arXiv subjects

Stefano Morisi

Publications and source records attributed to Stefano Morisi.

At least 19 recordsLinked to original sources

arXiv2026

Insights into 1-loop corrections to neutrino low-scale type-I seesaw mechanism

The standard type-I seesaw can also be regarded as a low-scale seesaw by using the freedom of the Casas-Ibarra parameterization. In this framework, radiative corrections to the neutrino mass matrix can dominate over the tree-level contribution. We show that a naive use of the Casas-Ibarra parametrization in the presence of 1-loop corrections leads to incorrect predictions for the neutrino oscillation parameters. By using a modified Casas-Ibarra parametrization, in which 1-loop corrections are reabsorbed into the right-handed neutrino mass matrix, we obtain a light neutrino mass matrix consistent with experimental values. On the other hand, we show that physical processes related to right-handed neutrino propagation, such as heavy neutral lepton searches, do not depend on the 1-loop corrections. Moreover, we show that ${\rm Br}(μ\to e γ)$ provides competitive constraints on the parameter space of heavy neutral lepton search experiments for masses above $100$ GeV.

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arXiv2025

Axionless strong CP problem solution: the spontaneous CP violation case

We propose an alternative to the axion mechanism for addressing the charge parity (CP) problem in quantum chromodynamics (QCD). Our approach involves imposing CP as an inherent symmetry of the Lagrangian, which is then spontaneously broken. To generate the correct texture for the Yukawa matrices, we introduce a discrete $\mathbb{Z}_2$ symmetry that is softly broken by the scalar potential. By identifying a benchmark point for the Yukawa couplings that aligns with the measured quark masses, the CKM matrix, and low-energy flavor-changing constraints, our findings suggest that this model offers a viable solution to the CP problem.

hep-ph↗

arXiv2025

Rescuing 331 bileptons from the Landau pole

Among the particles being searched for at the LHC beyond the Standard Model are bileptons, which are doubly charged gauge bosons. Bileptons are predicted by several Standard Model extensions, including the so-called 331 models with $β= \sqrt 3$. The minimal formulation of these models is generally plagued by a "low energy" Landau pole, which can undermine current predictions for TeV-scale bileptons. We analyze this issue and investigate the possibility to shift the Landau pole at higher energy scales by extending the troublesome minimal 331 models.

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arXiv2024

Impact of primordial black holes on heavy neutral leptons searches in the framework of resonant leptogenesis

We investigate the effects on sub-TeV resonant leptogenesis of Primordial Black Holes with masses from $10^6$ to $\sim 10^9$ g. The latter might dominate the energy content of the Universe altering its evolution and, eventually, diluting the final baryon asymmetry. We find that, depending on the mass and abundance of Primordial Black Holes, the parameter space of sub-TeV resonant leptogenesis shrinks towards higher Right-Handed Neutrino masses and smaller active-sterile mixing. Remarkably, this translates into important implications for the experimental searches of heavy neutral leptons. Conversely, we demonstrate that a possible future detection of sub-TeV heavy neutral leptons would disfavour regions of the parameter space of Primordial Black Holes currently allowed.

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arXiv2024

Heavy neutral lepton search and $μ\to e γ$ constraints in case of type-I seesaw

Within type-I seesaw mechanism it is possible to have large (order one) light-heavy neutrino mixing even in case of low right-handed neutrino mass scale (of the order of GeV). This implies large lepton flavor violation. As example we consider the process $μ\to e γ$ that can have a branching up to $10^{-8}$ within type-I seesaw (in contrast with the tiny value $10^{-54}$ expected). Such an enhancing of lepton flavor violation can be used to constraint the parameter space of long lived particle experiments.

hep-ph↗

arXiv2024

331 Models and Bilepton Searches at LHC

Despite being remarkable predictive, the Standard Model leaves unanswered several important issues, which motivate an ongoing search for its extensions. One fashionable possibility are the so-called 331 models, where the electroweak gauge group is extended to $SU_L(3)\times U(1)$. We focus on a minimal extension which includes vector-like quarks (VLQs) and new gauge bosons, performing a consistent analysis of the production at LHC of a pair of doubly-charged bileptons. We include for the first time all the relevant processes where VLQs contribute, and in particular the associate production VLQ-bilepton. Finally, we extract the bound on the bilepton mass, $m_Y>$ 1300 GeV, from a reinterpretation of a recent ATLAS search for doubly-charged Higgs bosons in multi-lepton final states.

