arXiv subjects

Gerasimos Rigopoulos

Publications and source records attributed to Gerasimos Rigopoulos.

40 records · Page 3Linked to original sources

arXiv2010

Non-linear mode coupling and the growth of perturbations in LCDM

Cosmic structures at small non-linear scales $k>L\sim 0.2 h $ Mpc$^{-1}$ have an impact on the longer (quasi-)linear wavelengths with $k<L$ via non-linear UV-IR mode coupling. We evaluate this effect for a $Λ$CDM universe applying the effective fluid method of Baumann, Nicolis, Senatore and Zaldarriaga. For $k<L$ the $Λ$CDM growth function for the density contrast is found to receive a scale dependent correction and an effective anisotropic stress sources a shift between the two gravitational potentials, setting $ϕ$ - $ψ\neq 0$. Since such a situation is generically considered as a signature of modified gravity and/or dark energy, these effects should be taken into account before any conclusions on the dark sector are drawn from the interpretation of future observations.

astro-ph.CO↗

arXiv2010

The Subdominant Curvaton

We present a systematic study of the amplitude of the primordial perturbation in curvaton models with self-interactions, treating both renormalizable and non-renormalizable interactions. In particular, we consider the possibility that the curvaton energy density is subdominant at the time of the curvaton decay. We find that large regions in the parameter space give rise to the observed amplitude of primordial perturbation even for non-renormalizable curvaton potentials, for which the curvaton energy density dilutes fast. At the time of its decay, the curvaton energy density may typically be subdominant by a relative factor of 10^-3 and still produce the observed perturbation. Field dynamics turns out to be highly non-trivial, and for non-renormalizable potentials and certain regions of the parameter space we observe a non-monotonous relation between the final curvature perturbation and the initial curvaton value. In those cases, the time evolution of the primordial perturbation also displays an oscillatory behaviour before the curvaton decay.

astro-ph.CO↗

arXiv2009

Supernovae data and perturbative deviation from homogeneity

We show that a spherically symmetric perturbation of a dust dominated $Ω=1$ FRW universe in the Newtonian gauge can lead to an apparent acceleration of standard candles and provide a fit to the magnitude-redshift relation inferred from the supernovae data, while the perturbation in the gravitational potential remains small at all scales. We also demonstrate that the supernovae data does not necessarily imply the presence of some additional non-perturbative contribution by showing that any Lemaitre-Tolman-Bondi model fitting the supernovae data (with appropriate initial conditions) will be equivalent to a perturbed FRW spacetime along the past light cone.

astro-ph.CO↗

arXiv2004

On second-order superhorizon perturbations in multifield inflationary models

We present a method for the study of second-order superhorizon perturbations in multi field inflationary models with non trivial kinetic terms. We utilise a change of coordinates in field space to separate isocurvature and adiabatic perturbations generalizing previous results. We also construct second order gauge invariant variables related to them. It is found that with an arbitrary metric in field space the isocurvature perturbation sources the gravitational potential on long wavelengths even for ``straight'' trajectories. The potential decouples from the isocurvature perturbations if the background fields' trajectory is a geodesic in field space. Taking nonlinear effects into account shows that, in general, the two types of perturbations couple to each other. This is an outline of a possible procedure to study nonlinear and non-Gaussian effects during multifield inflation.

astro-ph↗