkowski state remains pure, and the induced states associated with null-shifted wedges are pure tensor-product states. The observed thermal behaviour arises from Bogoliubov mixing and modular time evolution rather than horizon-induced entanglement or Gibbsian mixedness. These results demonstrate the existence of inequivalent purifications of thermal spectra and clarify the distinct roles of horizon structure, observer dependence, Bogoliubov transformations, and entanglement in relativistic quantum field theory. The null-shifted construction may be viewed as a converse of the Unruh effect, in which thermal spectra arise without entanglement-induced mixedness, highlighting the operational independence of thermality and entanglement.

hep-th↗

arXiv2024

Selective Thermalization, Chiral Excitations, and a Case of Quantum Hair in the Presence of Event Horizons

The Unruh effect is a well-understood phenomenon, where one considers a vacuum state of a quantum field in Minkowski spacetime, which appears to be thermally populated for a uniformly accelerating Rindler observer. In this article, we derive a variant of the Unruh effect involving two distinct accelerating observers and aim to address the following questions: (i) Is it possible to selectively thermalize a subset of momentum modes for the case of massless scalar fields, and (ii) Is it possible to excite only the left-handed massless fermions while keeping right-handed fermions in a vacuum state or vice versa? To this end, we consider a Rindler wedge $R_1$ constructed from a class of accelerating observers and another Rindler wedge $R_2$ (with $R_2 \subset R_1$) constructed from another class of accelerating observers such that the wedge $R_2$ is displaced along a null direction w.r.t $R_1$ by a parameter $\Delta$. By first considering a massless scalar field in the $R_1$ vacuum, we show that if we choose the displacement $\Delta$ along one null direction, the positive momentum modes are thermalized, whereas negative momentum modes remain in vacuum (and vice versa if we choose the displacement along the other null direction). We then consider a massless fermionic field in a vacuum state in $R_1$ and show that the reduced state in $R_2$ is such that the left-handed fermions are excited and are thermal for large frequencies. In contrast, the right-handed fermions have negligible particle density and vice versa. We argue that the toy models involving shifted Rindler spacetime may provide insights into the particle excitation aspects of evolving horizons and the possibility of Rindler spacetime having a quantum strand of hair. Additionally, based on our work, we hypothesize that massless fermions underwent selective chiral excitations during the radiation-dominated era of cosmology.

hep-th↗

arXiv2023

On the Observer Dependence of the Quantum Effective Potential

In this short paper, we investigate the consequences of observer dependence of the quantum effective potential for an interacting field theory. Specializing to $d+2$ dimensional Euclidean Rindler space, we develop the formalism to calculate the effective potential. While the free energy diverges due to the presence of the Rindler horizon, the effective potential, which is a local function of space, is finite after the necessary renormalization procedure. We apply the results of our formalism to understand the restoration of spontaneously broken $\mathbb{Z}_2$ symmetry in three and four dimensions.

hep-th↗

arXiv2023

On Aspects of Spontaneous Symmetry Breaking in Rindler and Anti-de Sitter spacetimes for the $O(N)$ Linear Sigma Model

We investigate aspects of spontaneous breakdown of symmetry for $O(N)$ symmetric linear sigma model in the background of Rindler and Anti-de Sitter spacetimes respectively. In the large $N$ limit, by computing the one-loop effective action, we report that in three dimensional Rindler space, there is a phase transition from the disordered phase to an ordered phase past a certain critical Rindler acceleration parameter `$a$'. Connections with finite temperature field theory results are established, thereby further reinforcing the idea that Rindler space can indeed be a proxy for Minkowski spacetime with finite temperature. We extend our calculations to Anti-de Sitter space in various dimensions and observe that symmetry is broken in three dimensions, but not in four dimensions. We discuss the implications of our results.

