A Z2 orbifold compactification of the heterotic string is considered. The resulting 6D GUT groups can be SO(16) or E7 × SU(2) plus some hidden sector groups. The N = 4 supersymmetry is reduced to N = 2. In particular, the SO(16) 6D model with one spinor representation 128 can reduce to the previous 5D SO(16) or SO(14) family unification models after compactifying the sixth dimension. To obtain ...

We study a family of unstable heterotic string theories in more than ten dimensions which are connected via tachyon condensation to the ten-dimensional supersymmetric vacuum of heterotic string theory with gauge group SO(32). Calculating the spectrum of these theories, we find evidence for an S-duality which relates type I string theory in ten dimensions with n additional ninebrane-antininebran...

We study a system of Nc D3-branes intersecting D7-branes and O7-planes in 1 + 1-dimensions. We use anomaly cancellation and string dualities to argue that there must be chiral fermion zero-modes on the D3-branes which are localized near the O7planes. Away from the orientifold limit we verify this by using index theory as well as explicit construction of the zero-modes. This system is related to...

We briefly review attempts to construct string theories that yield the standard model, concentrating on models with a geometric interpretation. Calabi-Yau compactifications are discussed in the context of both the weakly coupled heterotic string and the strongly coupled version, heterotic M-theory. Similarly, we consider orbifold compactifications of weakly coupled heterotic theory and of Type ...

Abstract We present a number of D = 4 bosonic and heterotic string solutions with a covariantly constant null Killing vector which, like the solution of Nappi and Witten (NW), correspond to (gauged) WZW models and thus have a direct conformal field theory interpretation. A class of exact plane wave solutions (which includes the NW solution) is constructed by ‘boosting’ the twisted products of t...

In this paper we consider heterotic compactifications on K3 × T as well as type II compactifications on K3-fibred Calabi-Yau spaces with certain fluxes for the gauge and RR field strengths F and H turned on. By providing an identification of corresponding fluxes we show that the well-known N = 2 heterotic/type II string-string duality still holds for a subset of all possible fluxes, namely thos...

A top-down approach to the flavor puzzle leads eclectic groups which include modular and traditional symmetries. Based on examples of semirealistic T2/Z3 orbifold compactifications heterotic string theory, we discuss breakdown patterns group via interplay vacuum expectation values (vevs) moduli flavon fields. This an attractive scheme with various possibilities obtain "flavor hierarchies" throu...