TY - JOUR

T1 - Coupled vector dark energy

AU - Nakamura, Shintaro

AU - Kase, Ryotaro

AU - Tsujikawa, Shinji

N1 - Publisher Copyright:
© 2019 IOP Publishing Ltd and Sissa Medialab.

PY - 2019

Y1 - 2019

N2 - We provide a general framework for studying the evolution of background and cosmological perturbations in the presence of a vector field Aμ coupled to cold dark matter (CDM) . We consider an interacting Lagrangian of the form Q f(X) Tc, where Q is a coupling constant, f is an arbitrary function of X=-AμAμ/2, and Tc is a trace of the CDM energy-momentum tensor. The matter coupling affects the no-ghost condition and sound speed of linear scalar perturbations deep inside the sound horizon, while those of tensor and vector perturbations are not subject to modifications. The existence of interactions also modifies the no-ghost condition of CDM density perturbations. We propose a concrete model of coupled vector dark energy with the tensor propagation speed equivalent to that of light. In comparison to the Q=0 case, we show that the decay of CDM to the vector field leads to the phantom dark energy equation of state wDE closer to-1. This alleviates the problem of observational incompatibility of uncoupled models in which wDE significantly deviates from-1. The maximum values of wDE reached during the matter era are bounded from the CDM no-ghost condition of future de Sitter solutions.

AB - We provide a general framework for studying the evolution of background and cosmological perturbations in the presence of a vector field Aμ coupled to cold dark matter (CDM) . We consider an interacting Lagrangian of the form Q f(X) Tc, where Q is a coupling constant, f is an arbitrary function of X=-AμAμ/2, and Tc is a trace of the CDM energy-momentum tensor. The matter coupling affects the no-ghost condition and sound speed of linear scalar perturbations deep inside the sound horizon, while those of tensor and vector perturbations are not subject to modifications. The existence of interactions also modifies the no-ghost condition of CDM density perturbations. We propose a concrete model of coupled vector dark energy with the tensor propagation speed equivalent to that of light. In comparison to the Q=0 case, we show that the decay of CDM to the vector field leads to the phantom dark energy equation of state wDE closer to-1. This alleviates the problem of observational incompatibility of uncoupled models in which wDE significantly deviates from-1. The maximum values of wDE reached during the matter era are bounded from the CDM no-ghost condition of future de Sitter solutions.

KW - Dark energy theory

KW - modified gravity

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U2 - 10.1088/1475-7516/2019/12/032

DO - 10.1088/1475-7516/2019/12/032

M3 - Article

AN - SCOPUS:85080881410

VL - 2019

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 12

M1 - 032

ER -