D=4 Chiral String Compactifications from Intersecting Branes

TL;DR

This work demonstrates a systematic construction of four-dimensional chiral gauge theories from intersecting D-branes wrapped on cycles within toroidal-orbifold spaces, covering D6-, D4-, and D5-brane configurations. It analyzes RR tadpole cancellation and anomaly inflow, showing that mixed U(1) anomalies are canceled by a generalized Green-Schwarz mechanism mediated by untwisted and twisted RR fields, with anomalous U(1)s becoming string-scale massive. The authors provide explicit three-generation Standard Model-like models (non-supersymmetric) and discuss tachyonic instabilities, their potential elimination via orbifolds or orientifolds, and the intriguing possibility that tachyons may play the role of Higgs fields triggering symmetry breaking. They also discuss the phenomenological relevance of low string scales and the existence of (meta)stable brane configurations, highlighting a flexible bottom-up approach to string phenomenology in open-string vacua.

Abstract

Intersecting Dp-branes often give rise to chiral fermions living on their intersections. We study the construction of four-dimensional chiral gauge theories by considering configurations of type II D(3+n)-branes wrapped on non-trivial n-cycles on T^{2n} x(R^{2(3-n)}/Z_N), for n=1,2,3. The gauge theories on the four non-compact dimensions of the brane world-volume are generically chiral and non-supersymmetric. We analyze consistency conditions (RR tadpole cancellation) for these models, and their relation to four-dimensional anomaly cancellation. Cancellation of U(1) gauge anomalies involves a Green-Schwarz mechanism mediated by RR partners of untwisted and/or twisted moduli. This class of models is of potential phenomenological interest, and we construct explicit examples of SU(3) x SU(2) x U(1) three-generation models. The models are non-supersymmetric, but the string scale may be lowered close to the weak scale so that the standard hierarchy problem is avoided. We also comment on the presence of scalar tachyons and possible ways to avoid the associated instabilities. We discuss the existence of (meta)stable configurations of D-branes on 3-cycles in (T^2)^3, free of tachyons for certain ranges of the six-torus moduli.