arXiv subjects

S. Pascoli

Publications and source records attributed to S. Pascoli.

48 records · Page 3Linked to original sources

arXiv2003

Neutrino Masses, Mixing and Neutrinoless Double-Beta Decay

The predictions for the effective Majorana mass | | in neutrinoless double-beta decay in the case of 3-neutrino mixing and massive Majorana neutrinos are reviewed. The physics potential of the experiments, searching for neutrinoless double-beta decay and having sensitivity to $| | \gtap 0.01$ eV, for providing information on the type of the neutrino mass spectrum, on the absolute scale of neutrino masses and on the Majorana CP-violation phases in the PMNS neutrino mixing matrix is also discussed.

hep-ph↗

arXiv2003

On the Connection of Leptogenesis with Low Energy CP Violation and LFV Charged Lepton Decays

Assuming only a hierarchical structure of the heavy Majorana neutrino masses and of the neutrino Dirac mass matrix m_D of the see-saw mechanism, we find that in order to produce the observed baryon asymmetry of the Universe via leptogenesis, the scale of m_D should be given by the up-quark masses. Lepton flavor violating decays μ\to e + γ, τ\to μ+ γand τ\to e + γare considered and a characteristic relation between their decay rates is predicted. The effective Majorana mass in neutrinoless double beta decay depends on the CP violating phase controlling the leptogenesis if one of the heavy Majorana neutrinos is much heavier than the other two. Successful leptogenesis requires a rather mild mass hierarchy between the latter. The compatibility of this hierarchical see-saw model with the low energy neutrino mixing phenomenology requires that the mixing angle limited by the CHOOZ and Palo Verde experiments should be relatively large, \sin^2θ_3 \gtap 0.01. The CP violation effects in neutrino oscillations can be observable. In general, there is no direct connection between the latter and the CP violation in leptogenesis. If the CP violating phases of the see-saw model satisfy certain relations, the baryon asymmetry of the Universe and the rephasing invariant J_{CP} which determines the magnitude of the CP violation effects in neutrino oscillations, depend on the same CP violating phase and their signs are correlated.

hep-ph↗

arXiv2003

Quasi-Degenerate Neutrino Mass Spectrum, μ-> e + γDecay and Leptogenesis

In a large class of SUSY GUT models with see-saw mechanism of neutrino mass generation, lepton flavor violating (LFV) decays $μ\to e + γ$, $τ\to μ+ γ$, etc., are predicted with rates that are within the reach of present and planned experiments. A crucial element in these predictions is the matrix of neutrino Yukawa couplings $\ynu$ which can be expressed in terms of the light and RH heavy neutrino masses, the neutrino mixing PMNS matrix $U$, and an orthogonal matrix $\mathbf{R}$. Leptogenesis can take place only if $\mathbf{R}$ is complex. Considering the case of quasi-degenerate neutrinos and assuming that $\mathbf{R}$ is complex, we derive simple analytical expressions for the $μ\to e + γ$, $τ\to μ+ γ$ and $τ\to e + γ$ decay rates. Taking into account the leptogenesis constraints on the relevant parameters we show that the predicted rates of the LFV decays $μ\to e + γ$, and $τ\to e + γ$ are generically enhanced by a factor of $\sim 10^{3}$ to $\sim 10^{6}$ with respect to the rates calculated for real $\mathbf{R}$, while the $τ\to μ+ γ$ decay rate is enhanced approximately by two orders of magnitude.

hep-ph↗

arXiv2002

On the Neutrino Mass Spectrum and Neutrinoless Double-Beta Decay

Assuming 3-nu mixing, neutrino oscillation explanation of the solar and atmospheric neutrino data and of the first KamLAND results, massive Majorana neutrinos and neutrinoless double-beta decay generated only by the (V-A) charged current weak interaction via the exchange of the three Majorana neutrinos, we analyze in detail the possibility of determining the type of the neutrino mass spectrum by measuring of the effective Majorana mass | | in neutrinoless double-beta decay. The three possible types of neutrino mass spectrum are considered: i) normal hierarchical (NH), m1 << m2 << m3, ii) inverted hierarchical (IH), m1 << m2 \simeq m3, and iii) quasi-degenerate (QD), m1 \simeq m2 \simeq m3 \geq 0.20 eV. The uncertainty in the measured value of | | due to the imprecise knowledge of the relevant nuclear matrix elements is taken into account in the analysis. We derive the ranges of values of tan^2 theta_\odot, theta_\odot being the mixing angle which controls the solar neutrino oscillations, and of the nuclear matrix element uncertainty factor, for which the measurement of | | would allow one to discriminate between the NH and IH, NH and QD and IH and QD spectra.