hep-ph↗

arXiv2023

Limits on light primordial black holes from high-scale leptogenesis

We investigate the role that the evaporation of light primordial black holes may have played in the production of the baryon asymmetry of the Universe through the high-scale leptogenesis. In particular, for mass of primordial black hole in the range [$10^6$-$10^9$] g, we find a dilution of thermally generated lepton asymmetry via entropy injection in the primordial plasma after the sphaleron freeze-out. As a consequence, we can put strong constraints on the primordial black hole parameters, showing the mutual exclusion limits between primordial black holes and high-scale leptogenesis. Remarkably, we point out an interplay between the upper bound on the initial abundance of primordial black holes and the active neutrino mass scale.

hep-ph↗

arXiv2023

Heavy decaying dark matter at future neutrino radio telescopes

In the next decades, ultra-high-energy neutrinos in the EeV energy range will be potentially detected by next-generation neutrino telescopes. Although their primary goals are to observe cosmogenic neutrinos and to gain insight into extreme astrophysical environments, they can also indirectly probe the nature of dark matter. In this paper, we study the projected sensitivity of up-coming neutrino radio telescopes, such as RNO-G, GRAND and IceCube-gen2 radio array, to decaying dark matter scenarios. We investigate different dark matter decaying channels and masses, from $10^7$ to $10^{15}$ GeV. By assuming the observation of cosmogenic or newborn pulsar neutrinos, we forecast conservative constraints on the lifetime of heavy dark matter particles. We find that these limits are competitive with and highly complementary to previous multi-messenger analyses.

hep-ph↗

arXiv2023

The Radiative Flavor Template at the LHC: Lepton non-universality and g-2

The Standard Model of Particle Physics and its description of Nature have been recently challenged by a series of precision measurements performed via different accelerator machines. Statistically significant anomalies emerged in the heavy meson physics sector, when measuring the muon magnetic momentum, and very recently when deducing the mass of the W boson. Here we consider a radiative extension of the Standard Model devised to be sufficiently versatile to reconcile the various experimental results while further predicting the existence of new bosons and fermions with a mass spectrum in the TeV energy scale. The resulting spectrum is, therefore, within the energy reach of the proton-proton collisions at the LHC experiments at CERN. The model investigated here allows to interpolate between composite and elementary extensions of the Standard Model with emphasis on a new modified Yukawa sector that is needed to accommodate the anomalies. Focusing on the radiative regime of the model, we introduce interesting search channels of immediate impact for the ATLAS and CMS experimental programs such as the associate production of Standard Model particles with either invisible or long-lived particles. We further show how to adapt earlier SUSY-motivated searchers of new physics to constrain the spectrum and couplings of the new scalars and fermions. Overall, the new physics template simultaneously accounts for the bulk of the observed experimental anomalies while suggesting a wide spectrum of experimental signatures relevant for the current LHC experiments.

hep-ph↗

arXiv2023

Constraining scalar leptoquarks using COHERENT data

Neutrino-nucleus coherent scattering measurements by the COHERENT collaboration provide us with a unique capability to test various beyond the standard model scenarios. In this work, we constrain scalar leptoquarks (LQs) using the COHERENT data. LQs arise in many extensions of the Standard Model (SM). Generally, the mass of the LQs is assumed to be very high to avoid the bounds from proton decay. However, there are low-scale LQ models which prohibit proton decay by construction. We consider two electroweak doublet scalar LQ models with hypercharge Y=1/6, and Y=7/6 and provide the bounds in the plane of the Yukawa coupling and the mass of LQ. We also compare the bounds on LQs coming from various other experiments and find that the COHERENT one covers a wide range of LQ masses from MeV to TeV and in certain regions the constraints are competitive with the others.

