arXiv subjects

Asmaa Abada

Publications and source records attributed to Asmaa Abada.

At least 19 recordsLinked to original sources

arXiv2026

Multi-component Dark Matter in a Novel Three-Loop Inverse Scotogenic Seesaw Model

We consider a model which provides an explanation of the origin of light neutrino masses, the baryon asymmetry of the Universe -- via leptogenesis -- and explains the observed dark matter relic abundance with several components. In this scenario, Majorana masses of the active neutrinos are produced by the inverse seesaw (ISS) mechanism with the lepton-number-violating mass parameter being dynamically generated at three loops with a novel topology. This model is based on an extension of the Standard Model gauge symmetry by a global $U(1)'$ and a discrete $\mathbb{Z}_2\otimes \mathbb{Z}_3$. The latter, which is responsible for the radiative origin of the ISS lepton-number-violating parameter, survives the spontaneous breaking of the global $U(1)'$ and, at the same time, ensures the stabilization of the dark sector. The lightest particles carrying non-trivial residual charges are stable, becoming potentially viable dark matter candidates. The model complies with bounds and constraints from neutrino data, collider and high-intensity charged lepton flavor-violating observables, as well as dark matter relic density and direct detection. To efficiently explore the model's high-dimensional parameter space and identify phenomenologically viable regions, we perform a global numerical scan using the MultiNest algorithm.

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arXiv2026

Challenging Majorana neutrino effects in $B\to K^{(\ast)}\nu\nu$ and $K\to \pi\nu\nu$ decays

We investigate the contributions of Lepton Number Violating (LNV) effective operators to the rare decays $B\to K^{(\ast)}\nu\nu$ and $K\to \pi\nu\nu$. Such operators can modify the kinematic distributions of these processes, providing distinctive probes of physics beyond the Standard Model. Through a renormalization-group analysis, we show that the Standard Model Effective Field Theory (SMEFT) operators responsible for these effects are subject to stringent indirect constraints from neutrino physics. In particular, we find that the mild excess reported by Belle-II in the $B^+\to K^+\nu\nu$ channel cannot be explained by LNV SMEFT operators without introducing significant fine-tuning in neutrino masses. We then show that these constraints can be evaded in the SMEFT minimally extended by a light right-handed neutrino, allowing for sizable effects in rare meson decays. Finally, we explore the implications of this viable scenario for low-energy processes, including neutrinoless double-beta decays.

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arXiv2025

Dynamical scotogenic generation of the Linear and Inverse seesaws

We propose an economical model in which the tiny active neutrino masses arise from an interplay of linear and inverse seesaw mechanisms. The Standard Model is extended by a local $U(1)'$ gauge symmetry and discrete $\mathbb{Z}_{3}\otimes\mathbb{Z}_{4}$ symmetries, together with gauge-singlet scalars and neutral leptons. Owing to the preserved discrete symmetries after spontaneous symmetry breaking, the linear and inverse seesaw mechanisms are dynamically generated at the two-loop level, while the same symmetries ensure the stability of both scalar and fermionic dark matter candidates. One of the distinctive features of the model is a fermionic dark matter candidate whose mass is generated at one loop, whereas scalar dark matter masses arise at tree level. The model satisfies current constraints from neutrino oscillation data, dark matter direct detection, invisible Higgs decays, $Z'$ searches, and charged lepton flavor violation, in addition we also discuss predictions for muonium states. The outcome of our analysis is that the inverse seesaw contribution dominates over the linear one, suggesting that atmospheric neutrino mass squared splitting arises from the inverse seesaw mechanism, whereas the solar one is generated from the linear seesaw. Finally, our model offers an explanation of the hierarchy between the atmospheric and solar neutrino mass squared splittings, in addition to the smallness of active neutrino masses, feature not presented in many low-scale seesaw models. In addition, our parameter-space scan shows a slight preference for the normal neutrino mass ordering.

