[Show abstract][Hide abstract] ABSTRACT: Assuming that the observed pattern of 3-neutrino mixing is related to the
existence of a (lepton) flavour symmetry, corresponding to a non-Abelian
discrete symmetry group $G_f$, and that $G_f$ is broken to specific residual
symmetries $G_e$ and $G_\nu$ of the charged lepton and neutrino mass terms, we
derive sum rules for the cosine of the Dirac phase $\delta$ of the neutrino
mixing matrix $U$. The residual symmetries considered are: i) $G_e = Z_2$ and
$G_{\nu} = Z_n$, $n > 2$ or $Z_n \times Z_m$, $n,m \geq 2$, ii) $G_e = Z_n$, $n
> 2$ or $G_e = Z_n \times Z_m$, $n,m \geq 2$ and $G_{\nu} = Z_2$, iii) $G_e =
Z_2$ and $G_{\nu} = Z_2$, iv) $G_e$ is fully broken and $G_{\nu} = Z_n$, $n >
2$ or $Z_n \times Z_m$, $n,m \geq 2$, and v) $G_e = Z_n$, $n > 2$ or $Z_n
\times Z_m$, $n,m \geq 2$ and $G_{\nu}$ is fully broken. For given $G_e$ and
$G_\nu$, the sum rules for $\cos\delta$ thus derived are exact, within the
approach employed, and are valid, in particular, for any $G_f$ containing $G_e$
and $G_\nu$ as subgroups. We identify the cases when the value of $\cos\delta$
cannot be determined, or cannot be uniquely determined, without making
additional assumptions on unconstrained parameters. In a large class of cases
considered the value of $\cos\delta$ can be unambiguously predicted once the
flavour symmetry $G_f$ is fixed. We present predictions for $\cos\delta$ in
these cases for the flavour symmetry groups $G_f = S_4$, $A_4$, $T^\prime$ and
$A_5$, requiring that the measured values of the 3-neutrino mixing parameters
$\sin^2\theta_{12}$, $\sin^2\theta_{13}$ and $\sin^2\theta_{23}$, taking into
account their respective $3\sigma$ uncertainties, are successfully reproduced.
[Show abstract][Hide abstract] ABSTRACT: We perform a detailed analysis of the one-loop corrections to the light
neutrino mass matrix within low scale type I seesaw extensions of the Standard
Model and their implications in experimental searches for neutrinoless double
beta decay. We show that a sizable contribution to the effective Majorana
neutrino mass from the exchange of heavy Majorana neutrinos is always possible,
provided one requires a fine-tuned cancellation between the tree-level and
one-loop contribution to the light neutrino masses. We quantify the level of
fine-tuning as a function of the seesaw parameters and introduce a
generalisation of the Casas-Ibarra parametrization of the neutrino Yukawa
matrix, which easily allows to include the one-loop corrections to the light
neutrino masses.
[Show abstract][Hide abstract] ABSTRACT: Using the fact that the neutrino mixing matrix $U = U^\dagger_{e}U_{\nu}$,
where $U_{e}$ and $U_{\nu}$ result from the diagonalisation of the charged
lepton and neutrino mass matrices, we analyse the predictions based on the sum
rules which the Dirac phase $\delta$ present in $U$ satisfies when $U_{\nu}$
has a form dictated by, or associated with, discrete flavour symmetries and
$U_e$ has a "minimal" form (in terms of angles and phases it contains) that can
provide the requisite corrections to $U_{\nu}$, so that the reactor,
atmospheric and solar neutrino mixing angles $\theta_{13}$, $\theta_{23}$ and
$\theta_{12}$ have values compatible with the current data.
