9,916 research outputs found
Multiplicative Conservation of Baryon Number and Baryogenesis
In the canonical seesaw mechanism of neutrino mass, lepton number is only
multiplicatively conserved, which enables the important phenomenon of
leptogenesis to occur, as an attractive explanation of the present baryon
asymmetry of the Universe. A parallel possibility, hitherto unrecognized, also
holds for baryon number and baryogenesis. This new idea is shown to be
naturally realized in the context of a known supersymmetric string-inspired
extension of the Standard Model, based on E(6) particle content, and having an
extra U(1)_N gauge symmetry. Within this framework, two-loop radiative neutrino
masses are also possible, together with a new form of very long-lived matter.Comment: 9 pages, 4 figures, 3 table
Theoretical Expectations for Rare and Forbidden Tau Decays
Given the experimental evidence for oscillations, the
existence of lepton flavor violation in decays is a theoretical
certainty. In this brief review, I consider the connection between models of
neutrino mass and the expected observability of some decays.Comment: Talk at TAU 02 (Santa Cruz, CA
Flavor and Spin Structure of Octet Baryons at Large x
The quark flavor and spin distributions in octet baryons are calculated both
in the SU(6) quark spectator diquark model and in a perturbative QCD (pQCD)
based model. It is shown that the has the most significant difference
in flavor structure at large between the two models, though the flavor and
spin structure of other baryons can also provide tests of different models. The
Drell-Yan process for beams on isoscalar targets can be used to
test different predictions concerning the valence quark flavor structure of the
.Comment: 24 pages, 11 figures, version published in Nucl.Phys.B 574 (2000) 33
Light Charged Higgs Bosons in Supersymmetric Models
We point out that present experimental limits from searches for neutral Higgs
bosons at LEP already imply stringent lower bounds on the mass of the charged
Higgs boson in the Minimal Supersymmetric Standard Model (MSSM); these bounds
are especially severe for low values of \tanb (\tanb \leq 3), where the coupling is large. However, these indirect constraints are much
weaker in simple extensions of the MSSM Higgs sector involving the introduction
of an extra U(1) gauge group or an extra Higgs singlet
field; in the latter case charged Higgs bosons can even be light enough to be
pair produced at LEP.Comment: LaTeX with equation.sty, 3 PS figures. Version to appear in PLB:
Added one paragraph concerning charged Higgs searches at the Tevatro
Scalar Mass Bounds in Two Supersymmetric Extended Electroweak Gauge Models
In two recently proposed supersymmetric extended electroweak gauge models,
the reduced Higgs sector at the 100-GeV energy scale consists of only two
doublets, but they have quartic scalar couplings different from those of the
minimal supersymmetric standard model. In the SU(2) X SU(2) X U(1) model, there
is an absolute upper bound of about 145 GeV on the mass of the lightest neutral
scalar boson. In the SU(3) X U(1) model, there is only a parameter-dependent
upper bound which formally goes to infinity in a particular limitComment: 9 pages (6 figures not included), UCRHEP-T128 (July 1994
Inhibition of food intake in obese subjects by peptide YY3-36
Background: The gut hormone fragment peptide YY3-36 (PYY) reduces appetite and food intake when infused into subjects of normal weight. In common with the adipocyte hormone leptin, PYY reduces food intake by modulating appetite circuits in the hypothalamus. However, in obesity there is a marked resistance to the action of leptin, which greatly limits its therapeutic effectiveness. We investigated whether obese subjects were also resistant to the anorectic effects of PYY.Methods: We compared the effects of PYY infusion on appetite and food intake in 12 obese and 12 lean subjects in a double-blind, placebo-controlled, crossover study. The plasma levels of PYY, ghrelin, leptin, and insulin were also determined.Results: Caloric intake during a buffet lunch offered two hours after the infusion of PYY was decreased by 30 percent in the obese subjects (P<0.001) and 31 percent in the lean subjects (P<0.001). PYY infusion also caused a significant decrease in the cumulative 24-hour caloric intake in both obese and lean subjects. PYY infusion reduced plasma levels of the appetite-stimulatory hormone ghrelin. Endogenous fasting and postprandial levels of PYY were significantly lower in obese subjects (the mean [+/-SE] fasting PYY levels were 10.2+/-0.7 pmol per liter in the obese group and 16.9+/-0.8 pmol per liter in the lean group, P<0.001). Furthermore, the fasting PYY levels correlated negatively with the body-mass index (r=-0.84, P<0.001).Conclusions: We found that obese subjects were not resistant to the anorectic effects of PYY. Endogenous PYY levels were low in the obese subjects, suggesting that PYY deficiency may contribute to the pathogenesis of obesity
Scale of SU(2)_R symmetry breaking and leptogenesis
Models of leptogenesis often invoke the out-of-equilibrium decays of heavy
right-handed neutrinos in order to create a baryon asymmetry of the universe
through the electroweak phase transition. Their presumed existence argues
strongly for the presence of an gauge symmetry. We study the
equilibrating effects of the resulting additional right-handed interactions and
find that successful leptogenesis requires that GeV if
, and
if , where is the mass of the lightest right-handed
neutrino. However, the option is excluded in a supersymmetric
theory with gravitinos.Comment: 4 pages (Revtex); accepted for publication with small modifications;
conclusions unchange
The Quark-Antiquark Asymmetry of the Nucleon Sea from and Fragmentation
We present a general analysis of the spin transfer for and
production in deep-inelastic scattering of polarized charged
leptons on the nucleon, and find that the pattern of different behaviors of
and production observed by the E665 Collaboration
suggests the possibility of quark-antiquark asymmetries either in the quark to
fragmentation functions and/or in the quark and antiquark
distributions of the target proton. We also point out that the
strange-antistrange asymmetry of the nucleon sea may produce an observable
contribution to the different behaviors of and
production. We find that a softer than as predicted by the
light-cone baryon-meson fluctuation model of intrinsic quark-antiquark pairs of
the nucleon sea might lead to a reasonable picture. However, the magnitude is
still too small to explain the E665 data and the conclusion has also strong
model-dependence. This may suggest the importance of quark-antiquark asymmetry
in the quark to fragmentation functions, provided that the E665 data
are confirmed.Comment: 15 latex pages, 2 figure
The universe seen at different scales
A large-scale smoothed-out model of the universe ignores small-scale
inhomogeneities, but the averaged effects of those inhomogeneities may alter
both observational and dynamical relations at the larger scale. This article
discusses these effects, and comments briefly on the relation to gravitational
entropy.Comment: 17 pages; matches published version in Phys. Lett. A (Einstein
special issue
Inclusive Photoproduction of Polarized Quarkonium
We analyse inclusive photoproduction of polarized quarkonium in the
framework of QCD. To separate nonperturbative and perturbative parts in the
density matrix of the produced quarkonium we use a method , which is equivalent
to the diagramatic expansion widely used in analysing deeply inelastic
scatterings. A systematic expansion in a small velocity , with which a heavy
quark moves inside the quarkonium in its rest frame, is performed for the
nonperturbative parts, and they are expressed as matrix elements in
nonrelativistic QCD. At the leading order of there are four matrix elements
representing nonperturbative physics. The perturbative parts are calculated at
the leading order of coupling constants. Some numerical results, especially,
numerical results for HERA are given.Comment: 19 pages+7 Figures as one compressed and encoded postcript fil
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