3,871 research outputs found
Tau Polarizations in the Three-body Slepton Decays with Stau as the NLSP
In the gauge-mediated supersymmetry breaking models with scalar tau as the
next-to-lightest supersymmetric particle, a scalar lepton may decay dominantly
into its superpartner, tau lepton, and the lightest scalar tau particle. We
give detailed formulas for the three-body decay amplitudes and the polarization
asymmetry of the outgoing tau lepton . We find that the tau polarizations are
sensitive to the model parameters such as the stau mixing angle, the neutralino
to slepton mass ratio and the neutralino mixing effect.Comment: 13 pages, 5 figures, RevTe
Symmetries at ultrahigh energies and searches for neutrino oscillations
Motivated by the possibility that new (gauge) symmetries which are broken at
the grand- (string-) unification scale give rise to texture zeros in the
fermion mass matrices which are at the origin of the hierarchy of masses and
mixings we explore the effect of such zeros on the neutrino spectrum of
SUSY-GUT models. We find that the quadratic-seesaw spectrum on which most
expectations are focused is neither the only nor the most interesting
possibility. Cases of strong or
mixing are present for a specific texture structure of the Yukawa matrices and
experimental evidence can thus throw some light on the latter. In contrast if
the quadratic-seesaw scenario should be confirmed very little could be said
about the symmetries of the Yukawa sector.Comment: 13 pages of LATE
Discovering New Physics in the Decays of Black Holes
If the scale of quantum gravity is near a TeV, the LHC will be producing one
black hole (BH) about every second, thus qualifying as a BH factory. With the
Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may
produce new, undiscovered particles with masses ~100 GeV. The probability of
producing a heavy particle in the decay depends on its mass only weakly, in
contrast with the exponentially suppressed direct production. Furthemore, BH
decays with at least one prompt charged lepton or photon correspond to the
final states with low background. Using the Higgs boson as an example, we show
that it may be found at the LHC on the first day of its operation, even with
incomplete detectors.Comment: 4 pages, 3 figure
Is There a Peccei-Quinn Phase Transition?
The nature of axion cosmology is usually said to depend on whether the
Peccei-Quinn (PQ) symmetry breaks before or after inflation. The PQ symmetry
itself is believed to be an accident, so there is not necessarily a symmetry
during inflation at all. We explore these issues in some simple models, which
provide examples of symmetry breaking before and after inflation, or in which
there is no symmetry during inflation and no phase transition at all. One
effect of these observations is to relax the constraints from isocurvature
fluctuations due to the axion during inflation. We also observe new
possibilities for evading the constraints due to cosmic strings and domain
walls, but they seem less generic.Comment: 14 pages. Several references adde
Gauge Unification in Higher Dimensions
A complete 5-dimensional SU(5) unified theory is constructed which, on
compactification on the orbifold with two different Z_2's (Z_2 and Z_2'),
yields the minimal supersymmetric standard model. The orbifold accomplishes
SU(5) gauge symmetry breaking, doublet-triplet splitting, and a vanishing of
proton decay from operators of dimension 5. Until 4d supersymmetry is broken,
all proton decay from dimension 4 and dimension 5 operators is forced to vanish
by an exact U(1)_R symmetry. Quarks and leptons and their Yukawa interactions
are located at the Z_2 orbifold fixed points, where SU(5) is unbroken. A new
mechanism for introducing SU(5) breaking into the quark and lepton masses is
introduced, which originates from the SU(5) violation in the zero-mode
structure of bulk multiplets. Even though SU(5) is absent at the Z_2' orbifold
fixed point, the brane threshold corrections to gauge coupling unification are
argued to be negligibly small, while the logarithmic corrections are small and
in a direction which improves the agreement with the experimental measurements
of the gauge couplings. Furthermore, the X gauge boson mass is lowered, so that
proton decay to e^+ \pi^0 is expected with a rate within about one order of
magnitude of the current limit. Supersymmetry breaking occurs on the Z_2'
orbifold fixed point, and is felt directly by the gauge and Higgs sectors,
while squarks and sleptons acquire mass via gaugino mediation, solving the
supersymmetric flavor problem.Comment: 21 pages, Latex, references added, final versio
Phenomenology, Astrophysics and Cosmology of Theories with Sub-Millimeter Dimensions and TeV Scale Quantum Gravity
We recently proposed a solution to the hierarchy problem not relying on
low-energy supersymmetry or technicolor. Instead, the problem is nullified by
bringing quantum gravity down to the TeV scale. This is accomplished by the
presence of new dimensions of sub-millimeter size, with the SM
fields localised on a 3-brane in the higher dimensional space. In this paper we
systematically study the experimental viability of this scenario. Constraints
arise both from strong quantum gravitational effects at the TeV scale, and more
importantly from the production of massless higher dimensional gravitons with
TeV suppressed couplings. Theories with are safe due mainly to the
infrared softness of higher dimensional gravity. For , the six dimensional
Planck scale must be pushed above TeV to avoid cooling SN1987A and
distortions of the diffuse photon background. Nevertheless, the particular
implementation of our framework within type I string theory can evade all
constraints, for any , with string scale TeV. We also
explore novel phenomena resulting from the existence of new states propagating
in the higher dimensional space. The Peccei-Quinn solution to the strong CP
problem is revived with a weak scale axion in the bulk. Gauge fields in the
bulk can mediate repulsive forces times stronger than
gravity at sub-mm distances, and may help stabilize the proton.
