612 research outputs found
Neutrino Mass Constraints on R violation and HERA anomaly
R parity violating trilinear couplings of the minimal
supersymmetric standard model (MSSM) are constrained from the limit on the
electron neutrino mass. Strong limits on these couplings follow from the
earlier neglected contribution due to sneutrino vacuum expectation values. The
limits on most of the couplings derived here are stronger than
the existing ones for a wide range in parameters of MSSM. These limits strongly
constrain the interpretation of recent HERA results in scattering in
terms of production of squarks through violating couplings. In particular,
the interpretation in terms of production off strange quark as
suggested recently is not viable for wide ranges in MSSM parameters.Comment: 15 pages with 5 figures, minor typos corrected and a new reference
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Modelling electron interactions: a semi-rigorous method
We report total electron scattering cross sections (TCS) for SF6, SF5 CF3, and CF3I, molecules of interest to the plasma industry over the energy range from threshold to 2000 eV. We also report the total scattering cross sections for e-formaldehyde for which there are currently no theoretical or experimental results reported. The ionization cross sections for these targets are also estimated using the Deustch and Maerk formalism and are compared with Binary Encounter Bethe (BEB) data of Kim
Type I seesaw mechanism for quasi degenerate neutrinos
We discuss symmetries and scenarios leading to quasi-degenerate neutrinos in
type-I seesaw models. The existence of degeneracy in the present approach is
not linked to any specific structure for the Dirac neutrino Yukawa coupling
matrix and holds in general. Basic input is the application of the
minimal flavour violation principle to the leptonic sector. Generalizing this
principle, we assume that the structure of the right handed neutrino mass
matrix is determined by and the charged lepton Yukawa coupling matrix
in an effective theory invariant under specific groups
contained in the full symmetry group of the kinetic energy terms.
invariance also leads to specific structure for the departure from degeneracy.
The neutrino mass matrix (with degenerate mass ) resulting after seesaw
mechanism has a simple form in one
particular scenario based on supersymmetry. This form is shown to lead to
correct description of neutrino masses and mixing angles. The thermal
leptogenesis after inclusion of flavour effects can account for the observed
baryon asymmetry of the universe within the present scenario. Rates for lepton
flavour violating processes can occur at observable levels in the
supersymmetric version of the scenario.Comment: 14 pages; two figure
New model for the neutrino mass matrix
I suggest a model based on a softly broken symmetry L_e - L_mu - L_tau and on
Babu's mechanism for two-loops radiative generation of the neutrino masses. The
model predicts that one of the physical neutrinos (nu_3) is massless and that
its component along the nu_e direction (U_e3) is zero. Moreover, if the
soft-breaking term is assumed to be very small, then the vacuum oscillations of
nu_e have almost maximal amplitude and solve the solar-neutrino problem. New
scalars are predicted in the 10 TeV energy range, and a breakdown of e-mu-tau
universality should not be far from existing experimental bounds.Comment: 7 pages including 3 figure
Implications of partially degenerate neutrinos at a high scale in the light of KamLAND and WMAP
Electroweak radiative corrections can generate the neutrino (mass)
difference required for the large mixing angle solution (LMA) to the solar
neutrino problem if two of the neutrinos are assumed degenerate at high energy.
We test this possibility with the existing experimental knowledge of the low
energy neutrino mass and mixing parameters. We derive restrictions on ranges of
the high scale mixing matrix elements and obtain predictions for the low energy
parameters required in order to get the LMA solution of the solar neutrino
problem picked out by KamLAND. We find that in the case of standard model this
is achieved only when the (degenerate) neutrino masses lie in the range
(0.7-2) \eV which is at odds with the cosmological limit m_{\nu}<0.23 \eV
(at ) established recently using WMAP results. Thus SM radiative
corrections cannot easily generate the LMA solution in this scenario. However,
the LMA solution is possible in case of the MSSM electroweak corrections with
(almost) degenerate spectrum or with inverted mass hierarchy for limited ranges
in the high scale parameters.Comment: 15 pages, LATEX includes five postscript figure
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