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arXiv2025

Investigating DUNE oscillations sensitivity to sterile Pseudo-Dirac Neutrinos

We explore the sensitivity of the Deep Underground Neutrino Experiment (DUNE) to sterile neutrino oscillations within a $3+$(pseudo-Dirac pair) framework. We first consider a pair of two sterile neutrinos forming a pseudo-Dirac pair, then we consider a low-scale seesaw realization, that we name ``Linear-Inverse Seesaw" model. This scenario features two nearly degenerate sterile neutrino states at the keV scale, characterized by a small mass splitting arising from a small amount of lepton number violation. In this scenario, the oscillation behavior can be described in three distinct regimes depending on the sterile-sterile mass-squared difference : low ($< 1\,\mathrm{eV}^2$), resonant ($1$--$100\,\mathrm{eV}^2$), and high ($> 100\,\mathrm{eV}^2$) regimes, recovering in both low- and high-mass regimes an effective non-unitarity of the leptonic mixing matrix. A distinctive feature of this framework is that observable effects persist even in the low-mass limit, unlike the case of standard $3+1$ scenarios, due to rapid oscillation averaging from larger keV-scale splittings. We leverage the complementarity of both near and far detectors to explore the sensitivity for $\nu_e$ and $\nu_\mu$ disappearance and $\nu_e$ and $\nu_{\tau}$ appearance oscillation probabilities. Our analysis reveals that DUNE can achieve significant improvements over current experimental constraints, especially in neutrino appearance modes. Additionally, we show that new CP-violating phases associated with the sterile sector can dramatically alter the sensitivity, with destructive interference potentially suppressing signals by orders of magnitude.

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arXiv2025

Neutrino Theory in the Precision Era

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. \textbf{A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology.} Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, \textbf{we propose to establish a CERN Neutrino Physics Centre.} Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

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arXiv2024

Phenomenology of scotogenic-like 3-loop neutrino mass models

In this talk, we discuss the phenomenology of radiative 3-loop seesaw models. The 3-loop suppression allows the new particles to have masses at the TeV scale, along with relatively large Yukawa couplings, while retaining consistency with neutrino masses and mixing, as observed in neutrino oscillation experiments. This leads to a rich phenomenology, especially in searches for charged lepton flavor violation, where the models predict sizable rates, well within future experimental reach. The models provide viable fermionic or scalar dark matter candidates, as is typical within the scotogenic paradigm. We discuss specific realizations in which the W-mass anomaly and the baryon asymmetry of the Universe can be accommodated, while complying with current constraints imposed by electroweak precision observables, charged-lepton flavor violation and neutrinoless double-beta decay.

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arXiv2024

Pheno & Cosmo Implications of Scotogenic 3-loop Neutrino Mass Models

Radiative seesaw models are examples of interesting and testable extensions of the Standard Model to explain the light neutrino masses. In radiative models at 1-loop level, such as the popular scotogenic model, in order to successfully reproduce neutrino masses and mixing, one has to rely either on unnaturally small Yukawa couplings or on a very small mass splitting between the CP-even and CP-odd components of the neutral scalar mediators. We discuss here scotogenic-like models where light-active neutrino masses arise at the three-loop level, providing a more natural explanation for their smallness. The proposed models are consistent with the neutrino oscillation data and allow to successfully accommodate the measured dark matter relic abundance. Depending on the specific realization, it is also possible to explain the W-mass anomaly and to generate the baryon asymmetry of the Universe via leptogenesis. The models lead to rich phenomenology, predicting sizable charged-lepton flavor violation rates, potentially observable in near future experiments, while satisfying all current constraints imposed by neutrinoless double-beta decay, charged-lepton flavor violation and electroweak precision observables.

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arXiv2024

Electric dipole moments of charged leptons in models with pseudo-Dirac sterile fermions

In this work, we address the impact of a small lepton number violation on charged lepton electric dipole moments - EDMs. Low-scale seesaw models protected by lepton number symmetry and leading to pseudo-Dirac pairs in the neutrino heavy spectrum provide a natural explanation for the smallness of neutrino masses with potentially testable consequences. Among which, it was thought that the small mass gap in each pair of pseudo-Dirac neutrinos may induce important contribution to the charged lepton EDMs. Recently, it has been shown that the contribution from some of the Feynman diagrams to charged lepton EDMs exactly cancel by virtue of the Ward-Takahashi identity in quantum electrodynamics. We thus consider here the Standard Model minimally extended with pairs of pseudo-Dirac sterile fermions and derive the complete analytical formula at two loops for the charged lepton EDMs. In addition, we numerically evaluate the order of the predicted EDMs consistent with the experimental bounds and constraints such as neutrino oscillation data, charged lepton flavour violating processes, sterile neutrino direct searches, meson decays, sterile neutrino decays, and cosmological and astrophysical observations. We find that, in the minimal setup accommodating neutrino data (masses and mixings) with only two pseudo-Dirac pairs, the predicted electron EDM is $\mathcal{O}(10^{-36})~e\hspace{0.05cm}\mathrm{cm}$, at most, which is much smaller than the current experimental bound and even future sensitivity. Hopefully, the electron EDM might reach future sensitivity, once extra pseudo-Dirac neutrinos are taken into account. The analytical formulae we derive are generic to any model involving pseudo-Dirac pairs in the heavy neutrino spectrum.

