arXiv subjects

Diego Portillo-Sánchez

Publications and source records attributed to Diego Portillo-Sánchez.

7 recordsLinked to original sources

arXiv2025

Lepton number violating and conserving heavy baryon four-body decays in the presence of two almost degenerate heavy neutrinos

We study the four-body heavy baryon decay, including two leptons in the final state, of the form $B_A \to B_B P \ell_α\ell_β$, which can be either a lepton number conserving (LNC) or a lepton number violating (LNV) process (where $B$, $P$ and $\ell$ are baryons, pseudoscalar mesons and leptons, respectively), including all kinematic allowed lepton pair possibilities. We work beyond the simplified assumption of a single heavy Majorana neutrino mixing with the active sector, considering potential interference effects when including two nearly degenerate heavy Majorana neutrinos. Particularly, we provide a first estimate of the decay channels involving different flavors for the external leptons (e.g., muon-tau), and elaborate on the interference pattern due to leptons exchange. We show that the results for the two heavy almost degenerate neutrinos can be recast into a single Majorana neutrino, and exhibit the features for both the LNC and LNV scenarios. We determine the potential exclusion region for the mass and heavy-light mixing parameters, of the neutrinos driving the decay, including finite size detector effects, and compare them with those from direct searches and $τ$ and meson decays. We also obtain the Branching ratio as a function of the heavy neutrino mass for the current upper limit of the heavy-light mixings.

hep-ph↗

arXiv2025

Proton-box contribution to $a_μ^{\rm{HLbL}}$

We analyze the proton$\text{-}$box contribution to the hadronic light$\text{-}$by$\text{-}$light part of the muon's anomalous magnetic moment, which is the first reported baryonic contribution to this piece. We follow the quark$\text{-}$loop analysis, incorporating the relevant data$\text{-}$driven and lattice proton form factors. Although the heavy mass expansion would yield a contribution of $\mathcal{O}(10^{-10})$, the damping of the form factors in the regions where the kernel peaks, explains our finding $a_μ^{\rm{p-box}}=1.82 (7)\times 10^{-12}$, two orders of magnitude smaller than the forthcoming uncertainty on the $a_μ$ measurement and on its Standard Model prediction.

hep-ph↗

arXiv2024

Authentic Majorana versus singlet Dirac neutrino contributions to $μ^{+}μ^{+}\to \ell^{+}\ell^{+}$ $(\ell=e,τ)$ transitions

We revisited the computation of the cross section for the $μ^+μ^+\to \ell^+\ell^{+}$ $(\ell^+=τ^+,\, e^+)$ transitions in the presence of new heavy Majorana neutrinos. We focus on scenarios where the masses of the new states are around some few TeV, the so-called low-scale seesaw models. Our analysis is set in a simple model with only two new heavy Majorana neutrinos considering the current limits on the heavy-light mixings. Our results illustrate the difference between the genuine effects of two nondegenerate heavy Majorana states and the degenerate case where they form a Dirac singlet field.

hep-ph↗

arXiv2024

Dirac-Majorana neutrinos distinction in four-body decays

A novel method to differentiate the effects of Dirac and Majorana (D-M) neutrinos in four-body decays has been discussed in arXiv:2106.11785. There, it is concluded that the back-to-back kinematic scenario seems to avoid the constraint imposed by the "practical Dirac-Majorana confusion theorem", as one does not need to fully integrate over neutrino and antineutrino momenta. In this paper, we propose to analyse radiative leptonic lepton-decays ($\ell\to\ell'ν\barνγ$), as an independent alternative process to study the possible Majorana nature of neutrinos. Our approach demonstrates that, in the back-to-back kinematic configuration (for the $\ell'- γ$ and $ν-\barν$ systems, respectively), the distinction between Dirac and Majorana cases disappears when the inaccessible neutrino angle is integrated out, which might appear unexpected considering the claims in arXiv:2106.11785. Our results apply in absence of non-standard interactions, which can enhance generally the sensitivity to the neutrino nature.

hep-ph↗

arXiv2023

$τ^- \to π^- ην_τ$ decay induced by QED one-loop effects

The $τ^- \to π^-ην_τ$ decay is forbidden in the Standard Model in the limit of exact $G$-parity, it becomes a rare decay due to isospin symmetry breaking and it is very sensitive to the effects of effective scalar interactions. Since the parameters driving isospin breaking, $(m_d-m_u)/(m_s-\bar{m})$ and $α$, are of the same order, one may expect their $G$-parity breaking effects in this decay can be of similar magnitudes. In this work, we evaluate the effects of isospin-breaking amplitudes originated from a virtual photon at one-loop in a resonance dominance model to describe photon-hadron interactions. We find that these effects can shift the leading SM predictions based on the $u-d$ quark mass difference by roughly $12\%$, and should be taken into consideration in a precision comparison of theory and experiment in order to draw meaningful conclusions on New Physics. The effects in the rate of the analogous $τ^- \to π^-η'ν_τ$ decay can be larger ($\sim$ $78\%$), under the approximations assumed in this model.

hep-ph↗

arXiv2023

Ultraviolet extensions of the Scotogenic model

The Scotogenic model is a popular scenario that induces radiative Majorana neutrino masses and includes a weakly-interacting dark matter candidate. We classify all possible ultraviolet extensions of the Scotogenic model in which (i) the dark $\mathbb{Z}_2$ parity emerges at low energies after the spontaneous breaking of a global $\rm U(1)_L$ lepton number symmetry, and (ii) the low-energy effective theory contains a naturally small lepton number breaking parameter, suppressed by the mass of a heavy mediator integrated out at tree-level. We find $50$ such models and discuss two of them in detail to illustrate our setup. We also discuss some general aspects of the phenomenology of the models in our classification, exploring possible lepton flavor violating signals, collider signatures and implications for dark matter. The phenomenological prospects of these scenarios are very rich due to the presence of additional scalar states, including a massless Goldstone boson.

hep-ph↗

arXiv2022

Resonant Majorana neutrino effects in $Δ$L=2 four-body hyperon decays

We computed the $Σ^{-}\to nπ^+e^-\ell^-$ ($\ell=e,μ$), $Ξ^-\to Λπ^+e^-e^-$, and $Λ\to pπ^+e^-e^-$ lepton number violating (LNV) hyperon decays mediated by a resonant Majorana neutrino. The expected hyperon production rate of experiments like BES-III of around $10^6-10^8$ may allow searching for these rare hyperon decays at enough sensitivities. We illustrate the limits on the new heavy mixing parameters derived from these hyperon channels and compare them with other LNV meson decays in similar mass regions of the resonant neutrino state.

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