A Compact Codimension Two Braneworld with Precisely One Brane

Building on earlier work on football shaped extra dimensions, we construct a compact codimension two braneworld with precisely one brane. The two extra dimensions topologically represent a 2-torus which is stabilized by a bulk cosmological constant and magnetic flux. The torus has positive constant curvature almost everywhere, except for a single conical singularity at the location of the brane. In contradistinction to the football shaped case, there is no fine-tuning required for the brane tension. We also present some plausibility arguments why the model should not suffer from serious stability issues.Comment: 13 pages, 2 figures; references added, typos fixes; essentially the version published in PR

Thresholds for Intersecting D-branes Revisited

Gauge threshold corrections for intersecting D6-brane string models on toroidal orbifold backgrounds are reconsidered. Both by dimensionally regularising the appearing open string one-loop diagrams in tree-channel as well as by zeta-function regularisation of the corresponding loop-channel one-loop diagrams, we arrive at a result which takes into account the infrared divergence from the contribution of the massless states in the running of the gauge coupling constant as well as the contribution of states, which become light in certain regions of the moduli space.Comment: 14 page

Instantons and Holomorphic Couplings in Intersecting D-brane Models

We clarify certain aspects and discuss extensions of the recently introduced string D-instanton calculus (hep-th/0609191). The one-loop determinants are related to one-loop open string threshold corrections in intersecting D6-brane models. Utilising a non-renormalisation theorem for the holomorphic Wilsonian gauge kinetic functions, we derive a number of constraints for the moduli dependence of the matter field Kaehler potentials of intersecting D6-brane models on the torus. Moreover, we compute string one-loop corrections to the Fayet-Iliopoulos terms on the D6-branes finding that they are proportional to the gauge threshold corrections. Employing these results, we discuss the issue of holomorphy for E2-instanton corrections to the superpotential. Eventually, we discuss E2-instanton corrections to the gauge kinetic functions and the FI-terms.Comment: 28 pages, 5 figure

Pure Gauge SU(2) Seiberg-Witten Theory and Modular Forms

We identify the spectral curve of pure gauge SU(2) Seiberg-Witten theory with the Weierstrass curve \mathbbm{C}/L \ni z \mapsto (1,\wp(z),\wp(z)') and thereby obtain explicitely a modular form from which the moduli space parameter $u$ and lattice parameters $a$, $a_D$ can be derived in terms of modular respectively theta functions. We further discuss its relationship with the $c=-2$ triplet model conformal field theory.Comment: 11 + 2 pages, no figures, shortened, to be published in jm

D-brane Instantons in 4D Supersymmetric String Vacua

We review some aspects of D-instantons in intersecting D-brane models. In particular, we present applications of the recently proposed instanton calculus to computations of charged matter superpotential couplings and corrections to the gauge kinetic function in the low energy effective action of type IIA orientifolds. As an interesting byway, we also discuss how one-loop corrections to the gauge kinetic function can be deduced from gauge threshold corrections in the type IIA setting.Comment: 16 pages, 3 figures. Contribution to the proceedings of the BW2007 Workshop "Challenges Beyond the Standard Model", September 2-9, 2007, Kladovo, Serbi

Gauge Thresholds and Kaehler Metrics for Rigid Intersecting D-brane Models

The gauge threshold corrections for globally consistent Z2 x Z2' orientifolds with rigid intersecting D6-branes are computed. The one-loop corrections to the holomorphic gauge kinetic function are extracted and the Kaehler metrics for the charged chiral multiplets are determined up to two constants.Comment: 22 pages, 1 figure; v2: minor modifications, version to appear in JHE

Relative entropy as a measure of inhomogeneity in general relativity

We introduce the notion of relative volume entropy for two spacetimes with preferred compact spacelike foliations. This is accomplished by applying the notion of Kullback-Leibler divergence to the volume elements induced on spacelike slices. The resulting quantity gives a lower bound on the number of bits which are necessary to describe one metric given the other. For illustration, we study some examples, in particular gravitational waves, and conclude that the relative volume entropy is a suitable device for quantitative comparison of the inhomogeneity of two spacetimes.Comment: 15 pages, 7 figure

Formation and characterization of FeLV iscoms.

Immunostimulating complexes (ISCOMs) have been prepared from feline leukaemia virus (FeLV) envelope proteins. The ISCOMs were characterized biochemically in SDS-polyacrylamide gel electrophoresis showing the presence of proteins of estimated molecular weights of 15,000, 27,000 and 70,000. Immunoblotting showed that both the transmembrane protein p15E and the external glycoprotein gp70 (making up the gp85 protein) were present in the ISCOM. Furthermore, a degradation product of gp70 with an estimated molecular weight of 32,000 was identified in the immunoblot. The FeLV ISCOM was shown by electron microscopy to have the characteristic cage-like structure of an ISCOM with a mean diameter of 37 nm. About 10% of the total amount of gp70 in the culture fluid was recovered in the ISCOMs. The largest loss was encountered during the sedimentation of the virus. In a preliminary immunization experiment in mice the FeLV ISCOMs elicited after a booster gave a clear-cut immune response against gp70