Instabilities in relativistic two-component (super)fluids

Oct 7, 2015
23 pages
Published in:
  • Phys.Rev.D 93 (2016) 2, 025011
  • Published: Jan 14, 2016
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Abstract: (APS)
We study two-fluid systems with nonzero fluid velocities and compute their sound modes, which indicate various instabilities. For the case of two zero-temperature superfluids we employ a microscopic field-theoretical model of two coupled bosonic fields, including an entrainment coupling and a nonentrainment coupling. We analyze the onset of the various instabilities systematically and point out that the dynamical two-stream instability can occur only beyond Landau’s critical velocity, i.e., in an already energetically unstable regime. A qualitative difference is found for the case of two normal fluids, where certain transverse modes suffer a two-stream instability in an energetically stable regime if there is entrainment between the fluids. Since we work in a fully relativistic setup, our results are very general and are of potential relevance for (super)fluids in neutron stars and, in the nonrelativistic limit of our results, in the laboratory.
Note:
  • 25 pages, 7 figures, v2: minor modifications; references added; parts of Sec III.B moved into new appendix B; version published in Phys. Rev. D
  • fluid: velocity
  • boson: coupling
  • stability
  • field theoretical model
  • nonrelativistic
  • neutron star
  • transverse
  • superfluid