arXiv subjects

Alessio Giarnetti

Publications and source records attributed to Alessio Giarnetti.

12 recordsLinked to original sources

arXiv2026

Constraining the Neutrino Mixing Matrix via Single-Sector Charged-Lepton Rotations in the JUNO Precision Era

The unprecedented precision now being achieved in the measurement of the Pontecorvo--Maki--Nakagawa--Sakata (PMNS) lepton mixing matrix opens a new window onto the underlying structure of the neutrino mass matrix and the possibly associated flavor symmetries. In this work, we investigate the constraints imposed on the unitary matrix $U_\nu$ that diagonalises the neutrino mass matrix, under the hypothesis that the charged-lepton mixing matrix $U_l$ consists of a single two-by-two rotation in one of the three sectors: (1,2), (1,3), or (2,3). For this analysis, we considered the latest global fit which incorporates the precision measurement of $\theta_{12}$ from the JUNO experiment. For each scenario, we also derive analytical expressions for the entries of $U_\nu$ in terms of the measured PMNS parameters to obtain compact sum-rule-like formulae.

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arXiv2024

Solar Neutrinos and the Strongest Oscillation Constraints on Scalar NSI

Scalar non-standard neutrino interactions (sNSI) is a scenario where neutrinos can develop a medium dependent contribution to their mass due to a new scalar mediator. This scenario differs from the commonly discussed vector mediator case in that the oscillation effect scales with density rather than density and neutrino energy. Thus the strongest oscillation constraint comes from solar neutrinos which experience the largest density in a neutrino oscillation experiment. We derive constraints on all the sNSI parameters as well as the absolute neutrino mass scale by combining solar and reactor data and find solar neutrinos to be $>1$ order of magnitude more sensitive to sNSI than terrestrial probes such as long-baseline experiments.

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arXiv2024

Exploring new physics with DUNE high energy flux: the case of Lorentz Invariance Violation, Large Extra Dimensions and Long Range Forces

DUNE is a next-generation long-baseline neutrino oscillation experiment. It is expected to measure with an unprecedent precision the atmospheric oscillation parameters, including the CP-violating phase $\delta_{CP}$. Moreover, several studies have suggested that its unique features should allow DUNE to probe several new physics scenarios. In this work, we explore the performances of the DUNE far detector in constraining new physics if a high-energy neutrino flux is employed (HE-DUNE). We take into account three different scenarios: Lorentz Invariance Violation (LIV), Long Range Forces (LRF) and Large Extra Dimensions (LED). Our results show that HE-DUNE should be able to set bounds competitive to the current ones and, in particular, it can outperform the standard DUNE capabilities in constraining CPT-even LIV parameters and the compactification radius $R_{ED}$ of the LED model.

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arXiv2024

On quark-lepton mixing and the leptonic CP violation

In the absence of a Grand Unified Theory framework, connecting the values of the mixing parameters in the quark and lepton sector is a difficult task, unless one introduces ad-hoc relations among the matrices that diagonalize such different kinds of fermions. In this paper, we discuss in detail the possibility that the PMNS matrix is given by the product U_{PMNS}=V^\ast_{CKM} T^\ast where T comes from the diagonalization of a see-saw like mass matrix that can be of a Bimaximal (BM), Tri-Bimaximal (TBM) and Golden Ratio (GR) form, and identify the leading corrections to such patterns that allow a good fit to the leptonic mixing matrix as well as to the CP phase. We also show that the modified versions of BM, TBM and GR can easily accommodate the solar and atmospheric mass differences

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arXiv2024

Neutrino masses from new Weinberg-like operators: Phenomenology of TeV scalar multiplets

The unique dimension-$5$ effective operator, $LLHH$, known as the Weinberg operator, generates tiny Majorana masses for neutrinos after electroweak spontaneous symmetry breaking. If there are new scalar multiplets that take vacuum expectation values (VEVs), they should not be far from the electroweak scale. Consequently, they may generate new dimension-$5$ Weinberg-like operators which in turn also contribute to Majorana neutrino masses. In this study, we consider scenarios with one or two new scalars up to quintuplet SU(2) representations. We analyse the scalar potentials, studying whether the new VEVs can be induced and therefore are naturally suppressed, as well as the potential existence of pseudo-Nambu-Goldstone bosons. Additionally, we also obtain general limits on the new scalar multiplets from direct searches at colliders, loop corrections to electroweak precision tests and the $W$-boson mass.

