Invariance of cosmological number counts under disformal transformations

TL;DR

This paper demonstrates that cosmological number counts, a key observable in large scale structure studies, remain invariant under disformal transformations, extending previous results from conformal transformations.

Contribution

It shows that cosmological number counts are invariant under disformal transformations, broadening the understanding of frame-invariance in cosmology.

Findings

Number counts are invariant under disformal transformations.

Invariance previously established for conformal transformations now extended to disformal cases.

Brief discussion on invariance of other cosmological observables.

Abstract

We investigate whether true physical observables associated with the measurements of large scale structure in the universe are frame-independent. In particular, we study if cosmological observables such as the galaxy number counts are invariant under the disformal transformations. In a previous work, it was shown that this frame-invariance holds true for the case of conformal transformations. In this work, we find that the invariance also holds true for the case of a simple disformal transformation. We further briefly comment on the disformal invariance of other cosmological observables.