arXiv subjects

Ángel Rodríguez

Publications and source records attributed to Ángel Rodríguez.

3 recordsLinked to original sources

arXiv2026

Numerical Study of Some Generalizations of the Starobinsky Inflationary Model

In this work, we perform a numerical study of three Starobinsky--type inflationary scenarios: the $α$--Starobinsky inflationary model, the power--law Starobinsky inflationary model, and the power--law $α$--Starobinsky inflationary model. For an appropriate choice of parameters, each scenario reproduces the standard Starobinsky limit. For each case, we derive the relevant slow--roll expressions in order to compute numerically the scalar and tensor power spectra over the corresponding parameter space and evaluate the associated inflationary observables. Finally, we provide a comparative analysis in the $(n_\sca,A_\sca)$ and $(r,n_\sca)$ parameter spaces using contour plots. Our results indicate that, for certain choices of parameters, the $α$--Starobinsky model and the power--law $α$--Starobinsky model are favored by \textit{Planck} 2018 observations.

astro-ph.CO↗

arXiv2025

AGN Feedback-Induced Stellar Density Expansion in the Inner Regions of Early-Type Galaxies

Observations indicate that early-type galaxies exhibit varying slopes in the relation between their central stellar surface density and stellar mass ($Σ_1 - M_{\star}$). Low-mass galaxies tend to follow a steep slope, close to one, while the slope flattens for high-mass early type galaxies. In our study, we investigate the $Σ_1 - M_{\star}$ scaling relation and its evolution using the NIHAO suite of cosmological simulations and compare our findings with recent results from the MaNGA survey. Our analysis shows that NIHAO galaxies successfully reproduce the observed scaling relation based on MANGA survey. Our analysis suggests that AGN feedback plays a critical role in flattening the $Σ_1$ slope by expelling gas from galactic centers, leading to a decrease in both stellar and dark matter density as the gravitational potential becomes shallower. To further support our findings, we conducted high-resolution N-body simulations, which confirmed that ({\it sudden}) gas removal does substantially alter the stellar density in the central region, consistent with results from NIHAO. Furthermore, our numerical experiments show that even if the same amount of gas is re-accreted on a typical ({\it longer}) free-fall time, it is not able to restore the original stellar density. Our study concludes that AGN feedback assisted gas removal presents a plausible explanation for the decline in central stellar surface density as observed in massive elliptical galaxies.

astro-ph.GA↗

arXiv2025

Realization of Two-dimensional Discrete Time Crystals with Anisotropic Heisenberg Coupling

A discrete time crystal (DTC) is the paradigmatic example of a phase of matter that occurs exclusively in systems out of equilibrium. This phenomenon is characterized by the spontaneous symmetry breaking of discrete time-translation and provides a rich playground to study a fundamental question in statistical physics: what mechanism allows for driven quantum systems to exhibit emergent behavior that deviates from their counterparts with time-independent evolution? Unlike equilibrium phases, DTCs exhibit macroscopic manifestations of coherent quantum dynamics, challenging the conventional narrative that thermodynamic behavior universally erases quantum signatures. However, due to the difficulty of simulating these systems with either classical or quantum computers, previous studies have been limited to a set of models with Ising-like couplings -- and mostly only in one dimension -- thus precluding our understanding of the existence (or not) of DTCs in models with interactions that closely align with what occurs in nature. In this work, by combining the latest generation of IBM quantum processors with state-of-the-art tensor network methods, we are able to demonstrate the existence of a DTC in a two-dimensional system governed by anisotropic Heisenberg interactions. Our comprehensive analysis reveals a rich phase diagram encompassing spin-glass, ergodic, and time-crystalline phases, highlighting the tunability of these phases through multiple control parameters. Crucially, our results emphasize the interplay of initialization, interaction anisotropy, and driving protocols in stabilizing the DTC phase. By extending the study of Floquet matter beyond simplified models, we lay the groundwork for exploring how driven systems bridge the gap between quantum coherence and emergent non-equilibrium thermodynamics.

quant-ph↗