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arXiv2024

Three-Loop Inverse Scotogenic Seesaw Models

We propose a class of models providing an explanation of the origin of light neutrino masses, the baryon asymmetry of the Universe via leptogenesis and offering viable dark matter candidates. In these models the Majorana masses of the active neutrino are generated by the inverse seesaw mechanism with the lepton number violating right-handed Majorana neutrino masses $μ$ arising at three loops. The latter is ensured by the preserved discrete symmetries, which also guarantee the stability of the dark matter candidate. We focus on one of these models and perform a detailed analysis of the phenomenology of its leptonic sector. The model can successfully accommodate baryogenesis through leptogenesis in both weak and strong washout regimes. The lightest heavy fermion turns out to be a viable dark matter candidate, provided that the entries of the Majorana submatrix $μ$ are in the keV to MeV range. The solutions are consistent with the experimental constraints, accommodating both mass orderings for active neutrinos, in particular charged-lepton flavor violating decays $μ\to eγ$, $μ\to eee$, and the electron-muon conversion processes get sizable rates within future sensitivity reach.

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arXiv2023

Phenomenology of a scotogenic neutrino mass model at 3-loops

By extending the minimal scotogenic model with a spontaneously broken global symmetry $U(1)'$ and a preserved $\mathbb{Z}_2$ symmetry, we build a seesaw model for generating neutrino masses at three-loop level. The new particles have masses at the TeV scale and relatively large Yukawa couplings, which leads to sizable rates for charged lepton flavor violation processes, well within future experimental reach. The model is able to successfully explain the $W$ mass anomaly and provides a viable fermionic or scalar dark matter candidate, while satisfying all current constraints imposed by neutrinoless double-beta decay, charged-lepton flavor violation, and electroweak precision observables.

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arXiv2023

Phenomenological and cosmological implications of a scotogenic three-loop neutrino mass model

We propose a scotogenic model for generating neutrino masses through a three-loop seesaw. It is a minimally extended inert doublet model with a spontaneously broken global symmetry $U(1)'$ and a preserved $\mathbb{Z}_2$ symmetry. The three-loop suppression allows the new particles to have masses at the TeV scale without fine-tuning the Yukawa couplings. The model leads to a rich phenomenology while satisfying all the current constraints imposed by neutrinoless double-beta decay, charged-lepton flavor violation, and electroweak precision observables. The relatively large Yukawa couplings lead to sizable rates for charged lepton flavor violation processes, well within future experimental reach. The model could also successfully explain the $W$ mass anomaly and provides viable fermionic or scalar dark matter candidates.

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arXiv2022

Collider Searches for Heavy Neutral Leptons: beyond simplified scenarios

With very few exceptions, the large amount of available experimental bounds on heavy neutral leptons - HNL - have been derived relying on the assumption of the existence of a single (usually Majorana) sterile fermion state that mixes with only one lepton flavour. However, most of the extensions of the Standard Model involving sterile fermions predict the existence of several HNLs, with complex mixing patterns to all flavours. Consequently, most of the experimental bounds for HNLs need to be recast before being applied to a generic scenario. In this work, we focus on LHC searches of heavy neutral leptons and discuss how to reinterpret the available bounds when it comes to consider mixings to all active flavours, not only in the case with a single HNL, but also in the case when more heavy neutral leptons are involved. In the latter case, we also consider the possibility of interference effects and show how the bounds on the parameter space should be recast.

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arXiv2022

Heavy Neutral Leptons Beyond Simplified Scenarios

Heavy neutral leptons (HNL) constitute the building blocks of several neutrino mass generation mechanisms. Experimental searches depend on their masses and mixings with the active neutrinos, and exclusion regions in the plane of mass and mixing rely most of the time on two assumptions: $(i)$ the existence of $one$ HNL, which $(ii)$ mixes dominantly with only $one$ lepton flavor. In this work we discuss how to reinterpret the limits from collider searches relaxing these assumptions, providing a simple recipe to recast the bounds in models with generic mixing patterns, and in which at least two HNLs are coupled to the active sector.

