Type IIB orientifolds on Gepner points

TL;DR

This work develops a systematic framework for Type IIB orientifolds at Gepner points, combining the torus, Klein bottle, cylinder, and Möbius strip amplitudes to construct consistent open-descendant theories in $D=8,6,$ and $4$ dimensions. By modding the internal $N=2$ Gepner blocks with discrete phase symmetries and cyclic permutations, the authors show controlled reductions in generations, possible gauge-group enhancements or breakings, and topology changes, including the introduction of antibrane sectors for non-supersymmetric vacua. The approach hinges on exact modular-invariant constructions of supersymmetric characters, tadpole cancellation through Chan-Paton factors, and factorization constraints that tie closed- and open-string data together, with explicit illustrative models and spectra provided in the eight-, six-, and four-dimensional examples. The results offer a concrete, algebraic path toward phenomenologically interesting Gepner-based orientifolds and point toward extensions to broader classes of Gepner and coset constructions, including potential heterotic duals and non-diagonal invariants.

Abstract

We study various aspects of orientifold projections of Type IIB closed string theory on Gepner points in different dimensions. The open string sector is introduced, in the usual constructive way, in order to cancel RR charges carried by orientifold planes. Moddings by cyclic permutations of the internal N=2 superconformal blocks as well as by discrete phase symmetries are implemented. Reduction in the number of generations, breaking or enhancements of gauge symmetries and topology changes are shown to be induced by such moddings. Antibranes sector is also considered; in particular we show how non supersymmetric models with antibranes and free of closed and open tachyons do appear in this context. A systematic study of consistent models in D=8 dimensions and some illustrative examples in D=6 and D=4 dimensions are presented.