Neutrino CP Violation Research Articles

Large non-perturbative effects of small Δm221/Δm231and sin θ13on neutrino oscillation and CP violation in matter

In the framework of three generations, we consider the CP violation in neutrino oscillation with matter effects. At first, we show that the non-perturbative effects of two small parameters, \Delta m_{21}^2/\Delta m_{31}^2 and \sin \theta_{13}, become more than 50% in certain ranges of energy and baseline length. This means that the non-perturbative effects should be considered in detailed analysis in the long baseline experiments. Next, we propose a method to include these effects in approximate formulas for oscillation probabilities. Assuming the two natural conditions, \theta_{23}=45^\circ and the fact that the matter density is symmetric, a set of approximate formulas, which involve the non-perturbative effects, has been derived in all channels.

Non-perturbative Effects for Neutrino Oscillation and CP Violation in Matter

Non-perturbative Effects for Neutrino Oscillation and CP Violation in Matter

Running of low-energy neutrino masses, mixing angles and CP violation

We calculate the running of low-energy neutrino parameters from the bottom–up, parameterizing the unknown seesaw parameters in terms of the dominance matrix R. We find significant running only if the R matrix is non-trivial and the light-neutrino masses are moderately degenerate. If the light-neutrino masses are very hierarchical, the quark–lepton complementarity relation θ c + θ 12 = π / 4 is quite stable, but θ 13 , 23 may run beyond their likely future experimental errors. The running of the oscillation phase δ is enhanced by the smallness of θ 13 , and jumps in the mixing angles occur in cases where the light-neutrino mass eigenstates cross.

Bi-large neutrino mixing and CP violation in an SO(10) SUSY GUT for fermion masses

We construct a simple SO(10) SUSY GUT with D3 family symmetry and low energy R-parity. The model describes fermion mass matrices with 14 parameters and gives excellent fits to 20 observable masses and mixing angles in both quark and lepton sectors, giving 6 predictions. Bi-large neutrino mixing is obtained with hierarchical quark and lepton Yukawa matrices; thus avoiding the possibility of large lepton flavor violation. The model naturally predicts small 1–3 neutrino mixing, sinθ13≃0.05, and a CP violating phase δ close to π/2. Among other interesting predictions is a tiny effective Majorana mass for neutrinoless double-beta decay. Leptogenesis is also possible with the decay of the lightest right-handed neutrino giving an acceptable CP violating asymmetry ε1 of order 10−6, and with the correct sign for the resultant baryon asymmetry. Note, similar models with the non-Abelian symmetry groups SU(2) or D4, instead of D3, can be constructed.

Simple Method to Estimate Neutrino Oscillation Probability and CP Violation in Matter without Usual First Order Perturbation

We study neutrino oscillation and CP violation in matter and propose a simple method to approximate the coefficients A , B and C , which do not depend on the CP phase δ , in the oscillation probability P ( ν e → ν μ ) = A cos δ + B sin δ + C . The coefficients A , B and C can be calculated easier than usual first order perturbation in arbitrary matter.

A New Method to Approximate Neutrino Oscillation Probability and CP Violation in Matter

A New Method to Approximate Neutrino Oscillation Probability and CP Violation in Matter

STUDY OF LEPTONIC CP VIOLATION

The "complementary" Ansatz, Tr (Mν)=0, where Mν is the prediagonal neutrino mass matrix, seems a plausible approximation for capturing in a self contained way some of the content of Grand Unification. We study its consequences in the form of relations between the neutrino masses and CP violation phases.

Proposal of a simple method to estimate neutrino oscillation probability and CP violation in matter

We study neutrino oscillation within the framework of three generations in matter. We propose a simple method to approximate the coefficients A,B and C which do not depend on the CP phase δ in the oscillation probability P(νe→νμ)=Acosδ+Bsinδ+C. An advantage of our method is that an approximate formula of the coefficients A,B and C in arbitrary matter without the usual first order perturbative calculations of the small parameter Δm212/Δm312 or sinθ13 can be derived. Furthermore, we show that all the approximate formulas for low, intermediate and high energy regions given by other authors in constant matter can be easily derived from our formula. It means that our formula is applicable over a wide energy region.

Radiative corrections to neutrino mixing andCPviolation in the minimal seesaw model with leptogenesis

Radiative corrections to neutrino mixing and CP violation are analyzed in the minimal seesaw model with two heavy right-handed neutrinos. We find that textures of the effective Majorana neutrino mass matrix are essentially stable against renormalization effects. Taking account of the Frampton-Glashow-Yanagida ansatz for the Dirac neutrino Yukawa coupling matrix, we calculate the running effects of light neutrino masses, lepton flavor mixing angles and CP-violating phases for both $m_1 =0$ (normal mass hierarchy) and $m_3 =0$ (inverted mass hierarchy) cases in the standard model and in its minimal supersymmetric extension. Very instructive predictions for the cosmological baryon number asymmetry via thermal leptogenesis are also given with the help of low-energy neutrino mixing quantities.

