Marios Petropoulos

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We study D-branes of the SL(2,R) WZW model, and of its discrete orbifolds. Gluing the currents by group automorphisms leads to three types of D-branes : two-dimensional hyperbolic planes (H2), de Sitter branes (dS2), or anti-de-Sitter branes (AdS2). We explain that the dS2 branes are unphysical, because the electric field on their worldvolume is(More)
BACKGROUND We undertook an epidemiological study to investigate whether measles, mumps, and rubella (MMR) vaccine may be causally associated with autism. METHODS Children with autism born since 1979 were identified from special needs/disability registers and special schools in eight North Thames health districts, UK. Information from clinical records was(More)
We investigate the non-perturbative equivalence of some heterotic/type II dual pairs with N = 2 supersymmetry. The perturbative heterotic scalar manifolds are respectively SU(1, 1)/U(1) × SO(2, 2 + NV )/SO(2)× SO(2 + NV ) and SO(4, 4 + NH)/SO(4)× SO(4 + NH) for moduli in the vector multiplets and hypermultiplets. The models under consideration correspond,(More)
We study a non-standard decoupling limit of the D1/D5-brane system, which interpolates between the near-horizon geometry of the D1/D5 background and the nearhorizon limit of the pure D5-brane geometry. The S-dual description of this background is actually an exactly solvable two-dimensional (worldsheet) conformal field theory: {nulldeformed SL(2,R)}·SU(2)·T(More)
We study renormalization-group flows by deforming a class of conformal sigmamodels. We consider overall scale factor perturbation of Einstein spaces as well as more general anisotropic deformations of three-spheres. At leading order in α′, renormalizationgroup equations turn out to be Ricci flows. In the three-sphere background, the latter is the Halphen(More)
We consider NS5-branes distributed along the circumference of an ellipsis and explicitly construct the corresponding gravitational background. This provides a continuous line of deformations between the limiting cases, considered before, in which the ellipsis degenerates into a circle or into a bar. We show that a slight deformation of the background(More)
We analyze asymmetric marginal deformations of SU(2)k and<lb>SL(2,R)k wzw<lb>models. These appear in heterotic string backgrounds with non-vanishing Neveu–Schwarz<lb>three-forms plus electric or magnetic fields, depending on whether the deformation is ellip-<lb>tic, hyperbolic or parabolic. Asymmetric deformations create new families of exact(More)
Starting from an initial classical four-dimensional flat background of the heterotic or type II superstrings, we are able to determine at the string one-loop level the quantum corrections to the effective potential due to the spontaneous breaking of supersymmetry by “geometrical fluxes”. Furthermore, considering a gas of strings at finite temperature, the(More)
Quasimodular forms were the heroes of a Summer school held June 20 to 26, 2010 at Besse et Saint-Anastaise, France. We give a short introduction to quasimodular forms. More details on this topics may be found in [1]. Formes quasimodulaires : une introduction Résumé Les formes quasimodulaires furent les héroines d’une école d’été qui s’est tenue du 20 au 26(More)
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