arXiv subjects

Davide Meloni

Publications and source records attributed to Davide Meloni.

At least 37 records · Page 2Linked to original sources

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.

hep-ph↗

arXiv2019

Lepton Flavor Violation and Neutrino Masses from $A_5$ and CP in the Non-Universal MSSM

We analyze the phenomenological consequences of embedding a flavor symmetry based on the groups $A_5$ and CP in a supersymmetric framework. We concentrate on the leptonic sector, where two different residual symmetries are assumed to be conserved at LO for charged and neutral leptons. All possible realizations to generate neutrino masses at tree level are investigated. Sizable flavor violating effects in the charged lepton sector are unavoidable due to the non-universality of soft-breaking terms determined by the symmetry. We derive testable predictions for the neutrino spectrum, lepton mixing and flavor changing processes with non-trivial relations among observables.

hep-ph↗

arXiv2019

Exploring New Physics from nu_tau events in OPERA

We analyze in details the impact of the $10$ $ν_τ$ events seen in the OPERA experiment in constraining the Non Standard Interaction parameter $\varepsilon_{μτ}$ affecting neutrino propagation in matter and the allowed parameter space of models with one sterile neutrino of the $3+1$ type.

hep-ph↗

arXiv2019

Research and Development for Near Detector Systems Towards Long Term Evolution of Ultra-precise Long-baseline Neutrino Experiments

With the discovery of non-zero value of $θ_{13}$ mixing angle, the next generation of long-baseline neutrino (LBN) experiments offers the possibility of obtaining statistically significant samples of muon and electron neutrinos and anti-neutrinos with large oscillation effects. In this document we intend to highlight the importance of Near Detector facilities in LBN experiments to both constrain the systematic uncertainties affecting oscillation analyses but also to perform, thanks to their close location, measurements of broad benefit for LBN physics goals. A strong European contribution to these efforts is possible.

physics.ins-det↗

arXiv2018

Neutrino masses and lepton mixing from $A_5\times{\rm CP}$

We analyse in detail the phenomenological implications for lepton masses and mixing derived by the breaking of the discrete symmetries $A_5 \times CP$ into the subgroups $Z_2 \times CP$ in the neutrino sector and $Z_5$ in the charged lepton sector. We derive accurate analytic expressions for the sum of the neutrino masses $Σ_i m_i$ as well as for the effective Majorana masses $m_β$ and $m_{ββ}$ under different hypotheses for the flavon vevs and compare them with the exact numerical results obtained from the diagonalization of the neutrino mass matrix.

hep-ph↗

arXiv2018

On the systematic uncertainties in DUNE and their role in New Physics studies

In the recent years experiments have established the existence of neutrino oscillations and most of the oscillation parameters have been measured with a good accuracy. The search for New Physics in neutrino oscillation will be an experimental concrete possibility in the next future. In this paper we investigate the ability of the DUNE facility to search for Non Standard Interaction (NSI) in neutrino propagation in matter, emphasizing the role of different assumptions on the shape and absolute normalization errors of both $ν_e$ and $ν_μ$ signals. We also study in detail the effects of NSI and systematics in the extraction of standard oscillation parameters.

hep-ph↗

arXiv2018

Radiative corrections of heavy scalar decays to gauge bosons in the singlet extension of the Standard Model

Assuming the existence of a new real scalar singlet $s^0$ coupled to the Standard Model via a scalar quartic portal interaction, we compute the radiative corrections to the decay rates of the heavy scalar mass eigenstate to a couple of gauge bosons $ZZ$ and $W^+W^-(γ)$, showing that they can give a contribution as large as ${\cal{O}}$(5\%) and ${\cal{O}}$(7\%), respectively. We also explicitly analyze in detail their dependence on the heavy mass $m_S$ and on the scalar mixing angle $α$, finding that, especially in the large-mass region, these depend on the sign of $\sinα$.

hep-ph↗

arXiv2018

Resonant production of dark photons in positron beam dump experiments

Positrons beam dump experiments have unique features to search for very narrow resonances coupled superweakly to $e^+ e^-$ pairs. Due to the continue loss of energy from soft photon bremsstrahlung, in the first few radiation lengths of the dump a positron beam can continuously scan for resonant production of new resonances via $e^+$ annihilation off an atomic $e^-$ in the target. In the case of a dark photon $A'$ kinetically mixed with the photon, this production mode is of first order in the electromagnetic coupling $α$, and thus parametrically enhanced with respect to the $O(α^2)$ $e^+e^- \to γA'$ production mode and to the $O(α^3)$ $A'$ bremsstrahlung in $e^--$nucleon scattering so far considered. If the lifetime is sufficiently long to allow the $A'$ to exit the dump, $A' \to e^+e^-$ decays could be easily detected and distinguished from backgrounds. We explore the foreseeable sensitivity of the Frascati PADME experiment in searching with this technique for the $17\,$MeV dark photon invoked to explain the $^8$Be anomaly in nuclear transitions.

