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 $\mathcal{B}(B\to K^{(*)}\nu\nu)$.
Highlights
The B-physics anomalies have triggered a renewed interest in theory and phenomenology of models containing leptoquark fields
Only the misalignment of quarks and leptons in Uð2Þξ space, encoded in W 1⁄4 W†qWl, is physical. (ii) The ratio between M1q;l and M1;3 determines the breaking of the Uð2Þq;l flavor symmetry of the light fermions
In this paper we have presented a systematic analysis of the impact of vectorlike fermions, beyond the tree level, in models based on the SUð4Þ × SUð3Þ0 × SUð2ÞL × Uð1ÞX gauge group
Summary
The B-physics anomalies have triggered a renewed interest in theory and phenomenology of models containing leptoquark fields. The purpose of this paper is to go beyond this limitation by analyzing the impact of one-loop corrections due to the exchange of massive vectorlike fermions The latter are a key ingredient for a successful description of the anomalies, and a necessary ingredient to describe the subleading entries in the effective Yukawa couplings of the SM-like chiral fermions [16,17,18,19,20]. Respect to the minimal version of the model, we present a systematic analysis of all the flavor-changing neutralcurrent (FCNC) amplitudes generated beyond the tree level at Oðα4Þ. The latter effects turn out to be relevant for processes such as b → sννor B–Bmixing, which do not receive a tree-level contribution in this class of models. Appendixes A and B provide further details on the vectorlike fermion implementation and on the loop computations, respectively
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