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arXiv2023

Neutrino masses from new seesaw models: Low-scale variants and phenomenological implications

With just the Standard Model Higgs doublet, there are only three types of seesaw models that generate light Majorana neutrino masses at tree level after electroweak spontaneous symmetry breaking. However, if there exist additional TeV scalars acquiring vacuum expectation values, coupled with heavier fermionic multiplets, several new seesaw models become possible. These new seesaws are the primary focus of this study and correspond to the tree-level ultraviolet completions of the effective operators studied in a companion publication. We are interested in the genuine cases, in which the standard seesaw contributions are absent. In addition to the tree-level generation of neutrino masses, we also consider the one-loop contributions. Furthermore, we construct low-energy versions that exhibit a very rich phenomenology. Specifically, we scrutinise the generation of dimension-6 operators and explore their implications, including non-unitarity of the leptonic mixing matrix, non-universal $Z-$boson interactions, and lepton flavor violation. Finally, we provide (Generalised) Scotogenic-like variants that incorporate viable dark matter candidates.

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arXiv2023

Enhancing Sensitivity to Leptonic CP Violation using Complementarity among DUNE, T2HK, and T2HKK

After the landmark discovery of non-zero $θ_{13}$ by the modern reactor experiments, unprecedented precision on neutrino mass-mixing parameters has been achieved over the past decade. This has set the stage for the discovery of leptonic CP violation (LCPV) at high confidence level in the next-generation long-baseline neutrino oscillation experiments. In this work, we explore in detail the possible complementarity among the on-axis DUNE and off-axis T2HK experiments to enhance the sensitivity to LCPV suppressing the $θ_{23}-δ_{\mathrm{CP}}$ degeneracy. We find that none of these experiments individually can achieve the milestone of 3$σ$ LCPV for at least 75% choices of $δ_{\mathrm{CP}}$ in its entire range of $[-180^{\circ} , 180^{\circ}]$, with their nominal exposures and systematic uncertainties. However, their combination can attain the same for all values of $θ_{23}$ with only half of their nominal exposures. We observe that the proposed T2HKK setup in combination with DUNE can further increase the CP coverage to more than 80% with only half of their nominal exposures. We study in detail how the coverage in $δ_{\mathrm{CP}}$ for $\ge$ 3$σ$ LCPV depends on the choice of $θ_{23}$, exposure, optimal runtime in neutrino and antineutrino modes, and systematic uncertainties in these experiments in isolation and combination. We find that with an improved systematic uncertainty of 2.7% in appearance mode, the standalone T2HK setup can provide a CP coverage of around 75% for all values of $θ_{23}$. We also discuss the pivotal role of intrinsic, extrinsic, and total CP asymmetries in the appearance channel and extrinsic CP asymmetries in the disappearance channel while analyzing our results.

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arXiv2023

How to Identify Different New Neutrino Oscillation Physics Scenarios at DUNE

Next generation neutrino oscillation experiments are expected to measure the remaining oscillation parameters with very good precision. They will have unprecedented capabilities to search for new physics that modify oscillations. DUNE, with its broad band beam, good particle identification, and relatively high energies will provide an excellent environment to search for new physics. If deviations from the standard three-flavor oscillation picture are seen however, it is crucial to know which new physics scenario is found so that it can be verified elsewhere and theoretically understood. We investigate several benchmark new physics scenarios by looking at existing long-baseline accelerator neutrino data from NOvA and T2K and determine at what sensitivity DUNE can differentiate among them. We consider sterile neutrinos and both vector and scalar non-standard neutrino interactions, all with new complex phases, the latter of which could conceivably provide absolute neutrino mass scale information. We find that, in many interesting cases, DUNE will have good model discrimination. We also perform a new fit to NOvA and T2K data with scalar NSI.

