Speaker
Description
Several tensions are currently challenging the standard cosmological model. Among them, the Hubble constant measured at early times is lower than the one inferred from late-time probes. Additionally, Planck indicates cosmological perturbations growing faster than what is inferred from large-scale structure probes. Consequently, it is fundamental to investigate potential deviations from its prediction and potential alternative theories.
In this paradigm, the evolution of the cluster mass function traces the growth
of the linear density perturbations and can be used as a probe for potential new physics. We present new constraints on deviations from general relativity by measuring the growth rate of structures and by investigating the Hu-Sawicki parametrization of f(R) gravity with the first SRG/eROSITA All-Sky Survey (eRASS1) cluster catalog in the Western Galactic Hemisphere in combination with the overlapping Dark Energy Survey Year-3, KiloDegree Survey, and Hyper Supreme Camera data for weak lensing mass calibration. We find a strict upper limit on the parameter log |fR0| < -4.12 jointly with a sum of the masses of the neutrinos smaller than 0.44 e.V. at a 95% confidence level. It is the first time that constraints are obtained from clusters only.
We then parameterized the growth factor with the cosmic linear growth index gamma, which fits LambdaCDM predictions well when gamma = 0.55. We present new constraints from cluster abundance by exploiting the statistical constraining power of eRASS1, the largest intra-cluster medium selected cluster sample to date.
We find a higher growth index than the general relativity prediction, in agreement with other large-scale structure probes. Those constraints suggest that eRASS1 clusters are better fitted with a reduction of the amplitude of the power spectrum.
We finally perform a direct measurement of the growth of structures by dividing the sample into five redshift bins containing the same number of clusters and measuring the cosmological parameters in each bin. In agreement with the cosmic linear growth index parameterization, we find that structures evolve slower than the predictions of the Planck satellite. Our results align with other cluster surveys but are tense with weak lensing shear predictions.
Deeper surveys with eROSITA will disentangle the origin of these findings and if the higher value of the cosmic linear growth index originates from a change in fundamental physics.
