arXiv subjects

Mauricio Lopez-Hernandez

Publications and source records attributed to Mauricio Lopez-Hernandez.

5 recordsLinked to original sources

arXiv2026

Dark energy from neutrino interactions in Unimodular Gravity

We investigate a dark energy scenario generated by neutrino interactions mediated by a light scalar field, in which finite-temperature corrections induce an effective neutrino mass that evolves with the thermal history of the Universe. Within the framework of Unimodular Gravity, these interactions give rise to a non-conservation current, leading to dynamical dark energy. We study one- and two-neutrino realizations of the model. In the one-neutrino case, the dark energy density evolves monotonically, whereas in the two-neutrino scenario it can reach a maximum at intermediate redshifts before decreasing at late times. Using late time cosmological datasets, we constrain the effective interaction strength for lightest-neutrino masses in the range $0.05 \,{\rm meV}\le m_1 \le 1 \,{\rm meV}$. We find preferred interaction scales of order $G_s\sim10^{12} \, {\rm eV}^{-2}$ with a significance of $2 σ$, with the inferred coupling decreasing as the assumed neutrino mass increases. Assuming neutrino couplings of order unity, this $G_s$ value corresponds to an ultralight mediator with mass $m_ϕ\sim10^{-6} \, {\rm eV}$. We further assess the impact of Planck distance-prior, finding a noticeable reduction in parameter degeneracies and a reconstructed dark energy evolution closer to that of a cosmological constant. Our results show that neutrino interactions can generate both monotonic and non-monotonic dark energy evolutions while remaining compatible with current cosmological observations. The inferred interaction strengths remain consistent with non-zero values for part of the explored neutrino-mass range, supporting neutrino-induced dark energy dynamics as a viable phenomenological extension of $Λ$CDM at the background level.

astro-ph.CO↗

arXiv2026

Crosschecking Cosmic Distances from DESI BAO and DES SNe

We perform a consistency check of DESI DR2 BAO constraints ($D_M/r_d, D_H/r_d)$ by reconstructing the same quantities from DES supernovae (SNe) in bins with the same effective redshift $z_{\textrm{eff}} \in \{ 0.510, 0.706, 0.934 \}$ and a Planck $r_d$ prior. Through mock analysis we show that $D_M(z_{\rm eff})$ and $D_{H}(z_{\rm eff})$ can be locally reconstructed model agnostically from $Λ$CDM and extended models, but only if one employs frequentist methods; purely Bayesian reconstructions from Markov Chain Monte Carlo (MCMC) exhibit bias. We find that the ratio of the three $D_M/r_d$ values at different $z_{\textrm{eff}}$ are consistent with a horizontal, thus confirming that the distance duality relation holds up to calibration. However, the $D_H/r_d$ ratio shows a decreasing trend driven by the $z_{\textrm{eff}} = 0.934$ bin, the significance of which varies from $2.5 σ$ with Bayesian methods down to $1.4 σ$ with frequentist methods. We show that replacing DES with DES-Dovekie SNe reduces the significance to $1.7 σ$ and $1.2 σ$ in Bayesian and frequentist approaches, respectively. We conclude that distances reconstructed from SNe show good agreement with DESI BAO distances across the redshifts studied. We also note that $D_M(z_{\rm eff} = 0.510)/r_d$ reconstructed from SNe favours DESI BAO over transversal BAO against a backdrop of a $3.7 σ$ disagreement.

astro-ph.CO↗

arXiv2026

Comparing Hemispheres: Anisotropy in the deceleration parameter $q_0$

We present a hemispherical comparison analysis of the deceleration parameter $q_0$ using the Pantheon+ sample of Type Ia supernovae to test the isotropy of cosmic acceleration and the robustness of redshift corrections. We detect directional variations in $q_0$ across redshift frames. Even in the $z_{\mathrm{HD}}$ frame, where corrections for the CMB dipole and peculiar velocities are applied, a residual dipolar anisotropy persists with $Δq_0 = 0.112$ and a maximum signal to noise $S/N = 2.155$, aligned with the CMB dipole direction and decreasing with increasing minimum redshift cut. The anisotropy is stronger in the $z_{\mathrm{hel}}$ and $z_{\mathrm{CMB}}$ frames, where kinematic corrections are incomplete, while the transition to $z_{\mathrm{HD}}$ reduces but does not remove the signal. Inferring the dipole from the supernovae data yields $v_{\odot} = 307.26^{+32.00}_{-22.28},\mathrm{km \, s^{-1}}$ toward $(\mathrm{RA},\mathrm{DEC}) = (156.40^{+4.72}_{-4.71}, -3.38^{+5.54}_{-8.23})^\circ$, mildly discrepant with the Planck CMB dipole at the $\sim 1.9σ$ level. When this SNe inferred dipole is incorporated into the redshift correction pipeline, the hemispherical anisotropy is suppressed, with the dipolar pattern disappearing and the maximum signal reduced to $S/N \lesssim 1.75$, while the remaining fluctuations become consistent with statistical noise, suggesting that part of the signal arises from residual mismatches in the modeling of the local velocity field. Since current redshift corrections rely on peculiar velocity reconstructions based on the density field, our results suggest a residual bulk flow not fully captured by these models, highlighting a source of systematic uncertainty in low redshift supernova cosmology.

astro-ph.CO↗

arXiv2026

On frequentist confidence intervals in a non-Gaussian regime

We study frequentist confidence intervals based on graphical profile likelihoods (Wilks' theorem, likelihood integration), and the Feldman-Cousins (FC) prescription, a generalisation of the Neyman belt construction, in a setting with non-Gaussian Markov chain Monte Carlo (MCMC) posteriors. Our simplified setting allows us to recycle the MCMC chain as an input in all methods, including mock simulations underlying the FC approach. We find all methods agree to within $10 \%$ in the close to Gaussian regime, but extending methods beyond their regime of validity leads to greater discrepancies. Importantly, we recover a $\sim 2 σ$ shift in cosmological parameters between low and high redshift cosmic chronometer data with the FC method, but only when one fits all parameters back to the mocks. We observe that fixing parameters, a common approach in the literature, risks underestimating confidence intervals.

astro-ph.CO↗

arXiv2025

Is there a dynamical tendency in H0 with late time measurements?

The discrepancy between the Hubble constant $H_0$ values derived from early-time and late-time measurements, reaching up to $4σ$, represents the most serious challenge in modern cosmology and astrophysics. In this work, we investigate if a similar tension exists between only late time measurements at different redshifts. We use the latest public datasets including Cosmic Chronometers, Megamasers, SNe Ia and DESI-BAO, that span from redshift $z \sim 0$ up to $z\sim 2.3$. By dividing the data into redshift bins, we derive $H_0$ values from each bin separately. Our analysis reveals a phenomenological dynamic evolution in $H_0$ across different redshift ranges, with a significance from $1.5σ$ and $2.3σ$, depending on the parameterization. Consistency of the model demands observational constancy of $H_0$ since it is an integration constant within the Friedmann-Lemaître-Robertson-Walker (FLRW) metric. Thus, these findings suggest that the observed Hubble tension might not only exist between early and late-time measurements but also among late-time data themselves, providing new insights into the nature of the Hubble tension.

astro-ph.CO↗