Modified gravity leaves a detectable mark on galaxy cluster counts

Working within DHOST theories that survive gravitational-wave constraints, this study models how density perturbations grow and collapse into galaxy clusters. Deviations from general relativity become pronounced late in cosmic history, suppressing small-scale structure growth while raising the density threshold needed for collapse. Comparing predicted cluster number counts against eROSITA survey benchmarks, the analysis finds that even the maximum allowed deviation — set by binary pulsar bounds — produces a measurable deficit of clusters relative to ΛCDM, particularly at high redshift. The authors caution that uncertainties in the spherical collapse formalism and mass function may partly drive this difference.