Cosmological constraints on deviations from Lorentz invariance in gravity and dark matter

Abstract

We consider a scenario where local Lorentz invariance is violated by the existence of a preferred time direction at every space-time point. This scenario can arise in the context of quantum gravity and its description at low energies contains a unit time-like vector field which parameterizes the preferred direction. The particle physics tests of Lorentz invariance preclude a direct coupling of this vector to the fields of the Standard Model, but do not bear implications for dark matter. We discuss how the presence of this vector and its possible coupling to dark matter affect the evolution of the Universe. At the level of homogeneous cosmology the only effect of Lorentz invariance violation is a rescaling of the expansion rate. The physics is richer at the level of perturbations. We identify three effects crucial for observations: the rescaling of the matter contribution to the Poisson equation, the appearance of an extra contribution to the anisotropic stress and the scale-dependent enhancement of dark matter clustering. These effects result in distinctive features in the power spectra of the CMB and density fluctuations. Making use of the data from Planck and WiggleZ we obtain the most stringent cosmological constraints to date on departures from Lorentz symmetry. Our analysis provides the first direct bounds on deviations from Lorentz invariance in the dark matter sector.

Phenomenology of theories of gravity without Lorentz invariance: The preferred frame case

“…This is is expected from general considerations connecting the anisotropic stress and corrections to graviton propagator [107]. The bounds on anisotropic stress are weaker since its effects are partially degenerate with an overall rescaling of the amplitude of the primordial perturbations 15 [88,102].…”

“…(44), has very interesting phenomenological consequences [84,102] To better understand them, one can take the Newtonian limit of (44). We already showed the first step in this direction in (29).…”

“…This comes from different phenomena [88,102]: first, the theory contains extra light degrees of freedom (a helicity-0 -the khronon-and also a helicity-1 vector for the Einstein-aether case), which are coupled to the metric and (maybe) to DM. Second, G c = G N which modifies the Poisson equation [103].…”

“…Furthermore, the misalignment of the perturbations with respect to the aether generates anisotropic stress in the effective energymomentum tensor. We now briefly discuss these effects, and refer the reader to the discussion (in particular the figures showing the different effects) in [88,102] for better understanding.…”

Minimal-supersymmetric extended inflation field in Horava–Lifshitz gravity

“…Among cosmologists, it isn't unfamiliar that, in inflationary Universe an ad hoc EoS for dark energy can be ruled out [26,27]. But for late time cosmology where HLG is conjectured to reduce to Einstein's GRG, evidences for dark energy appear.…”