Theoretical challenges for flavor physics

We discuss some highlights of the FCC-$$ee$$ ee flavor physics program. It will help to explore various aspects of flavor physics: to test precision calculations, to probe nonperturbative QCD methods, and to increase the sensitivity to physics beyond the standard model. In some areas, FCC-$$ee$$ ee will do much better than current and near-future experiments. We briefly discuss several probes that can be relevant for maximizing the gain from the FCC-$$ee$$ ee flavor program.

Flavour observables and composite dynamics: leptons

We review lepton flavor physics and corresponding observables in the composite Higgs framework with partial compositeness, considering ‘UV complete’ setups as well as effective and holographic approaches. This includes anarchic flavor setups, scenarios with flavor symmetries, and minimal incarnations of the see-saw mechanism that naturally predict non-negligible lepton compositeness. We focus on lepton flavor violating processes, dipole moments, and on probes of lepton flavor universality, all providing stringent tests of partial compositeness. We discuss the expected size of effects in the different approaches to lepton flavor, which will be useful to understand how a composite lepton sector could look like, given up-to-date experimental constraints.

Exploiting dijet resonance searches for flavor physics

In this work, we reinterpret ATLAS and CMS dijet resonance searches to set robust constraints on all hypothetical tree-level scalar and vector mediators with masses up to 5 TeV, assuming a diquark or a quark-antiquark coupling with an arbitrary flavor composition. To illustrate the application of these general results, we quantify the permissible size of new physics in $$ {\overline{B}}_q\to {D}_q^{\left(\ast \right)+}\left\{\pi, K\right\} $$ B ¯ q → D q ∗ + π K consistent with the absence of signal in dijet resonance searches. Along the way, we perform a full SMEFT analysis of the aforementioned non-leptonic B meson decays at leading-order in αs. Our findings uncover a pressing tension between the new physics explanations of recently reported anomalies in these decays and the dijet resonant searches. The high-pT constraints are crucial to drain the parameter space consistent with the low-pT flavor physics data.

Probing QCD with LHCb

While the LHCb detector was specifically designed for measuring heavy-flavor physics, it has also proven itself as a forward general purpose detector with flexible data acquisition, excellent lifetime resolution and charged particle identification. This makes LHCb an ideal laboratory for exploring phenomena related to quantum chromodynamics (QCD), particularly with heavy-flavor content. This review explores some of the novel QCD measurements from LHCb, with an emphasis placed on comparisons to predictions from the Pythia 8 Monte Carlo event generator.

Quark flavor physics and lattice QCD

For a long time, investigation into the weak interactions of quarks has guided us toward understanding the Standard Model we know today. Now in the era of high precision, these studies are still one of the most promising avenues for peering beyond the Standard Model. This is a large-scale endeavour with many tales and many protagonists. In these pages I follow a few threads of a complex story, those passing through the realm of lattice gauge theory.