SIMBAD references

There is mounting observational evidence that the expansion of our universe is undergoing an acceleration. A dark energy component has usually been invoked as the most feasible mechanism for the acceleration. However, it is desirable to explore alternative possibilities motivated by particle physics before adopting such an untested entity. In this work, we focus our attention on an acceleration mechanism arising from gravitational leakage into extra dimensions. We test this scenario with high-z Type Ia supernovae compiled by Tonry and coworkers and recent measurements of the X-ray gas mass fractions in clusters of galaxies published by Allen and coworkers. A combination of the two databases gives, at a 99% confidence level, Ω_m=0.29^+0.04_–0.02, Ω_rc=0.21±0.08, and Ω_k=-0.36^+0.31_–0.35, indicating a closed universe. We then constrain the model using the test of the turnaround redshift, z_q=0, at which the universe switches from deceleration to acceleration. We show that, in order to explain that acceleration happened earlier than z_q=0=0.6 within the framework of gravitational leakage into extra dimensions, a low matter density, Ω_m<0.27, or a closed universe is necessary.