242 research outputs found
Local triviality of the restriction map for immersions with normal crossings: An extension of a result of R. Palais
AbstractLet B, Y be smooth manifolds with dim B=dim Y and let Imm(B, Y) be the space of smooth immersions of B into Y. Let M be a smooth submanifold of B and let r:Imm(B, Y)âImm(M, Y) be the map induced by restriction. The question of when r is a fibration is now of interest in Continuum Mechanics. Let Immx(M, Y) denote the immersions with normal crossings, and let S=râ1(Immx(M, Y)). Using the stability of Immx(M, Y) in Câ(M, Y) under a group action, we show that rÌ:SâImmx(M, Y) is a locally trivial fibration. The result indicates that any obstruction to r being a locally trivial fibration lies at the fibers of those immersions of M into Y which violate a transversality condition
Radiative Corrections to Neutralino and Chargino Masses in the Minimal Supersymmetric Model
We determine the neutralino and chargino masses in the MSSM at one-loop. We
perform a Feynman diagram calculation in the on-shell renormalization scheme,
including quark/squark and lepton/slepton loops. We find generically the
corrections are of order 6%. For a 20 GeV neutralino the corrections can be
larger than 20%. The corrections change the region of
parameter space which is ruled out by LEP data. We demonstrate that, e.g., for
a given and the lower limit on the parameter can shift
by 20 GeV.Comment: 11 pages, JHU-TIPAC-930030, PURD-TH-93-13, uses epsf.sty, 6 uuencoded
postscript figures, added one sentence and a referenc
Anomalous prompt photon production in hadronic collisions at low-
We investigate the discrepancy that exists at low- between
the next--to--leading order QCD calculations of prompt photon production and
the measured cross section. The central values of the measured cross section
are of order 100\% larger than QCD predictions in this region. It has been
suggested that the bremsstrahlung contribution may account for this
discrepancy. The quark fragmentation function has not been
measured and an exactly known asymptotic form is normally used in calculations.
We examine the effect of much larger fragmentation functions on the QCD
predictions. After illustrating the effect of the large fragmentation functions
in some detail for recent CDF data at =1.8~TeV, we perform a
fit to 8 prompt photon data sets ranging in CMS energy from 24~GeV to 1.8~TeV.
While a large fragmentation function normalization may prove to play an
important role in resolving the discrepancy, the present theoretical and
experimental uncertainties prevent any definite normalization value from being
determined.Comment: 14 pages, LBL-33122 and UCB-PTH-92/38. 13 figures available by email,
specify postscript or topdrawe
Complete two-loop effective potential approximation to the lightest Higgs scalar boson mass in supersymmetry
I present a method for accurately calculating the pole mass of the lightest
Higgs scalar boson in supersymmetric extensions of the Standard Model, using a
mass-independent renormalization scheme. The Higgs scalar self-energies are
approximated by supplementing the exact one-loop results with the second
derivatives of the complete two-loop effective potential in Landau gauge. I
discuss the dependence of this approximation on the choice of renormalization
scale, and note the existence of particularly poor choices which fortunately
can be easily identified and avoided. For typical input parameters, the
variation in the calculated Higgs mass over a wide range of renormalization
scales is found to be of order a few hundred MeV or less, and is significantly
improved over previous approximations.Comment: 5 pages, 1 figure. References added, sample test model parameters
listed, minor wording change
Improved full one-loop corrections to A^0 -> \sf_1 \sf_2 and \sf_2 -> \sf_1 A^0
We calculate the full electroweak one-loop corrections to the decay of the
CP-odd Higgs boson A^0 into scalar fermions in the minimal supersymmetric
extension of the Standard Model. For this purpose many parameters of the MSSM
have to be properly renormalized in the on-shell renormalization scheme. We
have also included the SUSY-QCD corrections. For the decay into bottom squarks
and tau sleptons, especially for large \tan\b, the corrections can be very
large making the perturbation expansion unreliable. We solve this problem by an
appropriate definition of the tree-level coupling in terms of running fermion
masses and running trilinear couplings A_f. We also discuss the decay of heavy
scalar fermions into light scalar fermions and A^0. We find that the
corrections can be sizeable and therefore cannot be neglected.Comment: 42 pages, 20 figures (23 eps-files
Phenomenological implications of light stop and higgsinos
We examine the phenomenological implications of light and
higgsinos in the Minimal Supersymmetric Standard Model, assuming and heavy and gauginos. In this simplified setting,
we study the contributions to , , , , , and their interplay.Comment: plain LATEX, 6 figures, 23 A4 page
High-speed polarization sensitive optical frequency domain imaging with frequency multiplexing
Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm
Flavour constraints on scenarios with two or three heavy squark generations
We re-assess constraints from flavour-changing neutral currents in the kaon
system on supersymmetric scenarios with a light gluino, two heavy generations
of squarks and a lighter third generation. We compute for the first time limits
in scenarios with three heavy squark families, taking into account QCD
corrections at the next-to-leading order. We compare our limits with those in
the case of two heavy families. We use the mass insertion approximation and
consider contributions from gluino exchange to constrain the mixing between the
first and second squark generation. While it is not possible to perform a
general analysis, we assess the relevance of each kind of flavour- and
CP-violating parameters. We also provide ready to use magic numbers for the
computation of the Wilson coefficients at 2 GeV for these scenarios.Comment: 23 pages, 14 figures; v3: matches published version (contains
improvements in the presentation and clarifications
Neutralino relic density in supersymmetric GUTs with no-scale boundary conditions above the unification scale
We investigate SU(5) and SO(10) GUTs with vanishing scalar masses and
trilinear scalar couplings at a scale higher than the unification scale. The
parameter space of the models, further constrained by b-\tau Yukawa coupling
unification, consists of a common gaugino mass and of \tan\beta. We analyze the
low energy phenomenology, finding that A-pole annihilations of neutralinos
and/or coannihilations with the lightest stau drive the relic density within
the cosmologically preferred range in a significant region of the allowed
parameter space. Implications for neutralino direct detection and for CERN LHC
experiments are also discussed.Comment: 14 pages, 5 figures, JHEP style. Version accepted for publication in
JHE
Neutralino-Nucleon Cross Section and Charge and Colour Breaking Constraints
We compute the neutralino-nucleon cross section in several supersymmetric
scenarios, taking into account all kind of constraints. In particular, the
constraints that the absence of dangerous charge and colour breaking minima
imposes on the parameter space are studied in detail. In addition, the most
recent experimental constraints, such as the lower bound on the Higgs mass, the
branching ratio, and the muon are considered. The
astrophysical bounds on the dark matter density are also imposed on the
theoretical computation of the relic neutralino density, assuming thermal
production. This computation is relevant for the theoretical analysis of the
direct detection of dark matter in current experiments. We consider first the
supergravity scenario with universal soft terms and GUT scale. In this scenario
the charge and colour breaking constraints turn out to be quite important, and
\tan\beta\lsim 20 is forbidden. Larger values of can also be
forbidden, depending on the value of the trilinear parameter . Finally, we
study supergravity scenarios with an intermediate scale, and also with
non-universal scalar and gaugino masses where the cross section can be very
large.Comment: Final version to appear in JHE
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