arXiv subjects

Gabriel M. Salla

Publications and source records attributed to Gabriel M. Salla.

13 recordsLinked to original sources

arXiv2026

The effects of non Bunch-Davies initial conditions on gravitationally produced relics

Typical gravitational production of relics from amplification of inflationary perturbations assumes Bunch-Davies initial conditions, i.e. a vacuum with initially no particles. In this paper we investigate the impact of non Bunch-Davies initial conditions to the final abundance of relics, with particular attention to the parameter space where the total dark matter abundance is reproduced. We present a general framework for any initial condition, through which we show their non-trivial effect on both spectrum and late-time abundance. We argue that for particles whose source of conformal symmetry breaking comes only from a mass term (spin-1/2 fermions and conformally coupled scalars), the choice of initial conditions has little impact on the mass range relevant to dark matter. For other particles, e.g. the longitudinal mode of spin-1, we see a large deviation from the standard computation. We exemplify and quantify our results with an initial thermal state and a two-stage inflation scenario, highlighting that the total dark matter can be obtained for a wide range of masses.

gr-qc↗

arXiv2026

Decaying spin-3/2 dark matter from baryon number violation

We explore an uncharted corner of dark matter phenomenology: non-supersymmetric spin-$3/2$ dark matter with baryon number violating interactions. In an effective field theory description, we identify the leading baryonic portal between the spin-$3/2$ state and Standard Model quarks and show that it can account for the observed dark matter abundance through UV freeze-in and Boltzmann-suppressed freeze-in, while the freeze-out region is completely excluded. The resulting phenomenology is distinctive, with relic production controlled by the competition between baryon-violating single-particle processes and baryon-conserving pair production. We map the viable parameter space against indirect detection, direct detection, and LHC monojet bounds, finding strong complementarity between these probes and especially stringent limits when production and decay are tied to the same operator. We also present a dark QCD-like ultraviolet completion in which the spin-$3/2$ particle arises as a composite baryon, naturally generating the effective interactions and mitigating the main theoretical obstacles of elementary higher-spin states. This framework opens a novel and testable connection between baryonic portals, confining dark sectors, and higher-spin dark matter.

hep-ph↗

arXiv2026

Chasing Serendipity: Tackling Transient Sources with Neutrino Telescopes

The discovery of ultra-high-energy neutrinos by IceCube marked the beginning of neutrino astronomy. Yet, the origin and production mechanisms of these neutrinos remain an open question. With the observation of several neutrino events with energies about the PeV, transient sources - astrophysical objects that emit particles in brief, localized bursts - have emerged as promising candidates. In this work, we revisit the identification of such sources in IceCube and future neutrino telescopes, focusing on how both the timing and sky localization of the source affect the detection sensitivity. We present a framework to account for the source's right ascension in determining the effective area of detectors not located at the poles, such as KM3NeT. As a case study, we investigate evaporating primordial black holes (PBHs) as transient neutrino sources, showing that the detection prospects and localization accuracy are strongly influenced by the PBH's position in the sky. Our results emphasize the complementarity between neutrino and gamma-ray observatories and showcase the potential of a global network of neutrino detectors to identify and localize transient events that might be missed by traditional photon-based instruments.

astro-ph.HE↗

arXiv2026

Could a Primordial Black Hole Explosion Explain the extremely high-energy KM3NeT neutrino Event?

A black hole is expected to end its lifetime in a cataclysmic runaway burst of Hawking radiation, emitting all Standard Model particles with ultra-high energies. Thus, the explosion of a nearby primordial black hole (PBH) has been proposed as a possible explanation for the $\sim 220$~PeV neutrino-like event recently reported by the KM3NeT collaboration. If the event originated from a PBH, the source would need to lie at $(1-7)\times 10^{-5} \mathrm{pc}$ - depending on the assumed effective area - thus within the Solar System. At such proximity, the resulting flux of gamma rays and cosmic rays would be detectable at Earth. By incorporating the time-dependent field of view of gamma-ray observatories, we show that LHAASO should have recorded $\mathcal{O}(10^8)$ events between fourteen and seven hours prior to the KM3NeT detection. IceCube and KM3NeT \textit{itself} should likewise have detected of order a few hundred events in the range $1~\mathrm{TeV} \lesssim E_ν\lesssim 1~\mathrm{PeV}$ during the 24 hours preceding the burst. The absence of any such multi-messenger signal, particularly in gamma-ray data, strongly disfavors the interpretation of the KM3-230213A event as arising from evaporation in a minimal four-dimensional Schwarzschild scenario.