hep-th↗

arXiv2022

Test of Transitivity in Quantum Field theory using Rindler spacetime

We consider a massless scalar field in Minkowski spacetime $\cal{M} $ in its vacuum state, and consider two Rindler wedges $R_1$ and $R_2$ in this space. $R_2$ is shifted to the right of $R_1$ by a distance $\Delta$. We therefore have $R_2\subset R_1 \subset \cal{M}$ with the symbol $\subset$ implying a quantum subsystem. We find the reduced state in $R_2$ using two independent ways: a) by evaluation of the reduced state from vacuum state in $\cal{M}$ which yields a thermal density matrix, b) by first evaluating the reduced state in $R_1$ from $\cal{M} $ yielding a thermal state in $R_1$, and subsequently evaluate the reduced state in $R_2$ in that order of sequence. In this article we attempt to address the question whether both these independent ways yield the same reduced state in $R_2$. To that end, we devise a method which involves cleaving the Rindler wedge $R_1$ into two domains such that they form a thermofield double. One of the domains aligns itself along the wedge $R_2$ while the other is a diamond shaped construction between the boundaries of $R_1$ and $R_2$. We conclude that both these independent methods yield two different answers, and discuss the possible implications of our result in the context of quantum states outside a non-extremal black hole formed by collapsing matter.

hep-th↗

arXiv2021

Revisiting Vacuum Energy in Compact Spacetimes

We revisit the calculation of vacuum energy density in compact spacetimes. For the general case of $k$ compact spatial dimensions in $p+k$ dimensional Minkowski spacetime, we calculate the Casimir force on a piston placed in the presence of external electromagnetic fields. We observe that while the presence of a strong external magnetic field reduces the intensity of the Casimir force, the presence of an electric field enhances it instead. We discuss various physical cases, and also derive the particle production rate in the presence of such external fields in compact spacetimes. We observe that the pair production rate is enhanced in the presence of a piston.

hep-th↗

arXiv2020

Schwinger Effect in Compact Space

We consider a theory of scalar QED on a spatially compact 1+1-dimensional spacetime. By considering a constant electric field pointing down the compact dimension, we compute the quantum effective action by integrating out the scalar degrees of freedom in the Euclidean sector. Working in the saddle-point approximation we uncover two novel branches/physical regimes upon analytically continuing back to real time and discover a new result, hitherto unreported in previous literature. Implications of our results are discussed.

hep-th↗

arXiv2019

A Bound on Thermal Relativistic Correlators at Large Spacelike Momenta

We consider thermal Wightman correlators in a relativistic quantum field theory in the limit where the spatial momenta of the insertions become large while their frequencies stay fixed. We show that, in this limit, the size of these correlators is bounded by $e^{-\beta R}$, where $R$ is the radius of the smallest sphere that contains the polygon formed by the momenta. We show that perturbative quantum field theories can saturate this bound through suitably high-order loop diagrams. We also consider holographic theories in $d$-spacetime dimensions, where we show that the leading two-point function of generalized free-fields saturates the bound in $d = 2$ and is below the bound for $d > 2$. We briefly discuss interactions in holographic theories and conclude with a discussion of several open problems.

hep-th↗

arXiv2018

Schwinger Pair Production in Hot Anti-de Sitter Space

We consider particle production in $1+1$ dimensional thermal Anti-de Sitter space under the influence of a constant electric field. The vacuum-persistence amplitude is given by a non-relativistic tunnelling instanton once we interpret the system as being governed by an "equivalent" non-relativistic Schr\"odinger equation. Working in the WKB approximation, we calculate the tunnelling rate in anti de Sitter space at finite temperature and observe that the particle production rate is enhanced. Additionally, it is observed that there is a critical temperature beyond which the production rate is affected by the thermal environment. We claim this to be a new result for Anti-de Sitter space in the semi-classical approximation.

hep-th↗

arXiv2017

Phase Transitions of a (Super) Quantum Mechanical Matrix Model with a Chemical Potential

In this paper, we study the finite-temperature matrix quantum mechanics with chemical potential term linear in the single trace of U(N) matrices, via Monte Carlo simulation. In the bosonic case, we exhibit the existence of the Gross-Witten-Wadia (GWW) type third-order phase transition. We also extend our studies to the model with the fermionic degrees of freedom employing the non-lattice simulation via Fourier expansion, and explore the possibilities that there is a phase transition between the gapped and ungapped phase both in the absence and presence of the chemical potential term. We make a comparison of the phase diagram between the bosonic and fermionic cases.

