1,720,988 research outputs found
The interplay between "low" and "high" energy CP-violation in leptogenesis
No full textWe analyse, within the "flavoured" leptogenesis scenario of baryon asymmetry generation, the interplay of "low energy" CP-violation, originating from the PMNS neutrino mixing matrix U, and "high energy" CP-violation, which can be present in the matrix of neutrino Yukawa couplings, lambda, and can manifest itself only in "high" energy scale processes. The type I see-saw model with three heavy right-handed Majorana neutrinos having a hierarchical spectrum is considered. The "orthogonal" parameterisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. In this approach the matrix R is the source of "high energy" CP-violation. Results for normal hierarchical (NH) and inverted hierarchical (IH) light neutrino mass spectrum are derived in the case of decoupling of the heaviest right-handed Majorana neutrino. It is shown that taking into account the contribution to Y (B) due to the CP-violating phases in the neutrino mixing matrix U can change drastically the predictions for Y (B) , obtained assuming that only "high energy" CP-violation from the R-matrix is operative in leptogenesis. In the case of the IH spectrum, in particular, there exist significant regions in the corresponding parameter space where the purely "high energy" contribution in Y (B) plays a subdominant role in the production of baryon asymmetry compatible with the observations
Leptogenesis and low energy CP-violation in neutrino physics
No full textTaking into account the recent progress in the understanding of the lepton flavor effects in leptogenesis, we investigate in detail the possibility that the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana CP-violating phases in the PMNS neutrino mixing matrix U, and thus is directly related to the low energy CP-violation in the lepton sector (e.g., in neutrino oscillations, etc.). We first derive the conditions of CP-invariance of the neutrino Yukawa couplings lambda in the see-saw Lagrangian, and of the complex orthogonal matrix R in the "orthogonal" parametrization of lambda. We show, e.g. that under certain conditions (i) real R and specific CP-conserving values of the Majorana and Dirac phases can imply CP-violation, and (ii) purely imaginary R does not necessarily imply breaking of CP-symmetry. We study in detail the case of hierarchical heavy Majorana neutrino mass spectrum, presenting results for three possible types of light neutrino mass spectrum: (i) normal hierarchical, (ii) inverted hierarchical, and (iii) quasi -degenerate. Results in the alternative case of quasi -degenerate in mass heavy Majorana neutrinos, are also derived. The minimal supersymmetric extension of the standard theory with right-handed Majorana neutrinos and see-saw mechanism of neutrino mass generation is discussed as well. We illustrate the possible correlations between the baryon asymmetry of the Universe and (i) the rephasing invariant J(CP) controlling the magnitude of CP-violation in neutrino oscillations, or (ii) the effective Majorana mass in neutrinoless double beta decay, in the cases when the only source of CP-violation is respectively the Dirac or the Majorana phases in the neutrino mixing matrix. (c) 2007 Elsevier B.V. All rights reserved
Majorana neutrinos, neutrino mass spectrum, and the |m|∼10-3eV frontier in neutrinoless double beta decay
No full textIf future neutrino oscillation experiments show that the neutrino mass spectrum is with normal ordering, m(1) < m(2) < m(3), and the searches for neutrinoless double beta [(beta beta)(0 nu)] decay with sensitivity to values of the effective Majorana mass |< m >| greater than or similar to 10(-2) eV give negative results, the next frontier in the quest for (beta beta)(0 nu)-decay will correspond to |< m >| similar to 10(-3) eV. By assuming that massive neutrinos are Majorana particles and their exchange is the dominant mechanism generating (beta beta)(0 nu) - decay, we analyze the conditions under which |< m >|, in the case of three-neutrino mixing and a neutrino mass spectrum with normal ordering, would satisfy |< m >| >= 0.001 eV. We consider the specific cases of (i) a normal hierarchical neutrino mass spectrum, (ii) a relatively small value of the CHOOZ angle theta(13), as well as (iii) the general case of a spectrum with normal ordering, a partial hierarchy, and a value of theta(13) close to the existing upper limit. We study the ranges of the lightest neutrino mass m(1) and/or of sin(2)theta(13) for which |< m >| >= 0.001 eV and discuss the phenomenological implications of such scenarios. We provide also an estimate of |< m >| when the three-neutrino masses and the neutrino mixing originate from a neutrino mass term of the Majorana type for the (left-handed) flavor neutrinos and Sigma(3)(j)m(j)U(ej)(2) = 0, but there does not exist a symmetry which forbids the (beta beta)(0 nu)-decay