hep-ph↗

arXiv2022

The TopFlavor scheme in the context of $W'$ searches at LHC

Many extensions of the Standard Model predict the existence of new charged or neutral gauge bosons, with a wide variety of phenomenological implications depending on the model adopted. The search for such particles is extensively carried through at the Large Hadron Collider (LHC), and it is therefore of crucial importance to have for each proposed scenario quantitative predictions that can be matched to experiments. In this work we focus on the implications of one of these models, the TopFlavor Model, proposing a charged $\text{W}^\prime$ boson that has preferential couplings to the third generation fermions. We compare such predictions to the ones from the so called Sequential Standard Model (SSM), that is used as benchmark, being one of the simplest and most commonly considered models for searches at the LHC. We identify the parameter space still open for searches at the LHC, and in particular we show that the cross section for the processes $pp \to \text{W}^\prime \to τν$ and $pp \to \text{W}^\prime \to tb$ can be up to two orders of magnitude smaller with respect to the SSM, depending on the free parameters of the model, like the particle mass and its width. This study makes the case for further searches at the LHC, and shows how a complete and systematic model independent analysis of $\text{W}^\prime$ boson phenomenology at colliders is essential to provide guidance for future searches.

hep-ph↗

arXiv2022

Towards baryogenesis via absorption from Primordial Black Holes

Recently Dolgov and Pozdnyakov proposed a new baryogenesis mechanism in which baryon asymmetry is produced without violating baryon number at the Lagrangian level. In this scenario, baryon asymmetry is generated by absorption of a new particle X carrying baryon number onto Primordial Black Holes (PBHs). Assuming CP-violation, the particle X is absorbed at a different rate than the antiparticle $\bar{X}$, producing an asymmetry in the baryonic number. We independently test this scenario, finding that it suffers from two fundamental issues.\\ At the phenomenological level, strong absorption by PBHs initially increases the baryon asymmetry. However, at later times such asymmetry is completely absorbed by PBHs. In order to overcome this issue, we account for PBH evaporation, which provides a natural way of halting the absorption while keeping a finite baryon asymmetry. We provide a systematic study of the parameter space, identifying the regions leading to the production of the baryon asymmetry without violating the known constraints on PBHs concentration. At the theoretical level, a model realizing the CP-violation postulated in this scenario is difficult to realize. We show, by implementing a minimal model, that the framework proposed in the original work in order to produce CP-violation, even if qualitatively correct, is quantitatively in disagreement with the observed baryon asymmetry, namely this mechanism produces only a fraction of the total baryon asymmetry.

hep-ph↗

arXiv2021

Unified thermal model for photohadronic neutrino production in astrophysical sources

High-energy astrophysical neutrino fluxes are, for many applications, modeled as simple power laws as a function of energy. While this is reasonable in the case of neutrino production in hadronuclear $pp$ sources, it typically does not capture the behavior in photohadronic $pγ$ sources: in that case, the neutrino spectrum depends on the properties of the target photons the cosmic rays collide with and on possible magnetic-field effects on the secondary pions and muons. We show that the neutrino production from known photohadronic sources can be reproduced by a thermal (black-body) target-photon spectrum if one suitably adjusts the temperature, thanks to multi-pion production processes. This allows discussing neutrino production from most known $pγ$ sources, such as gamma-ray bursts, active galactic nuclei and tidal disruption events, in terms of a few parameters. We apply this thermal model to study the sensitivity of different classes of neutrino telescopes to photohadronic sources: we classify the model parameter space according to which experiment is most suitable for detection of a specific source class and demonstrate that different experiment classes, such as dense arrays, conventional neutrino telescopes, or radio-detection experiments, cover different parts of the parameter space. Since the model can also reproduce the flavor and neutrino-antineutrino composition, we study the impact on the track-to-shower ratio and the Glashow resonance.

astro-ph.HE↗

arXiv2021

Sensitivity of KM3NeT to Violation of Equivalence Principle

The symmetry of the theory of relativity under diffeomorphisms strongly depends on the equivalence principle. Violation of Equivalence Principle (VEP) can be tested by looking for deviations from the standard framework of neutrino oscillations. In recent works, it has been shown that strong constraints on the VEP parameter space can be placed by means of the atmospheric neutrinos observed by the IceCube neutrino telescope. In this paper, we focus on the KM3NeT neutrino telescope and perform a forecast analysis to assess its capacity to probe VEP. Most importantly, we examine the crucial role played by systematic uncertainties affecting the neutrino observations. We find that KM3NeT will constrain VEP parameters times the local gravitational potential at the level of $10^{-27}$. Due to the systematic-dominated regime, independent analyses from different neutrino telescopes are fundamental for robustly testing the equivalence principle.

