Spherical collapse and cluster number counts in dark energy models disformally coupled to dark matter

TL;DR

This paper studies how a disformal coupling between dark energy and dark matter affects galaxy cluster formation and counts, showing it can significantly alter predictions at low redshifts and be constrained by surveys like eROSITA.

Contribution

It introduces the impact of disformal coupling on spherical collapse and cluster counts, highlighting differences from conformal coupling and potential observational constraints.

Findings

Disformal coupling has negligible effects at high redshifts during matter domination.

It suppresses the linear density contrast and virial overdensity at low redshifts.

Disformal coupling can significantly alter cluster number counts, especially at low redshifts.

Abstract

We investigate the effects of a disformal coupling between dark energy and dark matter in the predictions of the spherical collapse and its signatures in galaxy cluster number counts. We find that the disformal coupling has no significant effects on spherical collapse at high redshifts, and in particular during matter domination epoch. However, at lower redshifts, the extrapolated linear density contrast at collapse close to redshift $z \lesssim 1$ and overdensity at virialization can be strongly suppressed by a disformal coupling between dark energy and dark matter. We also find that disformal coupling can have different imprints on cluster number counts compared with conformal coupling, such that the disformal coupling can strongly suppress the predicted number of clusters per redshift interval at $z > 0.1$ while enhance the number of cluster at $z < 0.05$. Using the specifications of eROSITA survey, we find that the disformal coupling between dark energy and dark matter can be tightly constrained by cluster number counts.