4,934 research outputs found

### Parallel hybrid textures of lepton mass matrices

We analyse the parallel hybrid texture structures in the charged lepton and
the neutrino sector. These parallel hybrid texture structures have physical
implications as they cannot be obtained from arbitrary lepton mass matrices
through weak basis transformations. The total sixty parallel hybrid texture
structures can be grouped into twelve classes, and all the hybrid textures in
the same class have identical physical implications. We examine all the twelve
classes under the assumption of non-factorizable phases in the neutrino mass
matrix. Five out of the total twelve classes are found to be phenomenologically
disallowed. We study the phenomenological implications of the allowed classes
for 1-3 mixing angle, Majorana and Dirac-type $CP$ violating phases.
Interesting constraints on effective Majorana mass are obtained for all the
allowed classes.Comment: Physical Review D (To appear

### Probing the deviation from maximal mixing of atmospheric neutrinos

Pioneering atmospheric muon neutrino experiments have demonstrated the
near-maximal magnitude of the flavor mixing angle $\theta_{23}$. But the
precise value of the deviation $D \equiv 1/2 - \sin^2 \theta_{23}$ from
maximality (if nonzero) needs to be known, being of great interest --
especially to builders of neutrino mass and mixing models. We quantitatively
investigate in a three generation framework the feasibility of determining $D$
in a statistically significant manner from studies of the atmospheric
$\nu_\mu,\bar\nu_\mu$ survival probability including both vacuum oscillations
and matter effects. We show how this determination will be sharpened by
considering the up-down ratios of observed $\nu_\mu$- and $\bar\nu_\mu$-induced
events and the differences of these ratios in specified energy and zenith angle
bins. We consider 1 Megaton year of exposure to a magnetized iron calorimeter
such as the proposed INO detector ICAL, taking into account both energy and
zenith angle resolution functions. The sensitivity of such an exposure and the
dependence of the determination of $D$ on the concerned oscillation parameters
are discussed in detail. The vital use of matter effects in fixing the octant
of $\theta_{23}$ is highlighted.Comment: Version to appear in PR

### Prospects of measuring the leptonic CP phase with atmospheric neutrinos

We have studied the prospects of measuring the CP violating phase with
atmospheric neutrinos at a large magnetized iron calorimeter detector
considering the muons (directly measurable) of the neutrino events generated by
a MonteCarlo event generator Nuance. The effect of $\theta_{13}$ and
$\delta_{CP}$ appears dominantly neither in atmospheric neutrino oscillation
nor in solar neutrino oscillation, but appears as subleading in both cases.
These are observable in range of $E \sim 1$ GeV for atmospheric neutrino, where
solar and atmospheric oscillation couple. In this regime, the quasi-elastic
events dominate and the energy resolution is very good, but the angular
resolution is very poor. Unlike beam experiments this poor angular resolution
acts against its measurements. However, we find that one can be able to
distinguish $\delta_{CP}\approx 0^\circ$ and $180^\circ$ at 90% confidence
level. We find no significant sensitivity for $\delta_{CP}\approx 90^\circ$ or
$270^\circ$.Comment: 9 pages, 7 figures, clarifying discussions on results added; accepted
in Phys. Rev.

### Renormalization group evolution of neutrino mixing parameters near $\theta_{13} = 0$ and models with vanishing $\theta_{13}$ at the high scale

Renormalization group (RG) evolution of the neutrino mass matrix may take the
value of the mixing angle $\theta_{13}$ very close to zero, or make it vanish.
On the other hand, starting from $\theta_{13}=0$ at the high scale it may be
possible to generate a non-zero $\theta_{13}$ radiatively. In the most general
scenario with non-vanishing CP violating Dirac and Majorana phases, we explore
the evolution in the vicinity of $\theta_{13}=0$, in terms of its structure in
the complex ${\cal U}_{e3}$ plane. This allows us to explain the apparent
singularity in the evolution of the Dirac CP phase $\delta$ at $\theta_{13}=0$.
We also introduce a formalism for calculating the RG evolution of neutrino
parameters that uses the Jarlskog invariant and naturally avoids this singular
behaviour. We find that the parameters need to be extremely fine-tuned in order
to get exactly vanishing $\theta_{13}$ during evolution. For the class of
neutrino mass models with $\theta_{13}=0$ at the high scale, we calculate the
extent to which RG evolution can generate a nonzero $\theta_{13}$, when the low
energy effective theory is the standard model or its minimal supersymmetric
extension. We find correlated constraints on $\theta_{13}$, the lightest
neutrino mass $m_0$, the effective Majorana mass $m_{ee}$ measured in the
neutrinoless double beta decay, and the supersymmetric parameter $\tan\beta$.Comment: 24 pages, 6 figures, revtex

