New Physics Hints from Flavour

TL;DR

This thesis explores recent B-meson decay anomalies and the lepton flavour puzzle within Flavour Physics, proposing new theoretical models and effective field theory frameworks to understand potential signs of physics beyond the Standard Model.

Contribution

It introduces a comprehensive analysis of B-meson anomalies and lepton mass hierarchies, combining effective field theories with supersymmetric models for the first time in this context.

Findings

Analysis of scalar leptoquark models for B-decay anomalies

Development of Rank-One Flavor Violation EFT framework

Proposal of supersymmetric modular invariant models for lepton masses

Abstract

This Thesis presents my personal contributions to two distinct fields, namely the recent experimental anomalies in B-meson decays, and the longstanding quest for a theoretical explanation of lepton masses and mixings, under a unifying umbrella: Flavour Physics. The modern view of the Standard Model as an effective theory is motivated, and the dual role of flavour, as a probe of New Physics effects on one side, and as a piece of the puzzle itself on the other, is emphasized. By jointly discussing two physics cases of different nature, I attempt to offer a broader perspective on the current status of Beyond Standard Model searches. The discussion begins with a preliminary review of Standard Model Effective Field Theories, in which some utility results in theory matching are presented. The focus then moves to B-meson decay anomalies: after introducing Lepton Flavour Universality, we discuss the phenomenology of a specific Standard Model extension by scalar leptoquarks, and also present the Effective Field Theory framework of Rank-One Flavor Violation, providing a less detailed but broader picture for the case of neutral-current anomalies. Finally, we tackle the Standard Model flavour puzzle, describing an attempt to address charged lepton mass hierarchies in the framework of supersymmetric modular invariant models of lepton flavour.