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Jilberto Zamora-Saa

Publications and source records attributed to Jilberto Zamora-Saa.

29 records · Page 2Linked to original sources
arXiv2019

Cosmic ray ensembles from ultra-high energy photons propagating in the galactic and intergalactic space

Propagation of ultra-high energy photons in the galactic and intergalactic space gives rise to cascades comprising thousands of photons. Using Monte Carlo simulations, we investigate the development of such cascades in the solar magnetosphere, and find that the photons in the cascades are distributed over hundreds of kilometers as they arrive at the top of the Earth's atmosphere. We also perform similar study for cascades starting as far as 10 Mpc away from us using relevant magnetic field models. A few photons correlated in time are expected to arrive at the Earth from the latter type of cascade. We present our simulation results and discuss the prospects for detection of these cascades with the Cosmic-Ray Extremely Distributed Observatory.

astro-ph.HE↗
arXiv2019

Probing heavy neutrino oscillations in rare W boson decays

In this work, we study the lepton number violating W boson and top quark decays via intermediate on-shell Majorana neutrinos Nj into three charged leptons and a light neutrino. We discuss the neutrino oscillation effects present in the decay due to the small mass gap between the heavy neutrino states. We focus on a scenario that contains at least two heavy Majorana neutrinos in the mass range 2-80 GeV. The results indicate that the modulation of the branching ratios as a function of the distance between the vertices may be detected in a future experiment such as High-Luminosity Large Hadron Collider. As a secondary result, the CP-violating phases could be explored.

hep-ph↗
arXiv2017

Corrections to (pseudo)scalars decay into a fermion pair from gravitational torsion

We study the contribution of the torsion-descendent four-fermion contact interaction to the decay width of a neutral (pseudo)scalar field into a fermion pair. This new interaction comes from the existence of gravitational torsion in models with extra dimensions. Additionally, we exemplify the formalism with two examples: first, the variation of the considered branching ratio of the Higgs in the context of the standard model, and second the proper variations of the scalar and pseudo scalar fields of the type II-1 two Higgs doublets model.

hep-ph↗
arXiv2017

Limits on beyond standard model messengers as ultra high energy cosmic rays

Up to date, there is no consensus regarding the origin of ultra-high energy cosmic rays (UHECR) beyond the Greisen--Zatsepin--Kuzmin (GZK) limit. In order for these UHECRs to reach the Earth, an extremely suppressed interaction between them and the cosmic microwave background (CMB) is required, which is impossible for standard model (SM) particles, except neutrinos. In this letter, we present constraints on the parameter space of models involving axion-like particles and dark photons, as candidates for UHECRs, by assuming that these particles can traverse the visible Universe without decaying. In the case of axion-like particles, the constraints are tighter than those given in previous works. We present for the first time constraints on the parameter space of dark photon models, by considering their kinetic term mixing with SM photons.

astro-ph.HE↗
arXiv2017

Resonant CP violation in rare tau decay

In this work, we study the lepton number violating tau decays via intermediate on-shell Majorana neutrinos $N_j$ into two scalar mesons and a lepton $τ^{\pm} \to M_1{}^{\pm} N_j \to M_1^{\pm} M_2^{\pm} \ell^{\mp}$. We calculate the Branching ratios $Br(τ^{\pm})$ and the CP asymmetry $(Γ(τ^+) - Γ(τ^-))/(Γ(τ^+) + Γ(τ^-))$ for such decays, in a scenario that contain at least two heavy Majorana neutrinos. The results show that the CP asymmetry is small, but becomes comparable with the branching ratio ${\rm Br}(τ^{\pm})$ when their mass difference is comparable with their decay width, $ΔM_N \sim Γ_N$. On the other hand, we present regions of the heavy-light neutrino mixing elements, in which the $CP$ asymmetry could be explore in future tau factories.

hep-ph↗
arXiv2017

Solar neutrinos, helicity effects and new affine gravity with torsion II

The cross section for neutrino helicity spin-flip obtained from a new f(R, T) model of gravitation with dynamic torsion field introduced by one of the authors in [1], is phenomenologically analyzed. To this end, due to the logarithmical energy dependence of the cross section, the relation with the axion decay constant fa (Peccei-Quinn parameter) is used. Consequently the link with the phenomenological energy/mass window is found from the astrophysical and high energy viewpoints. The highest helicity spin-flip cross-sectional values presented in this work coincide with a recent estimation on the axion mass computed in [2] in the framework of finite temperature extended lattice QCD and under cosmological considerations.

