726 research outputs found
Probing the Planck Scale with Proton Decay
We advocate the idea that proton decay may probe physics at the Planck scale
instead of the GUT scale. This is possible because supersymmetric theories have
dimension-5 operators that can induce proton decay at dangerous rates, even
with R-parity conservation. These operators are expected to be suppressed by
the same physics that explains the fermion masses and mixings. We present a
thorough analysis of nucleon partial lifetimes in models with a string-inspired
anomalous U(1)_X family symmetry which is responsible for the fermionic mass
spectrum as well as forbidding R-parity violating interactions. Protons and
neutrons can decay via R-parity conserving non-renormalizable superpotential
terms that are suppressed by the Planck scale and powers of the Cabibbo angle.
Many of the models naturally lead to nucleon decay near present limits without
any reference to grand unification.Comment: 11 pages,4 figures. Revised to drop the options y=-6, -7 that are not
phenomenologically viable anyway, following the revision of hep-ph/0312012
this work is based on. Conclusions unchange
Search for Higgs bosons of the Universal Extra Dimensions at the Large Hadron Collider
The Higgs sector of the Universal Extra Dimensions (UED) has a rather
involved setup. With one extra space dimension, the main ingredients to the
construct are the higher Kaluza-Klein (KK) excitations of the Standard Model
Higgs boson and the fifth components of the gauge fields which on
compactification appear as scalar degrees of freedom and can mix with the
former thus leading to physical KK-Higgs states of the scenario. In this work,
we explore in detail the phenomenology of such a Higgs sector of the UED with
the Large Hadron Collider (LHC) in focus. We work out relevant decay branching
fractions involving the KK-Higgs excitations. Possible production modes of the
KK-Higgs bosons are then discussed with an emphasis on their associated
production with the third generation KK-quarks and that under the cascade
decays of strongly interacting UED excitations which turn out to be the only
phenomenologically significant modes. It is pointed out that the collider
searches of such Higgs bosons face generic hardship due to soft end-products
which result from severe degeneracies in the masses of the involved excitations
in the minimal version of the UED (MUED). Generic implications of either
observing some or all of the KK-Higgs bosons at the LHC are discussed.Comment: 25 pages, 9 figures and 1 tabl
Atomic correlations in itinerant ferromagnets: quasi-particle bands of nickel
We measure the band structure of nickel along various high-symmetry lines of
the bulk Brillouin zone with angle-resolved photoelectron spectroscopy. The
Gutzwiller theory for a nine-band Hubbard model whose tight-binding parameters
are obtained from non-magnetic density-functional theory resolves most of the
long-standing discrepancies between experiment and theory on nickel. Thereby we
support the view of itinerant ferromagnetism as induced by atomic correlations.Comment: 4 page REVTeX 4.0, one figure, one tabl
Electronic structure investigation of CeB6 by means of soft X-ray scattering
The electronic structure of the heavy fermion compound CeB6 is probed by
resonant inelastic soft X-ray scattering using photon energies across the Ce 3d
and 4d absorption edges. The hybridization between the localized 4f orbitals
and the delocalized valence-band states is studied by identifying the different
spectral contributions from inelastic Raman scattering and normal fluorescence.
Pronounced energy-loss structures are observed below the elastic peak at both
the 3d and 4d thresholds. The origin and character of the inelastic scattering
structures are discussed in terms of charge-transfer excitations in connection
to the dipole allowed transitions with 4f character. Calculations within the
single impurity Anderson model with full multiplet effects are found to yield
consistent spectral functions to the experimental data.Comment: 9 pages, 4 figures, 1 table,
http://link.aps.org/doi/10.1103/PhysRevB.63.07510
Precise Calculation of the Relic Density of Kaluza-Klein Dark Matter in Universal Extra Dimensions
We revisit the calculation of the relic density of the lightest Kaluza-Klein
particle (LKP) in the model of Universal Extra Dimensions. The Kaluza-Klein
(KK) particle spectrum at level one is rather degenerate, and various
coannihilation processes may be relevant. We extend the calculation of
hep-ph/0206071 to include coannihilation processes with all level one KK
particles. In our computation we consider a most general KK particle spectrum,
without any simplifying assumptions. In particular, we do not assume a
completely degenerate KK spectrum and instead retain the dependence on each
individual KK mass. As an application of our results, we calculate the
Kaluza-Klein relic density in the Minimal UED model, turning on coannihilations
with all level one KK particles. We then go beyond the minimal model and
discuss the size of the coannihilation effects separately for each class of
level 1 KK particles. Our results provide the basis for consistent relic
density computations in arbitrarily general models with Universal Extra
Dimenions.Comment: 44 pages, 19 figures, typeset in JHEP styl
Realistic construction of split fermion models
The Standard Model flavor structure can be explained in theories where the
fermions are localized on different points in a compact extra dimension. We
show that models with two bulk scalars compactified on an orbifold can produce
such separations in a natural way. We study the shapes and overlaps of the
fermion wave functions. We show that, generically, realistic models of Gaussian
overlaps are unnatural since they require very large Yukawa couplings between
the fermions and the bulk scalars. We give an example of a five dimensional two
scalar model that accounts naturally for the observed quark masses, mixing
angles and CP violation.Comment: 15 pages, 5 figures, typos corrected, discussion on the implications
of SM rare decay processes added, to appear in PR
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