Quantum Gravitational Effects and Grand Unification

TL;DR

This paper explores how quantum gravitational effects in grand unified theories can significantly alter the unification scale and boundary conditions, potentially preventing unification altogether.

Contribution

It demonstrates that gravitational effects can be larger than two-loop corrections and may fundamentally impact the viability of coupling constant unification.

Findings

Gravitational effects can modify the unification scale.

These effects can be larger than standard two-loop corrections.

In some cases, they can prevent unification altogether.

Abstract

In grand unified theories with large numbers of fields, renormalization effects significantly modify the scale at which quantum gravity becomes strong. This in turn can modify the boundary conditions for coupling constant unification, if higher dimensional operators induced by gravity are taken into consideration. We show that the generic size of, and the uncertainty in, these effects from gravity can be larger than the two-loop corrections typically considered in renormalization group analyses of unification. In some cases, gravitational effects of modest size can render unification impossible.