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  • Letter
  • Open Access

Gapless nonhydrodynamic modes in relativistic kinetic theory

L. Gavassino*

  • *Contact author: lorenzo.gavassino@vanderbilt.edu
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Phys. Rev. Research 6, L042043 – Published 14 November, 2024

DOI: https://doi.org/10.1103/PhysRevResearch.6.L042043

Abstract

We provide rigorous criteria to determine whether the nonhydrodynamic sector of a relativistic kinetic theory is gapless. These general criteria apply to both Boltzmann's equation and approximate models thereof, provided that the latter are consistent with thermodynamic principles. As an application of these criteria, we prove that the nonhydrodynamic sector is gapless whenever the scattering cross section decays to zero at large energies. Physically, this happens because, if particles with very high energy (compared to the temperature) are free streaming, we can use them to build hot nonhydrodynamic waves, which live longer than any hydrodynamic wave. Since many standard cross sections in quantum field theory vanish at high energies, the existence of these nonthermal long-lived waves is a rather general feature of relativistic systems.

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Phys. Rev. Research 6, L042043– Published 14 November, 2024
  • Received 30 April 2024
  • Accepted 25 October 2024
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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