Simple Method to Approximate Neutrino Oscillation Probability and CP Violation in Matter

Simple Method to Approximate Neutrino Oscillation Probability and CP Violation in Matter

Flavor Changing Neutrino Interactions and CP Violation in Neutrino Oscillations

We investigate the interference effects of non-standard neutrino-matter interactions (NSNI) with the mass-induced neutrino oscillations. The NSNI is composed of flavor-changing neutrino interactions (FCNI) and flavor-diagonal neutrino interactions (FDNI). Both of the interactions are introduced in the \nu_\mu -\nu_\tau sector and the \nu_e -\nu_\mu sector in order to study their effects in \nu_\mu\to\nu_\tau and \nu_\mu\to\nu_e oscillations, respectively. The FCNI effect proves to possibly dominate the CP violating effect and significantly survive as a fake CP violating effct in the neutrino energy region where the pure CP violating effect, ordinary matter effect and FDNI effect fall, for example, above 4 GeV at the baseline of L=730 km in the \nu_\mu\to\nu_\tau oscillation for the maximum parameter values of FCNI and FDNI allowed by the atmospheric neutrino oscillation data. The FCNI and FDNI effects on CP violation in the $\nu_\mu\to\nu_e$ oscillation are negligibly small due to the stringent constraints on FCNI from the bounds on lepton flavor violating processes and on FDNI from the limits on lepton universality violation.

Can the Majorana Neutrino CP-Violating Phases be Restricted?

We reanalyze the constraints in neutrino masses and MNS lepton mixing parameters using the new data from the terrestrial (KamLAND) and astrophysical (WMAP) observations together with the Heidelberg–Moscow double beta decay experiment. It leads us to the almost degenerate or inverse hierarchy neutrino mass scenario. We discuss the possibility of getting the bound for the Majorana CP-violating phase.

Leptogenesis and CP violation in neutrino oscillations

Assuming the seesaw and leptogenesis mechanisms, I give some general remarks on possible connection or disconnection between CP violation in heavy Majorana neutrino decays and that in neutrino oscillations. A simple but predictive ansatz is proposed to simultaneously interpret the observed baryon asymmetry of the universe and oscillations of solar and atmospheric neutrinos.

Structure of neutrino mass matrix and CP violation

Structure of neutrino mass matrix and CP violation

How two neutrino superbeam experiments do better than one

We examine the use of two superbeam neutrino oscillation experiments with baselines ≲1000 km to resolve parameter degeneracies inherent in the three-neutrino analysis of such experiments. We find that with appropriate choices of neutrino energies and baselines two experiments with different baselines can provide a much better determination of the neutrino mass ordering than a single experiment alone. Two baselines are especially beneficial when the mass scale for solar neutrino oscillations δm2sol is ≳5×10−5 eV2. We also examine CP violation sensitivity and the resolution of other parameter degeneracies. We find that the combined data of superbeam experiments with baselines of 295 and 900 km can provide sensitivity to both the neutrino mass ordering and CP violation for sin22θ13 down to 0.03 for |δm2atm|≃3×10−3 eV2. It would be advantageous to have a 10% determination of |δm2atm| before the beam energies and baselines are finalized, although if |δm2atm| is not that well known, the neutrino energies and baselines can be chosen to give fairly good sensitivity for a range of |δm2atm|.

Cosmological sign of neutrino CP violation

It is shown how, in a class of models, the sign of the baryon number of the universe can be related to CP violation in neutrino oscillation experiments.

No-go for detecting CP violation via neutrinoless double beta decay

We present a necessary condition on the solar oscillation amplitude for CP violation to be detectable through neutrinoless double beta (0 νββ) decay. It depends only on the fractional uncertainty in the ν e – ν e element of the neutrino mass matrix. We demonstrate that even under very optimistic assumptions about the sensitivity of future experiments to the absolute neutrino mass scale, and on the precision with which nuclear matrix elements that contribute to 0 νββ decay are calculable, it will be impossible to detect neutrino CP violation arising from Majorana phases.

Nearly tri-bimaximal neutrino mixing and CP violation

We point out two simple but instructive possibilities to modify the tri-bimaximal neutrino mixing ansatz, such that leptonic CP violation can naturally be incorporated into the resultant scenarios of nearly tri-bimaximal flavor mixing. The consequences of two new ansatzes on solar, atmospheric and reactor neutrino oscillations are analyzed. We also discuss an interesting approach to construct lepton mass matrices under permutation symmetry, from which one may derive another nearly tri-bimaximal neutrino mixing scenario with no intrinsic CP violation in neutrino oscillations.

Cosmological sign of neutrino CP violation

Cosmological sign of neutrino CP violation

Neutrino oscillation and CP violation

We reconsider the meaning of observing CP violation in neutrino oscillation.