Implication of hidden sub-GeV bosons for the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo stretchy="false">(</mml:mo><mml:mi>g</mml:mi><mml:mo>−</mml:mo><mml:mn>2</mml:mn><mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mi>μ</mml:mi></mml:msub></mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Be</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>8</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow><mml:mtext>−</mml:mtext><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>He</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:mrow></mml:math> anomaly, proton charge radius, EDM of fermions, and dark axion portal

Abstract

We discuss new physics phenomenology of hidden scalar ($S$), pseudoscalar ($P$), vector ($V$) and axial-vector ($A$) particles coupled to nucleons and leptons, which could give contributions to proton charge radius, $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$, $^{8}\mathrm{Be}\text{\ensuremath{-}}^{4}\mathrm{He}$ anomaly and electric dipole moment (EDM) of Standard Model (SM) particles. In particular, we estimate sensitivity of $\mathrm{NA}64\ensuremath{\mu}$ experiment to observe muon missing energy events involving hidden scalar and vector particles. That analysis is based on geant4 Monte Carlo simulation of the signal process of muon scattering off target nuclei $\ensuremath{\mu}N\ensuremath{\rightarrow}\ensuremath{\mu}NS(V)$ followed by invisible boson decay into dark matter (DM) particles, $S(V)\ensuremath{\rightarrow}\ensuremath{\chi}\ensuremath{\chi}$. The existence of light sub-GeV bosons could possibly explain the muon ($g\ensuremath{-}2$) anomaly observed. We also summarize existing bounds on ATOMKI $X17({J}^{P}={0}^{\ensuremath{-}},{1}^{\ifmmode\pm\else\textpm\fi{}})$ boson coupling with neutron, proton, and electron. We implement these constraints to estimate the contribution of $P$, $V$. and $A$ particles to proton charge radius via direct 1-loop calculation of Sachs form factors. The analysis reveals the corresponding contribution is negligible. We also calculate bounds on dark axion portal couplings of dimension-five operators, which contribute to the EDMs of leptons and neutron.

Topics & Concepts