hep-ph↗
arXiv2016

Rare meson decays with three pairs of quasi-degenerate heavy neutrinos

We consider a scenario of Low Scale Seesaw where the masses of its heavy Majorana neutrinos are arranged in a pattern of three pairs of quasi degenerate ones, in the range of O(1-6 GeV). Since they can violate lepton number by two units, they contribute to rare decays of Ds and Bc mesons, providing, besides, conditions for maximal CP violation. We found that new phenomenology is possible depending on how many of on-shell pairs mediate these decays. In particular, we present new constraints on muon-heavy neutrinos mixing parameters.

hep-ph↗
arXiv2015

Oscillation of heavy sterile neutrino in decay of $B \to μe π$

In a scenario with two almost mass degenerate heavy sterile Majorana neutrinos with a mass $\sim 1$ GeV, we present the semileptonic decay widths of heavy charged pseudoscalars such as $B$ mesons, either lepton-number-violating ($B^{\pm} \to μ^{\pm} e^{\pm} π^{\mp}$), or lepton-number-conserving ($B^{\pm} \to μ^{\pm} e^{\mp} π^{\pm}$), mediated by such on-shell neutrinos. It had been explained in the literature that such decays may be eventually detected, and that they can present even detectable CP violation effects. In this work we point out that, in addition, such decays may present detectable effects of heavy neutrino oscillation, allowing us to extract the oscillation length and thus the heavy neutrino mass difference $ΔM_N$, as well as a CP-violating Majorana phase.

hep-ph↗
arXiv2015

Probing the Majorana neutrinos and their CP violation in decays of charged scalar mesons $π, K, D, D_s, B, B_c$

Some of the outstanding questions of particle physics today concern the neutrino sector, in particular whether there are more neutrinos than those already known and whether they are Dirac or Majorana particles.There are different ways to explore these issues. In this article we describe neutrino-mediated decays of charged pseudoscalar mesons such as $π^{\pm}$, $K^{\pm}$ and $B^{\pm}$, in scenarios where extra neutrinos are heavy and can be on their mass shell. We discuss semileptonic and leptonic decays of such kinds. We investigate possible ways of using these decays in order to distinguish between the Dirac and Majorana character of neutrinos. Further, we argue that there are significant possibilities of detecting CP violation in such decays when there are at least two almost degenerate Majorana neutrinos involved. This latter type of scenario fits well into the known neutrino minimal standard model ($ν$MSM) which could simultaneously explain the Dark Matter and Baryon Asymmetry of the Universe.

hep-ph↗
arXiv2014

CP violation in lepton number violating semihadronic decays of $K, D, D_s, B, B_c$

We study the CP violation in lepton number violating meson decays $M^{\pm} \to \ell_1^{\pm} \ell_2^{\pm} M^{' \mp}$, where $M$ and $M^{'}$ are pseudoscalar mesons, $M=K, D, D_s, B, B_c$ and $M^{'}=π, K, D, D_s$, and the charged leptons are $\ell_1, \ell_2 = e, μ$. It turns out that the CP-violating difference $S_{-}(M) \equiv [Γ(M^- \to \ell_1^- \ell_2^- M^{' +})-Γ(M^+ \to \ell_1^+ \ell_2^+ M^{' -})]$ can become appreciable when two intermediate on-shell Majorana neutrinos $N_j$ ($j=1,2$) participate in these decays. Our calculations show that the asymmetry becomes largest when the masses of $N_1$ and $N_2$ are almost degenerate, i.e., when the mass difference $ΔM_N$ becomes comparable with the (small) decay widths $Γ_N$ of these neutrinos: $ΔM_N \not\gg Γ_N$. We show that in such a case, the CP ratio ${\cal A}_{CP}(M) \equiv [Γ(M^- \to \ell_1^- \ell_2^- M^{' +})-Γ(M^+ \to \ell_1^+ \ell_2^+ M^{' -})]/[Γ(M^- \to \ell_1^- \ell_2^- M^{' +})+Γ(M^+ \to \ell_1^+ \ell_2^+ M^{' -})]$ becomes a quantity $\sim 1$. The observation of CP violation in these decays would be consistent with the existence of the well-motivated $ν$MSM model with two almost degenerate heavy neutrinos in the mass range between $M_N \sim 0.1$-$10^1$ GeV.

hep-ph↗