International Journal of Modern Physics A 04/2015; 30(13). DOI:10.1142/S0217751X15300355 · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We derive predictions for the Dirac phase $\delta$ present in the $3\times 3$
unitary neutrino mixing matrix $U = U_e^{\dagger} \, U_{\nu}$, where $U_e$ and
$U_{\nu}$ are $3\times 3$ unitary matrices which arise from the diagonalisation
respectively of the charged lepton and the neutrino mass matrices. After
performing a systematic search, we consider forms of $U_e$ and $U_{\nu}$
allowing us to express $\delta$ as a function of the Pontecorvo, Maki,
Nakagawa, Sakata (PMNS) mixing angles, $\theta_{12}$, $\theta_{13}$ and
$\theta_{23}$, present in $U$, and the angles contained in $U_{\nu}$. We derive
sum rules for $\cos\delta$ in the cases of forms for which the sum rules of
interest do not exist in the literature. We consider several forms of
$\tilde{U}_{\nu}$ determined by, or associated with, symmetries, tri-bimaximal
(TBM), bimaximal (BM), etc., for which the angles in $\tilde{U}_{\nu}$ are
fixed. For each of these forms and forms of $\tilde{U}_e$ allowing to reproduce
the measured values of the angles $\theta_{12}$, $\theta_{13}$ and
$\theta_{23}$, we construct the likelihood function for $\cos \delta$, using i)
the latest results of the global fit analysis of neutrino oscillation data, and
ii) the prospective sensitivities on the PMNS mixing angles. Our results, in
particular, confirm the conclusion reached in earlier similar studies that the
measurement of the Dirac phase in the PMNS mixing matrix, together with an
improvement of the precision on the mixing angles $\theta_{12}$, $\theta_{13}$
and $\theta_{23}$, can provide unique information about the possible existence
of symmetry in the lepton sector. Such measurements could also provide an
indication about the structure of the matrix $\tilde U_e$ originating from the
charged lepton sector, and thus about the charged lepton mass matrix.
European Physical Journal C 04/2015; 75(7). DOI:10.1140/epjc/s10052-015-3559-6 · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper we discuss a minor modification of a previous SU(5) x A5
flavour model which exhibits at leading order golden ratio mixing and sum rules
for the heavy and the light neutrino masses. Although this model could predict
all mixing angles well it fails in generating a sufficient large baryon
asymmetry via the leptogenesis mechanism. We repair this deficit here, discuss
model building aspects and give analytical estimates for the generated baryon
asymmetry before we perform a numerical parameter scan. Our setup has only a
few parameters in the lepton sector. This leads to specific constraints and
correlations between the neutrino observables. For instance, we find that in
the model considered only the neutrino mass spectrum with normal mass ordering
and values of the lightest neutrino mass in the interval 10-18 meV are
compatible with the current data on the neutrino oscillation parameters. With
the introduction of only one NLO operator, the model can accommodate
successfully simultaneously even at 1$\sigma$ level the current data on
neutrino masses, on neutrino mixing and the observed value of the baryon
asymmetry.
[Show abstract][Hide abstract] ABSTRACT: Using the fact that the neutrino mixing matrix , where and result from the diagonalisation of the charged lepton and neutrino mass matrices, we consider a number of forms of associated with a variety of flavour symmetries: i) bimaximal (BM) and ii) tri-bimaximal (TBM) forms, the forms corresponding iii) to the conservation of the lepton charge (LC), iv) to golden ratio type A (GRA) mixing, v) golden ratio type B (GRB) mixing, and vi) to hexagonal (HG) mixing. Employing the minimal form of , in terms of angles and phases it contains, that can provide the requisite corrections to so that reactor, atmospheric and solar neutrino mixing angles , and have values compatible with the current data, including a possible sizable deviation of from , we discuss the possibility to obtain predictions for the CP violation phases in the neutrino mixing matrix. Considering the “standard ordering” of the the 12 and the 23 rotations in and following the approach developed in [1] we derive predictions for the Dirac phase δ and the rephasing invariant in the cases of GRA, GRB and HG forms of (results for the TBM and BM (LC) forms were obtained in [1]). We show also that under rather general conditions within the scheme considered the values of the Majorana phases in the PMNS matrix can be predicted for each of the forms of discussed. We give examples of these predictions and of their implications for neutrinoless double beta decay. In the GRA, GRB and HG cases, as in the TBM one, relatively large CP violation effects in neutrino oscillations are predicted ( ). Distinguishing between the TBM, BM (LC), GRA, GRB and HG forms of requires a measurement of or a relatively high precision measurement of .
