Dynamics of Supersymmetric Chameleons

TL;DR

This paper explores the cosmological behavior of supersymmetric chameleon models, analyzing their impact on structure formation and power spectra, and identifying parameter regions consistent with current observations.

Contribution

It provides a detailed analysis of supersymmetric chameleon models' cosmological dynamics, including linear perturbations and power spectrum modifications, with conditions for viability.

Findings

Models can reproduce current cosmological measurements.

Deviations from LCDM are small but detectable in certain parameter regions.

Supergravity corrections effectively screen astrophysical objects.

Abstract

We investigate the cosmological dynamics of a class of supersymmetric chameleon models coupled to cold dark matter fermions. Supergravity corrections ensure that these models are efficiently screened in all astrophysical objects of interest, however this does not preclude the enhancement of gravity on linear cosmological scales. We analyse the background cosmology and solve the modified equations for the growth of cold dark matter density perturbations in closed form. Using this, we go on to derive the modified linear power spectrum which is characterised by two scales, the horizon size at matter-radiation equality and at the redshift when the chameleon reaches the minimum of its effective potential. The model includes a cosmological constant in the form of a Fayet-Illiopolous term, which emerges at late times due to the coupling of the chameleon to two charged scalars. We examine the conditions under which this leads to viable background cosmology and go on to analyse the deviations from the LCDM predictions in the linear regime. We find that for reasonable values in the model's parameter space there is generically a region where the model's cosmology is viable and current measurements can be reproduced. A small discrepancy of the matter power spectrum from its LCDM counterpart can be obtained in a smaller subset of the parameter space.