224 research outputs found

### 2540 km: Bimagic baseline for neutrino oscillation parameters

We show that a source-to-detector distance of 2540 km offers multiple
advantages for a low energy neutrino factory with a detector that can identify
muon charge. At this baseline, for any neutrino hierarchy, the wrong-sign muon
signal is almost independent of CP violation and $\theta_{13}$ in certain
energy ranges. This reduces the uncertainties due to these parameters and
allows the identification of the hierarchy in a clean way. In addition, part of
the muon spectrum is also sensitive to the CP violating phase and
$\theta_{13}$, so that the same setup can be used to probe these parameters as
well.Comment: 4 pages, 4 figures, Revtex4. Text modified. Version to appear in PR

### Radiatively broken symmetries of nonhierarchical neutrinos

Symmetry-based ideas, such as the quark-lepton complementarity (QLC)
principle and the tri-bimaximal mixing (TBM) scheme, have been proposed to
explain the observed mixing pattern of neutrinos. We argue that such symmetry
relations need to be imposed at a high scale $\Lambda \sim 10^{12}$ GeV
characterizing the large masses of right-handed neutrinos required to implement
the seesaw mechanism. For nonhierarchical neutrinos, renormalisation group
evolution down to a laboratory energy scale $\lambda \sim 10^3$ GeV tends to
radiatively break these symmetries at a significant level and spoil the mixing
pattern predicted by them. However, for Majorana neutrinos, suitable
constraints on the extra phases $\alpha_{2,3}$ enable the retention of those
high scale mixing patterns at laboratory energies. We examine this issue within
the Minimal Supersymmetric Standard Model (MSSM) and demonstrate the fact
posited above for two versions of QLC and two versions of TBM. The appropriate
constraints are worked out for all these four cases. Specifically, a preference
for $\alpha_2 \approx \pi$ (i.e. $m_1 \approx -m_2$) emerges in each case. We
also show how a future accurate measurement of $\theta_{13}$ may enable some
discrimination among these four cases in spite of renormalization group
evolution.Comment: 29 pages, 4 figures, revtex4. Minor changes in the Introduction,
references added. Final version to be published in Phys. Rev.

### Vacuum Stability Constraints on the Minimal Singlet TeV Seesaw Model

We consider the minimal seesaw model in which two gauge singlet right handed
neutrinos with opposite lepton numbers are added to the Standard Model. In this
model, the smallness of the neutrino mass is explained by the tiny lepton
number violating coupling between one of the singlets with the standard
left-handed neutrinos. This allows one to have the right handed neutrino mass
at the TeV scale as well as appreciable mixing between the light and heavy
states. This model is fully reconstructible in terms of the neutrino
oscillation parameters apart from the overall coupling strengths. We show that
the overall coupling strength $y_\nu$ for the Dirac type coupling between the
left handed neutrino and one of the singlets can be restricted by consideration
of the (meta)stability bounds on the electroweak vacuum. In this scenario the
lepton flavor violating decays of charged leptons can be appreciable which can
put further constraint on $y_\nu$, for right-handed neutrinos at TeV scale. We
discuss the combined constraints on $y_\nu$ for this scenario from the process
$\mu \rightarrow e \gamma$ and from the consideration of vacuum (meta)stability
constraints on the Higgs self coupling. We also briefly discuss the
implications for neutrinoless double beta decay and possible signatures of the
model that can be expected at colliders.Comment: One loop effective potential due to heavy neutrino included, 20
pages, 9 figure

### A Study of Invisible Neutrino Decay at DUNE and its Effects on $\theta_{23}$ Measurement

We study the consequences of invisible decay of neutrinos in the context of
the DUNE experiment. We assume that the third mass eigenstate is unstable and
decays to a light sterile neutrino and a scalar or a pseudo-scalar. We consider
DUNE running in 5 years neutrino and 5 years antineutrino mode and a detector
volume of 40 kt. We obtain the bounds on the rest frame life time $\tau_3$
normalized to the mass $m_3$ as $\tau_3/m_3 > 4.50\times 10^{-11}$ s/eV at 90\%
C.L. for a normal hierarchical mass spectrum. We also find that DUNE can
discover neutrino decay for $\tau_3/m_3 > 4.27\times 10^{-11}$ s/eV at 90\%
C.L. In addition, for an unstable $\nu_3$ with an illustrative value of
$\tau_3/m_3$ = $1.2 \times 10^{-11}$ s/eV, the no decay case gets disfavoured
at the $3\sigma$ C.L. At 90\% C.L. the allowed range for this true value is
obtained as $1.71 \times 10^{-11} > \tau_3/m_3 > 9.29\times 10^{-12}$ in units
of s/eV. We also study the correlation between a non-zero $\tau_3/m_3$ and
standard oscillation parameters and find an interesting correlation in the
appearance channel probability with the mixing angle $\theta_{23}$. This alters
the octant sensitvity of DUNE, favorably (unfavorably) for true $\theta_{23}$
in the lower (higher) octant. The effect of a decaying neutrino does not alter
the hierarchy or CP discovery sensitivity of DUNE in a discernible way.Comment: accepted and published in JHEP with additional figures and few
reference

### Threshold effects and renormalization group evolution of neutrino parameters in TeV scale seesaw models

We consider the threshold effect on the renormalization group (RG) evolution
of the neutrino masses and mixing angles in TeV scale seesaw models. We obtain
the analytic expressions using the factorization method in presence of
threshold effects. We also perform numerical study of RG effects in two
specific low scale seesaw models following the bottom-up approach and ascertain
the role of seesaw thresholds in altering the values of masses and mixing
angles during RG evolution.Comment: 31 pages, 8 figure

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