Nuclear Physics B 01/2015; 892. DOI:10.1016/j.nuclphysb.2015.01.011 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The process of Radiative Emission of Neutrino Pair (RENP) in atoms is
sensitive to the absolute neutrino mass scale, the type of spectrum neutrino
masses obey and the nature - Dirac or Majorana - of massive neutrinos. We
analyse the possibility to test the hypothesis of existence of neutrinos with
masses at the eV scale coupled to the electron in the weak charged lepton
current in an RENP experiment. The presence of eV scale neutrinos in the
neutrino mixing is associated with the existence of sterile neutrinos which mix
with the active flavour neutrinos. At present there are a number of hints for
active-sterile neutrino oscillations driven by $\Delta m^2 \sim 1~{\rm eV^2}$.
We perform a detailed analysis of the RENP phenomenology within the "3 + 1"
scheme with one sterile neutrino.
Physics Letters B 11/2014; 742. DOI:10.1016/j.physletb.2015.01.020 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Using the fact that the neutrino mixing matrix $U = U^\dagger_{e}U_{\nu}$,
where $U_{e}$ and $U_{\nu}$ result from the diagonalisation of the charged
lepton and neutrino mass matrices, we analyse the sum rules which the Dirac
phase $\delta$ present in $U$ satisfies when $U_{\nu}$ has a form dictated by
flavour symmetries and $U_e$ has a "minimal" form (in terms of angles and
phases it contains) that can provide the requisite corrections to $U_{\nu}$, so
that reactor, atmospheric and solar neutrino mixing angles $\theta_{13}$,
$\theta_{23}$ and $\theta_{12}$ have values compatible with the current data.
The following symmetry forms are considered: i) tri-bimaximal (TBM), ii)
bimaximal (BM) (or corresponding to the conservation of the lepton charge $L' =
L_e - L_\mu - L_{\tau}$ (LC)), iii) golden ratio type A (GRA), iv) golden ratio
type B (GRB), and v) hexagonal (HG). We investigate the predictions for
$\delta$ in the cases of TBM, BM (LC), GRA, GRB and HG forms using the exact
and the leading order sum rules for $\cos\delta$ proposed in the literature,
taking into account also the uncertainties in the measured values of
$\sin^2\theta_{12}$, $\sin^2\theta_{23}$ and $\sin^2\theta_{13}$. This allows
us, in particular, to assess the accuracy of the predictions for $\cos\delta$
based on the leading order sum rules and its dependence on the values of the
indicated neutrino mixing parameters when the latter are varied in their
respective 3$\sigma$ experimentally allowed ranges.
Nuclear Physics B 10/2014; 894. DOI:10.1016/j.nuclphysb.2015.03.026 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We show that the relatively large best fit value of $\sin^2 2 \theta_{13} =
0.14 \, (0.17)$ measured in the T2K experiment for fixed values of i) the Dirac
CP violation phase $\delta = 0$, and ii) the atmospheric neutrino mixing
parameters $\theta_{23} = \pi/4$, $|\Delta m^2_{32}| = 2.4 \times 10^{-3} \;
{\rm eV}^2$, can be reconciled with the Daya Bay result $\sin^2 2 \theta_{13} =
0.090 \pm 0.009$ if the effects of non-standard neutrino interactions (NSI) in
the relevant $\bar \nu_e \to \bar \nu_e$ and $\nu_\mu \to \nu_e$ oscillation
probabilities are taken into account.
Nuclear Physics B 05/2014; 886. DOI:10.1016/j.nuclphysb.2014.06.014 · 3.93 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The phenomenology of 3-neutrino mixing, the current status of our knowledge about the 3-neutrino mixing parameters, including the absolute neutrino mass scale, and of the Dirac and Majorana CP violation in the lepton sector, are reviewed. The problems of CP violation in neutrino oscillations and of determining the nature — Dirac or Majorana — of massive neutrinos, are discussed. The seesaw mechanism of neutrino mass generation and the related leptogenesis scenario of generation of the baryon asymmetry of the universe, are considered. The results showing that the CP violation necessary for the generation of the baryon asymmetry of the universe in leptogenesis can be due exclusively to the Dirac and/or Majorana CP-violating phase(s) in the neutrino mixing matrix U, are briefly reviewed.