hep-ph↗

arXiv2025

Spontaneous breaking of baryon number, baryogenesis and the bajoron

We explore the spontaneous breaking of global baryon number for baryogenesis. We introduce a model with three majorana fermions and a complex scalar carrying baryon number charge. After symmetry breaking, the baryon asymmetry is generated below the electroweak scale via the decays of one of the majorana fermions. The main focus of the paper is the phenomenology of the Nambu--Goldstone boson of $U(1)_B$, which we call the bajoron. With small sources of explicit baryon number violation, the bajoron acquires a small mass and is generally very long-lived. The model avoids proton decay, satisfies cosmological constraints, and offers interesting collider phenomenology for the Large Hadron Collider. These long-lived particles tied to baryogenesis strongly support the development of far-detector experiments such as MATHUSLA, FASER, SHiP, and others.

hep-ph↗

arXiv2024

Gravitationally produced Dark Matter and primordial black holes

We examine how the existence of a population of primordial black holes (PBHs) influences cosmological gravitational particle production (CGPP) for spin-0 and spin-1 particles. In addition to the known effects of particle production and entropy dilution resulting from PBH evaporation, we find that the generation of dark matter (DM) through CGPP is profoundly influenced by a possible era of PBH matter domination. This early matter dominated era results in an enhancement of the particle spectrum from CGPP. Specifically, it amplifies the peak comoving momentum $k_\star$ for spin-1 DM, while enhancing the plateau of the spectrum for minimally coupled spin-0 particles for low comoving momenta. At the same time, the large entropy dilution may partially or completely compensate for the increase of the spectrum and strongly mitigates the DM abundance produced by CGPP. Our results show that, in the computation of the final abundance, CGPP and PBH evaporation cannot be disentangled, but the parameters of both sectors must be considered together to obtain the final result. Furthermore, we explore the potential formation of PBHs from density fluctuations arising from CGPP and the associated challenges in such a scenario.

hep-ph↗

arXiv2024

A log story short: running contributions to radiative Higgs decays in the SMEFT

We investigate the renormalization of the radiative decays of the Higgs to two gauge bosons in the Standard Model Effective Field Theory at mass dimension eight. Given that these are loop-level processes, their one-loop renormalization can be phenomenologically important when triggered by operators generated through the tree-level exchange of heavy particles (assuming a weakly coupled UV model). By computing the tree-level matching conditions of all relevant extensions of the Standard Model, we demonstrate that this effect is indeed present in the $h\to γZ$ decay at dimension eight, even though it is absent at dimension six. In contrast, the $h\to gg$ and $h\to γγ$ decays can only be renormalized by operators generated by one-loop processes. For UV models with heavy vectors, this conclusion hinges on the specific form of their interaction with massless gauge bosons which is required for perturbative unitarity. We study the quantitative impact of the possible logarithmic enhancement of $h\to γZ$, and we propose an observable to boost the sensitivity to this effect. Given the expected increased precision of next-generation high-energy experiments, this dimension-eight contribution could be large enough to be probed and could therefore give valuable clues about new physics by revealing some of its structural features manifesting first at dimension eight.

hep-ph↗

arXiv2024

ALPs, the on-shell way

We study how the coupling between axion-like particles (ALPs) and matter can be obtained at the level of on-shell scattering amplitudes. We identify three conditions that allow us to compute amplitudes that correspond to shift-symmetric Lagrangians, at the level of operators with dimension 5 or higher, and we discuss how they relate and extend the Adler's zero condition. These conditions are necessary to reduce the number of coefficients consistent with the little-group scaling to the one expected from the Lagrangian approach. We also show how our formalism easily explains that the dimension-5 interaction involving one ALP and two massless spin-1 bosons receive corrections from higher order operators only when the ALP has a non-vanishing mass. As a direct application of our results, we perform a phenomenological study of the inelastic scattering $\ell^+\ell^- \to ϕh$ (with $\ell^\pm$ two charged leptons, $ϕ$ the ALP and $h$ the Higgs boson) for which, as a result of the structure of the 3-point and 4-point amplitudes, dimension-7 operators can dominate over the dimension-5 ones well before the energy reaches the cutoff of the theory.

