arXiv subjects

José Antonio Oller

Publications and source records attributed to José Antonio Oller.

5 recordsLinked to original sources

arXiv2026

Gravitational waves decay in vacuum

We show that gravitational waves (GW), treated as coherent graviton states, decay into photon pairs in vacuum. The process, even if suppressed by $G^2$, is lifted by two effects combined: the expected factor of the graviton number squared, $N^2$, and the coherence of the wave. We perform the calculation describing both gravity and the photons as quantized fields, though we show that the effect admits a semiclassical description once the metric is solved to second order. We estimate the resulting rates for compact binaries and a stochastic background, including the effect from stimulated decay to the cosmic microwave background (CMB). In theories with light degrees of freedom, an analogous decay into them is also possible, and more relevant for ultralight dark matter, as it can entail huge occupation numbers. We derive first constraints on cosmological GW sources by the corresponding injection of photons from CMB spectral distortions, extragalactic backgrounds, and light-nuclei photofission. In summary, the decay of GWs into photons offers a new (challenging) handle on the detection of GW sources, and represents a new mechanism to generate other particles across cosmic history.

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arXiv2025

Coupled-channel formalism

This article provides a pedagogical exploration of coupled-channel scattering in hadronic physics, focusing on theoretical methodologies, and practical applications. It covers key concepts such as the $N/D$ method, Castillejo-Dalitz-Dyson poles, and the generalization of these techniques to coupled channels. The article also presents a parameterization for partial wave amplitudes, ensuring unitarity and analyticity, and addresses scattering near the threshold of dominant channels, with use also of the Lippmann-Schwinger equation. Additionally, it explores final-state interactions, Omnès and Muskhelishvily solutions, the Khuri-Treiman approach, and the two-potential model for resonant event distributions, highlighting the role of Riemann sheets in resonance behavior. These methods are also applicable to related fields like nuclear and atomic physics.

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arXiv2023

Axion-pion thermalization rate in unitarized NLO chiral perturbation theory

We compute the axion-pion scattering $a π\to ππ$, relevant for the axion thermalization rate in the early universe, within unitarized NLO chiral perturbation theory. The latter extends the range of validity of the chiral expansion of axion-pion scattering and thus provides a crucial ingredient for the reliable determination of the relic density of thermal axions, whenever the axion decoupling temperature is below that of the QCD phase transition. Implications for cosmological observables are briefly discussed.

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arXiv2020

Assessment of systematic theory uncertainties in IAM unitarization

Effective Field Theories (EFTs) for Goldstone Boson scattering at a low order allow the computation of near--threshold observables in terms of a few coefficients arranged by a counting. As a matter of principle they should make sense up to an energy scale $E\sim 4πF$ but the expansion in powers of momentum violates exact elastic unitarity and renders the derivative expansion unreliable at much lower energies. If new--physics deviations from the Standard Model are found and encoded in low-energy coefficients, perhaps at the LHC, it will be profitable to extend the reach of the EFT to regimes where partial waves are saturating unitarity. The methods known in hadron physics as "Unitarized Chiral Perturbation Theory" extend the EFT up to its nominal reach or up to the first new physics resonance or structure (if found below that energy reach) in the partial wave amplitude, but they usually have unknown uncertainties. We recapitulate our analysis of the systematic theory uncertainties of the well known Inverse Amplitude Method (IAM).

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arXiv2000

The S-wave Λπphase shift is not large

We study the strong interaction S-wave Λπphase shift in the region of the Ξmass in the framework of a relativistic chiral unitary approach based on coupled channels. All parameters have been previously determined in a fit to strangeness S= -1 S-wave kaon-nucleon data. We find 0^\circ \le δ_0 \le 1.1^\circ in agreement with previous chiral perturbation theory calculations (or extensions thereof). We also discuss why a recent coupled channel K-matrix calculation gives a result for δ_0 that is negative and much bigger in magnitude. We argue why that value should not be trusted.

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