Precision neutrino oscillation physics with an intermediate baseline reactor neutrino experiment
No full textWe discuss the physics potential of intermediate Lsimilar to20-30 km baseline experiments at reactor facilities. Assuming that the solar neutrino oscillation parameters Deltam(circle dot)(2) and theta(circle dot) lie in the high LMA solution region, we show that such an intermediate baseline reactor experiment can determine both Deltam(circle dot)(2) and theta(circle dot) with a remarkably high precision. We perform also a detailed study of the sensitivity of the indicated experiment to Deltam(atm)(2), which drives the dominant atmospheric nu(mu) ((nu) over bar (mu)) oscillations, and to theta-the neutrino mixing angle limited by the data from the CHOOZ and Palo Verde experiments. Irrespective of the actual values of Deltam(circle dot)(2), we find that this experiment can improve the bounds on sin(2)theta, and, if the value of sin(2)theta is large enough, sin(2)thetagreater than or similar to0.02, the energy resolution of the detector is sufficiently good and if the statistics is relatively high, it can determine with extremely high precision the value of Deltam(atm)(2). We also explore the potential of the intermediate baseline reactor neutrino experiment for determining the type of the neutrino mass spectrum, which can be with normal or inverted hierarchy, assuming Deltam(circle dot)(2) to lie in the high LMA solution region. We show that the conditions under which the type of neutrino mass hierarchy can be determined are quite challenging, but are within the reach of the experiment under discussion
Erratum to: Leptogenesis in the Neutrino Option
No full textErratum to: JHEP10(2019)059
The related work by Vedran Brdar, Alexander J. Helmboldt, Sho Iwamoto and Kai Schmitz, who report consistent results on the viability of leptogenesis in the Neutrino Option [76] and examine possible embeddings of the Neutrino Option in a conformal theory [77, 78], was erroneously not cited in the original version of this paper
A case of subdominant/suppressed “high energy” contribution to the baryon asymmetry of the Universe in flavoured leptogenesis
No full textAbstractThe CP-violation necessary for the generation of the baryon asymmetry of the Universe YB in the “flavoured” leptogenesis scenario can arise from the “low energy” PMNS neutrino mixing matrix U and/or from the “high energy” part of neutrino Yukawa couplings, which can mediate CP-violating phenomena only at some high energy scale. The possible interplay between these two types of CP-violation is analysed. The type I see-saw model with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. We show that in the case of inverted hierarchical light neutrino mass spectrum, there exist regions in the corresponding leptogenesis parameter space where the relevant “high energy” phases have large CP-violating values, but the purely “high energy” contribution in YB plays a subdominant role in the production of baryon asymmetry compatible with the observations. In some of these regions the purely “high energy” contribution in YB is so strongly suppressed that one can have successful leptogenesis only if the requisite CP-violation is provided by the Majorana phase(s) in the neutrino mixing matrix
Analytical description of quasivacuum oscillations of solar neutrinos
No full textWe propose a simple prescription to calculate the solar neutrino survival probability Pee in the quasivacuum oscillation (QVO) regime. Such a prescription is obtained by matching perturbative and exact analytical results, which effectively take into account the density distribution in the Sun as provided by the standard solar model. The resulting analytical recipe for the calculation of Pee is shown to reach its highest accuracy (|ΔPee|<~2.6×10−2 in the whole QVO range) when the familiar prescription of choosing the solar density scale parameter r0 at the Mikheyev-Smirnov-Wolfenstein (MSW) resonance point is replaced by a new one, namely, when r0 is chosen at the point of “maximal violation of adiabaticity” (MVA) along the neutrino trajectory in the Sun. The MVA prescription admits a smooth transition from the QVO regime to the MSW transition one. We discuss in detail the phase acquired by neutrinos in the Sun, and show that it might be of relevance for the studies of relatively short time scale variations of the fluxes of the solar ν lines in the future real-time solar neutrino experiments. Finally, we elucidate the role of matter effects in the convective zone of the Sun
