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Papers by Marco San Martín

arXiv (Cornell University), Jan 24, 2023

The European Physical Journal C

We further investigate the dark energy model based on the Finsler geometry inspired osculating Ba... more 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 s...

Cornell University - arXiv, Jul 27, 2022

We introduce a modification of the Press-Schechter formalism aimed to derive general mass functio... more 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 ∼ 1000M 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.

arXiv: Cosmology and Nongalactic Astrophysics, 2018

We present a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia usin... more We present a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia using an alternative cosmological model named Delta Gravity. This model is based on a new Einstein-Hilbert action obtained by the extension of a new symmetry symbolized as tildedelta\tilde{\delta}tildedelta. This theory predicts an accelerating Universe without the need to introduce a cosmological constant Lambda\LambdaLambda by hand in the equations. We obtained a very good fit to the SN-Ia Data, and with this, we found the two free parameters of the theory called CCC and L_2L_2L2. With these values, we can predict different cosmological parameters. One of them is the Hubble constant. The last H0H_0H0 local value measurement is in tension with the CMB Data from Planck.\cite{Riess2016}. Therefore is very interesting to analyze it in this theory. DG predicts H0H_0H0 to be 74.47pm1.6374.47\pm 1.6374.47pm1.63 km/(s Mpc). This value is in concordance with the last measurement of the H0H_0H_0 local value, 73.83pm1.4873.83\pm 1.4873.83pm1.48 km/(s Mpc) \cite{Riess2018}.

Astronomy and Computing, 2022

This paper introduces the first release of Pytearcat, a Python package developed to compute tenso... more 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.

In this work we present the theory of perturbation of Delta Gravity, we discuss the gauge transfo... more In this work we present the theory of perturbation of Delta Gravity, we discuss the gauge transformations for metric and a perfect fluid in order to present the equations of the evolution of cosmological fluctuations using the hydrodynamic approximation. Then we compute the temperature fluctuations for photons coming from the time of last scattering t_L. Finally we present a formula for temperature multi-pole coefficients for scalar modes, which can be used to compare the theory with astronomical observations.

Universe, Feb 1, 2019

A gravitational field model based on two symmetric tensors, g µν andg µν , is studied, using a Ma... more A gravitational field model based on two symmetric tensors, g µν andg µν , is studied, using a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia. In this model, new matter fields are added to the original matter fields, motivated by an additional symmetry (δ symmetry). We call themδ matter fields. This theory predicts an accelerating Universe without the need to introduce a cosmological constant Λ by hand in the equations. We obtained a very good fit to the SN-Ia Data, and with this, we found the two free parameters of the theory called C and L 2. With these values, we have fixed all the degrees of freedom in the model. The last H 0 local value measurement is in tension with the CMB Data from Planck. Based on an absolute magnitude M V = −19.23 for the SN, Delta Gravity finds H 0 to be 74.47 ± 1.63 km/(s Mpc). This value is in concordance with the last measurement of the H 0 local value, 73.83 ± 1.48 km/(s Mpc).

The Astrophysical Journal, 2021

Delta-gravity (DG) is a gravitational model based on an extension of general relativity given by ... more Delta-gravity (DG) is a gravitational model based on an extension of general relativity given by a new symmetry called . In this model, new matter fields are added to the original matter fields, motivated by the additional symmetry. We call them matter fields. This model predicts an accelerating universe without the need to introduce a cosmological constant. In this work, we study the scalar cosmic microwave background (CMB) temperature (TT) power spectrum predicted by DG using an analytical hydrodynamic 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 Type Ia supernovae (SNe Ia) and CMB observations in the DG context. Finally, we obtain the scalar CMB TT power spectrum and the fitted parameters needed to explain both SN Ia data and CMB measurements. The results are in reasonable agreement with both observations considering the analytical approximation. We also discuss...

This paper introduces the first release of Pytearcat, a Python package developed to compute tenso... more 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 packa...

We have studied how local density perturbations could reconcile the Hubble tension. We reproduced... more We have studied how local density perturbations could reconcile the Hubble tension. We reproduced a local void through a perturbed FLRWmetric with a potentialΦ 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. We got a region of local parameters, qLo 0 and jLo 0 , which are in agreement with a local void of Ωm,void = −0.30± 0.15 explaining the differences between the local H0 and the Planck H0. However, when constraining local cosmological parameters with previous results, we found that neither ΛCDM nor Λ(ω)CDM could solve the Hubble tension.

arXiv (Cornell University), Jan 24, 2023

The European Physical Journal C

We further investigate the dark energy model based on the Finsler geometry inspired osculating Ba... more 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 s...

