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  • Open Access

Selective particle excitations in Rindler spacetime

Akhil U Nair*, Rakesh K Jha†, Prasant Samantray‡, and Sashideep Gutti§

  • *Contact author: p20200473@hyderabad.bits-pilani.ac.in
  • †Contact author: p20230070@hyderabad.bits-pilani.ac.in
  • ‡Contact author: prasant.samantray@hyderabad.bits-pilani.ac.in
  • §Contact author: sashideep@hyderabad.bits-pilani.ac.in
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Phys. Rev. D 111, 125016 – Published 20 June, 2025

DOI: https://doi.org/10.1103/6lwx-y72x

Abstract

The Unruh effect is a well-understood phenomenon in which a quantum field in a vacuum state within Minkowski spacetime appears 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 have a particle excitation for a selective subset of momentum modes for the case of massless scalar fields, and (ii) Is it possible to excite only the left-chiral massless fermions while keeping right-chiral fermionic fields in an unexcited state or vice versa? To this end, we consider a Rindler wedge R1 constructed from a class of accelerating observers and another Rindler wedge R2 (with R2⊂R1) constructed from another class of accelerating observers such that the wedge R2 is displaced along a null direction with respect to R1 by a parameter Δ. By first considering a massless scalar field in the R1 vacuum, we demonstrate that if we choose the displacement Δ along one null direction, the positive momentum modes are thermally populated, whereas negative momentum modes remain unaffected (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 R1 and show that the reduced state in R2 is such that the left-chiral fermions are excited and are thermal for large frequencies. In contrast, the right-chiral fermions have negligible particle density (and vice versa). We argue that the null-shifted Rindler spacetime considered in this article is a good toy model for understanding a class of evolving horizons. Additionally, based on our work, we hypothesize that massless fermions underwent selective chiral excitations during the radiation-dominated era of cosmology.

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Phys. Rev. D 111, 125016– Published 20 June, 2025
  • Received 5 December 2024
  • Accepted 28 May 2025
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