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arXiv2021

Gauged Inverse Seesaw from Dark Matter

We propose an economical model addressing the generation of the Inverse Seesaw mechanism from the spontaneous breaking of a local $U(1)_{B-L}$, with the Majorana masses of the sterile neutrinos radiatively generated from the dark sector. The field content of the Standard Model is extended by neutral scalars and fermionic singlets, and the gauge group is extended with a $U(1)_{B-L}$ and a discrete $\mathbb{Z}_4$ symmetries. Besides dynamically generating the Inverse Seesaw and thus small masses to the active neutrinos, our model offers two possible dark matter candidates, one scalar and one fermionic, stable thanks to a remnant $\mathbb{Z}_2$ symmetry. Our model complies with bounds and constraints form dark matter direct detection, invisible Higgs decays and $Z'$ collider searches for masses of the dark sector at the TeV scale.

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arXiv2021

Electric Dipole Moments in the Minimal Scotogenic Model

In this work we consider a minimal version of the scotogenic model capable of accounting for an electron electric dipole moment within experimental sensitivity reach in addition to providing a dark matter candidate and radiatively generating neutrino masses. The Standard Model is minimally extended by two sterile fermions and one inert scalar doublet, both having odd parity, while the Standard Model particles have an even parity, imposed by a Z2 symmetry. The neutrino Yukawa couplings provide additional sources of CP violation, and thus a possible impact on electric dipole moments of charged leptons. This model provides two possible dark matter candidates (one bosonic and one fermionic) and our results show that, independently of the ordering of the generated light neutrino spectrum, one can have sizeable electron electric dipole moment within ACME sensitivity reach in the case of fermionic dark matter candidate.

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arXiv2019

Low-scale leptogenesis with three heavy neutrinos

Leptogenesis induced by the oscillations of GeV-scale neutrinos provides a minimal and testable explanation of the baryon asymmetry of the Universe. In this work we extend previous studies invoking only two heavy neutrinos to the case of three heavy neutrinos. We find qualitatively new behaviour as a result of lepton number violating oscillations and decays, strong flavour effects in the washout and a resonant enhancement due to matter effects. An approximate global $B - \bar L$ symmetry (representing the difference of baryon and a generalised lepton number) can protect the light neutrino masses from large radiative corrections, while simultaneously providing the ingredients for the resonant enhancement of the lepton asymmetry due to thermal contributions to the heavy neutrino dispersion relations. This mechanism is particularly efficient for large heavy neutrino mixing angles near the current experimental limits, a regime in which leptogenesis is not feasible in the minimal scenario with two heavy neutrinos. In this new parameter regime, low-scale leptogenesis is testable by the LHC and other existing experiments.

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arXiv2019

Beta and Neutrinoless Double Beta Decays with KeV Sterile Fermions

Motivated by the capability of the KATRIN experiment to explore the existence of KeV neutrinos in the $[1-18.5]$ KeV mass range, we explore the viability of minimal extensions of the Standard Model involving sterile neutrinos (namely the 3 + $N$ frameworks) and study their possible impact in both the beta energy spectrum and the neutrinoless double beta decay effective mass, for the two possible ordering cases for the light neutrino spectrum. We also explore how both observables can discriminate between motivated low-scale seesaw realizations involving KeV sterile neutrinos. Our study concerns the prospect of a Type-I seesaw with two right-handed neutrinos, and a combination of the inverse and the linear seesaws where the Standard Model is minimally extended by two quasi-degenerate sterile fermions. We also discuss the possibility of exploring the latter case searching for double-kinks in KATRIN.

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arXiv2019

Inclusive Displaced Vertex Searches for Heavy Neutral Leptons at the LHC

The inclusion of heavy neutral leptons to the Standard Model particle content could provide solutions to many open questions in particle physics and cosmology. The modification of the charged and neutral currents from active-sterile mixing of neutral leptons can provide novel signatures in Standard Model processes. We revisit the displaced vertex signature that could occur in collisions at the LHC via the decay of heavy neutral leptons with masses of a few GeV emphasizing the implications of flavor, kinematics, inclusive production and number of these extra neutral fermions. We study in particular the implication on the parameter space sensitivity when all mixings to active flavors are taken into account. We also discuss alternative cases where the new particles are produced in a boosted regime.

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