Splitting Supersymmetry in String Theory

TL;DR

This paper demonstrates that type I string theory with internal magnetic fields can realize split supersymmetry, producing models with heavy squarks and sleptons but light gauginos and higgsinos, aligning with GUT-scale gauge coupling unification.

Contribution

It constructs realistic string-derived models exhibiting split supersymmetry, including mechanisms to protect gauginos and higgsinos from gravitational corrections, and revisits earlier dismissed string models as viable.

Findings

Gauginos are massless while squarks and sleptons are superheavy.

Models preserve gauge coupling relations and correct sin^2θ_W at GUT scale.

Proposes a discrete R-symmetry to protect gauginos and higgsinos from gravitational effects.

Abstract

We point out that type I string theory in the presence of internal magnetic fields provides a concrete realization of split supersymmetry. To lowest order, gauginos are massless while squarks and sleptons are superheavy. We build such realistic U(3)xU(2)xU(1) models on stacks of magnetized D9-branes. Though not unified into a simple group, these theories preserve the successful supersymmetric relation of gauge couplings, as they start out with equal SU(3) and SU(2) couplings and the correct initial sin^2\theta_W at the compactification scale of M_{GUT}\simeq 2x10^{16} GeV, and they have the minimal low-energy particle content of split supersymmetry. We also propose a mechanism in which the gauginos and higgsinos are further protected by a discrete R-symmetry against gravitational corrections, as the gravitino gets an invariant Dirac mass by pairing with a member of a Kaluza-Klein tower of spin-3/2 particles. In addition to the models proposed here, split supersymmetry offers novel strategies for realistic model-building. So, TeV-scale string models previously dismissed because of rapid proton decay, or incorrect sin^2\theta_W, or because there were no unused dimensions into which to dilute the strength of gravity, can now be reconsidered as candidates for realistic split theories with string scale near M_{GUT}, as long as the gauginos and higgsinos remain light.