arXiv subjects

Rafael A. Batista

Publications and source records attributed to Rafael A. Batista.

7 recordsLinked to original sources

arXiv2026

Generalist Vision-Language Models for Fast Radio Burst detection: a zero-shot benchmark against a specialized detector

Fast Radio Burst (FRB) detection increasingly relies on specialized deep learning models that require large task-specific training sets and cannot be redefined without retraining. We evaluate whether small, open-weight, locally run generalist Vision-Language Models (VLMs) can detect FRBs in dynamic spectra under a zero-shot, prompt-only regime. On a balanced binary benchmark of 2000 simulated L-band spectra, Gemma 4 E2B reaches an accuracy of 94.05\%, statistically indistinguishable from the specialized detector SwinYNet (92.85\%), with a far lower false-positive rate on structured RFI (4.8\% vs. 24.6\%) and none on pure noise, though SwinYNet ranks perfectly (ROC-AUC 1.0000 vs. 0.9520). Rewriting the prompt alone reconfigures the same models for three-class FRB/RFI/noise classification, reaching up to 86.0\% accuracy without a single false FRB while classifying each 2 s spectrum in 1.0--1.5 s, faster than the observation itself. Applied unchanged to the 1600 real FAST observations of FAST-FREX, they reject real interference almost perfectly (2 and 5 false positives in 1000 negatives) but recover only 28.5\% and 27.0\% of the 600 catalogued bursts, against 95.7\% reported for SwinYNet on the same files. Stratifying those bursts by the dispersed signal in the image shows the limit to be the input representation rather than the classifier, recall rising to 84--85\% where the sweep is unambiguous and collapsing to 1\% on the 13\% of positives carrying no detectable signal in a 2 s undedispersed full-band view. The simulated bursts are nearly 30 times brighter in median, and at matched brightness the recalls agree to within a few points.

cs.LG↗

arXiv2026

Constraints on Dark Energy and Modified Gravity Models from Fast Radio Bursts and Late-Time Geometric Probes

We investigate the impact of 104 localized FRBs on cosmological parameter estimation when combined with three established late-time probes: Cosmic Chronometers (CC), Type Ia Supernovae (SNe), and Baryon Acoustic Oscillations (BAO). By performing a Bayesian analysis of three dark energy models ($Λ$CDM, $w$CDM, and CPL) and three viable $f(R)$ gravity scenarios -- the Appleby-Battye (AB), Hu-Sawicki (HS), and Starobinsky (ST) models -- , we find that FRBs substantially improve the constraints on the baryon density $Ω_{\rm b}$ by $25\%$--$43\%$, the Hubble constant $H_0$ by $12\%$--$35\%$, and the SNe absolute magnitude $M_B$ by $10\%$--$32\%$. Constraints on dark energy parameters show more modest improvements, with $w$ improving by $\sim 9\%$ in $w$CDM and $(w_0,w_a)$ improving by $\sim(8,22)\%$ in the CPL parametrization. Modified gravity parameters remain weakly constrained, with improvements of only $6\%$--$15\%$, indicating the limited sensitivity of current datasets to departures from $Λ$CDM. The Figure of Merit analysis shows overall improvements ranging from $\sim 48\%$ ($Λ$CDM) to $\sim 91\%$ (CPL), driven by enhanced precision in the $(H_0, Ω_{\rm b})$ plane. Model comparison reveals moderate statistical preference for extensions beyond $Λ$CDM: AIC strongly favors $w$CDM, CPL, HS, and ST with $Δ\mathrm{AIC} < -7$, and LRT yields $p \leq 0.004$, while BIC returns to positive evidence ($-3.2 < Δ\mathrm{BIC} < -2.7$). These results show that FRBs may be useful as a complementary probe, particularly for constraining $Ω_{\rm b}$ and alleviating key late-time degeneracies.

astro-ph.CO↗

arXiv2026

Constraints on the baryon density from fast radio bursts using a non-parametric reconstruction of the Hubble parameter

In this study, we use a sample of 130 well-localized fast radio bursts (FRBs) to constrain the physical baryon density $Ω_{\rm b}h^2$, and the astrophysical contribution from host galaxies. The cosmological dependence entering the intergalactic dispersion measure is described through a non-parametric reconstruction of the Hubble parameter $H(z)$ obtained from cosmic chronometer data using the \texttt{ReFANN} neural-network framework, independently of the FRB sample. Within a Bayesian analysis, we jointly infer $Ω_{\rm b}h^2$ and the parameters of a log-normal host-galaxy distribution, namely its median $e^μ$ and logarithmic scatter $σ_{\rm host}$, using both real FRB data and a mock catalog. For the real sample, we obtain $Ω_{\rm b}h^2=0.02236\pm0.00090$, $e^μ=178.15^{+16.51}_{-16.97}~\mathrm{pc}\,\mathrm{cm}^{-3}$, and $σ_{\rm host}=0.794^{+0.064}_{-0.067}$. For the mock catalog, we find $Ω_{\rm b}h^2=0.02248\pm0.00018$, $e^μ=182.36^{+6.83}_{-6.48}~\mathrm{pc}\,\mathrm{cm}^{-3}$, and $σ_{\rm host}=0.711^{+0.024}_{-0.025}$. The baryon density constraint from the real FRB sample is in excellent agreement with both Big Bang Nucleosynthesis and Planck CMB determinations, differing from their central values by only $\simeq 0.05\%$. The mock analysis further illustrates the potential of future FRB samples, reducing the uncertainty on $Ω_{\rm b}h^2$ to the sub-percent level while remaining statistically consistent with early-Universe constraints. Our findings show that combining FRB dispersion measures with a non-parametric reconstruction of the expansion history provides a robust pathway to constrain both cosmological and astrophysical parameters, establishing FRBs as a complementary low-redshift probe of the baryon density.

