Gauge leptoquark as the origin of B-physics anomalies (1708.08450v2)

Abstract: The vector leptoquark representation, $U_\mu = (3,1,2/3)$, was recently identified as an exceptional single mediator model to address experimental hints on lepton flavour universality violation in semileptonic $B$-meson decays, both in neutral ($b \to s \mu \mu$) and charged ($b \to c \tau \nu$) current processes. Nonetheless, it is well-known that massive vectors crave an ultraviolet (UV) completion. We present the first full-fledged UV complete and calculable gauge model which incorporates this scenario while remaining in agreement with all other indirect flavour and electroweak precision measurements, as well as, direct searches at high-$p_T$. The model is based on a new non-abelian gauge group spontaneously broken at the TeV scale, and a specific flavour structure suppressing flavour violation in $\Delta F = 2$ processes while inducing sizeable semileptonic transitions.

• The paper introduces a vector leptoquark embedded in a UV complete gauge framework to explain semileptonic B-meson decay anomalies.
• It employs a gauge group SU(4) × SU(3)' × SU(2)_L × U(1)' to naturally suppress flavor-changing processes and meet precision measurements.
• The research provides predictive insights for collider experiments by linking lepton flavor universality violation to TeV-scale observable signatures.

Understanding the Gauge Leptoquark Model to Address B-Physics Anomalies

The presented paper, titled "Gauge leptoquark as the origin of B-physics anomalies," explores the potential of a vector leptoquark representation in addressing observed anomalies in semileptonic B-meson decays. This research integrates the leptoquark within a UV complete gauge model, adhering to constraints from electroweak precision measurements and high-energy physics experiments. The vector leptoquark, $U_\mu = (3,1,2/3)$, is posited as a singular mediator in lepton flavor universality (LFU) violation processes, notably the $b \to s \mu \mu$ and $b \to c \tau \nu$.

Model Framework

The model operates under a gauge group $SU(4) \times SU(3)' \times SU(2)_L \times U(1)'$, allowing a diagonal embedding of the Standard Model (SM) color and hypercharge factors. This framework ensures left-handed currents' dominance in semantics while naturally suppressing flavor anomalies, particularly in $\Delta F = 2$ processes. The scalar sector facilitates breaking the gauge symmetry at the TeV scale, rendering the vector leptoquark, along with a $Z'$ and a chromo-vector $g'$, to contribute significantly to the mediation of the B-physics anomalies.

Analytical Approach

The paper meticulously constructs the scenario by embedding $U_\mu$ into a broken non-abelian gauge group, thereby avoiding issues such as quadratically divergent loop observables evident in composite dynamics approaches. Also, the model uniquely suppresses the $Z'$ couplings to the first generation fermions, mitigating constraints from di-lepton search bounds. Key choices in the model include:

• Linking SM fermion representations to triplets of a shared flavor group.
• Constructing scalar potential configurations to achieve desired symmetry breaking patterns ensuring $G \to G_\text{SM}$.
• Addressing both charged and neutral current anomalies through $U_\mu$ integration, where it naturally suppresses unwanted processes, e.g., neutral meson mixing, due to its specific charge assignments.

Implications and Future Directions

The model implies a set of predictions vital for both future theoretical explorations and direct experimental verifications. The non-abelian gauge symmetry requires consistency across multiple couplings, ensuring uniformity in perturbative robust predictions. A large gauge coupling $g_4$ is instrumental in the model, creating potential challenges but also opportunities in observing these effects at $10^6$ GeV.

Future research should explore the parameter space further to ensure minimal impact from direct search anomalies, systematically addressing potential flavor misalignment effects. Furthermore, with the deployment of larger collider datasets, one might anticipate refining the constraints on vector leptoquarks and their associated anomalies to fine-tune the model's predictive power.

In conclusion, this research exemplifies an ambitious step towards reconciling experimental B-physics anomalies with theoretical frameworks, leveraging both phenomenology and robust gauge theories to elucidate potential physics beyond the Standard Model.