New physics in b→sℓℓ transitions at one loop

• Published in: The European physical journal. C, Particles and fields Vol. 80; no. 1
• Main Authors: Coy, Rupert, Frigerio, Michele, Mescia, Federico, Sumensari, Olcyr
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.01.2020; Springer Nature B.V
• Subjects: Anomalies; Astronomy; Astrophysics and Cosmology; Elementary Particles; Fermions; Field theory; Flavor (particle physics); Hadrons; Heavy Ions; Large Hadron Collider; Leptons; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Regular Article - Theoretical Physics; Standard model (particle physics); String Theory
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-019-7581-y

We investigate new-physics contributions to b → s ℓ ℓ transitions in the context of an effective field theory extension of the Standard Model, including operator mixing at one loop. We identify the few scenarios where a single Wilson coefficient, C / Λ 2 ∼ 1 / TeV 2 , induces a substantial shift in the lepton flavour universality ratios R K and R K ∗ at one loop, while evading Z -pole precision tests, collider bounds, and other flavour constraints. Novel fits to the present data are achieved by a left-handed current operator with quark-flavour indices (2, 2) or (3, 3). Interestingly, the running of the Standard Model Yukawa matrices gives the dominant effect for these scenarios. We match the favoured effective-theory scenarios to minimal, single-mediator models, which are subject to additional stringent constraints. Notably, we recognise three viable instances of a leptoquark with one coupling to fermions only. If the anomalies were confirmed, it appears that one-loop explanations have good prospects of being directly tested at the LHC.