arXiv subjects

Adriana Nadal-Matosas

Publications and source records attributed to Adriana Nadal-Matosas.

3 recordsLinked to original sources

arXiv2026

Bispectrum BAO and the baryon-dark matter relative velocity

We evaluate the Baryon Acoustic Oscillation (BAO) signal in the bispectrum as a tool to detect and characterize the relative velocity effect. We extend the existing framework by presenting an updated model for the redshift-space tree-level bispectrum that comprehensively incorporates all relative velocity terms. We introduce a novel, unbiased technique to extract the isotropic BAO dilation parameter ($α_{\rm iso}$) solely from the bispectrum monopole. Validated against N-body simulations, this template-based extraction successfully recovers the acoustic scale and enhances the statistical constraining power by $\sim30\%$, when analyzed in tandem with the pre-reconstruction power spectrum, offering a powerful complement to standard post-reconstruction pipelines. We quantify how individual relative velocity components distort both two- and three-point statistics. We find that these effects induce distinct systematic shifts in the extracted $α_{\rm iso}$ between the two probes. We find systematic discrepancies of up to $2\%$ for $b_{v^2}=\pm0.05$ and up to $20\%$ for $b_{δ^{bc}}\le-2$. This differences demonstrate that a direct comparison of independent power spectrum and bispectrum BAO measurements can break parameter degeneracies and isolate the amplitude of these biases. Finally, we provide a concrete prescription to detect and constrain the three associated relative velocity bias parameters, showing that a joint analysis is highly sensitive to the $b_{v^2}$ and $b_{δ^{bc}}$ amplitudes. This establishes the bispectrum BAO as a robust cosmological probe for current and next-generation galaxy surveys, serving both as a cross-check for standard analyses and a crucial diagnostic tool against systematic biases.

astro-ph.CO↗

arXiv2025

The thermal index of neutron-star matter in the virial approximation

Motivated by gravitational wave observations of binary neutron-star mergers, we study the thermal index of low-density, high-temperature dense matter. We use the virial expansion to account for nuclear interaction effects. We focus on the region of validity of the expansion, which reaches $10^{-3}$ fm$^{-3}$ at $T=5$ MeV up to almost saturation density at $T=50$ MeV. In pure neutron matter, we find an analytical expression for the thermal index, and show that it is nearly density- and temperature-independent, within a fraction of a percent of the non-interacting, non-relativistic value of $Γ_\text{th} \approx 5/3$. When we incorporate protons, electrons and photons, we find that the density and temperature dependence of the thermal index changes significantly. We predict a smooth transition between an electron-dominated regime with $Γ_\text{th} \approx 4/3$ at low densities to a neutron-dominated region with $Γ_\text{th} \approx 5/3$ at high densities. This behavior is by and large independent of proton fraction and is not affected by nuclear interactions in the region where the virial expansion converges. We model this smooth transition analytically and provide a simple but accurate parametrization of the inflection point between these regimes. When compared to tabulated realistic models of the thermal index, we find an overall agreement at high temperatures that weakens for colder matter. The discrepancies can be attributed to the missing contributions of nuclear clusters. The virial approximation provides a clear and physically intuitive framework for understanding the thermal properties of dense matter, offering a computationally efficient solution that makes it particularly well-suited for the regimes relevant to neutron star binary remnants.

nucl-th↗

arXiv2025

Testing the robustness of the BAO determination in the presence of massive neutrinos

We study the robustness of the Baryon Acoustic Oscillation (BAO) feature in galaxy clustering in the presence of massive neutrinos. In the standard BAO analysis pipeline a reference cosmological model is assumed to boost the BAO peak through the so-called reconstruction technique and in the modelling of the BAO feature to extract the cosmological information. State-of-the art spectroscopic BAO measurements, such as the Dark Energy Spectroscopic Instrument claim an aggregate precision of 0.52$\%$ on the BAO scale, with a systematic error of 0.1$\%$ associated to the assumption of a reference cosmology when measuring and analyzing the BAO feature. While the systematic effect induced by this arbitrary choice of fiducial cosmology has been studied for a wide range of $Λ$CDM-like models, it has not yet been tested for reference cosmologies with massive neutrinos with the precision afforded by next generation surveys. In this context, we employ the Quijote high-resolution dark-matter simulations with haloes above a mass of $M\sim 2\times10^{13} h^{-1}M_{\odot}$, with different values for the total sum of neutrinos masses, $\sum m_ν[{\rm eV}] = 0,\, 0.1,\, 0,2,\, 0.4$ to study and quantify the impact of the pipeline's built-in assumption of massless neutrinos on the measurement of the BAO signal, with a special focus on the BAO reconstruction technique. We determine that any additional systematic bias introduced by the assumption of massless neutrinos is no greater than $0.1\%$ ($0.2\%$) for the isotropic (anisotropic) measurement. We expect these conclusions also hold for galaxies provided that neutrino properties do not alter the galaxy-halo connection.

astro-ph.CO↗