Secluded U(1) below the weak scale (0811.1030v1)

Abstract: A secluded U(1) sector with weak admixture to photons, O(10^{-2}-10^{-3}), and the scale of the breaking below 1 GeV represents a natural yet poorly constrained extension of the Standard Model. We analyze g-2 of muons and electrons together with other precision QED data, as well as radiative decays of strange particles to constrain mass--mixing angle (m_V-\kappa) parameter space. We point out that m_V = 214 MeV and \kappa^2 > 3\times 10^{-5} can be consistent with the hypothesis of HyperCP collaboration, that seeks to explain the anomalous energy distribution of muon pairs in the \Sigma^+ \to p \mu^+\mu^- process by a resonance, without direct contradiction to the existing data on radiative kaon decays. The same parameters lead to O({\rm few} \times 10^{-9}) upward correction to the anomalous magnetic moment of the muon, possibly relaxing some tension between experimental value and theoretical determinations of g-2. The ultra-fine energy resolution scan of e^+e^-\to \mu^+\mu^- cross section and dedicated analysis of lepton spectra from K^+\to \pi^+ e^+e^- decays should be able to provide a conclusive test of this hypothesis and improve the constraints on the model.

• The paper introduces a secluded U(1) gauge extension with a light boson V that offers a potential explanation for the muon and electron g-2 anomalies.
• It rigorously compares theoretical predictions with experimental data from QED tests and particle decays to delineate the viable parameter space.
• The study highlights future e+e- collision searches and decay channel investigations as critical for validating or constraining the proposed model.

A Study of Secluded U(1) Below the Weak Scale

The paper by Maxim Pospelov investigates the implications of extending the Standard Model (SM) by introducing a new secluded U(1) gauge group, characterized by a weak kinetic mixing with the U(1) gauge group of the SM hypercharge. This extension proposes a new gauge boson, denoted as $V$, with its mass scale below 1 GeV and mixing parameter $\kappa$ in the range of 10$^{-2}$ to 10$^{-3}$. The exploration in this mass-mixing parameter space seeks to understand its compatibility with current precision tests and its potential to explain certain anomalous experimental results.

Key Findings and Analysis

The paper addresses both theoretical and experimental constraints on the proposed secluded U(1) sector with a focus on the $g-2$ anomalies of muons and electrons. The contributions of the $V$ boson are calculated and found to be consistent with observed anomalies, particularly offering a potential explanation for the muon's anomalous magnetic moment ($g-2$), which has long exhibited tension between experimental measurements and theoretical predictions. The paper highlights that values of $m_V$ around 214 MeV and $\kappa^2 > 3 \times 10^{-5}$ can relax this tension.

Experimental tests such as QED precision tests and radiative decays of strange particles provide significant constraints. The $e^+e^-$ collisions are proposed as a crucial area for future investigations, potentially allowing the discovery of $V$-mediated narrow resonances. Current constraints arising from hyperon and kaon decay processes are analyzed as well, revealing a parameter space partly unconstrained and inviting further experimental tests specifically tailored to probe the secluded U(1) model.

Implications and Future Directions

The findings in the paper have noteworthy implications for both theoretical and experimental physics. Theoretical constraints are derived from potential shifts in the fine structure constant due to the $V$ boson, impacting the high-precision measurements, primarily of $g-2$ values. Experimentally, secluded U(1) signatures could manifest as resonant structures in specific particle decay channels for both hyperons and kaons, necessitating dedicated searches in current and upcoming particle physics experiments. The HyperCP anomaly in particular, which observed unusual muon invariant mass distributions, might find an explanation within this model, pending further analysis and confirmation.

From a broader perspective, the introduction of additional U(1) groups prompts a closer review of interactions between visible and dark matter sectors, especially if these interactions could be mediated by $V$ bosons mixing with photons. Such interplay could alter the paradigm of how dark matter signatures are interpreted, creating new pathways for detection and understanding astrophysical observations.

In conclusion, the proposition of a secluded U(1) extension below the weak scale opens intriguing new possibilities in particle physics. While current experimental constraints do not eliminate the feasibility of such a model, future data—particularly from high precision QED tests and particle colliders—could either validate portions of this hypothesis or refine the parameter space significantly. The continued investigation into these possibilities is vital for expanding the boundaries of the Standard Model and potentially unearthing hidden sectors of particle interactions.