arXiv subjects

Kevin A. Urquía-Calderón

Publications and source records attributed to Kevin A. Urquía-Calderón.

6 recordsLinked to original sources

arXiv2026

Leptogenesis and Dark Matter in an Inverse Seesaw from gauged B-L breaking

We study a dynamical realization of the low-scale Inverse Seesaw mechanism in which the approximate $B-L$ symmetry is gauged and spontaneously broken. Anomaly cancellation requires additional chiral fermions, one of which becomes a stable dark matter candidate after symmetry breaking, while another remains massless and contributes to dark radiation. Focusing on the regime of feeble gauge interactions, we compute the dark matter relic abundance produced via the freeze-in mechanism through the $B-L$ gauge boson and identify the parameter space consistent with cosmological and laboratory constraints. We show that the same region naturally avoids thermalization of heavy neutral leptons, preserving the viability of ARS leptogenesis. The interplay between dark matter production, dark radiation constraints, and leptogenesis requirements leads to a predictive scenario where future cosmological surveys and intensity-frontier experiments such as SHiP can probe significant portions of the viable parameter space.

hep-ph↗

arXiv2026

Learning Standard Model structure from LHC data with Riemannian flow matching

In this work we demonstrate that a single transformer-based generative model can capture Standard Model structure spanning five decades of invariant mass, from the sub-GeV regime to the TeV continuum, a range that no single Monte Carlo sample covers. To achieve this we design \textsc{ShellFlow}, a Riemannian conditional flow matching model that, given the recorded event composition, generates each particle on its on-shell manifold. Its only physics priors are the on-shell condition and the invariant-mass formula. The model is trained on $\sim 10^{9}$ real $pp$ collision events from the ATLAS Open Data 13~TeV release and told nothing else. From a single training run, the model learns to reproduce all of the following: intra-particle kinematics, the dilepton resonances ($J/ψ$, $Υ$, $Z$) at their PDG positions, the leptonic Weinberg angle, the $W$ and top-quark masses, and inter-particle correlations that enter no training objective. A substantial fraction of the Standard Model is thus learnable directly from recorded collision data.

hep-ph↗

arXiv2026

Revisiting lepton flavor violation: $τ$ and meson decays

The minimal type-I seesaw model provides a simple explanation of neutrino flavor oscillations and induces charged lepton flavor violation (cLFV). Despite extensive previous studies, semileptonic cLFV channels remain underexplored. Using updated form factors, decay constants, and oscillation data, we revisit $τ$ and meson decay channels, performing a systematic comparison across the seesaw parameter space. Surprisingly, we find that decays such as $τ\to \ellρ$ can dominate over purely leptonic $τ$-sector probes, including $τ\to 3\ell$ and even $τ\to\ell\,γ$, in certain regions. In contrast, heavy-meson decays remain far below experimental sensitivity. Considering global constraints on the seesaw parameters, we derive branching ratios for the relevant cLFV processes and identify those within potential reach of next-generation experiments.

hep-ph↗

arXiv2025

Tree-level unitarity constraints on heavy neutral leptons

Heavy neutral leptons (HNLs) can explain the origin of neutrino masses and oscillations over a wide range of masses. Direct experimental probes of HNLs become unfeasible for masses significantly above the electroweak scale.Consequently, the strongest limits arise from the non-observation of charged lepton flavor-violating processes induced by HNLs at loop level.Counter-intuitively, these bounds tighten as the HNL mass increases, an effect that persists within the perturbative regime. This work explores the precise form of these bounds for HNLs with masses well beyond the electroweak scale by analyzing the full matrix of partial waves (tree-level unitarity). At high energies, the HNL model simplifies to a Yukawa theory, allowing unitarity constraints to be expressed in terms of the total Yukawa coupling $\left|Y_{\mathrm{tot}}\right|^2$ involving HNLs, lepton doublets, and the Higgs boson. Processes with $J=0$ and $J=1/2$ yield the well-known result $\left|Y_{\mathrm{tot}}\right|^2 \leq 8π$. However, the most stringent result arises from processes with $J = 1$, which is given by $\left|Y_{\mathrm{tot}}\right|^2 \leq 4π(\sqrt{5} -1) = 8π/φ\approx 15.533$, where $φ$ is the Golden ratio. These results remain valid provided that the Yukawa matrix has rank 1, a condition approximately satisfied in models with two or three HNLs, with large mixing angles, and radiactively small neutrino masses. Finally, we determine the maximum mass that an HNL can have in the type-I seesaw model while remaining the sole source of neutrino masses.

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arXiv2024

Long-lived heavy neutral leptons at lepton colliders as a probe of left-right symmetric models

Left-right symmetric models (LRSM) were proposed to reconcile the apparent parity violation in weak interactions with our intrinsic notion of fundamental parity symmetry. It was quickly realized that LRSM offers a viable framework for explaining neutrino masses by incorporating right-handed neutrinos, $N$, into its spectrum. In this study, we investigate for the first time the potential of future lepton colliders (including the FCC-ee, CEPC, ILC, CLIC, and a muon collider) to detect signals stemming from $N$'s, focusing primarily on displaced vertex signals, and on prompt signals to a lesser degree. Our results demonstrate that these signals can effectively probe the characteristic scales of LRSM, providing evidence that would be unobtainable through any other experimental means.

hep-ph↗

arXiv2023

Heavy Neutral Leptons -- Advancing into the PeV domain

Heavy neutral leptons (HNLs) are hypothetical particles able to explain neutrino oscillations and provide a mechanism for generating the baryon asymmetry of the Universe. Quantum corrections due to such particles give rise to flavor violating processes in the charged lepton sector. Based on the fact that these corrections grow with HNL masses, we improve existing constraints by orders of magnitude in mass and mixing angle. This allows us to probe part of the parameter space of leptogenesis with multi-TeV HNLs. We also show that one will be able to infer HNL parameters in a significant portion of the parameter space for TeV-PeV masses if charged lepton flavor violating signals are detected.

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