A model of vector leptoquarks in view of the $B$-physics anomalies (1709.00692v3)

Abstract: Lepton number as a fourth color is an intriguing theoretical idea which is combined with a possible left-right symmetry within the famous Pati-Salam (PS) model. In the conventional PS model, a spontaneous breaking of the PS gauge group down to the SM one can only take place at very high scales (above the PeV scale) due to the stringent bounds from $K_L\to\mu e$ and $K\to\pi\mu e$ induced by the resulting vector leptoquarks. In this paper, we show that these constraints can be avoided once additional vector-like fermions are introduced and thus a breaking at the TeV scale is possible. We consider the flavor phenomenology of this model in the context of the intriguing hints for new physics in semileptonic $B$ decays. The necessary violation of lepton flavor universality is induced by mixing SM and vector-like fermions. Concerning $R(D)$ and $R(D^*)$ we find that sizable effects are possible while respecting the bounds from other flavor observables but predicting a large enhancement of $B_s\to\tau^+\tau^-$. Furthermore, also in $b\to s\ell^+\ell^-$ transitions the observed deviations from the SM predictions (including $R(K)$ and $R(K^*)$) can be explained with natural values for the free parameters of the model without any fine-tuning, predicting sizable decay rates for $b\to s\tau\mu$. Finally, the anomaly in anomalous magnetic moment of the muon can be accounted for by a loop-contribution involving the vector leptoquark and vector-like leptons.

• The paper presents a novel vector leptoquark model with additional vector-like fermions that lowers the symmetry breaking scale while satisfying flavor physics constraints.
• The paper rigorously analyzes semileptonic B decay anomalies, demonstrating deviations in LFU observables like R(K) and R(D*), and illustrating potential enhancements in processes such as Bₛ→τ⁺τ⁻.
• The paper shows that loop contributions from vector leptoquarks can address the muon g-2 discrepancy, paving the way for targeted experimental validations at colliders.

An Evaluation of Vector Leptoquarks in Context of $B$-Physics Anomalies

This paper presents a theoretical model that explores the application of vector leptoquarks within the established framework of the Pati-Salam (PS) model with an eye towards addressing anomalies observed in $B$-physics. The authors propose a unique approach by integrating lepton flavors into the color charge concept, merging it with the distinguished Pati-Salam model's left-right symmetry. They explore the constraints and implications of breaking the Pati-Salam gauge group at accessible scales, precisely around a few TeVs, rather than the much higher PeV range, traditionally required by constraints from rare decay processes like $K_L\to\mu e$.

Theoretical Framework and Model Construction

The core idea hinges upon the introduction of additional vector-like fermions, which reconfigure the model's flavor structure. This configuration enables a lower symmetry breaking scale while simultaneously maintaining consistency with stringent flavor physics constraints. The innovative aspect of this model lies within its treatment of vector leptoquarks as $SU(4)$ gauge bosons in the PS group, with their theoretical intricacies and implications rigorously analyzed. The classic PS model itself demands a high symmetry breaking scale due to processes such as $K_L\to\mu e$ and $K\to\pi\mu e$, but this research shows that these limitations can be circumvented through strategic incorporation of new physics.

Addressing $B$-Physics Anomalies

Specific focus is provided to anomalies detected in semileptonic $B$ decay processes, particularly in observables such as $R(D)$, $R(D^*)$, $R(K)$ and $R(K^*)$. Here, the necessity to alter lepton flavor universality (LFU) naturally emerges from the mixing of standard model fermions with the introduced vector-like fermions. The results underscore the model's capacity to engender significant deviation from the standard predictions in these processes. For instance, the potential enhancement of $B_s\to\tau^+ \tau^-$ serves as an illustrative point.

Moreover, discrepancies in the anomalous magnetic moment of the muon could potentially be reconciled through loop contributions from vector leptoquarks and vector-like leptons. The paper rigorously evaluates multiple flavor observables to ensure that the predicted outcomes fall within empirical boundaries while also forecasting new experimental signatures, such as notable decay rates for $b\to s \tau \mu$ transitions.

Implications and Prospective Developments in AI

The implications for such a paper are extensive. On a theoretical plane, it suggests a novel realization of lepton coupling models that can potentially resolve enduring anomalies in particle physics. Practically, it establishes a groundwork for future experiments and model validation efforts at particle colliders, like the LHC, where traces of these lower-scale symmetry breaking effects might be detected.

From a perspective of computational developments, constructing and validating such complex models heavily depend on advanced AI and machine learning techniques, particularly when handling vast datasets from particle collision experiments. AI methods for data analysis and simulation can profoundly enhance the precision and scalability of such theoretical physics research.

Conclusion

In essence, this research offers a detailed paradigm for incorporating new physics via vector leptoquarks into the established framework of the Pati-Salam model while addressing significant $B$-physics anomalies. The proposed model has substantial implications for future experimental and theoretical research, potentially paving the way for deeper insights into the unification of forces and the intricate tapestry of particle interactions. The synthesis of theoretical innovation with empirical validation remains pivotal, and the research presented here exemplifies this integration.