Precision Gauge Unification from Extra Yukawa Couplings

TL;DR

This paper explores how extra Yukawa couplings with vector-like GUT multiplets can improve the precision of gauge coupling unification predictions, addressing discrepancies in the strong coupling constant.

Contribution

It demonstrates that Yukawa interactions with extra multiplets can resolve the two-loop discrepancy in alpha_3 predictions within SUSY GUT models.

Findings

Yukawa couplings can correct the two-loop prediction of alpha_3.

Holomorphic scheme simplifies the analysis of gauge coupling running.

The correction remains significant even in weakly-coupled regimes.

Abstract

We investigate the impact of extra vector-like GUT multiplets on the predicted value of the strong coupling. We find in particular that Yukawa couplings between such extra multiplets and the MSSM Higgs doublets can resolve the familiar two-loop discrepancy between the SUSY GUT prediction and the measured value of alpha_3. Our analysis highlights the advantages of the holomorphic scheme, where the perturbative running of gauge couplings is saturated at one loop and further corrections are conveniently described in terms of wavefunction renormalization factors. If the gauge couplings as well as the extra Yukawas are of O(1) at the unification scale, the relevant two-loop correction can be obtained analytically. However, the effect persists also in the weakly-coupled domain, where possible non-perturbative corrections at the GUT scale are under better control.