3,388 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

### 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

### Effects of a fundamental mass term in two-dimensional super Yang-Mills theory

We show that adding a vacuum expectation value to a gauge field left over
from a dimensional reduction of three-dimensional pure supersymmetric
Yang-Mills theory generates mass terms for the fundamental fields in the
two-dimensional theory while supersymmetry stays intact. This is similar to the
adjoint mass term that is generated by a Chern-Simons term in this theory. We
study the spectrum of the two-dimensional theory as a function of the vacuum
expectation value and of the Chern-Simons coupling. Apart from some symmetry
issues a straightforward picture arises. We show that at least one massless
state exists if the Chern-Simons coupling vanishes. The numerical spectrum
separates into (almost) massless and very heavy states as the Chern-Simons
coupling grows. We present evidence that the gap survives the continuum limit.
We display structure functions and other properties of some of the bound
states.Comment: 17 pp., 10 figs; substantially revised version to be published in
Phys. Rev.

### Neutrino degeneracy and cosmological nucleosynthesis, revisited

A reexamination of the effects of non-zero degeneracies on Big Bang Nucleosynthesis is made. As previously noted, non-trivial alterations of the standard model conclusions can be induced only if excess lepton numbers L sub i, comparable to photon number densities eta sub tau, are assumed (where eta sub tau is approx. 3 times 10(exp 9) eta sub b). Furthermore, the required lepton number densities (L sub i eta sub tau) must be different for upsilon sub e than for upsilon sub mu and epsilon sub tau. It is shown that this loophole in the standard model of nucleosynthesis is robust and will not vanish as abundance and reaction rate determinations improve. However, it is also argued that theoretically (L sub e) approx. (L sub mu) approx. (L sub tau) approx. eta sub b is much less than eta sub tau which would preclude this loophole in standard unified models

### Can Heavy WIMPs Be Captured by the Earth?

If weakly interacting massive particles (WIMPs) in bound solar orbits are
systematically driven into the Sun by solar-system resonances (as Farinella et
al. have shown is the case for many Earth-crossing asteroids), then the capture
of high-mass WIMPs by the Earth would be affected dramatically because
high-mass WIMPs are captured primarily from bound orbits. WIMP capture would be
eliminated for M_x>630 GeV and would be highly suppressed for M_x>~150 GeV.
Annihilation of captured WIMPs and anti-WIMPs is expected to give rise to
neutrinos coming from the Earth's center. The absence of such a neutrino signal
has been used to place limits on WIMP parameters. At present, one does not know
if typical WIMP orbits are in fact affected by these resonances. Until this
question is investigated and resolved, one must (conservatively) assume that
they are. Hence, limits on high-mass WIMP parameters are significantly weaker
than previously believed.Comment: 8 pages + 1 figure. Submitted to Ap

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