Cosmology with a Non-minimally Coupled Dark Matter Fluid II. Cosmological Perturbations
Abstract
We extend our study of a cosmological scenario in which dark matter is non-minimally coupled to gravity at the fluid level. In previous work, we showed that this interaction can drive an early phase of accelerated expansion, addressing the horizon and flatness problems, and can also lead to a cosmological bounce in the presence of negative spatial curvature. Here we analyse the evolution of linear perturbations in this framework. We derive the equations governing scalar, vector and tensor perturbations, and obtain analytic solutions in the relevant cosmological regimes. We find that perturbations generated during the accelerated expansion phase produce a strongly blue scalar power spectrum and are therefore incompatible with observations. By contrast, if primordial fluctuations are generated during the contracting phase of a bouncing solution, the model yields an approximately scale-invariant scalar power spectrum while keeping the tensor-to-scalar ratio compatible with current bounds. Although our treatment relies on simplifying approximations that should be refined in future work, these results indicate that an observationally viable primordial spectrum can be obtained only with a bouncing solution, and hence with a non-singular early-time evolution.
Versions
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BibTeX
@misc{silveravalle2026cosmology,
title = {{Cosmology with a Non-minimally Coupled Dark Matter Fluid II. Cosmological Perturbations}},
author = {Samuele Silveravalle and Andrea Lapi and Francesco Benetti and Stefano Liberati},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2607.00137},
eprint = {2607.00137},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.00137},
}
RIS
TY - UNPB
TI - Cosmology with a Non-minimally Coupled Dark Matter Fluid II. Cosmological Perturbations
AU - Samuele Silveravalle
AU - Andrea Lapi
AU - Francesco Benetti
AU - Stefano Liberati
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2607.00137
UR - https://arxiv.org/abs/2607.00137
AB - We extend our study of a cosmological scenario in which dark matter is non-minimally coupled to gravity at the fluid level. In previous work, we showed that this interaction can drive an early phase of accelerated expansion, addressing the horizon and flatness problems, and can also lead to a cosmological bounce in the presence of negative spatial curvature. Here we analyse the evolution of linear perturbations in this framework. We derive the equations governing scalar, vector and tensor perturbations, and obtain analytic solutions in the relevant cosmological regimes. We find that perturbations generated during the accelerated expansion phase produce a strongly blue scalar power spectrum and are therefore incompatible with observations. By contrast, if primordial fluctuations are generated during the contracting phase of a bouncing solution, the model yields an approximately scale-invariant scalar power spectrum while keeping the tensor-to-scalar ratio compatible with current bounds. Although our treatment relies on simplifying approximations that should be refined in future work, these results indicate that an observationally viable primordial spectrum can be obtained only with a bouncing solution, and hence with a non-singular early-time evolution.
ER -