1,830 research outputs found
Standard Coupling Unification in SO(10), Hybrid Seesaw Neutrino Mass and Leptogenesis, Dark Matter, and Proton Lifetime Predictions
We discuss gauge coupling unification of the SM descending directly from
SO(10) while providing solutions to the three outstanding problems: neutrino
masses, dark matter, and the baryon asymmetry of the universe. Conservation of
matter parity as gauged discrete symmetry in the model calls for high-scale
spontaneous symmetry breaking through Higgs representation. This
naturally leads to the hybrid seesaw formula for neutrino masses mediated by
heavy scalar triplet and right-handed neutrinos. The seesaw formula predicts
two distinct patterns of RH masses, one hierarchical and another not so
hierarchical (or compact) when fitted with the neutrino oscillation data.
Predictions of the baryon asymmetry via leptogenesis are investigated through
the decays of both the patterns of RH masses. A complete flavor analysis
has been carried out to compute CP-asymmetries and solutions to Boltzmann
equations have been utilized to predict the baryon asymmetry. The additional
contribution to vertex correction mediated by the heavy left-handed triplet
scalar is noted to contribute as dominantly as other Feynman diagrams. We have
found successful predictions of the baryon asymmetry for both the patterns of
RH masses. The triplet fermionic dark matter at the TeV scale carrying
even matter parity is naturally embedded into the non-standard fermionic
representation of SO(10). In addition to the triplet scalar and the
triplet fermion, the model needs a nonstandard color octet fermion of mass
GeV to achieve precision gauge coupling unification. Threshold
corrections due to superheavy components of and other representations
are estimated and found to be substantial. It is noted that the proton life
time predicted by the model is accessible to the ongoing and planned
experiments over a wide range of parameter space.Comment: 58 pages PDFLATEX, 19 Figures, Revised as suggested by JHEP Revie
Phase transitions in LuIrSi
We report the results of our investigations on a polycrystalline sample of
LuIrSi which crystallizes in the UCoSi type structure
(Ibam). These investigations comprise powder X-ray diffraction, magnetic
susceptibility, electrical resistivity and high temperature (120-300 K) heat
capacity studies. Our results reveal that the sample undergoes a
superconducting transition below 3.5 K. It also undergoes a first order phase
transition between 150-250 K as revealed by an upturn in the resistivity, a
diasmagnetic drop in the magnetic susceptibility and a large anomaly (20-30
J/mol K) in the specific heat data. We observe a huge thermal hysteresis of
almost 45 K between the cooling and warming data across this high temperature
transition in all our measurements. Low temperature X-ray diffraction
measurements at 87 K reveals that the compound undergoes a structural change at
the high temperature transition. Resistivity data taken in repeated cooling and
warming cycles indicate that at the high temperature transition, the system
goes into a highly metastable state and successive heating/cooling curves are
found to lie above the previous one and the resistance keeps increasing with
every thermal cycle. The room temperature resistance of a thermaly cycled piece
of the sample decays exponentialy with time with a decay time constant
estimated to be about 10 secs. The anomaly (upturn) in the resistivity and
the large drop (almost 45%) in the susceptibility across the high temperature
transition suggest that the observed structural change is accompanied or
induced by an electronic transition.Comment: 7 figures, 1 table and 18 reference
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