The persistent  tension and the improved supernova–BAO consistency under dynamical dark energy after DESI DR2 motivate rethinking how dark energy evolution is parametrized. We formulate it directly through the inertial mass density (IMD), $\rho+p$IMD, and show that an IMD evolving from a negative to an equal positive constant toward z->0 can induce a past sign change in  itself, with...
The cosmographic condition $j(z)=1$ provides the kinematical signature of the spatially flat $\Lambda$CDM model independently of any specific dark-energy or modified-gravity theory. We investigate the extent to which current observations permit departures from this condition by considering three phenomenological ``almost-$\Lambda$CDM'' cosmographic closures in which the cosmic jerk differs...
The $\Lambda$CDM model successfully explains a wide range of cosmological observations; however, persistent discrepancies most notably the $H_0$ tension between early and late time measurements challenge its completeness. No proposed extension has yet resolved this tension while retaining the overall success of $\Lambda$CDM. We have investigated whether the $H_0$ tension can be associated with...
In this work we study a scale invariant gravity theory containing two scalar fields, dust particles and a measure defined from degrees of freedom independent of the metric. The integration of the degrees of freedom that define the measure spontaneously break the scale symmetry, leaving us in the Einstein frame with an effective potential that is dependent on the density of the particles. The...
Cosmological tensions between early- and late-Universe probes, most notably the Hubble tension in $H_0$ have intensified scrutiny of the ΛCDM paradigm and motivated flexible dark-energy scenarios beyond a cosmological constant. A persistent obstacle is that the functional form of the dark-energy equation of state $w(a)$ is usually chosen by hand (e.g.wCDM or CPL), so potentially viable models...
In this seminar, I will present a novel mechanism for cosmic acceleration driven by primordial black holes with effective repulsive behavior. Using a new Swiss Cheese cosmological framework, I will discuss four black hole spacetimes—Hayward, Bardeen, Dymnikova, and de Sitter-Schwarzschild—to show that this acceleration emerges naturally from the geometry itself. The results suggest that...