hep-ph↗

arXiv2023

New Limits on Leptophilic Axionlike Particles and Majorons from ArgoNeuT

Axionlike particles are among the most studied extensions of the standard model. In this Letter we study the bounds that the ArgoNeuT experiment can put on the parameter space of two specific scenarios: leptophilic axionlike particles and Majorons. We find that such bounds are currently the most constraining ones in the (0.2 - 1.7) GeV mass range.

hep-ph↗

arXiv2023

Characterising Dark Matter-induced neutrino potentials

In this paper we explore interactions between neutrinos and Dark Matter. In particular, we study how the propagation of astrophysical neutrinos can be modified by computing the most general potential generated by the galactic DM background. We use on-shell techniques to compute this potential in a completely model independent way and obtain an expression valid for any Dark Matter mass and spin. Afterwards, we use this expression to analyse under what circumstances such potential can be important at the phenomenological level, and we find that under some assumptions only ultra light scalar Dark Matter could be of any relevance to oscillation experiments.

hep-ph↗

arXiv2022

(In)Visible signatures of the minimal dark abelian gauge sector

In this paper we study the present and future sensitivities of the rare meson decay facilities KOTO, LHCb and Belle II to a light dark sector of the minimal dark abelian gauge symmetry where a dark Higgs $S$ and a dark photon $Z_D$ have masses $\lesssim 10$ GeV. We have explored the interesting scenario where $S$ can only decay to a pair of $Z_D$'s and so contribute to visible or invisible signatures, depending on the life-time of the latter. Our computations show that these accelerator experiments can access the dark Higgs (mass and scalar mixing) and the dark photon (mass and kinetic mixing) parameters in a complementary way. We have also discussed how the CMS measurement of the SM Higgs total decay width and their limit on the Higgs invisible branching ratio can be used to extend the experimental reach to dark photon masses up to $\sim 10$ GeV, providing at the same time sensitivity to the gauge coupling associated with the broken dark abelian symmetry.

hep-ph↗

arXiv2022

An on-shell approach to neutrino oscillations

In the usual quantum field theoretical approach, neutrino oscillations are studied diagonalising either the mass or matter Hamiltonians. In this paper we analyse the problem from an on-shell amplitude perspective, where Lagrangians or Hamiltonians are not available. We start by studying in detail how flavor enters in the amplitudes and how the PMNS matrix emerges. We then analyse the elastic amplitude of two neutrinos and two charged leptons that induce matter effects and propose a strategy to obtain the known results of the standard oscillation theory without Hamiltonians. Finally, we extend the previously proposed procedure and use the most general elastic 4-point amplitude to study beyond the Standard Model effects on oscillations.

hep-ph↗

arXiv2021

Dark Photon bounds in the dark EFT

Dark photons are massive abelian gauge bosons that interact with ordinary photons via a kinetic mixing with the hypercharge field strength tensor. This theory is probed by a variety of different experiments and limits are set on a combination of the dark photon mass and kinetic mixing parameter. These limits can however be strongly modified by the presence of additional heavy degrees of freedom. Using the framework of dark effective field theory, we study how robust are the current experimental bounds when these new states are present. We focus in particular on the possible existence of a dark dipole interaction between the Standard Model leptons and the dark photon. We show that, under certain assumptions, the presence of a dark dipole modifies existing supernovæ bounds for cut-off scales up to $\mathcal{O}(10 - 100~\text{TeV})$. On the other hand, terrestrial experiments, such as LSND and E137, can probe cut-off scales up to $\mathcal{O}(3~\text{TeV})$. For the latter experiment we highlight that the bound may extend down to vanishing kinetic mixing.

hep-ph↗