40 research outputs found
Proton Stability In Supersymmetric SU(5)
Within supersymmetric SU(5) GUT we suggest mechanisms for suppression of
baryon number violating dimension five and six operators. The mechanism is
based on the idea of split multiplets (i.e. quarks and leptons are not coming
from a single GUT state) which is realized by an extension with additional
vector-like matter. The construction naturally avoids wrong asymptotic relation
. Thus, the long standing problems of the minimal SUSY
SU(5) GUT can be resolved.
In a particular example of flavor structure and with additional {\cal
U}(1)\tm {\cal Z}_{3N} symmetry we demonstrate how the split multiplet
mechanism works out. Namely, the considered model is compatible with successful
gauge coupling unification and realistic fermion mass pattern. The nucleon
decay rates are relatively suppressed and can be well compatible with current
experimental bounds.Comment: Discussions and some clarifications adde
Neutron - Mirror Neutron Oscillations: How Fast Might They Be?
We discuss the phenomenological implications of the neutron (n) oscillation
into the mirror neutron (n'), a hypothetical particle exactly degenerate in
mass with the neutron but sterile to normal matter. We show that the present
experimental data allow a maximal n-n' oscillation in vacuum with a
characteristic time much shorter than the neutron lifetime, in fact as
small as 1 sec. This phenomenon may manifest in neutron disappearance and
regeneration experiments perfectly accessible to present experimental
capabilities and may also have interesting astrophysical consequences, in
particular for the propagation of ultra high energy cosmic rays.Comment: 4 pages, 1 figure; revtex; matches paper published by P.R.
Majoron Decay in Matter
It is well known that the matter can significantly alter the picture of
neutrino oscillation \cite{W} or neutrino decay \cite{BV}. Here we show that
the presence of dense matter induces also the decay of {\it massless} majoron,
a Goldstone boson associated with the spontaneous lepton number violation, into
a couple of neutrinos with the same (or in some cases also opposite)
helicities. We calculate the rates of such matter induced majoron decays in
various cases, depending on the neutrino type and the chemical content of the
medium, and analyse their properties.Comment: 11 pages, no figures, LATEX, INFN-FE-04-9
Generation Symmetry and E_6 Unification
The group E_6 for grand unification is combined with the generation symmetry
group SO(3)_g. The coupling matrices in the Yukawa interaction are identified
with the vacuum expectation values of scalar fields which are representations
of the generation symmetry. These values determine the hierarchy of the
fermions as well as their mixings and CP-violation. This generation mixing
appears in conjunction with the mixing of the standard model fermions with the
heavy fermions present in the lowest representation of E_6. A close connection
between charged and neutral fermions is observed relating for instance the CKM
mixings with the mass splittings of the light neutrinos. Numerical fits with
only few parameters reproduce quantitatively all known fermion properties. The
model predicts an inverted neutrino hierarchy and gives rather strict values
for the light and heavy neutrino masses as well as for the 0\nu 2\beta decay
parameter. It also predicts that the masses of the two lightest of six `right
handed' neutrinos lie in the low TeV region.Comment: RevTex, typos corrected, refs. added. To appear in Phys Rev
Inverse Hierarchy Approach to Fermion Masses
The first fermion family might play a special role in understanding the
physics of flavour. This possibility is suggested by the observation that the
up-down splitting within quark families increases with the family number: , , . We construct a model that realizes this
feature of the spectrum in a natural way. The inter-family hierarchy is first
generated by radiative phenomena in a sector of heavy isosinglet fermions and
then transferred to quarks by means of a universal seesaw. A crucial role is
played by left-right parity and up-down isotopic symmetry. No family symmetry
is introduced. The model implies 0.5 and the Cabibbo angle is forced
to be . The top quark is naturally in the 100 GeV range,
but not too heavy: 150 GeV. Inspired by the mass matrices obtained in
the model for quarks, we suggest an ansatz also including charged leptons. The
differences between -, - and -type fermions are simply parametrized by
three complex coefficients \eps{u}, \eps{d} and \eps{e}. Additional
consistent predictions are obtained: =100-150 MeV and 0.75.Comment: 19 pages (standard TeX) + 1 table (cut out and LaTeX separately) + 1
figure (cut out and postscript separately); 2 additional figures available by
fax upon request, LBL-32889, LMU-13/9
Predictive SUSY SO(10) model with very low
The first fermion family might play a key role in understanding the structure
of flavour: a role of the mass unification point. The GUT scale running masses
are rather close, which may indicate an approximate symmetry
limit. Following this observation, we present a new predictive approach based
on the SUSY theory with . The inter-family hierarchy
is first generated in a sector of hypothetical superheavy fermions and then
transfered inversely to ordinary quarks and leptons by means of the universal
seesaw mechanism. The Yukawa matrices are simply parametrized by the small
complex coefficients \eps_{u,d,e} which are related by the symmetry
properties. Their values are determined by the ratio of the GUT scale
GeV to a higher (possibly string) scale GeV. The suggested ansatz correctly reproduces the fermion
mass and mixing pattern. By taking as input the masses of leptons and and
quarks, the ratio and the value of the Cabibbo angle, we compute
the quark masses, top mass and . The top quark is naturally
in the 100 GeV range, but with upper limit GeV, while the lower bound
GeV implies . can vary from 1.4 to 1.7. The
proton decaying operators are naturally suppressed.Comment: 11 pages, Latex, 2 figures not include
Leptogenesis via Collisions: Leaking Lepton Number to the Hidden Sector
We propose a lepto-baryogenesis mechanism in which the non-zero B-L of the
universe is produced in out-of-equilibrium, lepton number and CP violating
scattering processes that convert ordinary particles into particles of some
hidden sector. In particular, we consider the processes mediated by the heavy Majorana neutrinos of the seesaw
mechanism, where and are ordinary lepton and Higgs doublets and
, their hidden counterparts. Such a leptogenesis mechanism is
effective even if the reheating temperature is much smaller than the heavy
neutrino masses. In particular, it can be as low as GeV.Comment: 4 pages, revtex, 2 figures; as to appear in PRL, supplemented with an
additional remar