Related papers: Type-I vacua from non-geometric Orbifolds
The data from collider experiments and cosmic observatories indicates the existence of three light matter generations. In some classes of string compactifications the number of generations is related to a topological quantity, the Euler…
We discuss the construction of chiral four dimensional ${\bf T^6/(Z_3 \times Z_3)}$ orientifold compactifications of IIA theory, using D6-branes intersecting at angles and not aligned with the orientifold O6 planes. Cancellation of mixed…
We show that a large class of physical theories which has been under intensive investigation recently, share the same geometric features in their Hamiltonian formulation. These dynamical systems range from harmonic oscillations to WZW-like…
We consider differential forms associated to Campana's geometric orbifolds from a new perspective, namely, as a qfh-sheaf on the variety underlying the geometric orbifold. This approach avoids having to choose a covering of the underlying…
``Anomalous'' U(1) gauge symmetry with Green-Schwarz anomaly cancellation mechanism is discussed in the orbifold construction of four-dimensional heterotic string models. Some conditions are given as criteria to have ``anomalous'' U(1) in…
We construct a four dimensional chiral N=1 space-time supersymmetric perturbative Type I vacuum corresponding to a compactification on a toroidal Z_2 X Z_2 X Z_3 orbifold with a discrete Wilson line. This model is non-perturbative from the…
We investigate the effects of the leading tadpole potentials of 10D tachyon-free non-supersymmetric strings in warped products of flat geometries of the type M(p+1) x R x T(10-p-2) depending on a single coordinate. In the absence of fluxes…
Symmetric vacua of heterotic M-theory, characterized by vanishing cohomology classes of individual sources in the three-form Bianchi identity, are analyzed on smooth Calabi-Yau three-folds. We show that such vacua do not exist for…
We construct six- and four-dimensional toroidal compactifications of the Type I string with magnetic flux on the D-branes. The open strings in this background probe a noncommutative internal geometry. Phenomenologically appealing features…
The NAHE-set, that underlies the realistic free fermionic models, corresponds to Z2XZ2 orbifold at an enhanced symmetry point, with (h_{11},h_{21})=(27,3). Alternatively, a manifold with the same data is obtained by starting with a Z2XZ2…
Let $N_k$ denote the closed non-orientable surface of genus $k$. In this paper we study the behaviour of the `square map' from the group of isometries of hyperbolic 3-space to the subgroup of orientation preserving isometries. We show that…
We construct a class of Heterotic String vacua described by Landau--Ginzburg theories and consider orbifolds of these models with respect to abelian symmetries. For LG--vacua described by potentials in which at most three scaling fields are…
We extend the four-dimensional gauged supergravity analysis of type IIB vacua on $K3\times T^2/Z_2$ to the case where also D3 and D7 moduli, belonging to N=2 vector multiplets, are turned on. In this case, the overall special geometry does…
Intersecting D-brane worlds provide phenomenologically appealing constructions of four dimensional low energy string vacua. In this talk, a Z_4 x Z_2 orbifold background is taken into account. It is possible to obtain supersymmetric and…
We find the orbifold analog of the topological relation recently found by Freed and Witten which restricts the allowed D-brane configurations of Type II vacua with a topologically non-trivial flat $B$-field. The result relies in Douglas…
We consider classes of noncompact n-folds with trivial canonical bundle, that are linear foliations on nonsingular projective varieties, in general without a projection to the base. We obtain them as first-order deformations of total spaces…
We show that the first twisted cohomology group associated to closed 1-forms on compact manifolds is related to certain 2-dimensional representations of the fundamental group. In particular, we construct examples of nowhere-vanishing…
We analyze non-supersymmetric four dimensional open string models of type IIB string theory compactified on $T^2\times K3$ with Scherk-Schwarz deformation acting on an $S^1$ of the $T^2$ torus. We find that there are always two solutions to…
We give a simple geometric characterization of isospectral orbifolds covered by spheres, complex projective spaces and the quaternion projective line having cyclic fundamental group. The differential operators considered are…
We use the combined action of Z_2-chiral reflections (T-dualities) and shifts to build N=1,2 supersymmetric four-dimensional string compactifications with few moduli. In particular, we consider Z_2^4 asymmetric orbifolds of Type IIB on the…