Constraints on cosmological viscosity and self-interacting dark matter from gravitational wave observations

Abstract

It has been shown that gravitational waves propagate through ideal fluids without experiencing any dispersion or dissipation. However, if the medium has a non-zero shear viscosity η , gravitational waves will be dissipated at a rate proportional to G η. We constrain dark matter and dark energy models with non-zero shear viscosity by calculating the dissipation of gravitational waves from GW150914 which propagate over a distance of 410 Mpc through the dissipative fluid and comparing the data with the theoretical prediction. This provides a proof-of-principle demonstration of the fact that future observations gravitational waves at LIGO have the potential of better constraining the viscosity of dark matter and dark energy.The discovery of Gravitational Waves (GW) by the LIGO collaboration [1] opens a new window for astronomy and cosmology. The source of GW150914 could also be the source of the 1 sec x-ray burst observed by Fermi GBM [2] with a 0.4 sec delay w.r.t the GW event and with sky localization consistent with the LIGO observation. These measurements of gravitational waves and their possible electromagnetic counterparts can tell us about the nature of the astrophysical sources [3][4][5][6][7][8][9][10][11][12][13], test general relativity [14][15][16][17][18][19] and local Lorentz invariance [20]. Future observations of stochastic gravitational waves can tell us about the energy scales of the first order phase transitions in the early universe [21,22]. In this paper we study the effect of the medium on the propagation of gravitational waves with the aim of deducing the properties of dark matter and dark energy by studying the observed waveforms. It was shown by Ehlers et. al [23,24] in full generality that gravitational waves propagating through ideal fluids do not suffer any dispersion or dissipation. Prasanna [25] generalized this treatment to the case of non-ideal fluids and showed that only the coefficient of shear viscosity affects the gravitational waves as they can be attenuated by the medium. This general conclusion agrees with the earlier derivations of attenuation of gravitational waves due to non-ideal fluid in a Friedman-Robertson-Walker (FRW) background [26][27][28][29][30][31] where it was shown that the attenuation length is (16πGη) −1 (in this context, see also [32]). Shear and bulk viscosity have been invoked to avoid initial singularity at the Big Bang [33][34][35], and as dark energy [36][37][38]. Dark matter with self interaction i.e non-zero shear and bulk viscosity has been used [39][40][41][42][43] for explaining the lack of density spikes in the cores [44] or substructures [45], or the paucity of dwarf satellite galaxies [46] which are seen in simulations with collision-less ideal fluid dark matter.In this paper we study this effect in the context of the * gaurav.goswami@ahduni.edu.in † girish20@prl.res.in ‡ mohanty@prl.res.in § prasanna@prl.res.in recent observations of Gravitational Waves. We consider the possibility that the analysis of the GW150914 could allow us to put observati...

Gravitational waves in the presence of viscosity

“…If we specialize to the case of gravitational waves, it turns out that also here the viscosity concept has attracted attention [17][18][19][20]. When applying viscosity to cosmology, the following point needs however some attention.…”

Viscosity in cosmic fluids

“…We get the effective bulk-viscosity (31) and shear-viscosity (32) due to two different relaxation times because of two different processes, as in the reference [35], and these are inversely additive.…”

“…It ought to be noted that the baryon-DM interaction has also been considered in the literature to explain 21-cm line [26][27][28][29]. The damping of the gravitational waves in the viscous fluid can be used to constrain the mean free path and the DM mass [30,31]. In this work we critically examine the role of the viscosity that arises due to self-interaction among dark-matter particles.…”

Search for missing links between two extreme wind speed profiles: dark energy accretion and adiabatic fluid accretion

“…Dutta and Biswas have considered viscous MCG accretion in the reference [38]. Presently, the constraint of dissipation from the gravitational wave-event GW150914 predicted a nonzero value of the shear viscosity of DE through which the gravitational wave is propagating [39]. The upper-bound of the shear viscosity is found to be n < 5.2n crit 2.3 × 10 9 Pasec where n crit = ρ crit H −1 0 = 3.21 × 10 −5 (GeV ) 3 = 4.38 × 10 8 Pasec, using ρ crit = H 2 0 M 2 P L .…”