Cornell University - arXiv, Jul 27, 2022

We introduce a modification of the Press-Schechter formalism aimed to derive general mass functio... more 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 ∼ 1000M 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.

arXiv: Cosmology and Nongalactic Astrophysics, 2018

We present a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia usin... more We present a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia using an alternative cosmological model named Delta Gravity. This model is based on a new Einstein-Hilbert action obtained by the extension of a new symmetry symbolized as tildedelta\tilde{\delta}tildedelta. This theory predicts an accelerating Universe without the need to introduce a cosmological constant Lambda\LambdaLambda by hand in the equations. We obtained a very good fit to the SN-Ia Data, and with this, we found the two free parameters of the theory called CCC and L_2L_2L2. With these values, we can predict different cosmological parameters. One of them is the Hubble constant. The last H0H_0H0 local value measurement is in tension with the CMB Data from Planck.\cite{Riess2016}. Therefore is very interesting to analyze it in this theory. DG predicts H0H_0H0 to be 74.47pm1.6374.47\pm 1.6374.47pm1.63 km/(s Mpc). This value is in concordance with the last measurement of the H0H_0H_0 local value, 73.83pm1.4873.83\pm 1.4873.83pm1.48 km/(s Mpc) \cite{Riess2018}.

Astronomy and Computing, 2022

This paper introduces the first release of Pytearcat, a Python package developed to compute tenso... more 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.

In this work we present the theory of perturbation of Delta Gravity, we discuss the gauge transfo... more In this work we present the theory of perturbation of Delta Gravity, we discuss the gauge transformations for metric and a perfect fluid in order to present the equations of the evolution of cosmological fluctuations using the hydrodynamic approximation. Then we compute the temperature fluctuations for photons coming from the time of last scattering t_L. Finally we present a formula for temperature multi-pole coefficients for scalar modes, which can be used to compare the theory with astronomical observations.

Universe, Feb 1, 2019

A gravitational field model based on two symmetric tensors, g µν andg µν , is studied, using a Ma... more A gravitational field model based on two symmetric tensors, g µν andg µν , is studied, using a Markov Chain Monte Carlo (MCMC) analysis with the most updated catalog of SN-Ia. In this model, new matter fields are added to the original matter fields, motivated by an additional symmetry (δ symmetry). We call themδ matter fields. This theory predicts an accelerating Universe without the need to introduce a cosmological constant Λ by hand in the equations. We obtained a very good fit to the SN-Ia Data, and with this, we found the two free parameters of the theory called C and L 2. With these values, we have fixed all the degrees of freedom in the model. The last H 0 local value measurement is in tension with the CMB Data from Planck. Based on an absolute magnitude M V = −19.23 for the SN, Delta Gravity finds H 0 to be 74.47 ± 1.63 km/(s Mpc). This value is in concordance with the last measurement of the H 0 local value, 73.83 ± 1.48 km/(s Mpc).

The Astrophysical Journal, 2021

Delta-gravity (DG) is a gravitational model based on an extension of general relativity given by ... more Delta-gravity (DG) is a gravitational model based on an extension of general relativity given by a new symmetry called . In this model, new matter fields are added to the original matter fields, motivated by the additional symmetry. We call them matter fields. This model predicts an accelerating universe without the need to introduce a cosmological constant. In this work, we study the scalar cosmic microwave background (CMB) temperature (TT) power spectrum predicted by DG using an analytical hydrodynamic 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 Type Ia supernovae (SNe Ia) and CMB observations in the DG context. Finally, we obtain the scalar CMB TT power spectrum and the fitted parameters needed to explain both SN Ia data and CMB measurements. The results are in reasonable agreement with both observations considering the analytical approximation. We also discuss...

This paper introduces the first release of Pytearcat, a Python package developed to compute tenso... more 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 packa...

We have studied how local density perturbations could reconcile the Hubble tension. We reproduced... more We have studied how local density perturbations could reconcile the Hubble tension. We reproduced a local void through a perturbed FLRWmetric with a potentialΦ 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. We got a region of local parameters, qLo 0 and jLo 0 , which are in agreement with a local void of Ωm,void = −0.30± 0.15 explaining the differences between the local H0 and the Planck H0. However, when constraining local cosmological parameters with previous results, we found that neither ΛCDM nor Λ(ω)CDM could solve the Hubble tension.