astro-ph.CO↗

arXiv2026

Cosmographic constraints from late-time probes including fast radio bursts

In this study, we use late-time probes, such as well-localized fast radio bursts (FRBs), baryon acoustic oscillations (BAO), supernovae (SNe), and cosmic chronometers (CC) to constrain cosmological parameters through a model-independent cosmographic approach. By integrating FRB data with BAO from DESI DR2, SNe, and CC, we derive constraints on the Hubble constant ($H_0$), the deceleration parameter ($q_0$), and the jerk parameter ($j_0$), using Markov Chain Monte Carlo (MCMC) analysis for parameter estimation. The cosmographic approach with FRBs alone provides $H_0 = 66.35^{+4.13}_{-5.04} \, \text{km} \, \text{s}^{-1} \, \text{Mpc}^{-1}$, $q_0 = -0.33^{+0.21}_{-0.15}$, and $j_0 = 0.83^{+0.57}_{-0.67}$, corresponding to a precision of $\sim 6\%$ for the Hubble constant and showing consistency with the $Λ$CDM expectation. The DESI+CMB dataset yields $H_0 = 65.59^{+1.25}_{-1.24} \, \text{km} \, \text{s}^{-1} \, \text{Mpc}^{-1}$, $q_0 = -0.29^{+0.07}_{-0.08}$, and $j_0 = 0.58^{+0.03}_{-0.04}$, providing a $\sim 2\%$ precision on $H_0$ and may suggest a possible tension in the late-time kinematic sector relative to the $Λ$CDM expectation when BAO measurements are calibrated with a Planck-inferred sound horizon. Combining the FRB, SNe, DESI+CMB, and CC datasets further tightens the constraints to $H_0 = 68.03^{+0.53}_{-0.52} \, \text{km} \, \text{s}^{-1} \, \text{Mpc}^{-1}$, $q_0 = -0.41 \pm 0.02$, and $j_0 = 0.55 \pm 0.02$, with the jerk parameter remaining lower than $j_0 = 1$ at the $1σ$ confidence level. These findings hint at a possible late-time kinematic tension, as indicated by the inferred value of the jerk parameter, which is primarily driven by the DESI+CMB dataset under standard early-Universe assumptions for the sound horizon.

astro-ph.CO↗

arXiv2025

Stefan-Boltzmann Law and Thermal Casimir Effect in Neutron Star Spacetime via Thermo Field Dynamics

We investigate the thermal Casimir effect for a massless scalar field in the curved spacetime of a neutron star within the Thermo Field Dynamics (TFD) formalism. Starting from the renormalized energy-momentum tensor, we generalize the Stefan-Boltzmann law to include gravitational redshift and curvature corrections governed by the Tolman-Oppenheimer-Volkoff (TOV) metric. Finite temperature and spatial compactification are introduced simultaneously, allowing a unified and consistent treatment of both vacuum and thermal contributions inside and outside the star. Analytical expressions are derived for the high- and low-temperature limits, showing explicitly how curvature and redshift modify the characteristic $T^4$ dependence of thermal radiation. The results reveal that strong gravity significantly alters the local energy density and pressure, demonstrating the nontrivial interplay between quantum vacuum fluctuations and compact astrophysical geometries. A polytropic model is considered to perform numerical analyses, highlighting the influence of the spacetime background on vacuum fluctuations.

gr-qc↗

arXiv2016

Relative Likelihood for Life as a Function of Cosmic Time

Is life most likely to emerge at the present cosmic time near a star like the Sun? We address this question by calculating the relative formation probability per unit time of habitable Earth-like planets within a fixed comoving volume of the Universe, dP(t)/dt, starting from the first stars and continuing to the distant cosmic future. We conservatively restrict our attention to the context of "life as we know it" and the standard cosmological model, LCDM. We find that unless habitability around low mass stars is suppressed, life is most likely to exist near 0.1 solar-mass stars ten trillion years from now. Spectroscopic searches for biosignatures in the atmospheres of transiting Earth-mass planets around low mass stars will determine whether present-day life is indeed premature or typical from a cosmic perspective.

astro-ph.CO↗

arXiv2011

Wavelets Applied to the Detection of Point Sources of UHECRs

In this work we analyze the effect of smoothing maps containing arrival directions of cosmic rays with a gaussian kernel and kernels of the mexican hat wavelets of orders 1, 2 and 3. The analysis is performed by calculating the amplification of the signal-to-noise ratio for several anisotropy patterns (noise) and different number of events coming from a simulated source (signal) for an ideal detector capable of observing the full sky with equal probability. We extend this analysis for a virtual detector located within the array of detectors of the Pierre Auger Observatory, considering an acceptance law.

astro-ph.IM↗