hep-ph↗

arXiv2021

Primordial Black Hole Dark Matter evaporating on the Neutrino Floor

Primordial black holes (PBHs) hypothetically generated in the first instants of life of the Universe are potential dark matter (DM) candidates. Focusing on PBHs masses in the range $[5 \times10^{14} - 5 \times 10^{15}]$g, we point out that the neutrinos emitted by PBHs evaporation can interact through the coherent elastic neutrino nucleus scattering (CE$ν$NS) producing an observable signal in multi-ton DM direct detection experiments. We show that with the high exposures envisaged for the next-generation facilities, it will be possible to set bounds on the fraction of DM composed by PBHs improving the existing neutrino limits obtained with Super-Kamiokande. We also quantify to what extent a signal originating from a small fraction of DM in the form of PBHs would modify the so-called "neutrino floor", the well-known barrier towards detection of weakly interacting massive particles (WIMPs) as the dominant DM component.

hep-ph↗

arXiv2021

IceCube constraints on Violation of Equivalence Principle

Among the information provided by high energy neutrinos, a promising possibility is to analyze the effects of a Violation of Equivalence Principle (VEP) on neutrino oscillations. We analyze the recently released IceCube data on atmospheric neutrino fluxes under the assumption of a VEP and obtain updated constraints on the parameter space with the benchmark choice that neutrinos with different masses couple with different strengths to the gravitational field. In this case we find that the VEP parameters times the local gravitational potential at Earth can be constrained at the level of $10^{-27}$. We show that the constraints from atmospheric neutrinos strongly depend on the assumption that the neutrino eigenstates interacting diagonally with the gravitational field coincide with the mass eigenstates, which is not \textit{a priori} justified: this is particularly clear in the case that the basis of diagonal gravitational interaction coincide with the flavor basis, which cannot be constrained by the observation of atmospheric neutrinos. Finally, we quantitatively study the effect of a VEP on the flavor composition of the astrophysical neutrinos, stressing again the interplay with the basis in which the VEP is diagonal: we find that for some choices of such basis the flavor ratio measured by IceCube can significantly change.

hep-ph↗

arXiv2020

Observable features in (ultra)high energy neutrinos due to active-sterile secret interactions

We consider the effects of active-sterile secret neutrino interactions, mediated by a new pseudoscalar particle, on high- and ultra high-energy neutrino fluxes. In particular, we focus on the case of 3 active and 1 sterile neutrino coupled by a flavor dependent interaction, extending the case of 1 active and 1 sterile neutrino we have recently examined. We find that, depending on the kind of interaction of sterile neutrino with the active sector, new regions of the parameter space for secret interactions are now allowed leading to interesting phenomenological implications on two benchmark fluxes we consider, namely an astrophysical power law flux, in the range below 100 PeV, and a cosmogenic flux, in the Ultrahigh energy range. First of all, the final active fluxes can present a measurable depletion observable in future experiments. Especially, in the case of only tau neutrino interacting, we find that the effects on the astrophysical power law flux can be so large to be already probed by the IceCube experiment. Moreover, we find intriguing features in the energy dependence of the flavor ratio.

hep-ph↗

arXiv2020

Cosmogenic neutrino fluxes under the effect of active-sterile secret interactions

Ultra High Energy cosmogenic neutrinos may represent a unique opportunity to unveil possible new physics interactions once restricted to the neutrino sector only. In the present paper we study the observable effects of a secret active-sterile interactions, mediated by a pseudoscalar, on the expected flux of cosmogenic neutrinos. The results show that for masses of sterile neutrinos and pseudoscalars of hundreds MeV, necessary to evade cosmological, astrophysical and elementary particle constraints, the presence of such new interactions can significantly change the energy spectrum of cosmogenic neutrinos at Earth in the energy range from PeV to ZeV. Interestingly, the distortion of the spectrum results to be detectable at GRAND apparatus if the scalar mediator mass is around 250 MeV and the UHECRs are dominated by the proton component. Larger mediator masses or a chemical composition of UHECRs dominated by heavier nuclei would require much larger cosmic rays apparatus which might be available in future.

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