Flavor Physics Constraints for Physics Beyond the Standard Model (1002.0900v2)

Abstract: In the last decade, huge progress in experimentally measuring and theoretically understanding flavor physics has been achieved. In particular, the accuracy in the determination of the CKM elements has been greatly improved, and a large number of flavor changing neutral current processes, involving b -> d, b -> s and c -> u transitions, and of CP violating asymmetries, have been measured. No evidence for new physics has been established. Consequently, strong constraints on new physics at high scale apply. In particular, the flavor structure of new physics at the TeV scale is strongly constrained. We review these constraints and we discuss which are the future prospects to better understand the flavor structure of physics beyond the Standard Model.

• The paper analyzes how recent experimental precision in flavor physics, particularly measurements of the CKM matrix, FCNCs, and CP violation, strongly constrain theories beyond the Standard Model.
• Precise measurements of processes like B-B mixing set stringent limits on new physics contributions, suggesting that any new physics must occur at a high energy scale or adhere to minimal flavor violation principles.
• Combining data from high-energy colliders and low-energy flavor observables is highlighted as a key strategy for future searches to reveal the nature of new physics at the TeV scale.

Overview of "Flavor Physics Constraints for Physics Beyond the Standard Model"

This paper provides a comprehensive analysis of flavor physics constraints and their implications for theories beyond the Standard Model (BSM). Authored by Gino Isidori, Yosef Nir, and Gilad Perez, the paper discusses the significant advances in experimental precision and theoretical understanding in flavor physics over the past decade. Particularly, it focuses on the stringent constraints on BSM physics derived from the accurate determination of CKM matrix elements and measurements of flavor-changing neutral currents (FCNCs) and CP-violating processes.

Theoretical Framework

The authors explore the implications of flavor physics within the Standard Model (SM) and establish the CKM matrix as the primary source of flavor and CP violation in the SM. Within this context, flavor physics involves interactions that distinguish between different flavors of particles—specifically, quarks and leptons—and flavor-changing processes where these interactions result in a change in the type of quark or lepton.

The paper dissects the flavor sector of the SM, where the Yukawa interactions are the source of flavor physics, breaking the larger global flavor symmetry down to observed structures. These interactions play a crucial role in dictating the masses of the fermions and the mixing angles in the CKM matrix.

Constraints on New Physics

A pivotal aspect of the paper is its discussion on model-independent constraints and methods applied to the search for new physics. The researchers develop effective field theories to paper new interactions at higher energy scales, represented by additional operators beyond the renormalizable interactions of the SM.

The authors consider several types of new physics contributions to low-energy processes, focusing on $\Delta F=2$ transitions and FCNCs, which are highly suppressed within the SM, making them sensitive probes for new physics. They emphasize that any BSM contributions to these processes must not exceed the SM's predictions unless aligned in a manner that respects observed constraints.

A detailed analysis of these processes, including $K^0-\bar{K}^0$ and $B_{d,s}^0-\bar{B}_{d,s}^0$ mixing, provides strong limits on the parameters of possible BSM theories. The constraints demand that any new physics has either a highly suppressed energy scale or features minimal flavor violation (MFV) aligning with the SM's flavor structure.

Minimal Flavor Violation and Beyond

The concept of Minimal Flavor Violation (MFV) is discussed as a natural solution to the flavor problem, where new physics respects the flavor structure of the SM, specifically through the Yukawa couplings. This notion mitigates significant deviations in FCNC processes and complies with the CKM matrix-driven interactions. Despite this, the authors acknowledge MFV’s limitations, including its lack of explanatory power regarding the origin of the SM’s flavor structure.

The discussion extends to scenarios beyond MFV, such as models incorporating additional symmetries or fields leading to different flavor structures and CP violations. The paper assesses supersymmetry and extra-dimensional theories as well, detailing how these frameworks inherently introduce new flavor dynamics and potential FCNC contributions that need careful alignment to avoid contradicting empirical data.

Future Prospects

In assessing the future of flavor physics, the authors project the potential for new discoveries that could refine or disrupt the landscape of the standard and BSM physics. Upcoming advancements in experimental techniques, combined with precise theoretical predictions, hold promise for probing deeper into the SM's flavor sector and scrutinizing the constrained landscape of BSM theories.

The paper concludes with a prospective on how combining high-energy collider data with low-energy flavor observables will play a pivotal role in unveiling the nature of new physics at the TeV scale. This combination holds the key to understanding the fundamental forces shaping the universe, guiding experimentalists and theorists in their search for the underlying theory extending the Standard Model.