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  • Open Access

Superfluids in expanding backgrounds and attractor times

Guri K. Buza1,*, Toshali Mitra2,3,†, and Alexander Soloviev1,‡

  • *Contact author: guri.buza@fmf.uni-lj.si
  • †Contact author: toshali.mitra@apctp.org
  • ‡Contact author: alexander.soloviev@fmf.uni-lj.si
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Phys. Rev. D 112, 076022 – Published 17 October, 2025

DOI: https://doi.org/10.1103/45fr-wb1w

Abstract

We determine the behavior of an out-of-equilibrium superfluid, composed of a U(1) Goldstone mode coupled to hydrodynamic modes in a Müller-Israel-Stewart theory, in expanding backgrounds relevant to heavy ion collision experiments and cosmology. For suitable initial conditions, the evolution of the hydrodynamic variables leads to a change in the potential of the Goldstone mode, spontaneously breaking the symmetry. After some time, the condensate becomes small, leading the system evolution to be well described via hydrodynamic attractors for a timescale that we determine in Bjorken and Gubser flows. We define this new timescale as the attractor time and show its dependence on initial conditions. In the case of the Gubser flow, we provide for the first time a complete description of the nonlinear evolution of the system, including a novel nonlinear regime of constant anisotropy not found in the Bjorken evolution. Finally, we consider the superfluid in the dynamical Friedmann-Lemaitre-Roberston-Walker (FLRW) background, where we observe a similar attractor behavior, dependent on the initial conditions, that at late times approaches a regime dominated by the condensate.

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Outline

Information

Phys. Rev. D 112, 076022– Published 17 October, 2025
  • Received 24 October 2024
  • Accepted 27 September 2025
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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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