Vector Leptoquarks Beyond Tree Level III: Vector-like Fermions and Flavor-Changing Transitions

TL;DR

This paper investigates the effects of vector-like fermions on flavor-changing processes in models with vector leptoquarks, revealing significant loop-level contributions that impact B-physics observables and could explain anomalies.

Contribution

It extends previous models by including vector-like fermions and next-to-leading order calculations, showing their role in flavor-changing neutral currents and B-physics anomalies.

Findings

Vector-like fermions induce new flavor symmetry breaking effects.

Loop-level flavor-changing neutral currents are significantly affected.

Predicted 10-50% enhancement in B→K(*)νν decays in relevant parameter regions.

Abstract

Extending previous work on this subject, we evaluate the impact of vector-like fermions at next-to-leading order accuracy in models with a massive vector leptoquark embedded in the $SU(4)\times SU(3)^\prime\times SU(2)_L\times U(1)_X$ gauge group. Vector-like fermions induce new sources of flavor symmetry breaking, resulting in tree-level flavor-changing couplings for the leptoquark not present in the minimal version of the model. These, in turn, lead to a series of non-vanishing flavor-changing neutral-current amplitudes at the loop level. We systematically analyze these effects in semileptonic, dipole and $\Delta F=2$ operators. The impact of these corrections in $b\to s\nu\nu$ and $b\to c\tau\nu$ observables are discussed in detail. In particular, we show that, in the parameter region providing a good fit to the $B$-physics anomalies, the model predicts a $10\%$ to $50\%$ enhancement of $\mathcal{B}(B\to K^{(*)}\nu\nu)$.