hep-th↗

arXiv2016

Chaotic dynamics of strings in charged black hole backgrounds

We study the motion of a string in the background of Reissner-Nordstrom black hole, in both AdS as well as asymptotically flat spacetimes. We describe the phase space of this dynamical system through largest Lyapunov exponent, Poincare sections and basins of attractions. We observe that string motion in these settings is particularly chaotic and comment on its characteristics.

hep-th↗

arXiv2016

Evolution of Temperature Fluctuation in a Thermal bath and, its implications in Hadronic and Heavy-Ion Collisions

The evolution equation for inhomogeneous and anisotropic temperature fluctuations inside a medium is derived within the ambit of Boltzmann Transport Equation. Also, taking some existing realistic inputs we have analyzed the Fourier space variation of temperature fluctuation for the medium created after heavy-ion collisions. The effect of viscosity on the variation of fluctuations is investigated. Further, possible implications in hadronic and heavy-ion collisions are explored.

hep-ph↗

arXiv2016

The Schwinger Mechanism in (Anti) de Sitter Spacetimes

We present a short and novel derivation of the Schwinger mechanism for particle pair production in $1+1$ dimensional de Sitter and Anti de Sitter spacetimes. We work directly in the flat embedding space and derive the pair production rates in these spacetimes via instanton methods. The derivation is manifestly coordinate independent, and also lends support to the possible deep connection between two conceptually disparate quantum phenomena - Schwinger effect and the Davies-Unruh effect.

hep-th↗

arXiv2015

Time Evolution of Temperature Fluctuation in a Non-Equilibrated System

The evolution equation for inhomogeneous and anisotropic temperature fluctuation inside a medium is derived within the ambit of Boltzmann Transport Equation (BTE) for a hot gas of massless particles. Also, specializing to a situation created after heavy-ion collision (HIC), we analyze the Fourier space variation of temperature fluctuation of the medium using its temperature profile. The effect of viscosity on the variation of fluctuations in the latter case is investigated and possible implications for early universe cosmology, and its connection with HICs are also explored.

hep-ph↗

arXiv2013

Quantum Non-Barking Dogs

Quantum weak measurements with states both pre- and postselected offer a window into a hitherto neglected sector of quantum mechanics. A class of such systems involves time dependent evolution with transitions possible. In this paper we explore two very simple systems in this class. The first is a toy model representing the decay of an excited atom. The second is the tunneling of a particle through a barrier. The postselection criteria are chosen as follows: at the final time, the "atom" remains in its initial excited state for the first example and the particle remains behind the barrier for the second. We then ask what weak values are predicted in the physical environment of the "atom" (to which no net energy has been transferred) and in the region beyond the barrier (to which the particle has not tunneled). Previous work suggests that very large weak values might arise in these regions for long durations between pre- and postselection times. Our calculations reveal some distinct differences between the two model systems.

quant-ph↗

arXiv2013

Conformal Symmetry, Rindler Space and The AdS/CFT Correspondence

Field theories in black hole spacetimes undergo dimensional reduction near horizon (in the Rindler limit) to two dimensional conformal field theories. We investigate this enhancement of symmetries in the context of gauge/gravity duality by considering Rindler space as boundary of Anti-de Sitter space in three spacetime dimensions. We show that the loxodromy conjugacy class of the SO(2,2) isometry group is responsible for generating the special conformal transformations on the boundary under RG flow. We use this approach to present an alternative derivation of the two-point function in Rindler space using AdS/CFT correspondence.

hep-th↗

arXiv2012

All the Stationary Vacuum States of De Sitter Space

We obtain all the stationary vacua of de Sitter space by classifying the inequivalent timelike isometries of the de Sitter group. Besides the static vacuum, de Sitter space also admits a family of rotating vacua, which we use to obtain Kerr-de Sitter solutions in various dimensions. By writing the metric in a coordinate system adapted to the rotating Hamiltonian, we show that empty de Sitter space admits not only an observer-dependent horizon but also an observer-dependent ergosphere.

hep-th↗