hep-ph↗

arXiv2017

GUT and flavor models for neutrino masses and mixing

In the recent years neutrino experiments have studied in detail the phenomenon of neutrino oscillations and most of the oscillation parameters have been measured with a good accuracy. However, in spite of many interesting ideas, the problem of flavor in the lepton sector remains an open issue. In this review, we discuss the state of the art of models for neutrino masses and mixings formulated in the context of flavor symmetries, with particular emphasis on the role played by grand unified gauge groups.

hep-ph↗

arXiv2017

Neutrino-nucleus interactions and the determination of oscillation parameters

We review the status and prospects of theoretical studies of neutrino-nucleus interactions, and discuss the influence of the treatment of nuclear effects on the determination of oscillation parameters. The models developed to describe the variety of reaction mechanisms contributing to the nuclear cross sections are analysed, with emphasis placed on their capability to reproduce the available electron scattering data.The impact of the uncertainties associated with the description of nuclear dynamics on the the oscillation parameters is illustrated through examples, and possible avenues towards a better understanding of the signals detected by long baseline experiments are outlined.

nucl-th↗

arXiv2017

Probability Densities of the effective neutrino masses $m_{β}$ and $m_{ββ}$

We compute the probability densities of the effective neutrino masses $m_{β}$ and $m_{ββ}$ using the Kernel Density Estimate (KDE) approach applied to a distribution of points in the $(m_{\min}, m_{ββ})$ and $(m_{β}, m_{ββ})$ planes, obtained using the available Probability Distribution Functions (PDFs) of the neutrino mixing and mass differences, with the additional constraints coming from cosmological data on the sum of the neutrino masses. We show that the reconstructed probability densities strongly depend on the assumed set of cosmological data: for $\sum_j m_j \leq 0.68\ @\ 95\% \ \mathrm{CL}$ a sensitive portion of the allowed values are already excluded by null results of experiments searching for $m_{ββ}$ and $m_{β}$, whereas in the case $\sum_j m_j \leq 0.23\ @\ 95\% \ \mathrm{CL}$ the bulk of the probability densities are below the current bounds.

hep-ph↗

arXiv2017

Renormalization Group Running of Fermion Observables in an Extended Non-Supersymmetric SO(10) Model

We investigate the renormalization group evolution of fermion masses, mixings and quartic scalar Higgs self-couplings in an ${\it extended}$ non-supersymmetric SO(10) model, where the Higgs sector contains the ${\bf 10}_{\rm H}$, ${\bf 120}_{\rm H}$, and ${\bf 126}_{\rm H}$ representations. The group SO(10) is spontaneously broken at the GUT scale to the Pati-Salam group and subsequently to the Standard Model (SM) at an intermediate scale $M_{\rm I}$. We explicitly take into account the effects of the change of gauge groups in the evolution. In particular, we derive the renormalization group equations for the different Yukawa couplings. We find that the computed physical fermion observables can be successfully matched to the experimental measured values at the electroweak scale. Using the same Yukawa couplings at the GUT scale, the measured values of the fermion observables cannot be reproduced with a SM-like evolution, leading to differences in the numerical values up to around 80 %. Furthermore, a similar evolution can be performed for a ${\it minimal}$ SO(10) model, where the Higgs sector consists of the ${\bf 10}_{\rm H}$ and ${\bf 126}_{\rm H}$ representations only, showing an equally good potential to describe the low-energy fermion observables. Finally, for both the extended and the minimal SO(10) models, we present predictions for the three Dirac and Majorana CP-violating phases as well as three effective neutrino mass parameters.

hep-ph↗

arXiv2017

Inelastic Neutrino-Nucleus Interactions within the Spectral Function Formalism

We report the results of a study of neutrino-carbon interactions at beam energies ranging between few hundreds MeV and few tens of GeV, carried out within the framework of the impulse approximation using a realistic spectral function. The contributions of quasi elastic scattering, resonance production and deep inelastic scattering---consistently obtained, for first time, from a model based on a realistic description of the nuclear ground state---are compared and analyzed.