hep-ph↗

arXiv2002

On the CP Violation Associated with Majorana Neutrinos and Neutrinoless Double-Beta Decay

Assuming 3-neutrino mixing and massive Majorana neutrinos, we analyze the possibility of establishing the existence of CP-violation associated with Majorana neutrinos in the lepton sector i) by measuring of the effective Majorana mass | | in neutrinoless double beta-decay with a sufficient precision and ii) by measuring of, or obtaining a stringent upper limit on, the lightest neutrino mass m1. Information on m1 can be obtained in the tritium beta decay experiment KATRIN and from astrophysical and cosmological observations. Proving that the indicated CP-violation takes place requires, in particular, a relative experimental error on the measured value of | | not bigger than 20 %, a ``theoretical uncertainty'' in the value of | | due to an imprecise knowledge of the corresponding nuclear matrix elements smaller than a factor of 2, a value of tan^2 theta_(solar) larger than 0.55, and values of the relevant Majorana CP-violating phases typically within the intervals of (Pi/2 - 3 Pi/4) and (5Pi/4 - 3Pi/2).

hep-ph↗

arXiv2002

The SNO Solar Neutrino Data, Neutrinoless Double Beta-Decay and Neutrino Mass Spectrum

Assuming 3 neutrino mixing and massive Majorana neutrinos, we analyze the implications of the results of the solar neutrino experiments, including the latest SNO data, which favor the LMA MSW solution of the solar neutrino problem with \tan^2 θ_sol < 1, for the predictions of the effective Majorana mass | | in neutrinoless double beta decay. For \cos (2 θ_sol) \geq 0.26, which follows from the analysis of the new solar neutrino data, we find significant lower limits on | | in the cases of quasi-degenerate and inverted hierarchy neutrino mass spectrum, | | \geq 0.035 eV and | | \geq 8.5 10^-3 eV, respectively. If the spectrum is hierarchical the upper limit holds | | \leq 8.2 10^-3 eV. Correspondingly, not only a measured value of | | \neq 0, but even an experimental upper limit on | | of the order of few 10^-2 eV can provide information on the type of the neutrino mass spectrum; it can provide also a significant upper limit on the mass of the lightest neutrino m1. A measured value of | | \geq 0.2 eV, combined with data on neutrino masses from the tritium beta-decay experiment KATRIN might allow to establish whether the CP-symmetry is violated in the lepton sector.

hep-ph↗

arXiv2002

Dynamics of tachyonic preheating after hybrid inflation

We study the instability of a scalar field at the end of hybrid inflation, using both analytical techniques and numerical simulations. We improve previous studies by taking the inflaton field fully into account, and show that the range of unstable modes depends sensitively on the velocity of the inflaton field, and thereby on the Hubble rate, at the end of inflation. If topological defects are formed, their number density is determined by the shortest unstable wavelength. Finally, we show that the oscillations of the inflaton field amplify the inhomogeneities in the energy density, leading to local symmetry restoration and faster thermalization. We believe this explains why tachyonic preheating is so effective in transferring energy away from the inflaton zero mode.

hep-ph↗

arXiv2002

Majorana Neutrinos, CP-Violation, Neutrinoless Double-Beta and Tritium-Beta Decays

If the present or upcoming searches for neutrinoless double beta decay give a positive result, the Majorana nature of massive neutrinos will be established. From the determination of the value of the effective Majorana mass parameter | |, it would be possible to obtain information on the type of neutrino mass spectrum. Assuming 3-neutrino mixing and massive Majorana neutrinos, we discuss the information a measurement of, or an upper bound on, | | can provide on the value of the lightest neutrino mass m1. With additional data on the neutrino masses obtained in tritium beta decay experiments, it might be possible to establish whether the CP-symmetry is violated in the lepton sector. This would require very high precision measurements. If CP-invariance holds, the allowed patterns of the relative CP-parities of the massive Majorana neutrinos would be determined.

