arXiv subjects

Iolanda Navone

Publications and source records attributed to Iolanda Navone.

2 recordsLinked to original sources

arXiv2026

Interpretation of the binned SNe Ia Master Sample data via a scalar quintessence component: phantom transition?

We study a modified cosmological scenario for the late Universe, involving an evolutionary dark energy model associated with the dynamics of a self-interacting scalar field in a potential-dominated regime. Through the analogy with a fluid energy-momentum tensor, we introduce a viscous contribution to the scalar dynamics, accounting for effective non-equilibrium behaviour of the self-interacting scalar cluster. The resulting picture is that of an intrinsic quintessence contribution which, due to the bulk viscosity, admits an effective equation of state parameter that can also take values below -1. Within this framework, we set up the diagnostic tool of the so-called "effective running Hubble constant", which allows us to trace possible deviations from a standard LambdaCDM model. We then compare this theoretical function with binned data from the Master Sample of Supernovae Ia, constructed assuming a LambdaCDM model in the MCMC procedure performed in each bin. We show that the self-interacting scalar field corresponding to the best fit satisfies a slow-rolling condition, since the kinetic energy remains small compared to the potential contribution throughout the redshift interval. The key finding is that, when limiting the model to specific regions of the parameter space and fitting it to the data, the transition only occurs at redshifts significantly lower than the redshift value identified by the DESI Collaboration. Furthermore, for the parameter values ensuring the best fit, no quintessence-to-phantom transition occurs (i.e., the effective equation of state parameter remains below -1 across the whole redshift domain). In other words, Supernovae data alone provide no indication of a change in the nature of the dark energy.

astro-ph.CO↗

arXiv2025

Creation of Viscous Dark Energy by the Hubble Flow: Comparison with SNe Ia Master Sample Binned Data

We study a family of cosmological models featuring dynamical dark energy (DE), based on the idea that the creation of its constituents arises from the gravitational field of the expanding universe, whose non-equilibrium physics is described by a non-zero bulk viscosity coefficient. We consider the complete scenario, in which both matter creation and bulk viscosity are present, together with its two limiting cases, in which only one of the two effects is retained. Once each model is constrained by requiring its present-day deceleration parameter $q_0$ to match specific values, the complete scenario introduces up to two additional free parameters with respect to the $\Lambda$CDM model, one of which is the equation of state parameter $w$ of the created dark energy. \textcolor{blue}{We consider two choices for $q_0$: the value predicted by the $\Lambda$CDM model, and one obtained from a background analysis of Fazzari et. al. (2025). To perform the analysis, we construct the effective running Hubble constant, i.e. a theoretical function corresponding to the ratio between the Hubble parameter of our models and the $\Lambda$CDM expansion rate. The theoretical predictions for the effective running Hubble constant of the three models are tested against the Master binned sample of Type Ia Supernovae (SNe Ia), through a Markov Chain Monte Carlo procedure with up to four free parameters. The most important result emerging from this analysis is that, when using the cosmographic $q_0$, all three models exhibit a quintessence-to-phantom transition in the effective equation of state parameter of the dark energy; on the contrary, when using the $q_0$ coming from the $\Lambda$CDM limit, the transition cannot happen, and the effective equation of state parameter is entirely of phantom nature across the considered redshift range.

astro-ph.CO↗