Effective Theory Approach to New Physics with Flavour: General Framework and a Leptoquark Example

Abstract

Extending the Standard Model with higher-dimensional operators in an effective-field-theory (EFT) approach provides a systematic framework to study new-physics (NP) effects from a bottom-up perspective, as long as the NP scale is sufficiently large compared to the energies probed in the experimental observables. However, when taking into account the different quark and lepton flavours, the number of free parameters increases dramatically, which makes generic studies of the NP flavour structure infeasible. In this paper, we address this issue in view of the recently observed "flavour anomalies" in $B$-meson decays, which we take as a motivation to develop a general framework that allows us to systematically reduce the number of flavour parameters in the EFT. This framework can be easily used in global fits to flavour observables at Belle II and LHCb as well as in analyses of flavour-dependent collider signatures at the LHC. Our formalism represents an extension of the well-known minimal-flavour-violation approach, and uses Froggatt-Nielsen charges to define the flavour power-counting. As a relevant illustration of the formalism, we apply it to the flavour structures which could be induced by a $U_1$ vector leptoquark, which represents one of the possible explanations for the recent hints of flavour non-universality in semileptonic $B$-decays. We study the phenomenological viability of this specific framework performing a fit to low-energy flavour observables.

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References in corpus (11)

• B-physics anomalies: a guide to combined explanations
• Search for lepton-universality violation in $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ decays
• Gauge leptoquark as the origin of B-physics anomalies
• Baryon Number and Lepton Universality Violation in Leptoquark and Diquark Models
• $SU(2)\times U(1)$ gauge invariance and the shape of new physics in rare $B$ decays
• $R(D^{\ast })$, $|V_{cb}|$, and the Heavy Quark Symmetry relations between form factors
• Extraction of $|V_{cb}|$ from $B\to D^{(\ast )}\ell {\nu }_{\ell }$ and the Standard Model predictions of $R(D^{(\ast )})$
• Leptoquark Flavor Patterns & B Decay Anomalies
• High-pT Signatures in Vector-Leptoquark Models
• With or without U(2)? Probing non-standard flavor and helicity structures in semileptonic B decays
• Probing Lepton Flavour Universality with $K\to \pi \nu \bar{\nu }$ decays

Cited by in corpus (1)

• Lepton flavour violation in rare ${\Lambda }_b$ decays