Grand unification through gravitational effects

TL;DR

This paper explores how gravitationally induced dimension-5 operators can modify gauge coupling unification scales in grand unified theories, potentially achieving unification at or near the Planck scale.

Contribution

It demonstrates that gravitational effects via dimension-5 operators can significantly alter unification scales in non-supersymmetric SU(5) and SO(10) models, aligning them with the Planck scale.

Findings

Unification scales can be shifted to the Planck scale due to gravitational operators.

Models satisfy proton decay constraints with natural Wilson coefficients.

Unification of gauge and gravitational interactions at high scales is feasible.

Abstract

We systematically study the unification of gauge couplings in the presence of (one or more) effective dimension-5 operators cHGG/4MPl, induced into the grand unified theory by gravitational interactions at the Planck scale MPl. These operators alter the usual condition for gauge coupling unification, which can, depending on the Higgs content H and vacuum expectation value, result in unification at scales MX significantly different than naively expected. We find non-supersymmetric models of SU(5) and SO(10) unification, with natural Wilson coefficients c, that easily satisfy the constraints from proton decay. Furthermore, gauge coupling unification at scales as high as the Planck scale seems feasible, possibly hinting at simultaneous unification of gauge and gravitational interactions. In the Appendix we work out the group theoretical aspects of this scenario for SU(5) and SO(10) unified groups in detail; this material is also relevant in the analysis of non-universal gaugino masses obtained from supergravity.