3,961 research outputs found
The Fate of SUSY Flat Directions and their Role in Reheating
We consider the role of supersymmetric flat directions in reheating the
Universe after inflation. One or more flat directions can develop large vevs
during inflation, which can potentially affect reheating by slowing down
scattering processes among inflaton decay products or by coming to dominate the
energy density of the Universe. Both effects occur only if flat directions are
sufficiently long-lived. The computation of their perturbative decay rate, and
a simple estimate of their nonperturbative decay have led to the conclusion
that this is indeed the case. In contrast, we show that flat directions can
decay quickly through nonperturbative channels in realistic models. The mass
matrix for MSSM excitations around flat directions has nondiagonal entries,
which vary with the phase of the (complex) flat directions. The quasi-periodic
motion of the flat directions results in a strong parametric resonance, leading
to the rapid depletion of the flat direction within its first few rotations.
This may preclude any significant role for the flat directions in reheating the
Universe after inflation in models in which the inflaton decays perturbatively.Comment: 30 pages, 6 .ps figures. Final published versio
Exploration of Elastic Scattering Rates for Supersymmetric Dark Matter
We explore the possible cross sections for the elastic scattering of
neutralinos chi on nucleons p,n in the minimal supersymmetric extension of the
standard model (MSSM). Universality of the soft supersymmetry-breaking scalar
masses for the Higgs multiplets is not assumed, but the MSSM parameters are
nevertheless required to lead consistently to an electroweak vacuum. We explore
systematically the region of MSSM parameter space where LEP and other
accelerator constraints are respected, and the relic neutralino density lies in
the range 0.1 < Omega_chi h^2 < 0.3 preferred by cosmology. We also discuss
models with Omega_chi h^2 < 0.1, in which case we scale the density of
supersymmetric dark matter in our galactic halo by Omega_chi h^2 / 0.1,
allowing for the possible existence of some complementary form of cold dark
matter. We find values of the cross sections that are considerably lower than
the present experimental sensitivities. At low neutralino masses, m_chi < 100
GeV, the cross sections may be somewhat higher than in the constrained MSSM
with universal soft Higgs masses, though they are generally lower. In the case
of large m_chi, the cross sections we find may be considerably larger than in
the constrained model, but still well below the present experimental
sensitivity.Comment: 25 pages LaTeX, 7 eps figure
Search for Higgs and New Phenomena at Colliders
The present status of searches for the Higgs boson(s) and new phenomena is
reviewed. The focus is on analyses and results from the current runs of the
HERA and Tevatron experiments. The LEP experiments have released their final
combined MSSM Higgs results for this conference. Also included are results from
sensitivity studies of the LHC experiments and lepton flavour violating
searches from the B factories, KEKB and PEP-II.Comment: XXII International Symposium on Lepton-Photon Interactions at High
Energy (11 pages, 16 figures, 2 tables
Flipped Angles and Phases: A Systematic Study
We discuss systematically the fermion mass and mixing matrices in a generic
\linebreak field-theoretical flipped model, with particular
applications to neutrino and baryon number-changing physics. We demonstrate
that the different quark flavour branching ratios in proton decay are related
to the Cabibbo-Kobayashi-Maskawa angles, whereas the lepton flavour branching
ratios are undetermined. The light neutrino mixing angles observable via
oscillation effects are related to the heavy conjugate (right-handed) neutrino
mass matrix, which also plays a key role in cosmological baryogenesis. The
ratios of neutrino and charged lepton decay modes in baryon decay may also be
related to neutrino oscillation parameters. Plausible Ans\"atze for the
generation structure of coupling matrices motivate additional relations between
physical observables, and yield a satisfactory baryon asymmetry.Comment: 13 pages, no figures, latex (twice), CERN-TH.6842/93, UMN-TH-1130/93,
CTP-TAMU-11/9
LiBeB, Cosmic Rays and Gamma-Ray Line Astronomy
This article is a summary of a recently held conference on the light
elements, Li, Be and B, and their relationship to cosmic-ray origin and
gamma-ray astronomy. The proceedings will be published by the PASP.Comment: latex 6 pages, uses aasms4.sty To appear in the Publications of the
Astronomical Society of the Pacific (PASP
Exploration of the MSSM with Non-Universal Higgs Masses
We explore the parameter space of the minimal supersymmetric extension of the
Standard Model (MSSM), allowing the soft supersymmetry-breaking masses of the
Higgs multiplets, m_{1,2}, to be non-universal (NUHM). Compared with the
constrained MSSM (CMSSM) in which m_{1,2} are required to be equal to the soft
supersymmetry-breaking masses m_0 of the squark and slepton masses, the Higgs
mixing parameter mu and the pseudoscalar Higgs mass m_A, which are calculated
in the CMSSM, are free in the NUHM model. We incorporate accelerator and dark
matter constraints in determining allowed regions of the (mu, m_A), (mu, M_2)
and (m_{1/2}, m_0) planes for selected choices of the other NUHM parameters. In
the examples studied, we find that the LSP mass cannot be reduced far below its
limit in the CMSSM, whereas m_A may be as small as allowed by LEP for large tan
\beta. We present in Appendices details of the calculations of
neutralino-slepton, chargino-slepton and neutralino-sneutrino coannihilation
needed in our exploration of the NUHM.Comment: 92 pages LaTeX, 32 eps figures, final version, some changes to
figures pertaining to the b to s gamma constrain
Accelerator Constraints on Neutralino Dark Matter
The constraints on neutralino dark matter \chi obtained from accelerator
searches at LEP, the Fermilab Tevatron and elsewhere are reviewed, with
particular emphasis on results from LEP 1.5. These imply within the context of
the minimal supersymmetric extension of the Standard Model that m_\chi \ge 21.4
GeV if universality is assumed, and yield for large tan\beta a significantly
stronger bound than is obtained indirectly from Tevatron limits on the gluino
mass. We update this analysis with preliminary results from the first LEP 2W
run, and also preview the prospects for future sparticle searches at the LHC.Comment: Presented by J. Ellis at the Workshop on the Identification of Dark
Matter, Sheffield, September, 1996. 14 pages; Latex; 12 Fig
What if the Higgs Boson Weighs 115 GeV?
If the Higgs boson indeed weighs about 114 to 115 GeV, there must be new
physics beyond the Standard Model at some scale \la 10^6 GeV. The most
plausible new physics is supersymmetry, which predicts a Higgs boson weighing
\la 130 GeV. In the CMSSM with R and CP conservation, the existence, production
and detection of a 114 or 115 GeV Higgs boson is possible if \tan\beta \ga 3.
However, for the radiatively-corrected Higgs mass to be this large, sparticles
should be relatively heavy: m_{1/2} \ga 250 GeV, probably not detectable at the
Tevatron collider and perhaps not at a low-energy e^+ e^- linear collider. In
much of the remaining CMSSM parameter space, neutralino-stau coannihilation is
important for calculating the relic neutralino density, and we explore
implications for the elastic neutralino-nucleon scattering cross section.Comment: 17 pages, 5 eps figure
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