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Burgers equation for the bulk viscous pressure of quark matter

José Luis Hernández1,2,3,*, Cristina Manuel1,2,†, Saga Säppi1,2,‡, and Laura Tolos1,2,§

  • *Contact author: hernandez@ice.csic.es
  • †Contact author: cristina.manuel@csic.es
  • ‡Contact author: sappi@ieec.cat
  • §Contact author: tolos@ice.csic.es
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Phys. Rev. D 113, 014032 – Published 27 January, 2026

DOI: https://doi.org/10.1103/3v42-8dpw

Abstract

The dissipative properties of relativistic strongly interacting nuclear matter significantly influence the damping of stellar oscillations and density fluctuations during compact star mergers. In this work, we derive the evolution equation for the bulk viscous pressure in unpaired quark matter under small deviations from equilibrium. Our analysis reveals that it behaves like a two-component Burgers fluid. We identify four key transport coefficients—two relaxation times and two bulk viscosity coefficients—expressed in terms of equilibrium parameters and electroweak nonleptonic and semileptonic decay rates. The transport coefficients are evaluated for two distinct equations of state: one based on perturbative quantum chromodynamics and the other on a modified MIT bag model, valid in different density regimes. We also determine the temperature and density region where nonleptonic electroweak processes dominate the dissipation. Our formulation establishes a new way of describing bulk viscous effects in quark matter, applicable for numerical simulations of compact star mergers.

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Phys. Rev. D 113, 014032– Published 27 January, 2026
  • Received 9 July 2025
  • Accepted 2 January 2026
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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. Funded by SCOAP3.

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