346 research outputs found
Dirac neutrino mixings from hidden symmetry
We explore masses and mixings for Dirac neutrinos in models where lepton
number is conserved, under the guidance of a hidden, but broken,
exchange symmetry, that makes itself evident in the squared hermitian mass
matrix. We study the parameter space in the most general theory as allowed by
current neutrino oscillation experiment data. By using a general
parameterization of the mass matrix which contains only observable parameters
we stablish that the amount of breaking of the symmetry is in the range of the
atmospheric mass scale, without regard to the neutrino hierarchy, the absolute
neutrino mass and the Dirac CP phase. An estimate of the invisible branching
ratio for a Higgs boson decaying into Dirac neutrinos,
, is given and compared to recent measurements
in this context.Comment: Some references adde
Radion Cosmology in Theories with Universal Extra Dimensions
We discuss cosmology of models with universal extra dimensions, where the
Standard Model degrees of freedom live in a dimensional brane, with
compact and small extra spatial dimensions. In these models, the simplest way
to obtain the conventional 4-dimensional Planck scale starting with a low
string scale is to have also some larger extra dimensions, where only gravity
propagates. In such theories, dimensional reduction generically leads to at
least two radion fields, one associated with the total volume of the extra
spatial dimensions, and the other with the ratio of the sizes of small and
large extra dimensions. In this paper, we discuss the impact of the radion
fields on cosmology. We emphasize various aspects of radion physics such as
radion coupling to the Standard Model fields, bare and dressed radion masses
during inflation, dynamical stabilization of radions during and after
inflation, radion decay life time and its late dominance in thermal history of
the Universe as well as its quantum fluctuations during inflation. We argue
that models where the radion plays the role of an inflaton or the inflaton is a
brane scalar field, run into problems. We then present a successful inflation
model with bulk scalar fields that seems to have all the desired properties. We
also briefly discuss the possibility of radion as a cold dark matter candidate.Comment: 37 pages + 3 figure
Dynamical charge and spin density wave scattering in cuprate superconductor
We show that a variety of spectral features in high-T_c cuprates can be
understood from the coupling of charge carriers to some kind of dynamical order
which we exemplify in terms of fluctuating charge and spin density waves. Two
theoretical models are investigated which capture different aspects of such
dynamical scattering. The first approach leaves the ground state in the
disordered phase but couples the electrons to bosonic degrees of freedom,
corresponding to the quasi singular scattering associated with the closeness to
an ordered phase. The second, more phenomological approach starts from the
construction of a frequency dependent order parameter which vanishes for small
energies. Both theories capture scanning tunneling microscopy and angle-resoved
photoemission experiments which suggest the protection of quasiparticles close
to the Fermi energy but the manifestation of long-range order at higher
frequencies.Comment: 27 pages, 13 figures, to appear in New J. Phy
Type II Seesaw and a Gauge Model for the Bimaximal Mixing Explanation of Neutrino Puzzles
We present a gauge model for the bimaximal mixing pattern among the neutrinos
that explains both the atmospheric and solar neutrino data via large angle
vacuum oscillation among the three known neutrinos. The model does not include
righthanded neutrinos but additional Higgs triplets which acquire naturally
small vev's due to the type II seesaw mechanism. A combination of global
and symmetries constrain the mass matrix for both
charged leptons and neutrinos in such a way that the bimaximal pattern emerges
naturally at the tree level and needed splittings among neutrinos at the one
loop level. This model predicts observable branching ratios for , which could be used to test it.Comment: Latex file, 8 pages, five figures include
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