209 research outputs found
Bi-maximal mixing at GUT, the low energy data and the leptogenesis
In the framework of the minimum supersymmetric model with right-handed
neutrinos, we consider the Bi-maximal mixing which is realized at the GUT scale
and discuss a question that this model can reproduce the low energy phenomena
and the leptogenesis.Comment: Talk given by E. Takasugi at NuFact04, Osaka, Japan, July 26 - August
1,2004 - 3 pages, 4 figure
Yukawa Matrix for the Neutrino and Lepton Flavour Violation
We estimate the magnitude of Lepton Flavour Violation (LFV) from the phase of
the neutrino Yukawa matrix. In the minimal supersymmetric standard model with
right-handed neutrinos, the LFV processes l_i \to l_j \gamma can appear through
the slepton mixing, which comes from the renormalization group effect on the
right-handed neutrino Yukawa interaction between the Grand Unified Theory scale
and the heavy right-handed neutrino mass scale. Two types of phases exist in
the neutrino Yukawa matrix. One is the Majorana phase, which can change the
magnitude of the LFV branching ratios by a few factor. The other phases relate
for the size of the Yukawa hierarchy and its phase effect can change the LFV
branching ratios by several orders of magnitude.Comment: Talk given by K. Tsumura at NuFact04, Osaka, Japan, July 26 - August
1,2004 - 3 pages, 2 figure
Noncommutative geometry and nonabelian Berry phase in the wave-packet dynamics of Bloch electrons
Motivated by a recent proposal on the possibility of observing a monopole in
the band structure, and by an increasing interest on the role of Berry phase in
spintronics, we studied the adiabatic motion of a wave packet of Bloch
functions, under a perturbation varying slowly and incommensurately to the
lattice structure. We show using only the fundamental principles of quantum
mechanics that its effective wave-packet dynamics is conveniently described by
a set of equations of motion (EOM) for a semiclassical particle coupled to a
nonabelian gauge field associated with a geometric Berry phase. Our EOM can be
viewed as a generalization of the standard Ehrenfest's theorem, and their
derivation was asymptotically exact in the framework of linear response theory.
Our analysis is entirely based on the concept of local Bloch bands, a good
starting point for describing the adiabatic motion of a wave packet. One of the
advantages of our approach is that the various types of gauge fields were
classified into two categories by their different physical origin: (i)
projection onto specific bands, (ii) time-dependent local Bloch basis. Using
those gauge fields, we write our EOM in a covariant form, whereas the
gauge-invariant field strength stems from the noncommutativity of covariant
derivatives along different axes of the reciprocal parameter space. The
degeneracy of Bloch bands makes the gauge fields nonabelian. We applied our
formalism to the analyses on various types of Hall and polarization currents.
We highlighted their behavior under time reversal (T) and space inversion (I).
The concept of parity polarization current was also introduced. Together with
charge/spin Hall/polarization currents, this type of orbital current is
expected to be a potential probe for detecting and controling Berry phase.Comment: 39 pages. Typos corrected in the revised versio
Phase effects from the general neutrino Yukawa matrix on lepton flavor violation
We examine contributions from Majorana phases to lepton flavor violating
processes in the framework of the minimal supersymmetric standard model with
heavy right-handed neutrinos. All phases in the complex neutrino Yukawa matrix
are taken into account in our study. We find that in the scenario with
universal soft-breaking terms sizable phase effects can appear on the lepton
flavor violating processes such as , , and
. In particular, the branching ratio of
can be considerably enhanced due to the Majorana phases, so that it can be much
greater than that of .Comment: 14 pages, 4 eps figures, revtex
Enhancement of lepton flavor violation in a model with bi-maximal mixing at the grand unification scale
We study phenomenological predictions in the scenario with the
quasi-degenerate relation among neutrino Dirac masses, m_D1 simeq m_D2 < m_D3,
assuming the bi-maximal mixing at the grand unification scale in supersymmetric
standard models with right-handed neutrinos. A sufficient lepton number
asymmetry can be produced for successful leptogenesis. The lepton flavor
violating process mu to e gamma can be enhanced due to the Majorana phase, so
that it can be detectable at forthcoming experiments. The processes tau to e
gamma and tau to mu gamma are suppressed because of the structure of neutrino
Dirac masses, and their branching ratios are smaller than that of mu to e
gamma.Comment: 15 pages, 5 figure
CP violation in scatterings, three body processes and the Boltzmann equations for leptogenesis
We obtain the Boltzmann equations for leptogenesis including decay and
scattering processes with two and three body initial or final states. We
present an explicit computation of the CP violating scattering asymmetries. We
analyze their possible impact in leptogenesis, and we discuss the validity of
their approximate expressions in terms of the decay asymmetry. In scenarios in
which the initial heavy neutrino density vanishes, the inclusion of CP
asymmetries in scatterings can enforce a cancellation between the lepton
asymmetry generated at early times and the asymmetry produced at later times.
