arXiv subjects

Fernando Quevedo

Publications and source records attributed to Fernando Quevedo.

94 records · Page 6Linked to original sources

arXiv1993

Baryon Asymmetry, Supersymmetry and Gravitational Anomalies

We discuss two independent issues about the baryon asymmetry of the universe. First, assuming that it is generated by an unspecified source at high temperatures, we study the effects of non-perturbative $SU(2)_W$ dynamics above the electroweak scale, in the context of supersymmetric models. We find that there is a substantial difference with the nonsupersymmetric case with the net effect of relaxing previous bounds on B and L violating interactions. In particular supersymmetry allows neutrino masses as large as 10 eV (preferred by solar neutrino and COBE data and measurable at future neutrino oscillation experiments). Second, we argue that the existence of a mixed lepton number-gravitational anomaly in the standard model will induce B-L violating interactions. These transitions would be catalized by Einstein-Yang-Mills instantons or sphalerons and could create a primordial B-L asymmetry at Planck temperatures or lower. Gravity (and the anomaly structure of the standard model) could then be the ultimate source of the baryon asymmetry. We analyze the viability of the presently known gravitational instantons and sphalerons to realize this scenario. (Talk presented by FQ at the Texas/Pascos Conference, Berkeley Dec.1992.)

hep-ph↗

arXiv1992

Noncompact Coset Spaces in String Theory

A brief overview of strings propagating on noncompact coset spaces G/H is presented in terms of WZW models. The role played by isometries in the existence of target space duality and by fixed points of the gauge transformations in the existence of singularities and horizons, is emphasized. A general classification of the spaces with a single time-like coordinate is presented. The spacetime geometry of a class of models, existing for every dimension and having cosmological and black hole-like interpretations, is discussed.

hep-th↗

arXiv1992

Supersymmetry Protects the Primordial Baryon Asymmetry

It has been argued that any primordial B+L asymmetry existing at very high temperatures can be subsequently erased by anomalous electroweak effects. We argue that this is not necessarily the case in the supersymmetric standard model because, apart from B and/or L, there are, above a certain temperature $T_{SS}$, two other anomalous U(1) currents. As a consequence, anomalous electroweak effects are only able to partially transform a B+L excess into a generation of primordial sparticle (e.g. gaugino) density. This relaxes recent bounds on B,L-violating non-renormalizable couplings by several orders of magnitude. In particular, dimension-5 couplings inducing neutrino masses may be 4 orders of magnitude larger than in the non-supersymmetric case, allowing for neutrino masses of the order of 10 eV. These values are consistent with a MSW+see-saw explanation of the solar-neutrino data and also with possible neutrino oscillations measurable at accelerators. Cosmological bounds on other rare processes, such as neutron-antineutron oscillations get also relaxed by several orders of magnitude compared with previous estimates.

hep-ph↗

arXiv1992

Strings on Curved Spacetimes: Black Holes, Torsion, and Duality

We present a general discussion of strings propagating on noncompact coset spaces $G/H$ in terms of gauged WZW models, emphasizing the role played by isometries in the existence of target space duality. Fixed points of the gauged transformations induce metric singularities and, in the case of abelian subgroups $H$, become horizons in a dual geometry. We also give a classification of models with a single timelike coordinate together with an explicit list for dimensions $D\leq 10$. We study in detail the class of models described by the cosets $SL(2,\IR)\otimes SO(1,1)^{D-2}/SO(1,1)$. For $D\geq 2$ each coset represents two different spacetime geometries: (2D black hole)$\otimes \IR^{D-2}$ and (3D black string)$\otimes \IR^{D-3}$ with nonvanishing torsion. They are shown to be dual in such a way that the singularity of the former geometry (which is not due to a fixed point) is mapped to a regular surface (i.e.\ not even a horizon) in the latter . These cosets also lead to the conformal field theory description of known and new cosmological string models.

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