Talk detail

Participant	Romano, Antonio Enea
Institution	University of Antioquia - N/A - Medellin - Antioquia - Colombia

Session	OC1	Accepted		Order	Time
Talk	Oral abstract	Title	Effects of inhomogeneities on apparent cosmological observables: "fake'' evolving dark energy
Co-authors
Abstract	Using the exact Lemaitre-Bondi-Tolman solution with a non-vanishing cosmological constant $\Lambda$, we investigate how the presence of a local spherically-symmetric inhomogeneity can affect apparent cosmological observables, such as the deceleration parameter or the effective equation of state of dark energy (DE), derived from the luminosity distance under the assumption that the real space-time is exactly homogeneous and isotropic. The presence of a local underdensity is found to produce apparent phantom behavior of DE, while a locally overdense region leads to apparent quintessence behavior. Our study shows how observations in an inhomogeneous $\Lambda$CDM universe with initial conditions compatible with the inflationary beginning, if interpreted under the wrong assumption of homogeneity, can lead to the wrong conclusion about the presence of ``fake'' evolving dark energy instead of $\Lambda$.

Session	TC3	Accepted		Order	Time
Talk	Oral abstract	Title	Effect of inhomogeneities on the apparent cosmological deceleration parameter
Co-authors
Abstract	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 the presence of a cosmological constant in a homogeneous Universe. For central observer in a spherically symmetric pressureless matter dominated space-time (LTB) it has been proved that the central apparent deceleration parameter qapp 0 cannot be negative. We study the low-redshift conditions to obtain an apparent negative deceleration parameter qapp(z) obtained from the luminosity distance DL(z) for a central observer in a LTB space. We calculate qapp(z) with two different methods to solve the null geodesic equations, one based on a local central expansion of the solution and the other one using the exact analytical solution. The latter method is particularly convenient for numerical applications since it doesn’t require any numerical integration of the Einstein’s equations.