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Flavour Changing Neutral Current Processes

Andrzej J. Buras

TL;DR

This work surveys the status of flavour-changing neutral-current processes, detailing the theoretical framework (OPE and RG-improved perturbation theory) and the standard unitarity-triangle analyses used to extract CKM parameters. It synthesizes results across K and B decays, including ε'/ε, B→X_s γ, B→μμ, and K→πνν, highlighting the role of NLO corrections and nonperturbative inputs. The paper assesses the potential for future measurements to constrain or reveal new physics, discusses various strategies for clean extractions of CKM phases (α,β,γ), and outlines how FCNC observables can signal physics beyond the Standard Model. It emphasizes the complementary strengths of kaon and B-meson decays in pinning down CKM parameters and probing new dynamics, anticipating significant advances from upcoming experiments.

Abstract

We review the status of the flavour-changing neutral-current processes (FCNC). In particular we discuss: i) Main targets of the field, ii) The theoretical framework for FCNC, iii) Standard analysis of the unitarity triangle, iv) $\varepsilon'/\varepsilon$, v) Radiative, rare and CP-violating decays, vi) CP-asymmetries in B-decays, vii) Comparision of the potentials of $K \to πν\barν$ and CP-B asymmetries, vii) Some aspects of the physics beyond the Standard Model.

Flavour Changing Neutral Current Processes

TL;DR

This work surveys the status of flavour-changing neutral-current processes, detailing the theoretical framework (OPE and RG-improved perturbation theory) and the standard unitarity-triangle analyses used to extract CKM parameters. It synthesizes results across K and B decays, including ε'/ε, B→X_s γ, B→μμ, and K→πνν, highlighting the role of NLO corrections and nonperturbative inputs. The paper assesses the potential for future measurements to constrain or reveal new physics, discusses various strategies for clean extractions of CKM phases (α,β,γ), and outlines how FCNC observables can signal physics beyond the Standard Model. It emphasizes the complementary strengths of kaon and B-meson decays in pinning down CKM parameters and probing new dynamics, anticipating significant advances from upcoming experiments.

Abstract

We review the status of the flavour-changing neutral-current processes (FCNC). In particular we discuss: i) Main targets of the field, ii) The theoretical framework for FCNC, iii) Standard analysis of the unitarity triangle, iv) , v) Radiative, rare and CP-violating decays, vi) CP-asymmetries in B-decays, vii) Comparision of the potentials of and CP-B asymmetries, vii) Some aspects of the physics beyond the Standard Model.

Paper Structure

This paper contains 48 sections, 70 equations, 4 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Grand View
  3. Main Targets of FCNC Processes
  4. The CKM Matrix and the Unitarity Triangle
  5. Theoretical Framework
  6. Standard Analysis
  7. Basic Formulae
  8. Numerical Results
  9. Input Parameters
  10. Output of the Standard Analysis
  11. $\varepsilon'/\varepsilon$
  12. Radiative and Rare B Decays
  13. $B\to X_s\gamma$
  14. $B\to X_s \mu^+\mu^-$
  15. $B\to\mu\bar{\mu}$ and $B\to X_s\nu\bar{\nu}$
  16. ...and 33 more sections

Figures (4)

  • Figure 1: Typical Penguin and Box Diagrams.
  • Figure 2: Unitarity Triangle.
  • Figure 3: The ideal Unitarity Triangle. For artistic reasons the value of $\bar{\eta}$ has been chosen to be higher than the fitted central value $\bar{\eta}\approx 0.35.$
  • Figure 4: Unitarity Triangle 1996.