International Journal of Modern Physics A 03/2014; 29(11n12). DOI:10.1142/S0217751X14300282 · 1.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We discuss how two birds—the little hierarchy problem of low-scale type-I seesaw models and the search for a viable dark matter candidate—are (proverbially) killed by one stone: a new inert scalar state.
European Physical Journal C 01/2014; 74(2). DOI:10.1140/epjc/s10052-014-2774-x · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We show that the relatively large best fit value of sin22θ13=0.14(0.17) measured in the T2K experiment for fixed values of i) the Dirac CP violation phase δ=0δ=0, and ii) the atmospheric neutrino mixing parameters θ23=π/4θ23=π/4, |Δm322|=2.4×10−3 eV2, can be reconciled with the Daya Bay result sin22θ13=0.090±0.009 if the effects of non-standard neutrino interactions (NSI) in the relevant ν¯e→ν¯e and νμ→νeνμ→νe oscillation probabilities are taken into account.
[Show abstract][Hide abstract] ABSTRACT: We analyse the interplay of generalised CP transformations and the
non-Abelian discrete group $T^{\prime}$ and use the semi-direct product $G_f=
T^{\prime}\rtimes H_{\text{CP}}$, as family symmetry acting in the lepton
sector. The family symmetry is shown to be spontaneously broken in a
geometrical manner. In the resulting flavour model, naturally small Majorana
neutrino masses for the light active neutrinos are obtained through the type I
see-saw mechanism. The known masses of the charged leptons, lepton mixing
angles and the two neutrino mass squared differences are reproduced by the
model with a good accuracy. The model allows for two neutrino mass spectra with
normal ordering (NO) and one with inverted ordering (IO). For each of the three
spectra the absolute scale of neutrino masses is predicted with relatively
small uncertainty. The value of the Dirac CP violation (CPV) phase $\delta$ in
the lepton mixing matrix is predicted to be $\delta \cong \pi/2~{\rm or}~
3\pi/2$. Thus, the CP violating effects in neutrino oscillations are predicted
to be maximal (given the values of the neutrino mixing angles) and
experimentally observable. We present also predictions for the sum of the
neutrino masses, for the Majorana CPV phases and for the effective Majorana
mass in neutrinoless double beta decay. The predictions of the model can be
tested in a variety of ongoing and future planned neutrino experiments.
Journal of High Energy Physics 12/2013; 2014(2). DOI:10.1007/JHEP02(2014)050 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We perform a detailed analysis of lepton flavour violation (LFV) within minimal see-saw type extensions of the Standard Model (SM), which give a viable mechanism of neutrino mass generation and provide new particle content at the electroweak scale. We focus, mainly, on predictions and constraints set on each scenario from μ → eγ, μ → 3e and μ − e conversion in the nuclei. In this class of models, the flavour structure of the Yukawa couplings between the additional scalar and fermion representations and the SM leptons is highly constrained by neutrino oscillation measurements. In particular, we show that in some regions of the parameters space of type I and type II see-saw models, the Dirac and Majorana phases of the neutrino mixing matrix, the ordering and hierarchy of the active neutrino mass spectrum as well as the value of the reactor mixing angle θ
13 may considerably affect the size of the LFV observables. The interplay of the latter clearly allows to discriminate among the different low energy see-saw possibilities.
Journal of High Energy Physics 09/2013; 2012(8). DOI:10.1007/JHEP08(2012)125 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigate the predictions for neutrinoless double beta ($(\beta
\beta)_{0 \nu}$-) decay effective Majorana mass $\left| \langle \, m \, \rangle
\right|$ in the 3+1 and 3+2 schemes with one and two additional sterile
neutrinos with masses at the eV scale. The two schemes are suggested by the
neutrino oscillation interpretation of the reactor neutrino and Gallium
"anomalies" and of the data of the LSND and MiniBooNE experiments. We analyse
in detail the possibility of a complete or partial cancellation between the
different terms in $\left| \langle \, m \, \rangle \right|$, leading to a
strong suppression of $\left| \langle \, m \, \rangle \right|$. We determine
the regions of the relevant parameter spaces where such a suppression can
occure. This allows us to derive the conditions under which the effective
Majorana mass satisfies $\left| \langle \, m \, \rangle \right| > 0.01$ eV,
which is the range planned to be exploited by the next generation of $(\beta
\beta)_{0 \nu}$-experiments.
