# Strongly Coupled Dark Energy with Warm dark matter vs. LCDM

## TL;DR

This paper explores a cosmological model combining strongly coupled dark energy and warm dark matter, showing it closely mimics LCDM predictions while addressing some of its conceptual issues, and analyzing its observational signatures.

## Contribution

It demonstrates the recovery of the attractor solution in the model, compares CMB spectra with LCDM, and discusses parameter dependencies and numerical challenges.

## Key findings

- CMB anisotropy spectra are nearly indistinguishable from LCDM.
- Linear spectra depend on parameters more at large k but remain consistent with data.
- Numerical difficulties at high k motivate further detailed analysis.

## Abstract

Cosmologies including strongly Coupled (SC) Dark Energy (DE) and Warm dark matter (SCDEW) are based on a conformally invariant (CI) attractor solution modifying the early radiative expansion. Then, aside of radiation, a kinetic field $\Phi$ and a DM component account for a stationary fraction, $\sim 1\, \%$, of the total energy. Most SCDEW predictions are hardly distinguishable from LCDM, while SCDEW alleviates quite a few LCDM conceptual problems, as well as its difficulties to meet data below the average galaxy scale. The CI expansion begins at the inflation end, when $\Phi$ (future DE) possibly plays a role in reheating, and ends at the Higgs' scale. Afterwards, a number of viable options is open, allowing for the transition from the CI expansion to the present Universe. In this paper: (i) We show how the attractor is recovered when the spin degrees of freedom decreases. (ii) We perform a detailed comparison of CMB anisotropy and polarization spectra for SCDEW and LCDM, including tensor components, finding negligible discrepancies. (iii) Linear spectra exhibit a greater parameter dependence at large $k$'s, but are still consistent with data for suitable parameter choices. (iv) We also compare previous simulation results with fresh data on galaxy concentration. Finally, (v) we outline numerical difficulties at high $k$. This motivates a second related paper, where such problems are treated in a quantitative way.