arXiv subjects

Marco San Martín

Publications and source records attributed to Marco San Martín.

6 recordsLinked to original sources

arXiv2023

Hubble tension and matter inhomogeneities: a theoretical perspective

We have studied how local density perturbations could reconcile the Hubble tension. We reproduced a local void through a perturbed FLRW metric with a potential $Φ$ which depends on both time and space. This method allowed us to obtain a perturbed luminosity distance, which is compared with both local and cosmological data. However, when constraining local cosmological parameters with previous results, we found that neither $Λ$CDM nor $Λ(ω)$CDM cannot solve the Hubble tension.

astro-ph.CO↗

arXiv2023

Cosmological tests of the osculating Barthel-Kropina dark energy model

We further investigate the dark energy model based on the Finsler geometry inspired osculating Barthel-Kropina cosmology. The Barthel-Kropina cosmological approach is based on the introduction of a Barthel connection in an osculating Finsler geometry, with the connection having the property that it is the Levi-Civita connection of a Riemannian metric. From the generalized Friedmann equations of the Barthel-Kropina model, obtained by assuming that the background Riemannian metric is of the Friedmann-Lemaitre-Robertson-Walker type, an effective geometric dark energy component can be generated, with the effective, geometric type pressure, satisfying a linear barotropic type equation of state. The cosmological tests, and comparisons with observational data of this dark energy model are considered in detail. To constrain the Barthel-Kropina model parameters, and the parameter of the equation of state, we use 57 Hubble data points, and the Pantheon Supernovae Type Ia data sample. The st statistical analysis is performed by using Markov Chain Monte Carlo (MCMC) simulations. A detailed comparison with the standard $Λ$CDM model is also performed, with the Akaike information criterion (AIC), and the Bayesian information criterion (BIC) used as the two model selection tools. The statefinder diagnostics consisting of jerk and snap parameters, and the $Om(z)$ diagnostics are also considered for the comparative study of the Barthel-Kropina and $Λ$CDM cosmologies. Our results indicate that the Barthel-Kropina dark energy model gives a good description of the observational data, and thus it can be considered a viable alternative of the $Λ$CDM model.

gr-qc↗

arXiv2023

Extended primordial black hole mass functions with a spike

We introduce a modification of the Press-Schechter formalism aimed to derive general mass functions for primordial black holes (PBHs). In this case, we start from primordial power spectra (PPS) which include a monochromatic spike, typical of ultra slow-roll inflation models. We consider the PBH formation as being associated to the amplitude of the spike on top of the linear energy density fluctuations, coming from a PPS with a blue index. By modelling the spike with a log-normal function, we study the properties of the resulting mass function spikes, and compare these to the underlying extended mass distributions. When the spike is at PBH masses which are much lower than the exponential cutoff of the extended distribution, very little mass density is held by the PBHs within the spike, and it is not ideal to apply the Press-Schechter formalism in this case as the resulting characteristic overdensity is too different from the threshold for collapse. It is more appropriate to do so when the spike mass is similar to, or larger than the cutoff mass. Additionally, it can hold a similar mass density as the extended part. Such particular mass functions also contain large numbers of small PBHs, especially if stable PBH relics are considered, and they can provide $\sim 1000M_\odot$ seeds for the supermassive black holes at the centres of present-day galaxies. The constraints on the fraction of dark matter in PBHs for monochromatic mass functions are somewhat relaxed when there is an additional underlying extended distribution of masses.

astro-ph.CO↗

arXiv2022

Pytearcat: PYthon TEnsor AlgebRa calCulATor

This paper introduces the first release of Pytearcat, a Python package developed to compute tensor algebra operations in the context of theoretical physics, for instance, in general relativity. Given that working with tensors can become a complex task, people often rely on computational tools to perform tensor calculations. We aim to build a tensor calculator based on Python, which benefits from being free and easy to use. Pytearcat syntax resembles the usual physics notation for tensor calculus, such as the Einstein notation for index contraction. This version allows the user to perform many tensor operations, including derivatives and series expansions, along with routines to obtain the typical General Relativity tensors. A particular concern was put in the execution times, leading to incorporate an alternative core for the symbolic calculations, enabling to reach much faster execution times. The syntax and the versatility of Pytearcat are the most important features of this package, where the latter can be used to extend Pytearcat to other areas of theoretical physics.

gr-qc↗

arXiv2020

Cosmological Fluctuations in Delta Gravity

About 70\% of the Universe is Dark Energy, but the physics community still does not know what it is. Delta Gravity (DG) is an alternative theory of gravitation that could solve this cosmological problem. Previously, we studied the Universe's accelerated expansion, where DG was able to explain the SNe-Ia data successfully. In this work, we explore the cosmological fluctuations that give rise to the CMB through a hydrodynamic approximation. We calculate the gauge transformations for the metric and the perfect fluid to present the equations of the evolution of cosmological fluctuations, providing the necessary equations to solve in a semi-analytical way the scalar TT Power Spectrum. These equations will be useful for comparing the DG theory with astronomical observations and thus being able to constraint the DG cosmology, testing, in the future, the compatibility with the CMB Planck data, which are currently in controversy with SNe-Ia.

astro-ph.CO↗

arXiv2020

Observational constraints in Delta Gravity: CMB and supernovas

Delta Gravity is a gravitational model based on an extension of General Relativity given by a new symmetry called $\tildeδ$. In this model, new matter fields are added to the original matter fields, motivated by the additional symmetry. We call them $\tildeδ$ matter fields. This model predicts an accelerating Universe without the need to introduce a cosmological constant. In this work, we study the Delta Gravity prediction about the scalar CMB TT power spectrum using an analytical hydrodynamical approach. To fit the Planck satellite's data with the DG model, we used a Markov Chain Monte Carlo analysis. We also include a study about the compatibility between SNe-Ia and CMB observations in the Delta Gravity Context. Finally, we obtain the scalar CMB TT power spectrum and the fitted parameters needed to explain both SNe-Ia Data and CMB measurements. The results are in a reasonable agreement with both observations considering the analytical approximation. We also discuss if the Hubble Constant and the Accelerating Universe are in concordance with the observational evidence in the Delta Gravity context.

astro-ph.CO↗