Adiabatic instability in coupled dark energy/dark matter models

Rachel Bean, Éanna É. Flanagan, and Mark Trodden
Phys. Rev. D 78, 023009 – Published 10 July 2008

Abstract

We consider theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the Universe. Such theories can possess an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, which is set by the local dark matter density. We show that if the coupling strength is much larger than gravitational, then the adiabatic regime is always subject to an instability. The instability, which can also be thought of as a type of Jeans instability, is characterized by a negative sound speed squared of an effective coupled dark matter/dark energy fluid, and results in the exponential growth of small scale modes. We discuss the role of the instability in specific coupled cold dark matter and mass varying neutrino models of dark energy and clarify for these theories the regimes in which the instability can be evaded due to nonadiabaticity or weak coupling.

  • Figure
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  • Received 14 September 2007

DOI:https://doi.org/10.1103/PhysRevD.78.023009

©2008 American Physical Society

Authors & Affiliations

Rachel Bean1, Éanna É. Flanagan1,2, and Mark Trodden3

  • 1Department of Astronomy, Cornell University, Ithaca, New York 14853, USA
  • 2Laboratory for Elementary Particle Physics, Cornell University, Ithaca, New York 14853, USA
  • 3Department of Physics, Syracuse University, Syracuse, New York 13244, USA

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Issue

Vol. 78, Iss. 2 — 15 July 2008

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