5,288 research outputs found
A variety of lepton number violating processes related to Majorana neutrino masses
A Majorana type of the neutrino mass matrix induces a class of lepton number
violating processes. Cross sections of these reactions are given in terms of
the neutrino mass matrix element, and a semi-realistic event rate is estimated.
These processes provide mass and mixing parameters not directly accessible by
the neutrino oscillation experiments. If these processes are discovered with a
larger rate than given here, it would imply a new physics of the lepton number
violation not directly related to the Majorana neutrino mass, such as R-parity
violating operators in SUSY models.Comment: 15 pages, 1 figur
Weak Magnetic Order in the Bilayered-hydrate NaCoOHO Structure Probed by Co Nuclear Quadrupole Resonance - Proposed Phase Diagram in Superconducting NaCoO HO
A weak magnetic order was found in a non-superconducting bilayered-hydrate
NaCoOHO sample by a Co Nuclear Quadrupole Resonance
(NQR) measurement. The nuclear spin-lattice relaxation rate divided by
temperature shows a prominent peak at 5.5 K, below which a Co-NQR peak
splits due to an internal field at the Co site. From analyses of the Co NQR
spectrum at 1.5 K, the internal field is evaluated to be 300 Oe and is
in the -plane. The magnitude of the internal field suggests that the
ordered moment is as small as using the hyperfine coupling
constant reported previously. It is shown that the NQR frequency
correlates with magnetic fluctuations from measurements of NQR spectra and
in various samples. The higher- sample has the stronger
magnetic fluctuations. A possible phase diagram in NaCoOHO is depicted using and , in which the crystal distortion
along the c-axis of the tilted CoO octahedron is considered to be a
physical parameter. Superconductivity with the highest is seemingly
observed in the vicinity of the magnetic phase, suggesting strongly that the
magnetic fluctuations play an important role for the occurrence of the
superconductivity.Comment: 5 pages, 6 figures, submitted to J. Phys. Soc. Jp
Prolonged Decay and CP-asymmetry
Time evolution of unstable particles that occur in the expanding universe is
investigated. The off-shell effect not included in the Boltzmann-like equation
is important for the decay process when the temperature becomes much below the
mass of unstable particle. When the off-shell effect is taken into account, the
thermal abundance of unstable particles at low temperatures has a power law
behavior of temperature ,
unlike the Boltzmann suppressed , with the power related to
the spectral rise near the threshold of the decay and with the decay
rate. Moreover, the relaxation time towards the thermal value is not governed
by the exponential law; instead, it is the power law of time. The evolution
equation for the occupation number and the number density of the unstable
particle is derived, when both of these effects, along with the cosmic
expansion, are included. We also critically examine how the scattering off
thermal particles may affect the off-shell effect to the unstable particle. As
an application showing the importance of the off-shell effect we compute the
time evolution of the baryon asymmetry generated by the heavy boson decay.
It is shown that the out-of equilibrium kinematics previously discussed is
considerably changed.Comment: 33 pages, LATEX file with 9 PS figure
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