The MESS of cosmological perturbations

Abstract

We introduce two new effective quantities for the study of comoving curvature perturbations $\zeta$: the space dependent effective sound speed (SESS) and the momentum dependent effective sound speed (MESS) . We use the SESS and the MESS to derive a new set of equations which can be applied to any system described by an effective stress-energy-momentum tensor (EST), including multi-fields systems, supergravity and modified gravity theories. We show that this approach is completely equivalent to the standard one and it has the advantage of requiring to solve only one differential equation for $\zeta$ instead of a system, without the need of explicitly computing the evolution of entropy perturbations. The equations are valid for perturbations respect to any arbitrary flat spatially homogeneous background, including any inflationary and bounce model. As an application we derive the equation for $\zeta$ for multi-fields $KGB$ models and show that observed features of the primordial curvature perturbation spectrum are compatible with the effects of an appropriate local variation of the MESS in momentum space. The MESS is the natural quantity to parametrize in a model independent way the effects produced on curvature perturbations by multi-fields systems, particle production and modified gravity theories and could be conveniently used in the analysis of LSS observations, such as the ones from the upcoming EUCLID mission or CMB radiation measurements.

We study the MESS of cosmological perturbations, version accepted in Physics Letters B

References in corpus (2)

• Effects of particle production during inflation
• Revisiting the oscillations in the CMB angular power spectra at $\ell \sim 120$ in the Planck2015 data

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• Gravitoelectromagnetic quadrirefringence
• Effects of the modification of gravity on the production of primordial black holes
• Non-Singular Bouncing cosmology from Phantom Scalar-Gauss-Bonnet Coupling: Reconstruction with Observational Insights
• Effective speed of cosmological perturbations
• Reconstructing homospectral inflationary potentials
• An effective fluid description of scalar-vector-tensor theories under the sub-horizon and quasi-static approximations