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arXiv2022

Model-Independent Constraints on Non-Unitary Neutrino Mixing from High-Precision Long-Baseline Experiments

Our knowledge on the active 3$ν$ mixing angles ($θ_{12}$, $θ_{13}$, and $θ_{23}$) and the CP phase $δ_{\mathrm{CP}}$ is becoming accurate day-by-day enabling us to test the unitarity of the leptonic mixing matrix with utmost precision. Future high-precision long-baseline experiments are going to play an important role in this direction. In this work, we study the impact of possible non-unitary neutrino mixing (NUNM) in the context of next-generation long-baseline experiments DUNE and T2HKK/JD+KD having one detector in Japan (T2HK/JD) and a second detector in Korea (KD). We estimate the sensitivities of these setups to place direct, model-independent, and competitive constraints on various NUNM parameters. We demonstrate the possible correlations between the NUNM parameters, $θ_{23}$, and $δ_{\mathrm{CP}}$. Our numerical results obtained using only far detector data and supported by simple approximate analytical expressions of the oscillation probabilities in matter, reveal that JD+KD has better sensitivities for $|α_{21}|$ and $α_{22}$ as compared to DUNE, due to its larger statistics in the appearance channel and less systematic uncertainties in the disappearance channel, respectively. For $|α_{31}|$, $|α_{32}|$, and $α_{33}$, DUNE gives better constraints as compared to JD+KD, due to its larger matter effect and wider neutrino energy spectrum. For $α_{11}$, both DUNE and JD+KD give similar bounds. We also show how much the bounds on the NUNM parameters can be improved by combining the prospective data from DUNE and JD+KD setups. We find that due to zero-distance effects, the near detectors alone can also constrain $α_{11}$, $|α_{21}|$, and $α_{22}$ in both these setups. Finally, we observe that the $ν_τ$ appearance sample in DUNE can improve the constraints on $|α_{32}|$ and $α_{33}$.

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arXiv2021

Probing Source and Detector NSI parameters at the DUNE Near Detector

We investigate the capability of the DUNE Near Detector (ND) to constrain Non Standard Interaction parameters (NSI) describing the production of neutrinos ($\varepsilon_{αβ}^s$) and their detection ($\varepsilon_{αβ}^d$). We show that the DUNE ND is able to reject a large portion of the parameter space allowed by DUNE Far Detector analyses and to set the most stringent bounds from accelerator neutrino experiments on $|\varepsilon_{μe}^{s,d}|$ for wide intervals of the related phases. We also provide simple analytic understanding of our results as well as a numerical study of their dependence on the systematic errors, showing that the DUNE ND offers a clean environment where to study source and detector NSI.

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arXiv2021

Neutrino Invisible Decay at DUNE: a multi-channel analysis

The hypothesis of the decay of neutrino mass eigenstates leads to a substantial modification of the appearance and disappearance probabilities of flavor eigenstates. We investigate the impact on the standard oscillation scenario caused by the decay of the heaviest mass eigenstate $ν_3$ (with a mass $m_3$ and a mean life $τ_3$) to a sterile state in DUNE. We find that the lower bound of $5.1 \times 10^{-11}~s/eV$ at 90\% CL on the decay parameter $τ_3/m_3$ can be set if the Neutral Current data are included in the analysis, thus providing the best long-baseline expected limit so far. We also show that the $ν_τ$ appearance channel would give only a negligible contribution to the decay parameter constraints. Our numerical results are corroborated by analytical formulae for the appearance and disappearance probabilities in vacuum (which is a useful approximation for the study of the invisible decay model) that we have developed up to the second order in the solar mass splitting and to all orders in the decay factor $t/τ_3$.

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arXiv2019

On the Role of the $ν_τ$ Appearance in DUNE in Constraining Standard Neutrino Physics and Beyond

We consider the $ν_μ\to ν_τ$ appearance channel in the future Deep Underground Neutrino Experiment (DUNE) which offers a good statistics of the $ν_τ$ sample. In order to measure its impact on constraining the oscillation parameters, we consider several assumptions on the efficiency for $ν_τ$ charged-current signal events (with subsequent $τ\to e$ decay) and the related backgrounds and study the effects of various systematic uncertainties. Two different neutrino fluxes have been considered, namely a CP-violation optimized flux and a $ν_τ$ optimized flux. Our results show that the addition of the $ν_μ\to ν_τ$ appearance channel does not reduce the current uncertainties on the standard 3-$ν$ oscillation parameters while it can improve in a significant way the sensitivity to the Non-Standard Interaction parameter $|ε_{μτ}|$ and to the new mixing angle $θ_{34}$ of a sterile neutrino model of the $3+1$ type.

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