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Register a new userTestable constraint on near-tribimaximal neutrino mixing
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General lowest order perturbations to hermitian squared mass matrices of leptons are considered away from the tribimaximal (TBM) limit in which a weak flavor basis with mass diagonal charged leptons is chosen. The three measurable TBM deviants are expressed linearly in terms of perturbation induced dimensionless coefficients appearing in the charged lepton and neutrino flavor eigenstates. With unnatural cancellations assumed to be absent and the charged lepton perturbation contributions to their flavor eigenstates argued to be small, we analytically derive the following result. Within lowest order perturbations, a deviation from maximal atmospheric neutrino mixing and the amount of CP violation in neutrino oscillations cannot both be large (i.e. $12$-$17 % $), posing the challenge of verification to forthcoming experiments at the intensity frontier.
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In this work we analyze the corrections to tribimaximal (TBM), bimaximal (BM) and democratic (DC) mixing matrices for explaining large reactor mixing angle $theta_{13}$ and checking the consistency with other neutrino mixing angles. The corrections are parameterized in terms of small orthogonal rotations (R) with corresponding modified PMNS matrix of the form $R_{ij}cdot U cdot R_{kl}$ where $R_{ij}$ is rotation in ij sector and U is any one of these special matrices. We showed the rotations $R_{13}cdot U cdot R_{23}$, $R_{12}cdot U cdot R_{13}$ for BM and $R_{13}cdot U cdot R_{13}$ for TBM perturbative case successfully fit all neutrino mixing angles within $1sigma$ range. The perturbed PMNS matrix $R_{12}cdot U cdot R_{13}$ for DC, TBM and $R_{23}cdot U cdot R_{23}$ for TBM case is successful in producing mixing angles at 2$sigma$ level. The other rotation schemes are either excluded or successful in producing mixing angles at $3sigma$ level.
We scrutinize corrections to tribimaximal (TBM), bimaximal (BM) and democratic (DC) mixing matrices for explaining recent global fit neutrino mixing data. These corrections are parameterized in terms of small orthogonal rotations (R) with corresponding modified PMNS matrices of the forms big($R_{ij}^lcdot U,~Ucdot R_{ij}^r,~U cdot R_{ij}^r cdot R_{kl}^r,~R_{ij}^l cdot R_{kl}^l cdot U$big ) where $R_{ij}^{l, r}$ is rotation in ij sector and U is any one of these special matrices. We showed that for perturbative schemes dictated by single rotation, only big($ R_{12}^lcdot U_{BM},~R_{13}^lcdot U_{BM},~U_{TBM}cdot R_{13}^r$ big ) can fit the mixing data at $3sigma$ level. However for $R_{ij}^lcdot R_{kl}^lcdot U$ type rotations, only big ($R_{23}^lcdot R_{13}^l cdot U_{DC} $big ) is successful to fit all neutrino mixing angles within $1sigma$ range. For $Ucdot R_{ij}^rcdot R_{kl}^r$ perturbative scheme, only big($U_{BM} cdot R_{12}^rcdot R_{13}^r$,~$U_{DC} cdot R_{12}^rcdot R_{23}^r$,~$U_{TBM} cdot R_{12}^rcdot R_{13}^r$big ) are consistent at $1sigma$ level. The remaining double rotation cases are either excluded at 3$sigma$ level or successful in producing mixing angles only at $2sigma-3sigma$ level. We also updated our previous analysis on PMNS matrices of the form big($R_{ij}cdot U cdot R_{kl}$big ) with recent mixing data. We showed that the results modifies substantially with fitting accuracy level decreases for all of the permitted cases except big($R_{12}cdot U_{BM}cdot R_{13}$, $R_{23}cdot U_{TBM}cdot R_{13}$ and $R_{13}cdot U_{TBM} cdot R_{13}$big ) in this rotation scheme.
In the context of A_4 symmetry, neutrino tribimaximal mixing is achieved through the breaking of A_4 to Z_3 (Z_2) in the charged-lepton (neutrino) sector respectively. The implied vacuum misalignment of the (1,1,1) and (1,0,0) directions in A_4 space is a difficult technical problem, and cannot be treated without many auxiliary fields and symmetries (and perhaps extra dimensions). It is pointed out here that an alternative scenario exists with A_4 alone and no redundant fields, if neutrino masses are scotogenic, i.e. radiatively induced by dark scalar doublets as recently proposed.
We propose a seesaw scenario that possible corrections to the tribimaximal pattern of lepton mixing are due to the small phase splitting of the right-handed neutrino mass matrix. we show that the small deviations can be expressed analytically in terms of two splitting parameters($delta_1$ and $delta_2$) in the leading order. The solar mixing angle $theta_{12}$ favors a relatively smaller value compared to zero order value ($35.3^circ$), and the Dirac type CP phase $delta$ chooses a nearly maximal one. The two Majorana type CP phases $rho$ and $sigma$ turn out to be a nearly linear dependence. Also a normal hierarchy neutrino mass spectrum is favored due to the stability of perturbation calculations.
In this work, we present an analysis of the sensitivity to the active-sterile neutrino mixing with the Indian Scintillator Matrix for Reactor Anti-Neutrino (ISMRAN) experimental set-up at very short baseline. In this article, we have considered the measurement of electron antineutrino induced events employing a single detector which can be placed either at a single position or moved between near and far positions from the given reactor core. Results extracted in the later case are independent of the theoretical prediction of the reactor anti-neutrino spectrum and detector related systematic uncertainties. Our analysis shows that the results obtained from the measurement carried out at a combination of the near and far detector positions are improved significantly at higher $Delta m^{2}_{41}$ compared to the ones obtained with the measurement at a single detector position only. It is found that the best possible combination of near and far detector positions from a 100 MW$_{th}$ power DHRUVA research reactor core are 7 m and 9 m, respectively, for which ISMRAN set-up can exclude in the range 1.4 $eV^{2} leq Delta m^{2}_{41} leq$ 4.0 $eV^{2}$ of reactor antineutrino anomaly region along with the present best-fit point of active-sterile neutrino oscillation parameters. At those combinations of detector positions, the ISMRAN set-up can observe the active sterile neutrino oscillation with a 95$%$ confidence level provided that $sin^{2}2theta_{14}geq 0.09$ at $Delta m^{2}_{41}$ = 1 eV$^{2}$ for an exposure of 1 ton-yr. The active-sterile neutrino mixing sensitivity can be improved by about 22% at the same exposure by placing the detector at near and far distances of 15 m and 17 m, respectively, from the compact proto-type fast breeder reactor (PFBR) facility which has a higher thermal power of 1250 MW$_{th}$.
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