F(R) gravity theories in the Palatini formalism constrained from strong lensing

Abstract

f(R) gravity, capable of driving the late-time acceleration of the universe, is emerging as a promising alternative to dark energy. Various f(R) gravity models have been intensively tested against probes of the expansion history, including Type Ia supernovae (SNIa), the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO). In this paper, we propose to use the statistical lens sample from Sloan Digital Sky Survey Quasar Lens Search Data Release 3 (SQLS DR3) to constrain f(R) gravity models. This sample can probe the expansion history up to z ∼ 2.2, higher than what probed by current SNIa and BAO data. We adopt a typical parametrization of the form f(R) = R - αH20(-R/H20) β with α and β constants. For β = 0 [Λ cold dark matter (ΛCDM)], we obtain the best-fitting value of the parameter α = -4.193, for which the 95 per cent confidence interval that is [-4.633, -3.754]. This best-fitting value of α corresponds to the matter density parameter Ωm0 = 0.301, consistent with constraints from other probes. Allowing β to be free, the best-fitting parameters are (α, β) = (-3.777, 0.06195). Consequently, we give Ωm0 = 0.285 and the deceleration parameter q0 = -0.544. At the 95 per cent confidence level, α and β are constrained to [-4.67, -2.89] and [-0.078, 0.202], respectively. Clearly, given the currently limited sample size, we can only constrain β within the accuracy of Δβ ∼ 0.1 and thus cannot distinguish between ΛCDM and f(R) gravity with high significance, and actually, the former lies in the 68 per cent confidence contour. We expect that the extension of the SQLS DR3 lens sample to the SDSS DR5 and SDSS-II will make constraints on the model more stringent. © 2009 RAS.