arXiv subjects

Rakesh K Jha

Publications and source records attributed to Rakesh K Jha.

3 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↗

arXiv2026

Thermality Breakdown in Null-Shifted Rindler Wedges

We investigate the behaviour of quantum fields in null-shifted Rindler wedges and analyse the particle spectra perceived by accelerated observers associated with these null deformations. Unlike the standard Unruh effect, our analysis compares two accelerated frames connected by a null displacement. We consider both massive scalar and Dirac fields, constructing their corresponding mode solutions in Rindler coordinates. Using normalised field expansions, we compute the Bogoliubov transformations between modes defined in the two null-shifted wedges. Our results demonstrate a fundamental breakdown of thermality: the presence of mass modifies the mode structure, rendering the characteristic exponential mixing of frequencies absent. This suggests that the massive field remains unexcited on this background, leading to a manifestly nonthermal response. These findings highlight that thermality in accelerated frames depends sensitively on the conformal symmetry of the field, which is broken by the introduction of a mass term.

hep-th↗