Brane-Antibrane Kinetic Mixing, Millicharged Particles and SUSY Breaking

TL;DR

This paper explores how kinetic mixing between hidden and visible U(1) gauge factors in nonsupersymmetric string setups can lead to millicharged particles and enhanced SUSY breaking communication, implying an upper string scale bound of around 10^8 GeV.

Contribution

It demonstrates that kinetic mixing occurs generically in nonsupersymmetric brane-antibrane configurations, affecting particle charges and supersymmetry breaking transmission.

Findings

Kinetic mixing induces millicharged particles.

Enhanced SUSY breaking communication surpasses gravitational effects.

String scale is bounded above by approximately 10^8 GeV.

Abstract

It is known that hidden U(1) gauge factors can couple to visible U(1)'s through Kinetic Mixing. This phenomenon is shown generically to occur in nonsupersymmetric string set-ups, between branes and antibranes. Kinetic Mixing acts either to give millicharges (of e.g. hypercharge) to would-be hidden sector fermions, or to generate an enhanced communication of supersymmetry breaking that dominates over the usual gravitational suppression. In either case, the conclusion is that the string scale in nonsupersymmetric brane configurations has a generic upper bound of M_s <~ 10^8 GeV.