Neutrino mass and kinetic gravity braiding degeneracies

TL;DR

This paper investigates how kinetic gravity braiding models can be distinguished from other theories despite degeneracies with massive neutrinos, highlighting unique signatures in the matter power spectrum and implications for cosmological tensions.

Contribution

It demonstrates that kinetic gravity braiding models produce distinctive large-scale features and explores their compatibility with current cosmological tensions and neutrino mass constraints.

Findings

A bump in the matter power spectrum acts as a signature of nKGB models.

n=1 nKGB models resolve the H0 tension.

All studied nKGB models exclude null neutrino mass.

Abstract

Modified theories of gravity yield an effective dark energy in the background dynamics that achieves an accelerated expansion of the universe. In addition, they present a fifth force that induces gravitational signatures in structure formation, and therefore in the matter power spectrum and related statistics. On the other hand, massive neutrinos suppress the power spectrum at scales that also modified gravity enhances it, so a degeneration of these effects has been recognized for some gravity models. In the present work, we study both effects using kinetic gravity braiding (nKGB) models to find that in spite of some degeneracies, the role of the fifth force at very large scales imprints a bump in the matter power spectrum as a distinctive signature of this model and, therefore, acts as a smoking gun that seems difficult to match within the present knowledge of power spectra. These models result interesting, however, since the n=1 presents no H0 tension, and all nKGB studied here present no sigma8 tension and, in addition, a null neutrino mass is excluded.