B-anomalies in a twin Pati-Salam theory of flavour including the 2022 LHCb $$ {R}_{K^{\left(\ast \right)}} $$ analysis

Abstract

We perform a comprehensive phenomenological analysis of the twin Pati-Salam theory of flavour, focussing on the parameter space relevant for interpreting the B-anomalies via vector leptoquark U1 exchange. This model provides a very predictive framework in which the U1 couplings and the Yukawa couplings find a common origin via mixing of chiral quarks and leptons with vector-like fermions, providing a direct link between the B-anomalies and the fermion masses and mixing. We propose and study a simplified model with three vector-like fermion families, in the massless first family approximation, and show that the second and third family charged fermion masses and mixings and the B-anomalies can be simultaneously explained and related. The model has the proper flavour structure to be compatible with all low-energy observables, and leads to predictions in promising observables such as τ → 3μ, τ → μγ and $$ B\to {K}^{\left(\ast \right)}\nu \overline{\nu} $$ B → K ∗ ν ν ¯ at Belle II and LHCb. The model also predicts a rich spectrum of TeV scale gauge bosons and vector-like fermions, all accessible to the LHC. In this updated version we have included an extended analysis considering the new 2022 LHCb data on $$ {R}_{K^{\left(\ast \right)}} $$ R K ∗ , which has slightly shifted the preferred parameter space with respect to the 2021 case. The model can still explain the $$ {R}_{D^{\left(\ast \right)}} $$ R D ∗ anomalies at 1σ in a narrow window, however we expect small deviations from the SM on the $$ {R}_{K^{\left(\ast \right)}} $$ R K ∗ ratios, to be tested in the future via more precise measurements by the LHCb collaboration. We also predict RD = $$ {R}_{D^{\ast }} $$ R D ∗ , with future measurements shifting the world averages to slightly smaller central values.

Electroweak-flavour and quark-lepton unification: a family non-universal path

“…From this perspective, the 4321 group should be viewed as the last-but-one step of the symmetry breaking chain from the UV theory down to the SM. Attempts of this type have been presented in [5,8,16,17]. In this paper we present a new proposal along this line, which is significantly different from all previous attempts.…”

$$\tau _{B_{s}}/\tau _{B_{d}}$$ and $$\Delta \Gamma _{s}$$ confront new physics in $$b\rightarrow s\tau \tau $$

“…A well motivated embedding for gauge U 1 leptoquarks is the Pati-Salam group [38], that provides a natural connection with quark-lepton unification. Moreover, explanations of the R D ( * ) anomalies via exchange of the U 1 vector leptoquark had been shown to be naturally connected with the origin of flavour hierarchies and the flavour structure of the SM [39][40][41][42][43][44][45]. Remarkably, the contributions of the U 1 vector leptoquark to R D ( * ) are correlated to an enhancement of b → sτ τ .…”

“…is a good benchmark for 4321 models featuring TeV scale third family quark-lepton unification [30][31][32]39,42,43], while the case C 23τ τ L R = 0 is a good benchmark for the flavour universal 4321 model [35,36,44,45]. Given that U 1 is a vector leptoquark, the leading contribution to M s arising at 1-loop depends on the specific UV completion.…”

“…Given that U 1 is a vector leptoquark, the leading contribution to M s arising at 1-loop depends on the specific UV completion. For the well-motivated case of 4321 models, the contribution to M s is dominated by a vector-like lepton running in the loop, and the most stringent constraints can be avoided as long as the mass of the vector-like lepton is around or below the TeV scale [31,36,45,47]. In this manner, the model is able to address R D ( * ) and the enhancement of B(B s → τ τ ) becomes a key prediction of the model.…”

Gravitational wave signals from leptoquark-induced first-order electroweak phase transitions

“…Leptoquarks (LQs) are hypothetical particles that can convert quarks into leptons and vice versa with great interest in elementary particle physics. From the theoretical aspect, it has been predicted naturally by the Pati-Salam unification of quarks and leptons [1,2], where the leptoquark is first raised, as well as many other grand unified theories [3][4][5][6][7][8][9]. From the experimental side, the existence of leptoquarks is strongly indicated by lepton flavour universality violation (LFUV) in semi-leptonic B decay [10][11][12][13][14][15].…”