arXiv subjects

Carlos G. Boiza

Publications and source records attributed to Carlos G. Boiza.

9 recordsLinked to original sources

arXiv2026

Three-form dark energy: constraints and multi-probe comparison with $Λ$CDM

Three-form fields provide a theoretically well-motivated framework for dark energy, arising in higher-dimensional theories and exhibiting a rich cosmological phenomenology. We investigate a minimally coupled three-form dark energy model with a Gaussian potential and constrain it using current cosmological observations, including CMB shift parameters, DESI DR2 baryon acoustic oscillation measurements, Pantheon+ supernovae with and without SH0ES calibration, cosmic chronometers, and gamma-ray bursts. Parameter estimation is performed within a Bayesian Markov-chain Monte Carlo framework, while model comparison relies on several information criteria and the Bayesian evidence, as well as tension statistics. We find that the three-form model provides a viable and competitive description of the expansion history of the Universe. It is mildly preferred over $Λ$CDM for the combination of early and late-time datasets that are heavily tensioned (CMB+BAO and Pantheon+SH0ES). This preference decreases to neutrality for the other, less tensioned combination of early and late-time data, while for individual early-time or late-time datasets analysed separately, the information criteria are neutral or favour $Λ$CDM. This suggests that the additional degrees of freedom of the three-form field may help accommodate cosmological observations of different origins within a common framework. The reconstructed dark energy dynamics exhibit a characteristic phantom phase at intermediate redshifts while approaching a cosmological-constant-like behaviour at early and late times, providing a distinctive observational signature. Although the model does not significantly alleviate the Hubble tension despite allowing higher values of $H_0$, it remains consistent with current observations and offers a well-motivated alternative to $Λ$CDM whose predictions can be tested by future cosmological surveys.

astro-ph.CO↗

arXiv2026

Observational constraints on 3-forms dark energy

3-forms are natural candidates for describing the late-time accelerated expansion of the Universe, as they can inherently reproduce a positive cosmological constant when lacking an evolving potential. When such a potential is present, a 3-form field may exhibit either quintessence-like or phantom-like behaviour. In this paper, we consider a late-time effective dark energy model described by a 3-form with a Gaussian potential, stable during the dark-energy-dominated era. We constrain this model observationally by performing a Markov Chain Monte Carlo (MCMC) analysis employing a comprehensive cosmological dataset, including Planck PR4 cosmic microwave background (CMB) data, DESI DR1 baryon acoustic oscillation (BAO) measurements, Pantheon+ Type Ia supernovae data, low-$z$ Cepheid calibrators, and DES Y1 large-scale structure observations. We demonstrate that the 3-form model successfully increases the predicted Hubble parameter of CMB and BAO data from $67.89\pm0.36{\rm km/s/Mpc}$ of $Λ$CDM model to $68.29^{+0.56}_{-0.61}{\rm km/s/Mpc}$ by approaching the potential peak at the right time, thus mildly reducing the tension with the late-time observation. Overall, the 3-form field serves as a promising candidate of phantom-like dark energy from both theoretical and observational points of view.

astro-ph.CO↗

arXiv2026

Dark energy driven by an oscillating generalised axion-like quintessence field

Generalised axion-like scalar fields provide a well-motivated framework for describing the late-time acceleration of the Universe. As the field evolves, it rolls down its potential and, depending on its mass and initial conditions, it may either still be approaching the minimum or already oscillating around it. These two dynamical regimes require distinct treatments of cosmological perturbations. In this work, we perform a detailed analysis of linear cosmological perturbations in the regime where the dark-energy scalar field undergoes coherent oscillations about the minimum of its potential. We show that the standard effective fluid description breaks down in this phase and develop a consistent field-based perturbation framework, which we use to assess the impact of oscillatory dark energy on the growth of cosmic structures.

astro-ph.CO↗

arXiv2026

Modified Teleparallel $f(T)$ Gravity, DESI BAO and the $H_0$ Tension

We investigate whether late-time modifications of gravity in the teleparallel framework can impact the current tension in the Hubble constant $H_0$, focusing on $f(T)$ cosmology as a minimal and well-controlled extension of General Relativity. We consider three representative $f(T)$ parametrisations that recover the teleparallel equivalent of General Relativity at early times and deviate from it only at late epochs. The models are confronted with unanchored Pantheon+ Type~Ia supernovae, DESI DR2 baryon acoustic oscillations, compressed Planck cosmic microwave background distance priors, and redshift-space distortion data, allowing us to jointly probe the background expansion and the growth of cosmic structures. Two of the three models partially shift the inferred value of $H_0$ towards local measurements, while the third worsens the discrepancy. This behaviour is directly linked to the effective torsional dynamics, with phantom-like regimes favouring higher $H_0$ and quintessence-like regimes producing the opposite effect. A global statistical comparison shows that the minimal $f(T)$ extensions considered here are not favoured over $Λ$CDM by the combined data. Nevertheless, our results demonstrate that late-time torsional modifications can non-trivially redistribute current cosmological tensions among the background and growth sectors.

