Structure Formation in Dark Matter Particle Production Cosmology
  We investigate a cosmological scenario in which the dark matter particles can
be created during the evolution of the Universe. By regarding the Universe as
an open thermodynamic system and using non-equilibrium thermodynamics, we
examine the mechanism of gravitational particle production. In this setup, we
study the large-scale structure (LSS) formation of the Universe in the
Newtonian regime of perturbations and derive the equations governing the
evolution of the dark matter overdensities. Then, we implement the cosmological
data from Planck 2018 CMB measurements, SNe Ia and BAO observations, as well as
the SH0ES local measurement for $H_0$ to provide some cosmological constraints
for the parameters of our model. We see that the best case of our scenario
($\chi_{{\rm tot}}^{2}=3834.40$) fits the observational data better than the
baseline $\Lambda$CDM model ($\chi_{{\rm tot}}^{2} = 3838.00$) at the
background level. We also see that this case results in the Hubble constant as
$H_0 = 68.79\pm 0.59\,{\rm km\,s^{-1}\,Mpc^{-1}}$ which is greater than $H_0 =
68.20^{+0.42}_{-0.38}\,{\rm km\,s^{-1}\,Mpc^{-1}}$ given by the $\Lambda$CDM
model, and hence we can alleviate the $H_0$ tension to some extent in our
framework. Furthermore, the best case of our scenario gives a lower value for
the best-fit of the $S_8$ parameter than the $\Lambda$CDM result, and therefore
it also reduces the LSS tension slightly. We moreover estimate the growth
factor of linear perturbations and show that the best case of our model
($\chi_{f\sigma_{8}}^{2}=40.84$) fits the LSS data significantly better than
the $\Lambda$CDM model ($\chi_{f\sigma_{8}}^{2}=44.29$). Consequently, our
model also makes a better performance at the level of the linear perturbations
compared to the standard cosmological model.