hep-ph↗

arXiv2001

Searching for the CP-Violation Associated with Majorana Neutrinos

The effective Majorana mass which determines the rate of the neutrinoless double beta decay, | |, is considered in the case of three-neutrino mixing and massive Majorana neutrinos. Assuming a rather precise determination of the parameters characterizing the neutrino oscillation solutions of the solar and atmospheric neutrino problems has been made, we discuss the information a measurement of | | > (0.005 - 0.010) eV can provide on the value of the lightest neutrino mass and on the CP-violation in the lepton sector. The implications of combining a measurement of | | with future measurement of the neutrino mass in tritium beta-decay experiments for the possible determination of leptonic CP-violation are emphasized.

hep-ph↗

arXiv2001

Majorana Neutrinos, Neutrino Mass Spectrum, CP-Violation and Neutrinoless Double Beta-Decay: I. The Three-Neutrino Mixing Case

Assuming mixing of three massive Majorana neutrinos, we study the implications of the neutrino oscillation solutions of the solar and atmospheric neutrino problems and of the results of the CHOOZ experiment for the predictions of the effective Majorana mass in neutrinoless double beta decay, |< m >|. The general case of CP-nonconservation is investigated. The predicted values of |< m >|, depend strongly on the type of the neutrino mass spectrum, on the solution of the solar neutrino problem, as well as on the values of the two Majorana CP-violating phases, present in the lepton mixing matrix. We find that i) $|< m >| \lesssim 0.02 $eV for a hierarchical neutrino mass spectrum, ii) $|< m >| \lesssim 0.09 $eV if the spectrum is of the inverted hierarchy type, and iii) $|< m >| \leq m$ in the case of three quasi-degenerate neutrinos, m > 0 being the common neutrino mass scale which is limited by the bounds from the $^3$H $β-$decay experiments, $m < 2.5 $eV. The observation of the $(ββ)_{0ν}-$decay with a rate corresponding to $|< m >| \gtrsim 0.02 $eV can provide unique information on the neutrino mass spectrum and on the CP-violation in the lepton sector, and if CP-invariance holds - on the relative CP-parities of the massive Majorana neutrinos.

hep-ph↗

arXiv2001

Majorana Neutrinos, Neutrino Mass Spectrum, CP-Violation and Neutrinoless Double Beta-Decay: II. Mixing of Four Neutrinos

Assuming four-neutrino mixing and massive Majorana neutrinos, we study the implications of the neutrino oscillation solutions of the solar and atmospheric neutrino problems, of the results of the LSND experiment and of the constraints on neutrino oscillations, obtained in reactor and accelerator experiments, for the predictions of the effective Majorana mass in neutrinoless double beta (\betabeta-)decay, \meff. All 4-neutrino mass spectra compatible with the existing neutrino mass and oscillation data are considered. The general case of CP-nonconservation is investigated. We have also analyzed in detail the question of whether a measurement of $\meff \gtap 0.01$ eV in the next generation of \betabeta-decay experiments (NEMO3, CUORE, EXO, GENIUS), combined with the data from the solar, atmospheric, reactor and accelerator neutrino oscillation experiments and from the future neutrino mass $^3$H $β-$decay experiment KATRIN would allow, and under what conditions, i) to determine the absolute values of the neutrino masses and thus the neutrino mass spectrum, and ii) to establish the existence of CP-violation in the lepton sector. For certain 4-neutrino mass spectra there exists a direct relation between \meff or the lightest neutrino mass $m_1$ and the neutrino mass measured in $^3$H $β-$decay, $m_{ν_e}$, and the measurement of $\meff \gtap 0.01$ eV and of $m_{ν_e} \gtap 0.4$ eV will give the unique possibility to determine the absolute values of all four neutrino masses and to obtain information on CP-violation in the lepton sector.

hep-ph↗

arXiv2001

Neutrino Mass Spectra, CP-Violation and Neutrinoless Double Beta-Decay

Assuming 3-neutrino mixing and massive Majorana neutrinos, we present some implications of the neutrino oscillation solutions of the solar and atmospheric neutrino problems and the results of the CHOOZ experiment for the predictions of the neutrinoless double-beta decay rate. If the present or upcoming searches of neutrinoless double-beta decay give a positive result, the Majorana nature of massive neutrinos will be established. From the determination of the value of the effective Majorana mass, it would be possible to obtain information on the neutrino mass spectrum. With additional information on the absolute value of neutrino masses, it might be possible to infer if CP-parity is violated in the lepton sector.

hep-ph↗