A D-Brane Alternative to the MSSM

The success of SU(5)-like gauge coupling unification boundary conditions $g_3^2=g_2^2=5/3 g_1^2$ has biased most attempts to embed the SM interactions into a unified structure. After discussing the limitations of the orthodox approach, we propose an alternative that appears to be quite naturally implied by recent developments based on D-brane physics. In this new alternative: 1) The gauge group, above a scale of order 1 TeV, is the minimal left-right symmetric extension $SU(3)\times SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ of the SM; 2) Quarks, leptons and Higgs fields come in three generations; 3) Couplings unify at an intermediate string scale $M_s= 9\times 10^{11}$ GeV with boundary conditions $g_3^2=g_L^2=g_R^2=32/3 g_{B-L}^2$. This corresponds to the natural embedding of gauge interactions into D-branes and is different from the standard SO(10) embedding which corresponds to $k_{B-L}=8/3$. Unification only works in the case of three generations; 4) Proton stability is automatic due to the presence of $Z_2$ discrete R-parity and lepton parities. A specific Type IIB string orientifold model with the above characteristics is constructed. The existence of three generations is directly related to the existence of three complex extra dimensions. In this model the string scale can be identified with the intermediate scale and SUSY is broken also at that scale due to the presence of anti-branes in the vacuum. We discuss a number of phenomenological issues in this model including Yukawa couplings and a built-in axion solution to the strong-CP problem. The present framework could be tested by future accelerators by finding the left-right symmetric extension of the SM at a scale of order 1 TeV.Comment: 50 pages, 7 figures. References adde

Standard-like Models with Broken Supersymmetry from Type I String Vacua

We construct D=4 Type I vacua with massless content remarkably close to that of the standard model of particle physics. They are tachyon-free non-supersymmetric models which are obtained starting with a standard D=4, N=1 compact Type IIB orientifold and adding the same number of Dp-branes and anti-Dp-branes distributed at different points of the underlying orbifold. Supersymmetry-breaking is felt by the observable world either directly, by gravity mediation or gauge mediation, depending on the brane configuration. We construct several simple three generation examples with the gauge group of the standard model or its left-right symmetric extensions. The models contain a number of U(1) gauge groups whose anomalies are cancelled by a generalized Green-Schwarz mechanism. These U(1)'s are broken but may survive as global symmetries providing for a flavour structure to the models. The value of the string scale may be lowered down to the intermediate scale (as required in the gravity mediation case) or down to 1-100 TeV for the non-SUSY models. Thus the present models are the first semirealistic string vacua realizing the possibility of a low string scale. The unbalanced force between the pairs of Dp- and anti-Dp-branes provides for an effect which tends to compactify some of the extra dimensions but no others. This could provide a new mechanism for radius stabilization.Comment: 58 pages, latex (typos corrected and references added

Daily and seasonal variations in the spatial distribution of zooplankton populations in relation to the physical structure in the Ligurian Sea Front

Results from five hydrographic and biological surveys at different seasons across the Ligurian Sea front, using horizontal continuous measurements and vertical profiles are presented. The vertical circulation across the front is described, and two divergences and one convergence are identified as permanent features from data. The key to find their location for each survey is given. The spatial patterns of 14 zooplankton taxa along the transect are established using variance analysis, principal component and correspondence analyses. The spatial distribution of each taxon is related to the physical structure, and the convection cells evidenced by the scheme appear as different biotopes. The daily variability of the spatial distributions is negligible compared to the annual variability. Distinctions are made between coastal species always inhabiting the peripheral (coastal zone) and others with distinct coastal, frontal and offshore distributions varying with the season. For the latter species the frontal zone is a preferential biotope during their seasonal growth period. Consequently the accumulation of organisms near the convergence cannot be created by only the dynamic causes. The role of biological processes in the observed distributions is discussed

A Single Nucleotide Polymorphism in STK11 Influences Insulin Sensitivity and Metformin Efficacy in Hyperinsulinemic Girls With Androgen Excess

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Complete set of Feynman rules for the MSSM -- ERRATUM

This erratum contains the full corrected version of the paper {\em Complete set of Feynman rules for the Minimal Supersymmetric Standard Model}, published in Phys. Rev. D41 (3464) 1990. The complete set of Feynman rules for the R-parity conserving MSSM is listed, including the most general form of flavour mixing. Propagators and vertices are computed in t'Hooft-Feynman gauge, convenient for perturbative calculations beyond the tree level.Comment: 46 pages, uses axodraw.sty. This is the "integrated" version of the erratum, i.e. full text of the paper with errors correcte