Higher-dimensional gravitons produced on our brane and captured on a different
"fat" brane can provide a natural dark matter candidate.Comment: 51 pages, late
Resonant sneutrino production at Tevatron Run II
We consider the single chargino production at Tevatron as induced by the resonant sneutrino
production via a dominant \RPV coupling of type \l'_{ijk} L_i Q_j D_k^c.
Within a supergravity model, we study the three leptons final state. The
comparison with the expected background demonstrate that this signature allows
to extend the sensitivity on the \susyq mass spectrum beyond the present LEP
limits and to probe the relevant \RPV coupling down to values one order of
magnitude smaller than the most stringent low energy indirect bounds. The
trilepton signal offers also the opportunity to reconstruct the neutralino mass
in a model independent way with good accuracy.Comment: 4 page
The Status of the Minimal Supersymmetric Standard Model and Beyond
The minimal supersymmetric extension of the Standard Model (MSSM) is
reviewed. In the most general framework with minimal field content and R-parity
conservation, the MSSM is a 124-parameter model (henceforth called MSSM-124).
An acceptable phenomenology occurs only at exceptional points (and small
perturbations around these points) of MSSM-124 parameter space. Among the
topics addressed in this review are: gauge coupling unification, precision
electroweak data, phenomenology of the MSSM Higgs sector, and supersymmetry
searches at present and future colliders. The implications of approaches beyond
the MSSM are briefly addressed.Comment: 17 pages, LaTeX, with espcrc2.sty style file, to appear in the
Proceedings of the 5th International Conference on Supersymmetries in Physics
(SUSY 97
Sneutrino Mixing Phenomena
In any model with nonzero Majorana neutrino masses, the sneutrino and
antisneutrino of the supersymmetric extended theory mix. We outline the
conditions under which sneutrino-antisneutrino mixing is experimentally
observable. The mass-splitting of the sneutrino mass eigenstates and sneutrino
oscillation phenomena are considered.Comment: 12 pages, revtex + axodraw, 1 figure included. Minor change
The 4-D Layer Phase as a Gauge Field Localization: Extensive Study of the 5-D Anisotropic U(1) Gauge Model on the Lattice
We study a 4+1 dimensional pure Abelian Gauge model on the lattice with two
anisotropic couplings independent of each other and of the coordinates. A first
exploration of the phase diagram using mean field approximation and monte carlo
techniques has demonstrated the existence of a new phase, the so called Layer
phase, in which the forces in the 4-D subspace are Coulomb-like while in the
transverse direction (fifth dimension) the force is confining. This allows the
possibility of a gauge field localization scheme. In this work the use of
bigger lattice volumes and higher statistics confirms the existence of the
Layer phase and furthermore clarifies the issue of the phase transitions'
order. We show that the Layer phase is separated from the strongly coupled
phase by a weak first order phase transition. Also we provide evidence that the
Layer phase is separated by the five-dimensional Coulomb phase with a second
order phase transition and we give a first estimation of the critical
exponents.Comment: 19 pages, 16 figure
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