nucl-th↗

arXiv2016

Phenomenology of SU(5) low-energy realizations: the diphoton excess and Higgs flavor violation

We discuss different $\rm SU(5)$ low-energy realizations and illustrate their use with the diphoton excess and Higgs flavor violation, which require new physics at the TeV scale. In particular, we study two scenarios for a $750$ GeV resonance: in the first one the resonance belongs to the adjoint of $\rm SU(5)$, being either an $\rm SU(2)_L$ singlet or a triplet, while in the second case the signal is due to the CP-even and CP-odd states of a new $\rm SU(2)_L$ Higgs doublet belonging to a ${\bf 45}_H$ or a ${\bf 70}_H$ representations, giving rise to a two-Higgs doublet model at low energies. We study the fine-tuning needed for the desired members of the multiplets to be light enough, while having the rest at the GUT scale. In these scenarios, the production and decay into photons of the new resonance are mediated by the leptoquarks (LQ) present in these large $\rm SU(5)$ representations. We analyse the phenomenology of such scenarios, focusing on the most relevant predictions that can help to disentangle the different models, like decays into gauge bosons, Standard Model (SM) fermions and LQs pair production. In the case of the ${\bf 45}_H$ (the Georgi-Jarlskog model), we also study the possibility to have Higgs flavor violation. We find that $B_s$ mixing limits (in addition to $τ\rightarrow μγ$) always imply that $\rm{BR}(h\rightarrow τμ,\,bs)\lesssim 10^{-5}$.

hep-ph↗

arXiv2016

Recent developments in Neutrino Physics

We discuss the recent progress in neutrino physics in the following fields: (i) interpretation of the short and long neutrino oscillation data in terms of neutrino flavor transitions; (ii) models for neutrino masses and mixings.

hep-ph↗

arXiv2015

Comparison of the calorimetric and kinematic methods of neutrino energy reconstruction in disappearance experiments

To be able to achieve their physics goals, future neutrino-oscillation experiments will need to reconstruct the neutrino energy with very high accuracy. In this work, we analyze how the energy reconstruction may be affected by realistic detection capabilities, such as energy resolutions, efficiencies, and thresholds. This allows us to estimate how well the detector performance needs to be determined a priori in order to avoid a sizable bias in the measurement of the relevant oscillation parameters. We compare the kinematic and calorimetric methods of energy reconstruction in the context of two muon-neutrino disappearance experiments operating in different energy regimes. For the calorimetric reconstruction method, we find that the detector performance has to be estimated with a ~10% accuracy to avoid a significant bias in the extracted oscillation parameters. On the other hand, in the case of kinematic energy reconstruction, we observe that the results exhibit less sensitivity to an overestimation of the detector capabilities.

hep-ph↗

arXiv2015

Effects of intermediate scales on renormalization group running of fermion observables in an SO(10) model

In the context of non-supersymmetric SO(10) models, we analyze the renormalization group equations for the fermions (including neutrinos) from the GUT energy scale down to the electroweak energy scale, explicitly taking into account the effects of an intermediate energy scale induced by a Pati--Salam gauge group. To determine the renormalization group running, we use a numerical minimization procedure based on a nested sampling algorithm that randomly generates the values of 19 model parameters at the GUT scale, evolves them, and finally constructs the values of the physical observables and compares them to the existing experimental data at the electroweak scale. We show that the evolved fermion masses and mixings present sizable deviations from the values obtained without including the effects of the intermediate scale.

hep-ph↗

arXiv2015

Lepton mixing from the interplay of the alternating group A5 and CP

Assuming three generations of Majorana neutrinos, we study the different mixing patterns that arise from the non-trivial breaking of the flavor group A5 and CP to the residual symmetries Z3, Z5 or Z2 x Z2 in the charged lepton and to Z2 x CP in the neutrino sector. All patterns contain only one free parameter theta and thus mixing angles as well as the Dirac and the two Majorana phases are strongly correlated. We perform an analytical and a numerical study of all possible mixing patterns. It turns out that only four patterns can describe the experimentally measured values of the mixing angles for a particular choice of theta well. All of them predict trivial Majorana phases, while the Dirac phase delta is maximal for two patterns and trivial for the two remaining ones. If delta is maximal, also the atmospheric mixing angle is fixed to be maximal.

hep-ph↗