Gauged D=7 Supergravity on the S**1/Z_2 Orbifold

TL;DR

This paper constructs a comprehensive model of seven-dimensional supergravity on an S^1/Z_2 orbifold, incorporating boundary theories and anomaly cancellation via a Green-Schwarz mechanism, with all couplings dictated by supersymmetry.

Contribution

It presents the most general couplings of 7D supergravity with boundary 6D theories, demonstrating anomaly cancellation without bulk Chern-Simons terms, using boundary Green-Schwarz terms.

Findings

All anomalies are canceled by boundary Green-Schwarz terms.

Boundary couplings are fully determined by supersymmetry.

No bulk Chern-Simons term is needed for anomaly cancellation.

Abstract

We construct the most general couplings of a bulk seven-dimensional Yang-Mills-Einstein N=2 supergravity with a boundary six-dimensional chiral N=(0,1) theory of vectors and charged hypermultiplets. The boundary consists of two brane worlds sitting at the fixed points of an S^1/Z_2 compactification of the seven-dimensional bulk supergravity. The resulting 6D massless spectrum surviving the orbifold projection is anomalous. By introducing boundary fields at the orbifold fixed points, we show that all anomalies are cancelled by a Green-Schwarz mechanism. In addition, all couplings of the boundary fields to the bulk are completely specified by supersymmetry. We emphasize that there is no bulk Chern-Simons term to cancel the anomalies. The latter is traded for a Green-Schwarz term which emerges in the boundary theory after a duality transformation implemented to construct the bulk supergravity.