Signatures of $f(Q)$-gravity in cosmology

TL;DR

This paper explores how $f(Q)$-gravity, a modified gravity model, affects cosmological observations, revealing measurable signatures at the perturbation level and implications for gravitational wave observations.

Contribution

It introduces a specific $f(Q)$-gravity model that mimics $ ext{Lambda CDM}$ at background level but shows distinct perturbation signatures regulated by a single parameter.

Findings

Positive $\alpha$ suppresses matter power spectrum and CMB lensing.

Negative $\alpha$ enhances ISW effect and matter clustering.

Predictions for gravitational wave luminosity distances differ from electromagnetic signals.

Abstract

We investigate the impact on cosmological observables of $f(Q)$-gravity, a specific class of modified gravity models in which gravity is described by the non-metricity scalar, $Q$. In particular we focus on a specific model which is indistinguishable from the $\Lambda$-cold-dark-matter ($\Lambda$CDM) model at the background level, while showing peculiar and measurable signatures at linear perturbation level. These are attributed to a time-dependent Planck mass and are regulated by a single dimensionless parameter, $\alpha$. In comparison to the $\Lambda$CDM model, we find for positive values of $\alpha$ a suppressed matter power spectrum and lensing effect on the Cosmic Microwave Background radiation (CMB) angular power spectrum and an enhanced integrated-Sachs-Wolfe tail of CMB temperature anisotropies. The opposite behaviors are present when the $\alpha$ parameter is negative. We also investigate the modified Gravitational Waves (GWs) propagation and show the prediction of the GWs luminosity distance compared to the standard electromagnetic one. Finally, we infer the accuracy on the free parameter of the model with standard sirens at future GWs detectors.