arXiv subjects

Antonio Nájera

Publications and source records attributed to Antonio Nájera.

3 recordsLinked to original sources

arXiv2022

Dynamical dark energy models in the light of Gravitational-Wave Transient Catalogues

The study of current gravitational waves (GW) catalogues provide an interesting model independent way to understand further the nature of dark energy. In this work, we present an update of the constrains related to dynamical dark energy parametrisations using recent Gravitational-Wave Transient catalogues (GWTC-1 and GWTC-2) along with Type Ia supernova (SNeIa) and Cosmic Chronometers (CC) catalogues. According to our Bayesian results using the full SNeIa+CC+GW database, the $Λ$CDM model shows a strong preference against two dark energy parameterisation known as Barboza-Alcaniz (BA) and the Low Correlation (LC) models. Also, we obtain a very strong preference against the Chevallier-Polarski-Linder (CPL) model. Furthermore, we generated a mock GW catalogue and estimate that we require approximately 1000 standard sirens to have a constrain of $H_0$ within 1\% relative error, quantity that is out of reach of current standard sirens candidates in GWTC-1 and GWTC-2 catalogues.

gr-qc↗

arXiv2022

Cosmological Perturbation Theory in $f(Q,T)$ Gravity

We developed the cosmological linear theory of perturbations for $f(Q,T)$ gravity, which is an extension of symmetric teleparallel gravity, with $Q$ the non-metricity and $T$ the trace of the stress-energy tensor. By considering an ansatz of $f(Q,T)=f_1(Q)+f_2(T)$, which has been broadly studied in the literature and the coincident gauge where the connection vanishes, we got equations consistent with $f(Q)$ gravity when $f_{T}=0$. In the case of the tensor perturbations, the propagation of gravitational waves was found to be identical to $f(Q)$, as expected. For scalar perturbations, outside the limit $f_T = 0$, we got that the coupling between $Q$ and $T$ in the Lagrangian produces a coupling between the perturbation of the density and the pressure. The presence of $T$ in the Lagrangian breaks the equation of the conservation of energy, which in turn breaks the standard $ρ' + 3\mathcal{H} (ρ+p) = 0$ relation. We also derived a coupled system of differential equations between $δ$, the density contrast and $v$ in the $\mathcal{H}<<k$ limit and with negligible time derivative of the scalar perturbation potentials, which will be useful in future studies to see whether this class of theories constitute a good alternative to dark matter. These results might also enable to test $f(Q,T)$ gravity with CMB and standard siren data that will help to determine if these models can reduce the Hubble constant tension and if they can constitute an alternative to the $Λ$CDM model.

gr-qc↗

arXiv2021

Fitting $f(Q,T)$ gravity models with a $Λ$CDM limit using H(z) and Pantheon data

We proposed five $f(Q,T)$ models, which are an extension of symmetric teleparallel gravity, where $Q$ is the non-metricity and $T$ is the trace of the stress-energy tensor. By taking specific values of their parameters, these models have a $Λ$CDM limit. Using cosmic chronometers and supernovae Ia data, we found that our models are consistent with $Λ$CDM at a 95\% confidence level. To see whether one of these models can challenge $Λ$CDM at a background perspective, we computed the Bayesian evidence for them and $Λ$CDM. According to it, the concordance model is preferred over four of them, showing a weak preference against $f(Q,T) = -Q/G_N + bT$ and $f(Q,T) = -(Q+2Λ)/G_N +bT$, a substantial preference against $f(Q,T) = -(Q+2 H_0^2 c (Q/(6H_0^2))^{n+1})/G_N + bT $, and a strong preference against $f(Q,T) = -(Q+2H_0^2c(Q/(6H_0^2))^{n+1} + 2Λ)/G_N + bT$. Interestingly, a model includying a $T^2$ dependence ($f(Q,T) = -(Q+2Λ)/G_N - ((16π)^2 G_N b)/(120 H_0^2) T^2$) showed a {substantial} preference against $Λ$CDM. {Therefore, we encourage further analyses of this model to test its viability outside the background perspective.}

gr-qc↗