Searcharxiv⌕ Search

arXiv subjects

Oscar del Barco

Publications and source records attributed to Oscar del Barco.

5 recordsLinked to original sources
arXiv2025

Picosecond-level corrections to the Shapiro time delay in a Schwarzschild spacetime

We present an exact analytical equation for the Shapiro time delay (STD) due to a spherical non-rotating body. As a result, accurate values of the STD in comparison with first and second-order expressions for Schwarzschild spacetime (1Sch and 2Sch) and first-order post-Newtonian formalism (1PN) are achieved. Accordingly, the lowest STD discrepancies between our exact equation and these approximations lie within the picosecond and sub-picosecond level for light beams affected by the Sun's gravity. Our results might be useful for time delay measurements in the solar system or extragalactic binary pulsar systems, where a high accuracy level is required.

gr-qc↗
arXiv2024

An accurate equation for the gravitational bending of light by a static massive object

An exact analytical expression for the bending angle of light due to a non-rotating massive object, considering the actual distances from source and observer to the gravitational mass, is derived. Our novel formula generalizes Darwin well-known equation for gravitational light bending [Proc. R. Soc. London A 263, 39-50 (1961)], where both source and observer are placed at infinite distance from the lensing mass, and provides excellent results in comparison with the post Newtonian (PPN) formalism up to first order. As a result, the discrepancy between our recent expression and the PPN approach is 6.6 mas for sun-grazing beams coming from planet Mercury, with significant differences up to 2 mas for distant starlight. Our findings suggest that these considerations should not be dismissed for both solar system objects and extragalactic sources, where non-negligible errors might be present in ultraprecise astrometry calculations.

astro-ph.IM↗
arXiv2023

Corneal retardation time as an ocular hypertension disease indicator

Objective. A detailed analysis of the corneal retardation time $τ$ as a highly related parameter to the intraocular pressure (IOP), and its plausible role as an indicator of ocular hypertension disease. Approach. A simple theoretical expression for $τ$ is derived within the corneal viscoelastic model of Kelvin-Voigt with 3 elements. This retardation time can be easily calculated from the well-known signal and pressure amplitudes of non-contact tonometers like the Ocular Response Analyzer (ORA). Then, a population-based study was performed where 100 subjects aged from 18 to 30 were analyzed (within this group, about 10% had an elevated IOP with more than 21 mmHg). Main results. A clear relationship between the corneal retardation time and the corneal-compensated intraocular pressure was found, underlying the risk for ocular hypertensive (OHT) subjects with lower $τ$ values to develop hypertension illnesses (due to the inability of poorly viscoelastic corneas to absorb IOP fluctuations, resulting in probable optic nerve damage). Significance. Our results might provide an useful tool to systematically discern which OHT patients (and even those with normal IOP values) are more likely to suffer glaucoma progression and, consequently, ensure an early diagnosis.

physics.bio-ph↗
arXiv2022

Gamma-ray emission from primordial black hole-neutron star interaction

The interaction of an asteroid-mass primordial black hole (PBH) with a slowly-rotating neutron star (NS) can lead to detectable gamma-ray emission via modern observatories like Fermi-LAT or e-ASTROGRAM. Depending on the specific PBH relativistic orbit in the NS Schwarschild spacetime and the relative orientation of this binary system with respect to Earth, the PBH Hawking radiation will show a characteristic temperature profile over time. Essentially, a moderate heating behaviour (or even a progressive and constant cooling phase) is found for the majority of the event, followed by a sudden and dramatic cool-down at the end of the burst. Our theoretical model might provide a means of identification of such hypothetical PBH-NS interactions, based on the distinctive temperature evolution of thermal-like gamma ray bursts (GRBs) described in this article.

astro-ph.HE↗