We examine the possibility of Primordial Black Holes (PBHs) formation in single field models of inflation. Using the adiabatic or wave function renormalization scheme in the short range modes, we show that one-loop correction to the power spectrum is free from quadratic UV divergence. We consider a framework in which PBHs are produced during the transition from Slow Roll (SR) to Ultra Slow Roll (USR) followed by the end of inflation. We demonstrate that the renormalized power spectrum soften the contribution of the logarithmic IR divergence and severely restricts the possible mass range of produced PBHs in the said transition, namely, $$M_\textrm{PBH}\sim 10^{2}\,\textrm{g}$$M PBH ∼ 10 2 g $$\hat{\textrm{a}}$$a ^ la a no-go theorem. In particular, we find that the produced PBHs are short lived ( $$t^\textrm{evap}_\textrm{PBH}\sim 10^{-20}\,\textrm{s}$$t PBH evap ∼ 10 - 20 s ) and the corresponding number of e-folds in the USR region is restricted to $$\Delta {\mathcal {N}}_\textrm{USR}\approx 2$$Δ N USR ≈ 2 .

We investigate inflationary dynamics in the framework of the Einstein-Gauss-Bonnet gravity. In the model under consideration, the inflaton field is nonminimally coupled to the Gauss-Bonnet curvature invariant, so that the latter appears to be dynamically important. We consider a quartic potential for the inflaton field, in particular, the one asymptotically connected to the Higgs inflation, and a wider class of coupling functions not considered in the earlier work. Keeping in mind the observational bounds on the parameters—the amplitude of scalar perturbations $A_s$, spectral index $n_s$ and tensor-to-scalar ratio $r$, we demonstrate that the model a quartic potential and the proposed coupling function is in agreement with observations.

In a class of single field models of inflation, the idea of primordial black holes (PBHs) production is studied. In this case, the dynamics on small cosmological scales differs significantly from that of the large scales probed by the observations of cosmic microwave background (CMB). This difference becomes a virtue in producing correct physical ambiance for the seeds required to produce PBHs. Thus, once the perturbed scales re-enter the horizon of our Universe during the later epochs of radiation domination and subsequent matter domination, these seeds collapses to produce PBHs. We have shown, in this class of model, depending on the model parameters and the class defining set parameters, one can have PBHs formed for a vast mass ranges from $$10^{-18}$$10-18 to $$10^{-6}$$10-6 solar mass ( $$M _\odot $$M⊙ ). We have also shown, for a particular class of model, the total dark matter density today can be attributed to the PBHs density. The vast range of the mass depending on the class parameter, gives ample opportunity to study enriched phenomenological implications associated with this model to probe the nascent Universe dynamics.

We consider a scenario of modified gravity, which is generic to late-time acceleration, namely, acceleration in the Jordan frame and no acceleration in the Einstein frame. The possibility is realized by assuming an interaction between dark matter and the baryonic component in the Einstein frame which is removed by going to the Jordan frame using a disformal transformation giving rise to an exotic effective fluid responsible for causing phantom crossing at late times. In this scenario, past evolution is not distinguished from $\mathrm{\Lambda }\mathrm{CDM}$ but late time dynamics is generically different due to the presence of phantom crossing that causes a monotonous increase in the expansion rate giving rise to distinctive late-time cosmic feature. The latter can play a crucial role in addressing the tension between the observed value of Hubble parameter by CMB (cosmic microwave background) measurements and the local observations. We demonstrate that the Hubble tension significantly reduces in the scenario under consideration for the chosen scale factor parametrizations. The estimated age of the universe in the model is well within the observational bounds in the low and high redshift regimes.

We study the late-time cosmological tensions using the low-redshift background and redshift-space distortion data by employing a machine learning (ML) technique. By comparing the generated observables with the standard cosmological scenario, our findings indicate support for the phantom nature of dark energy, which ultimately leads to a reduction in the existing tensions. The model-independent approach also enables us to examine the combined background and perturbative history, where tensions are reduced. Moreover, from a statistical perspective, we have shown that our results exhibit a better fit to the data when compared to the $\mathrm{\Lambda }\mathrm{CDM}$ model.