|Abstract : ||Large-scale structures in the Universe evolve under the influence of cosmic expansion and gravity. An important statistic in this context is the halo mass function, which measures the abundance of large-scale structures across epochs. Halo mass function is a sensitive probe of growth of cosmic structures, expansion history of the universe and nature of gravity and hence, constraining mass function can help us constrain cosmological parameters from observational data and effectively test GR on large-scales.
Because of the self-similar nature of hierarchical structure formation, mass function in the standard cosmological model, ΛCDM, can be expressed as a universal function across redshifts. This can ease the complications involved in the study of non-linear growth and evolution of structures.
We used a set of N-body simulations to formulate the halo mass function of two modified gravity models: f(R) and nDGP. We compared our results with ΛCDM predictions and found a systematic scale-dependent abundance which is a function of both redshift and cosmology. We also noticed that we can expect the same universality in mass function for modified gravity cosmologies. This shows that the self-similar nature of hierarchical structure formation is preserved in the case of modified gravity models. We have therefore used this nature of universality to develop a generic mass function for modified gravity models without the need to re-run expensive and time-consuming modified gravity N-body simulations. This will allow us to model non-linear structure formation in modified gravity cosmologies and forecast constraints on the fifth force.