1206.6164 (Antonio Enea Romano)

Effect of inhomogeneities on apparent cosmological acceleration    [PDF]

Antonio Enea Romano

In the attempt to explain luminosity distance observations it has been proposed that we may be inside a local inhomogeneity whose effects could be equivalent to the presence of a cosmological constant in a homogeneous Universe. Using a local Taylor expansion method we study the low-redshift conditions to obtain an apparent negative deceleration parameter $q^{app}(z)$ derived from the luminosity distance $D_L(z)$ for a central observer in a LTB space. We calculate $q^{app}(z)$ with two different methods to solve the null geodesic equations, one based on a local central expansion of the solution in terms of cosmic time and the other one using the exact analytical solution in terms of generalized conformal time. The expansion of the solution in terms of cosmic time is quite useful also for other applications requiring a foliation of space-time in space-like hyper-surfaces, such as spatial averaging, which is much more difficult to study using conformal time.

View original: http://arxiv.org/abs/1206.6164