Flavor Violating Higgs Decays (1209.1397v3)

Abstract: We study a class of nonstandard interactions of the newly discovered 125 GeV Higgs-like resonance that are especially interesting probes of new physics: flavor violating Higgs couplings to leptons and quarks. These interaction can arise in many frameworks of new physics at the electroweak scale such as two Higgs doublet models, extra dimensions, or models of compositeness. We rederive constraints on flavor violating Higgs couplings using data on rare decays, electric and magnetic dipole moments, and meson oscillations. We confirm that flavor violating Higgs boson decays to leptons can be sizeable with, e.g., h -> tau mu and h -> tau e branching ratios of order 10% perfectly allowed by low energy constraints. We estimate the current LHC limits on h -> tau mu and h -> tau e decays by recasting existing searches for the SM Higgs in the tau-tau channel and find that these bounds are already stronger than those from rare tau decays. We also show that these limits can be improved significantly with dedicated searches and we outline a possible search strategy. Flavor violating Higgs decays therefore present an opportunity for discovery of new physics which in some cases may be easier to access experimentally than flavor conserving deviations from the Standard Model Higgs framework.

• The paper demonstrates that Higgs-mediated flavor violating decays, such as h → τμ and h → τ e, can reach branching ratios around 10% without violating low-energy constraints.
• Researchers rederive limits on FV interactions using data from rare decays, dipole moments, and meson oscillations to challenge Standard Model predictions.
• The study proposes dedicated LHC search strategies, highlighting the cleaner signal of FV decays as a promising indicator of new physics.

An Examination of Flavor Violating Higgs Decays

The research presented in the paper titled "Flavor Violating Higgs Decays" by Roni Harnik, Joachim Kopp, and Jure Zupan focuses on an important aspect of particle physics—flavor changing neutral currents (FCNC) mediated by the Higgs boson. The standard model (SM) of particle physics predicts very specific decay modes for the Higgs boson, and any deviation from these predictions is of great interest as it could indicate new physics beyond the SM (BSM).

Key Findings and Methodology

The paper rederives constraints on flavor violating (FV) interactions of the Higgs boson with quarks and leptons using data from rare decay processes, electric and magnetic dipole moments, and meson oscillations. It confirms that FV Higgs boson decays to leptons can be significant, with decay processes like $h \to \tau\mu$ and $h \to \tau e$ potentially having branching ratios of $\mathcal{O}(10\%)$. This sizable branching ratio is not excluded by existing low-energy constraints, which opens up a practical avenue for the Large Hadron Collider (LHC) to improve bounds on these processes through dedicated searches.

Implications for Experimental Physics

The analysis illustrates that FV Higgs decays provide a cleaner signal for new physics than flavor conserving (FC) deviations from the SM, making them attractive targets for experimental verification. Specifically, the FV decays offer significant deviations from the SM predictions, which can be probed with greater ease than purely FC processes due to fewer background noise issues at the LHC.

Practical Constraints and Search Strategies

The paper outlines a potential strategy for LHC experiments to constrain FV decays by utilizing current search constraints from FV channels such as $h \to \tau\mu$ and $h \to \tau e$. Furthermore, it highlights the importance of revisiting existing LHC data with dedicated analyses to probe the FV parameter space further. The discrepancy between theory and current experimental limits for processes like $\tau \to \mu\gamma$ suggests that improved constraints could be derived from ongoing LHC experiments.

Theoretical and Computational Contributions

The comprehensive approach adopted in the paper accounts for one-loop and two-loop diagrammatic contributions to the FV decays. Notably, the authors have meticulously calculated contributions to the effective Lagrangian governing FV decays through scalar, vector, and electromagnetic dipole operators. This provides a robust theoretical framework that bridges the gap between theoretical prediction and experimental search techniques.

Concluding Remarks

The discovery of FV interactions involving the Higgs boson presents a crucial test for the SM and could potentially open a path to new physics. The research delineated in this paper significantly adds to our understanding of FV Higgs decays and guides future experiments by providing detailed constraints and improving the precision of theoretical predictions. While the LHC already offers some constraints on these processes, more dedicated searches are necessary to fully exploit the LHC's potential for unveiling new physics at the electroweak scale.

The paper successfully lays the groundwork for further exploration of FV decays in the Higgs sector, a topic that remains ripe for exploration as part of the ongoing quest to understand the underlying fabric of particle interactions and symmetries in the universe.