Atmospheric neutrino oscillations, theta (13) and neutrino mass hierarchy
No full textWe derive predictions for the Nadir angle (theta(n)) dependence of the ratio N(mu)/N(e) of the rates of the mu-like and e-like multi-GeV events measured in water-Cerenkov detectors in the case of 3-neutrino oscillations of the atmospheric nu(e) (antinu(e)) and nu(mu) (antinu(mu)), driven by one neutrino mass squared difference, |Delta m2(31)| ~ (2.5 - 3.0) x 10^(-3) eV^2 >> Delta m2(21). This ratio is particularly sensitive to the Earth matter effects in the atmospheric neutrino oscillations, and thus to the values of sin^2(theta(13)) and sin^2(theta(23)), theta(13) and theta(23) being the neutrino mixing angle limited by the CHOOZ and Palo Verde experiments and that responsible for the dominant atmospheric nu(mu) -> nu(tau) (antinu(mu) -> antinu(tau)) oscillations. It is also sensitive to the type of neutrino mass spectrum which can be with normal (Delta m2(31) > 0) or with inverted (Delta m2(31) 0.01, sin^2(theta(23)) > 0.5 and at cos(theta(n)) > 0.4, the Earth matter effects modify substantially the theta(n)-dependence of the ratio N(mu)/N(e) and in a way which cannot be reproduced with sin^2(theta(13)) = 0 and a different value of sin^2(theta(23)). For normal hierarchy the effects can be as large as ~ 25% for cos(theta(n)) ~ (0.5 - 0.8), can reach ~ 35% in the Earth core bin cos(theta(n)) ~ (0.84 - 1.0), and might be observable. They are typically by ~ 10% smaller in the inverted hierarchy case. An observation of the Earth matter effects in the Nadir angle distribution of the ratio N(mu)/N(e) would clearly indicate that sin^2(theta(13)) > 0.01 and sin^2(theta(23)) > 0.50
Effects of Lightest Neutrino Mass in Leptogenesis
No full textThe effects of the lightest neutrino mass in "flavoured" leptogenesis are investigated in the case when the CP-violation necessary for the generation of the baryon asymmetry of the Universe is due exclusively to the Dirac and/or Majorana phases in the neutrino mixing matrix U. The type I see-saw scenario with three heavy right-handed Majorana neutrinos having hierarchical spectrum is considered. The "orthogonal" parametrisation of the matrix of neutrino Yukawa couplings, which involves a complex orthogonal matrix R, is employed. Results for light neutrino mass spectrum with normal and inverted ordering (hierarchy) are obtained. It is shown, in particular, that if the matrix R is real and U-conserving and the lightest neutrino mass m(3) in the case of inverted hierarchical spectrum lies the interval 5 x 10(-4) eV less than or similar to m(3) less than or similar to 7 x 10(-3) eV, the predicted baryon asymmetry can be larger by a factor of similar to 100 than the asymmetry corresponding to negligible m(3) congruent to 0. As consequence, we can have successful thermal leptogenesis for 5 x 10(-6) eV less than or similar to m(3) less than or similar to 5 x 10(-2) eV even if R is real and the only source of CP-violation in leptogenesis is the Majorana and/or Dirac phase(s) in U. (C) 2008 Elsevier B.V. All rights reserved
U_{PMNS} = U_ell^dagger U_nu
No full textWe consider corrections to vanishing U_{e3} and maximal atmospheric neutrino mixing originating from the relation U = U_ell^dagger U_nu, where U is the PMNS mixing matrix and U_ell (U_nu) is associated with the diagonalization of the charged lepton (neutrino) mass matrix. We assume that in the limit of U_ell or U_nu being the unit matrix, one has U_{e3} = 0 and theta_{23} = pi/4, while the solar neutrino mixing angle is a free parameter. Well-known special cases of the indicated scenario are the bimaximal and tri-bimaximal mixing schemes. If U_{e3} \neq 0 and theta_{23} \neq pi/4 due to corrections from the charged leptons, |U_{e3}| can be sizable (close to the existing upper limit) and we find that the value of the solar neutrino mixing angle is linked to the magnitude of CP violation in neutrino oscillations. In the alternative case of the neutrino sector correcting U_{e3} = 0 and theta_{23} = pi/4, we obtain a generically smaller |U_{e3}| than in the first case. Now the magnitude of CP violation in neutrino oscillations is connected to the value of the atmospheric neutrino mixing angle theta_{23}. We find that both cases are in agreement with present observations. We also introduce parametrization independent "sum-rules" for the oscillation parameters
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