We argue that a sizeable amount of washout is crucial for spoiling this
cancellation, and we show that in the regimes in which the washouts are
particularly weak, the inclusion of CP violation in scatterings yields a
reduction in the final value of the lepton asymmetry. In the strong washout
regimes the inclusion of CP violation in scatterings still leads to a
significant enhancement of the lepton asymmetry at high temperatures; however,
due to the independence from the early conditions that is characteristic of
these regimes, the final value of the lepton asymmetry remains approximately
unchanged.Comment: 24 pages, 6 figures. One appendix added. Some numerical results and
corresponding figures (mainly fig. 3) corrected. Final version to be
published in JHE
Charged Lepton Decays L_i to L_j + gamma, Leptogenesis CP-Violating Parameters and Majorana Phases
We analyse the dependence of the rates of the LFV charged lepton decays mu to
e + gamma, tau to e + gamma, tau to mu + gamma (l_i to l_j + gamma) and their
ratios, predicted in the class of SUSY theories with see-saw mechanism of
nu-mass generation and soft SUSY breaking with universal boundary conditions at
the GUT scale, on the Majorana CP-violation phases in the PMNS neutrino mixing
matrix and the ``leptogenesis'' CP-violating (CPV) parameters. The case of
quasi-degenerate in mass heavy Majorana neutrinos is considered. The analysis
is performed for normal hierarchical (NH), inverted hierarchical (IH) and
quasi-degenerate (QD) light neutrino mass spectra. We show, in particular, that
for NH and IH nu-mass spectrum and negligible lightest neutrino mass, all three
l_i to l_j + gamma decay branching ratios, BR(l_i to l_j + gamma), depend on
one Majorana phase, one leptogenesis CPV parameter and on the 3-neutrino
oscillation parameters; if the CHOOZ mixing angle theta_13 is sufficiently
large, they depend on the Dirac CPV phase in the PMNS matrix. The ``double
ratios'' R(21/31) sim BR(mu to e + gamma)/BR(tau to e + gamma) and R(21/32) sim
BR(mu to e + gamma)/BR(tau to mu + gamma) are determined by these parameters.
The same Majorana phase enters into the NH and IH expressions for the effective
Majorana mass in neutrinoless double beta decay, .Comment: 27 pages, 5 figures, version to be published in Physical Review
Anomalous Hall effect in ferromagnetic semiconductors
We present a theory of the anomalous Hall effect in ferromagnetic (Mn,III)V
semiconductors. Our theory relates the anomalous Hall conductance of a
homogeneous ferromagnet to the Berry phase acquired by a quasiparticle
wavefunction upon traversing closed paths on the spin-split Fermi surface of a
ferromagnetic state. It can be applied equally well to any itinerant electron
ferromagnet. The quantitative agreement between our theory and experimental
data in both (In,Mn)As and (Ga,Mn)As systems suggests that this disorder
independent contribution to the anomalous Hall conductivity dominates in
diluted magnetic semiconductors.Comment: 4 pages, 2 figure
CP Violation and Lightest Neutrino Mass Effects in Thermal Leptogenesis
Effects of the lightest neutrino mass in "flavoured" leptogenesis 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 are discussed. 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 , is employed. Results for light
neutrino mass spectrum with normal and inverted ordering (hierarchy) are
reviewed.Comment: To appear in the proceedings of DISCRETE'08, Symposium on Prospects
in the Physics of Discrete Symmetries, IFIC, Valencia, Spain, 11-16 December
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