"Dark" Z implications for Parity Violation, Rare Meson Decays, and Higgs Physics (1203.2947v3)

Abstract: General consequences of mass mixing between the ordinary Z boson and a relatively light Z_d boson, the "dark" Z, arising from a U(1)_d gauge symmetry, associated with a hidden sector such as dark matter, are examined. New effects beyond kinetic mixing are emphasized. Z-Z_d mixing introduces a new source of low energy parity violation well explored by possible future atomic parity violation and planned polarized electron scattering experiments. Rare K (B) meson decays into pi (K) l^+ l^- (l = e, mu) and pi (K) nu anti-nu are found to already place tight constraints on the size of Z-Z_d mixing. Those sensitivities can be further improved with future dedicated searches at K and B factories as well as binned studies of existing data. Z-Z_d mixing can also lead to the Higgs decay H -> Z Z_d, followed by Z -> l_1^+ l_1^- and Z_d -> l_2^+ l_2^- or "missing energy", providing a potential hidden sector discovery channel at the LHC. An illustrative realization of these effects in a 2 Higgs doublet model is presented.

• The paper demonstrates that Z–Z₍d₎ mass mixing introduces a new source of low-energy parity violation, testable via atomic and polarized electron scattering experiments.
• It reveals that the mixing alters rare meson decay patterns, setting strict constraints on interaction strengths detectable at meson factories.
• The authors predict novel Higgs decay channels, with H→ZZ₍d₎ leading to distinctive leptonic and missing energy signals, offering new search avenues at the LHC.

Analysis of "Dark" $Z$ Implications for Parity Violation, Rare Meson Decays, and Higgs Physics

The paper by Davoudiasl, Lee, and Marciano explores the intriguing concept of mass mixing between the conventional $Z$ boson of the Standard Model (SM) and a relatively light $Z_d$ boson, referred to herein as the "dark" $Z$. This $Z_d$ boson arises from a $U(1)_d$ gauge symmetry associated with a hidden sector, which could potentially relate to dark matter. The authors aim to scrutinize the implications of this hidden gauge sector, particularly beyond the kinetically mixed scenarios that have been studied previously.

Key Findings and Analyses

The authors argue that the mixing between $Z$ and $Z_d$ provides a novel source of low-energy parity violation, intensifying the capabilities of future atomic parity violation experiments and polarized electron scattering experiments to detect such effects. Importantly, this mixing induces changes in rare meson decay processes, placing strict constraints on the strength of $Z$-$Z_d$ interactions. The analysis demonstrates that the mixing results in detectable shifts in decay patterns, presenting opportunities for further exploration at current and future meson factories and through analyses of existing data.

One of the most notable theoretical inferences is the possibility of Higgs decay paths via the $H \to Z Z_d$ channel that lead to either leptonic final states $Z \to \ell_1^+ \ell_1^-$ and $Z_d \to \ell_2^+ \ell_2^-$ or invisible decay paths resulting in missing energy signatures. This prediction holds significant implications for ongoing Large Hadron Collider (LHC) experiments, proposing a prospective hidden sector discovery channel should such rare decay channels be identified.

Additionally, the paper investigates an illustrative realization of these interaction effects within a two Higgs doublet model (2HDM), providing a theoretical framework that can reproduce the observed dynamics under certain conditions. This adds a layer of robustness to the conclusions drawn, grounding them in a model with enhanced predictive power.

Implications for Future Research

The implications for future developments are abundant. Practically, the identification of $Z$-$Z_d$ mixing would illuminate new pathways in particle physics, notably in the understanding of hidden sectors and their contributions to the universal structure. Moreover, the constraints outlined for this mixing underscore the experimental sensitivity required to detect or rule out such phenomena in future investigations.

Theoretically, the exploration of Higgs decay channels in the presence of a $Z_d$ boson opens a panorama of possible hidden sector interactions that could be more thoroughly detailed in extended versions of the SM or alternative frameworks such as supersymmetric models. As articulated, the detection of such properties would resonate fundamentally with our comprehension of parity violation and rare decay processes.

Speculations on Future Developments in AI

The application of AI techniques, such as machine learning algorithms, could significantly enhance the systematic paper of $Z_d$ involved processes by efficiently analyzing massive datasets from collider experiments to pinpoint anomalies indicative of new physics. Furthermore, AI-driven simulations may accelerate the development of theoretical models predicting such hidden sector phenomena.

Overall, this paper provides a solid foundation for further theoretical inquiry and experimental investigation into new gauge symmetries and their broader implications within the field of particle physics. It highlights the necessity for both precision and innovation in probing the potential existence of a hidden $Z$ boson, which may redefine elements of the Standard Model and reshape our understanding of parity and symmetry in fundamental particles.