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 θ23\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