Strong gravitational lensing inf(χ) = χ^3/2gravity

Abstract

We discuss the phenomenology of gravitational lensing in the purely metric f(χ) gravity, an f(R) gravity where the action of the gravitational field depends on the source mass. We focus on the strong lensing regime in galaxy-galaxy lens systems and in clusters of galaxies. By adopting point-like lenses and using an approximate metric solution accurate to second order of the velocity field v/c, we show how, in the f(χ) = χ3/2 gravity, the same light deflection can be produced by lenses with masses smaller than in General Relativity (GR); this mass difference increases with increasing impact parameter and decreasing lens mass. However, for sufficiently massive point-like lenses and small impact parameters, f(χ) = χ3/2 and GR yield indistinguishable light deflection angles: this regime occurs both in observed galaxy-galaxy lens systems and in the central regions of galaxy clusters. In the former systems, the GR and f(χ) masses are compatible with the mass of standard stellar populations and little or no dark matter, whereas, on the scales of the core of galaxy clusters, the presence of substantial dark matter is required by our point-like lenses both in GR and in our approximate f(χ) = χ3/2 solution. We thus conclude that our approximate metric solution of f(χ) = χ3/2 is unable to describe the observed phenomenology of the strong lensing regime without the aid of dark matter.

Constraints on Dark Energy Models from Galaxy Clusters and Gravitational Lensing Data

“…X-rays' observations currently offer a powerful technique for building catalogs of galaxy clusters, which are very important for modern cosmology [14]. The X-ray GC emission is given by S x = 1 4π(1 + z) 4 n 2 e Λ eH (µ e /µ H )dl,…”

“…The combination of X-rays and the SZ data leads to two useful cosmological tests, namely angular diameter distance d A [1] and gas mass fraction f gas of the GC [2]. Both tests have been used in the literature to investigate dark energy (DE) [3] and modified gravity (see [4] and reference therein). Additionally, the SGL observations also can be used to probe the dark matter (DM) and DE properties [3].…”

DYNAMICS OF CLUSTERS OF GALAXIES WITH EXTENDED F(chi) GRAVITY

“…Landau & Lifshitz 1982). That is, we cannot choose φ MOND (r) = +(GM a 0 ) 1/2 ln(r/r s ), unlike the treatment followed in Campigotto et al (2017). This fact explains their disagreement with the correct (−) sign found in Bernal et al (2011b); Mendoza et al (2013), and in this article.…”

“…In Mendoza et al (2013), the details of gravitational lensing for individual, groups and clusters of galaxies at the outer regions of those systems were obtained considering a point-mass lens. Campigotto et al (2017) compared those results with specific observations of gravitational lensing and found a large discrepancy between the O(2) terms in the metric coefficients of the f (χ) = χ 3/2 gravity and the observations. However, to obtain the correct gravitational lensing it is necessary to take into account the massdensity distribution, using a suitable gravitational potential.…”

Review of Solutions to the Cusp-Core Problem of the ΛCDM Model

“…On the other hand, MOND, introduced to fit galaxies rotation curves by Milgrom in 1983 [164,165], purports to replace DM. The DM effects of the MOND Newtonian modification also lead to other GR generalisations with the same aim [166][167][168][169] 2 A General Relativistic version of secondary infall models is at the root of works by a group including Mimoso and Le Delliou [188][189][190][191].…”