$\mathcal{P}$, $\mathcal{T}$-violating axion-mediated interactions in RaOH molecule

TL;DR

This work addresses $\mathcal{P}$, $\mathcal{T}$-violating axion-mediated electron–nucleon interactions in the RaOH molecule and investigates how rovibrational motion modulates the enhancement parameter $W_{ax}$ that governs the observable energy shift $\Delta E_{\mathcal{P},\mathcal{T}}$. The authors derive the electron–nucleon axion operator, relate $W_{ax}$ to the scalar–pseudoscalar limit $W_s$, and implement a twofold computational strategy—one-center restoration for accurate core-region behavior and a coupled-channels treatment of nuclear motion—to compute $W_{ax}$ across rovibrational states and axion masses. They find vibrational effects resemble those of short-range NE–SPS interactions, with a high-mass relation $W_{ax} \simeq \frac{\sqrt{2} A}{Z G_F}\, \frac{W_s}{m_a^2 c^2}$ and a sign flip near $m_a \sim 10^4$ eV; projected RaOH experiments offer competitive laboratory bounds for $m_a > 1$ eV, though they do not beat current astrophysical limits, and combining multiple molecular species can help distinguish different PT-odd mechanisms. The results inform experimental strategies and the interpretation of potential signals in polyatomic molecules as probes of axion-like particles in the laboratory.

Abstract

If axion simultaneously has the scalar couplings to the nucleons and pseudo-scalar couplings to the electrons, it may mediate a $\mathcal{P}$, $\mathcal{T}$-violating interaction between the electronic shell and nuclei in the molecules. The polyatomic molecule RaOH, which is considered as a promising platform for the $\mathcal{P}$, $\mathcal{T}$ violation searches, is studied for its sensitivity to such interactions. Due to the long-range nature (on molecular scales) of the axion-mediated interaction, it is important whether the enhancement parameter would be sensitive to the vibration of the molecule. Our results imply that the impact of the vibrations on the axion-mediated electron-nucleon interaction in the molecule is similar to the impact on the short-range electron-nucleon scalar-pseudoscalar interaction studied earlier.

Figures (6)

• Figure 1: Feynman diagram for the axion-mediated electron-nucleon interaction
• Figure 2: Jacobi coordinates
• Figure 3: The dependence of $W_{ax}$ on $R$ for $\theta=0^\circ$
• Figure 4: The dependence of $W_{ax}$ on $R$ and $\theta$
• Figure 5: The dependence of $W_{ax}$ on $m_a$