Strings, Matrix Models, and Meanders

I briefly review the present status of bosonic strings and discretized random surfaces in D>1 which seem to be in a polymer rather than stringy phase. As an explicit example of what happens, I consider the Kazakov-Migdal model with a logarithmic potential which is exactly solvable for any D (at large D for an arbitrary potential). I discuss also the meander problem and report some new results on its representation via matrix models and the relation to the Kazakov-Migdal model. A supersymmetric matrix model is especially useful for describing the principal meanders.Comment: 12 pages, 4 Latex figures, uses espcrc2.sty Talk at the 29th Ahrenshoop Symp., Buckow, Germany, Aug.29 - Sep.2, 199

Baryogenesis through leptogenesis

Baryogenesis by heavy-neutrino decay and sphaleron reprocessing of both baryon and lepton number is reconsidered, paying special attention to the flavour structure of the general evolution equations and developing an approximate but sufficiently accurate analytic solution to the prototype evolution equation. Two different models of neutrino masses are examined, based on an Abelian U(1) or a non-Abelian U(2) family symmetry. We show that a consistent picture of baryogenesis can emerge in both cases, although with significant differences.Comment: 14 pages. v4: revised using the corrected Boltzmann equations of hep-ph/031012

Spin-Spin Correlation Functions of Spin Systems Coupled to 2-D Quantum Gravity for 0

INTRODUCTION The calculation of the dressed scaling exponents is a milestone in the theory of twodimensional quantum gravity [1]. Strictly speaking, however, the derivation uses only finite size scaling arguments and involves only matter field correlators integrated over all space--time. The concept of a diverging correlation length at the critical point associated with the correlators is not used in the derivation and was never shown to actually exist. It is possible to define a correlation length by defining the two point correlator of a field OE(x) in terms of the reparametrization invariant geodesic distance R between two marked points: G OE (R; ) = R D[g]D[OE] e \GammaS G \GammaS M R d 2 xd 2 y<F

Leptogenesis with single right-handed neutrino dominance

We make an analytic and numerical study of leptogenesis in the framework of the (supersymmetric) standard model plus the seesaw mechanism with a U(1) family symmetry and single right-handed neutrino dominance. In presenting our analytic and numerical results we make a clear distinction between the theoretically clean asymmetry parameter ?1 and the baryon asymmetry YB. In calculating YB we propose and use a fit to the solutions to the Boltzmann equations which gives substantially more reliable results than parametrizations previously used in the literature. Our results show that there is a decoupling between the low energy neutrino observables and the leptogenesis predictions, but that nevertheless leptogenesis is capable of resolving ambiguities within classes of models which would otherwise lead to similar neutrino observables. For example we show that models where the dominant right-handed neutrino is the heaviest are preferred to models where it is the lightest and study an explicit example of a unified model of this type.<br/