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 $\nu_\mu - \nu_\tau$ oscillations, the existence of lepton flavor violation in $\tau$ decays is a theoretical certainty. In this brief review, I consider the connection between models of neutrino mass and the expected observability of some $\tau$ 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 $\Lambda$ has the most significant difference in flavor structure at large $x$ 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 $\Sigma^{\pm}$ beams on isoscalar targets can be used to test different predictions concerning the valence quark flavor structure of the $\Sigma^{\pm}$.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 $H^+ \bar{t} b$ 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 $SU(2) \times U(1)_Y$ 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

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 $SU(2)_R$ gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that $m_N \gtrsim 10^{16}$ GeV if $m_N > m_{W_R}$, and $m_{W_R} \gtrsim 3 \times 10^6 GeV (m_N /10^2 GeV)^{2/3}$ if $m_{N}<m_{W_R}$, where $m_{N}$ is the mass of the lightest right-handed neutrino. However, the $m_N > m_{W_R}$ 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 Λ\Lambda and Λˉ\bar{\Lambda} Fragmentation

We present a general analysis of the spin transfer for $\Lambda$ and $\bar{\Lambda}$ production in deep-inelastic scattering of polarized charged leptons on the nucleon, and find that the pattern of different behaviors of $\Lambda$ and $\bar{\Lambda}$ production observed by the E665 Collaboration suggests the possibility of quark-antiquark asymmetries either in the quark to $\Lambda$ 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 $\Lambda$ and $\bar{\Lambda}$ production. We find that a softer $\bar{s}(x)$ than $s(x)$ 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 $\Lambda$ 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

SUSY Contributions to RbR_b and Top Decay

I report on a systematic analysis of the MSSM parameter space to obtain the best SUSY solution to the $R_b$ anomaly within the constraint of top quark decay. Phenomenological implications for top decay and direct stop production at the Tevatron collider are discussed.Comment: Latex file (3 pages)+ 2 ps files containing figures. Invited talk at SUSY96, Maryland, May 199