### Leptogenesis bound on neutrino masses in left-right symmetric models with spontaneous D-parity violation

We study the baryogenesis via leptogenesis in a class of left-right symmetric
models, in which $D$-parity is broken spontaneously. We first discuss the
consequence of the spontaneous $D$-parity breaking on the neutrino masses. Than
we study the lepton asymmetry in various cases, from the decay of right handed
neutrino as well as the triplet Higgs, depending on their relative masses they
acquire from the symmetry breaking pattern. The leptogenesis bound on their
masses are discussed by taking into account the low energy neutrino oscillation
data. It is shown that a TeV scale leptogenesis is viable if there are
additional sources of CP violation like domain wall originating from the
spontaneous $D$-parity violation.Comment: 32 pages (revtex), 12 eps figures, clarifications are added in
section VII, A new section VIII is added, useful references are added.
Journal version, To appear in Phys. Rev.

### Non-standard interaction effects on astrophysical neutrino fluxes

We investigate new physics effects in the production and detection of high
energy neutrinos at neutrino telescopes. Analysing the flavor ratios
\phi_\mu/\phi_\tau and \phi_\mu/(\phi_\tau+\phi_e), we find that the Standard
Model predictions for them can be sensibly altered by new physics effects.Comment: 21 pages, 9 figures, REVTeX

### Determining the Neutrino Mass Hierarchy and CP Violation in NOvA with a Second Off-Axis Detector

We consider a Super-NOvA-like experimental configuration based on the use of
two detectors in a long-baseline experiment as NOvA. We take the far detector
as in the present NOvA proposal and add a second detector at a shorter
baseline. The location of the second off-axis detector is chosen such that the
ratio L/E is the same for both detectors, being L the baseline and E the
neutrino energy. We consider liquid argon and water-Cherenkov techniques for
the second off-axis detector and study, for different experimental setups, the
detector mass required for the determination of the neutrino mass hierarchy,
for different values of theta13. We also study the capabilities of such an
experimental setup for determining CP violation in the neutrino sector. Our
results show that by adding a second off-axis detector a remarkable enhancement
on the capabilities of the current NOvA experiment could be achieved.Comment: 20 p

### Supersymmetric Jarlskog Invariants: the Neutrino Sector

We generalize the notion of the Jarlskog invariant to supersymmetric models
with right--handed neutrinos. This allows us to formulate basis--independent
necessary and sufficient conditions for CP conservation in such models.Comment: 10 pages, no figure

### Possible textures of the fermion mass matrices

Texture specific fermion mass matrices have played an important role in
understanding several features of fermion masses and mixings. In the present
work, we have given an overview of all possible cases of Fritzsch-like as well
as non Fritzsch-like texture 6 and 5 zero fermion mass matrices. Further, for
the case of texture 4 zero Fritzsch-like quark mass matrices, the issue of the
hierarchy of the elements of the mass matrices and the role of their phases
have been discussed. Furthermore, the case of texture 4 zero Fritzsch-like
lepton mass matrices has also been discussed with an emphasis on the hierarchy
of neutrino masses for both Majorana and Dirac neutrinos.Comment: 21 pages, 3 figure

### Neutrino mass generation in the SO(4) model

Generation of neutrino mass in SO(4) model is proposed here. The algebraic
structure of SO(4) is same as to that of $SU(2)_{L}\times SU(2)_{R}$. It is
shown that the spontaneous symmetry breaking results three massive as well as
three massless gauge bosons. The standard model theory according to which there
exist three massive gauge bosons and a massless one is emerged from this model.
In the framework of $SU(2)_{L}\times SU(2)_{R}$ a small Dirac neutrino mass is
derived. It is also shown that such mass term may vanish with a special choice.
The Majorana mass term is not considered here and thus in this model the
neutrino mass does not follow seesaw structure.Comment: 7 pages, no figur

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