Journal of High Energy Physics 08/2013; 2013(11). DOI:10.1007/JHEP11(2013)146 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The lepton flavour violating (LFV) $\tau$ decays $\tau\to (e,\mu)\gamma$ and
$\tau\to 3\mu$ are investigated in the frameworks of the TeV scale type I
see-saw and Higgs Triplet (or type II see-saw) models. Predictions for the
rates of these processes are obtained. The implications of the existing
stringent experimental upper bounds on the $\mu\to e + \gamma$ and $\mu\to 3e$
decay branching ratios for the predictions of the $\tau\to (e,\mu)\gamma$ and
$\tau\to 3\mu$ decay rates are studied in detail. The possibilities to observe
the indicated LFV $\tau$ decays in present and future experiments are analysed.
Journal of High Energy Physics 08/2013; 2013(9). DOI:10.1007/JHEP09(2013)086 · 6.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We discuss how two birds---the little hierarchy problem of low-scale type-I
seesaw models and the search for a viable dark matter candidate---are
(proverbially) killed by one stone: a new inert scalar state
[Show abstract][Hide abstract] ABSTRACT: The compelling experimental evidences for oscillations of solar, reactor, atmospheric, and accelerator neutrinos imply the existence of 3-neutrino mixing in the weak charged lepton current. The current data on the 3-neutrino mixing parameters are summarised and the phenomenology of 3- mixing is reviewed. The properties of massive Majorana neutrinos and of their various possible couplings are discussed in detail. Two models of neutrino mass generation with massive Majorana neutrinos—the type I see-saw and the Higgs triplet model—are briefly reviewed. The problem of determining the nature, Dirac or Majorana, of massive neutrinos is considered. The predictions for the effective Majorana mass in neutrinoless double-beta-(-) decay in the case of 3-neutrino mixing and
massive Majorana neutrinos are summarised. The physics potential of the experiments, searching for -decay 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 briefly discussed. The opened questions and the main goals of future research in the field of neutrino physics are outlined.
Advances in High Energy Physics 04/2013; 2013(1-2). DOI:10.1155/2013/852987 · 2.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: After the successful determination of the reactor neutrino mixing angle
\theta_13 ~ 0.16 \neq 0, a new feature suggested by the current neutrino
oscillation data is a sizeable deviation of the atmospheric neutrino mixing
angle \theta_23 from \pi/4. Using the fact that the neutrino mixing matrix U =
U_e^\dagger U_\nu, where U_e and U_\nu result from the diagonalisation of the
charged lepton and neutrino mass matrices, and assuming that U_\nu has a i)
bimaximal (BM), ii) tri-bimaximal (TBM) form, or else iii) corresponds to the
conservation of the lepton charge L' = L_e - L_\mu - L_\tau (LC), we
investigate quantitatively what are the minimal forms of U_e, in terms of
angles and phases it contains, that can provide the requisite corrections to
U_\nu so that \theta_13, \theta_23 and the solar neutrino mixing angle
\theta_12 have values compatible with the current data. Two possible orderings
of the 12 and the 23 rotations in U_e, "standard" and "inverse", are
considered. The results we obtain depend strongly on the type of ordering. In
the case of "standard" ordering, in particular, the Dirac CP violation phase
\delta, present in U, is predicted to have a value in a narrow interval around
i) \delta ~ \pi in the BM (or LC) case, ii) \delta ~ 3\pi/2 or \pi/2 in the TBM
case, the CP conserving values \delta = 0, \pi, 2\pi being excluded in the TBM
case at more than 4\sigma.
Journal of High Energy Physics 02/2013; 2013(5). DOI:10.1007/JHEP05(2013)073 · 6.11 Impact Factor