gr-qc↗

arXiv2025

Addressing $H_0$ and $S_8$ tensions within $f(Q)$ cosmology

We investigate the viability of $f(Q)$ gravity as an alternative framework to address the $H_0$ and $S_8$ tensions in cosmology. Focusing on three representative $f(Q)$ models, we perform a comprehensive Bayesian analysis using a combination of cosmological observations, including cosmic chronometers, Type Ia supernovae, gamma-ray bursts, baryon acoustic oscillations, and CMB distance priors. Our results demonstrate that most of these models can yield higher values of $H_0$ than those predicted by $Λ$CDM, offering a partial alleviation of the tension. In addition, one model satisfies the condition $G_{\mathrm{eff}} < G$, making it a promising candidate for addressing the $S_8$ tension. However, these improvements are accompanied by mild internal inconsistencies between different subsets of data, which limit the overall statistical preference relative to $Λ$CDM. Despite this, $f(Q)$ gravity remains a promising and flexible framework for late-time cosmology, and our results motivate further exploration of extended or hybrid models that may reconcile all observational constraints.

astro-ph.CO↗

arXiv2025

Observational constraints on generalised axion-like potentials for the late Universe

Axions have emerged as compelling candidates for describing the dark sector of the Universe. In this work, we explore quintessence models inspired by axion-like potentials as a dynamical alternative to the cosmological constant. These models naturally exhibit a tracking behaviour, reducing the need for fine-tuned initial conditions. We perform a Markov chain Monte Carlo (MCMC) analysis on a complete cosmological dataset of Planck PR4 cosmic microwave background (CMB), DESI DR1 baryon acoustic oscillation (BAO), Pantheon+ type Ia supernovae, low-$z$ Cepheid anchors, and DES Y1 large scale structure measurement. Unfortunately, neither the Hubble tension nor the $S_8$ tension is eased. The model does reach parity with $Λ$CDM model statistically according to DIC, WAIC and Bayesian ratio, suggesting that a quintessence model may still help with the cosmic tension by further extending the model we have investigated.

astro-ph.CO↗

arXiv2025

Speeding up the Universe with a generalised axion-like potential

Understanding the late-time acceleration of the Universe is one of the major challenges in cosmology today. In this paper, we present a new scalar field model corresponding to a generalised axion-like potential. In fact, this model can be framed as a quintessence model based on physically motivated considerations. This potential is capable of alleviating the coincidence problem through a tracking regime. We will as well prove that this potential allows for a late-time acceleration period induced by an effective cosmological constant, which is reached without fine-tuning the initial conditions of the scalar field. In our model, the generalised axion field fuels the late-time acceleration of the Universe rather than fuelling an early dark energy era. Additionally, we will show how the late-time transition to dark energy dominance could be favoured in this model, since the density parameter of the scalar field will rapidly grow in the late phase of the tracking regime.

astro-ph.CO↗

arXiv2025

Cosmological perturbations in a generalised axion-like dark energy model

We analyse the cosmological evolution of a generalised axion-like field that drives the late-time acceleration of the Universe. This model can exhibit tracking behaviour, which alleviates the coincidence problem. The cosmological perturbations are carried within a multi-fluid approach where the scalar field is described by a non-adiabatic fluid, i.e., one whose speed of sound in the rest frame differs from the adiabatic one. The cosmological perturbations are solved since the radiation-dominated epoch, imposing initial adiabatic conditions for matter, radiation and the dark energy component, for modes well outside the Hubble horizon in the past. We analyse the homogeneous curvature perturbation, gravitational potential and dark energy perturbations in this model, as well as the matter power spectrum and fσ8. We discuss which parameters of the model are more favoured observationally.

astro-ph.CO↗

arXiv2021

(Pseudo-)Kähler-Einstein geometries

Solutions to vacuum Einstein field equations with cosmological constant, such as the de Sitter space and the anti-de Sitter space, are basic in different cosmological and theoretical developments. It is also well known that complex structures admit metrics of this type. The most famous example is the complex projective space endowed with the Fubini-Study metric. In this work, we perform a systematic study of Einstein complex geometries derived from a logarithmic Kähler potential. Depending on the different contribution to the argument of such logarithmic term, we shall distinguish among direct, inverted and hybrid coordinates. They are directly related to the signature of the metric and determine the maximum domain of the complex space where the geometry can be defined.

hep-th↗