33,610 research outputs found
Lower Limits on Soft Supersymmetry-Breaking Scalar Masses
Working in the context of the CMSSM, we argue that phenomenological
constraints now require the universal soft supersymmetry-breaking scalar mass
m_0 be non-zero at the input GUT scale. This conclusion is primarily imposed by
the LEP lower limit on the Higgs mass and the requirement that the lightest
supersymmetric particle not be charged. We find that m_0 > 0 for all tan beta
if mu 0 only when tan beta sim 8 and
one allows an uncertainty of 3+ GeV in the theoretical calculation of the Higgs
mass. Upper limits on flavour-changing neutral interactions in the MSSM squark
sector allow substantial violations of non-universality in the m_0 values, even
if their magnitudes are comparable to the lower limit we find in the CMSSM.
Also, we show that our lower limit on m_0 at the GUT scale in the CMSSM is
compatible with the no-scale boundary condition m_0 = 0 at the Planck scale.Comment: 11 pages, latex, 6 eps figure
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
Note on Signature Change and Colombeau Theory
Recent work alludes to various `controversies' associated with signature
change in general relativity. As we have argued previously, these are in fact
disagreements about the (often unstated) assumptions underlying various
possible approaches. The choice between approaches remains open.Comment: REVTex, 3 pages; to appear in GR
Parameters Affecting Cavitation and Some New Methods for Their Study [Final Report]
New experimental observations are presented which
support the high speed jet mechanism of cavitation damage.
A general discussion of the basic hydrodynamic theory involved is given and the importance of certain parameters on damage are pointed out. New techniques for studying the collapse of single cavities are described and the concept and development of a high speed photographic system using a ruby laser is outlined. Magnifications of up to fifty times at picture repetition rates as high as 1,600,000 per second and exposure times of 20 billionths of a second have been achieved
Jet Investigations Using the Radial Moment
We define the radial moment, , for jets produced in hadron-hadron
collisions. It can be used as a tool for studying, as a function of the jet
transverse energy and pseudorapidity, radiation within the jet and the quality
of a perturbative description of the jet shape. We also discuss how
non-perturbative corrections to the jet transverse energy affect .Comment: 14 pages, LaTeX, 6 figure
Full one-loop amplitudes from tree amplitudes
We establish an efficient polynomial-complexity algorithm for one-loop
calculations, based on generalized -dimensional unitarity. It allows
automated computations of both cut-constructible {\it and} rational parts of
one-loop scattering amplitudes from on-shell tree amplitudes. We illustrate the
method by (re)-computing all four-, five- and six-gluon scattering amplitudes
in QCD at one-loop.Comment: 27 pages, revte
A cosmic equation of state for the inhomogeneous Universe: can a global far-from-equilibrium state explain Dark Energy?
A system of effective Einstein equations for spatially averaged scalar
variables of inhomogeneous cosmological models can be solved by providing a
`cosmic equation of state'. Recent efforts to explain Dark Energy focus on
`backreaction effects' of inhomogeneities on the effective evolution of
cosmological parameters in our Hubble volume, avoiding a cosmological constant
in the equation of state. In this Letter it is argued that, if kinematical
backreaction effects are indeed of the order of the averaged density (or larger
as needed for an accelerating domain of the Universe), then the state of our
regional Hubble volume would have to be in the vicinity of a
far-from-equilibrium state that balances kinematical backreaction and average
density. This property, if interpreted globally, is shared by a stationary
cosmos with effective equation of state . It
is concluded that a confirmed explanation of Dark Energy by kinematical
backreaction may imply a paradigmatic change of cosmology.Comment: 7 pages, matches published version in Class. Quant. Gra
Convergence properties of the effective interaction
The convergence properties of two perturbative schemes to sum the so-called
folded diagrams are critically reviewed, with an emphasis on the intruder state
problem. The methods we study are the approaches of Kuo and co-workers and Lee
and Suzuki. The suitability of the two schemes for shell-model calculations are
discussed.Comment: 10 pages in revtex ver. 3.0. 3 figs can be obtained upon request.
Univerisity of Oslo report UiO/PHYS/93-2
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