Mimicking dark matter in galaxy clusters through a nonminimal gravitational coupling with matter

Abstract

In this work, one shows that a specific non-minimal coupling between the scalar curvature and matter can mimic the dark matter component of galaxy clusters. For this purpose, one assesses the Abell cluster A586, a massive nearby relaxed cluster of galaxies in virial equilibrium, where direct mass estimates and strong-lensing determinations are possible. One then extends the dark matter mimicking to a large sample of galaxy clusters whose density profiles are obtained from the Chandra high quality data, also in virial equilibrium. The total density, which generally follows a cusped profile and reveals a very small baryonic component, can be effectively described within this framework.

Modified Friedmann equation from nonminimally coupled theories of gravity

“…(8). This stemmed from the decomposition of the terms in the latter into constant or evolving with ρ, and precluded the possibility that the energy density is also constant.…”

“…Indeed, these can be coupled, for instance, in a nonminimal way [3] (see also Refs. [4][5][6] for early proposals in cosmology), a fact that can have a bearing on the dark matter [7,8] and dark energy [9,10] problems, as well as inflation [11,12] and structure formation [13]. This putative nonminimal coupling modifies the well-known energy conditions [14] and can give rise to several implications, from Solar System [15] and stellar dynamics [16][17][18][19] to close time-like curves [20] and wormholes [21].…”

The Layzer-Irvine equation in theories with non-minimal coupling between matter and curvature

“…Additionally, from Ref. [12] the best fit value of the index n for Abell 586 is n = 0.43. Thus, it results that R 0.43 ≡ 1/ √ r 0.43 ≈ 5.69 × 10 −8 m −1/2 , since the characteristic lenght for A586 is r 0.43 ∼ 0.01 pc [12].…”

“…(1). We consider a pressureless matter dominated Universe and the power-law function, f 2 (R) = (R/R n ) n , with n = 0.43 [12], in the sub-horizon approximation k 2 a 2 H 2 . We have also chosen for the Lagrangian density L = −ρ.…”

“…[7,8] for proposals in the context of cosmology). The later has a rich lore of theoretical and observational implications, and has bearings on issues such as stellar stability [9], preheating after inflation [10], mimicking of dark matter in galaxies [11] and clusters [12] and the large scale effect of dark energy [13] (see Ref. [14] for a review).…”