749 research outputs found
Roles of two successive phase transitions in new spin-Peierls system TiOBr
In this sturdy, we determine the roles of two successive phase transitions in
the new spin-Peierls system TiOBr by electron and synchrotron X-ray diffraction
analyses. Results show an incommensurate superstructure along the h- and
k-directions between Tc1=27K and Tc2=47K, and a twofold superstructure which is
related to a spin-Peierls lattice distortion below Tc1. The diffuse scattering
observed above Tc2 indicates that a structural correlation develops at a high
temperature. We conclude that Tc2 is a second-order lock-in temperature, which
is related to the spin-Peierls lattice distortion with the incommensurate
structure, and that Tc1 is from incommensurate to commensurate phase transition
temperature accompanying the first-order spin-Peierls lattice distortion.Comment: 4 pages, 5 figure
Affleck-Dine mechanism with negative thermal logarithmic potential
We investigate whether the Affleck-Dine (AD) mechanism works when the
contribution of the two-loop thermal correction to the potential is negative in
the gauge-mediated supersymmetry breaking models. The AD field is trapped far
away from the origin by the negative thermal correction for a long time until
the temperature of the universe becomes low enough. The most striking feature
is that the Hubble parameter becomes much smaller than the mass scale of the
radial component of the AD field, during the trap. Then, the amplitude of the
AD field decreases so slowly that the baryon number is not fixed even after the
onset of radial oscillation. The resultant baryon asymmetry crucially depends
on whether the Hubble parameter, , is larger than the mass scale of the
phase component of the AD field, , at the beginning of oscillation.
If holds, the formation of Q balls plays an essential role to
determine the baryon number, which is found to be washed out due to the
nonlinear dynamics of Q-ball formation. On the other hand, if
holds, it is found that the dynamics of Q-ball formation does not affect the
baryon asymmetry, and that it is possible to generate the right amount of the
baryon asymmetry.Comment: 18 pages, RevTeX4, 9 postscript figures included, final version to
appear in Phys.Rev.
The masses of active neutrinos in the nuMSM from X-ray astronomy
In an extention of the Standard Model by three relatively light right-handed
neutrinos (the nuMSM model) the role of the dark matter particle is played by
the lightest sterile neutrino. We demonstrate that the observations of the
extragalactic X-ray background allow to put a strong upper bound on the mass of
the lightest active neutrino and predict the absolute values of the mass of the
two heavier active neutrinos in the nuMSM, provided that the mass of the dark
matter sterile neutrino is larger than 1.8 keV.Comment: 6 pages. revtex
Hadronic Axion Model in Gauge-Mediated Supersymmetry Breaking and Cosmology of Saxion
Recently we have proposed a simple hadronic axion model within gauge-mediated
supersymmetry breaking. In this paper we discuss various cosmological
consequences of the model in great detail. A particular attention is paid to a
saxion, a scalar partner of an axion, which is produced as a coherent
oscillation in the early universe. We show that our model is cosmologically
viable, if the reheating temperature of inflation is sufficiently low. We also
discuss the late decay of the saxion which gives a preferable power spectrum of
the density fluctuation in the standard cold dark matter model when compared
with the observation.Comment: 24 pages, 3 figure
Supergravity Minimal Inflation and its Spectral Index Revisited
Natural supergravity models of new inflation are reconsidered as minimal
inflationary models within slow-roll approximation. Their running spectral
index is derived in a revised form with recent observational results and future
refinements in mind. This will possibly determine essential model parameters
with respect to Planck-suppressed operators.Comment: 7 pages, late
Predictions on the neutrinoless double beta decay from the leptogenesis via the LHu flat direction
If the baryon asymmetry in the present universe is generated by decays of the
flat direction, the observed baryon asymmetry requires the mass of the
lightest neutrino to be much smaller than the mass scale indicated from the
atmospheric and solar neutrino oscillations. Such a small mass of the lightest
neutrino leads to a high predictability on the rate of the neutrinoless double
beta () decay. In this letter we show general predictions on
the decay in the leptogenesis via the flat direction.Comment: 12 pages, LaTeX, 4 figure
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