Compatibility of CAST search with axion-like interpretation of PVLAS results

TL;DR

The paper addresses the tension between the PVLAS indication of a light axion-like particle (ALP) and the CAST non-detection and astrophysical bounds. It proposes a low-energy, two-paraphoton model in which an epsilon-charged fermion $f$ generates the ALP-photon coupling via a triangle diagram, with the effective charge suppressed in stellar plasmas by a low scale $\mu$, while remaining sizeable in vacuum. The key mechanism ties $1/M = (\alpha/\pi)\, q_f^2/v$ to a small $v$, and yields $q_f(0)=\epsilon$ but $q_f(\omega_P^2) \sim (\mu^2/\omega_P^2)\epsilon$, enabling compatibility with CAST and HB bounds for sub-eV scales $\mu$, $v$ (preferably around $\mathrm{meV}$). The work identifies viable parameter regions, discusses CAST-compatibility scenarios, and highlights that confirming PVLAS would point to new physics below the eV scale.

Abstract

The PVLAS collaboration has results that may be interpreted in terms of a light axion-like particle, while the CAST collaboration has not found any signal of such particles. We propose a particle physics model with paraphotons and with a low energy scale in which this apparent inconsistency is circumvented.

Figures (3)

• Figure 1: Triangle diagram for the $\phi\gamma\gamma$ vertex.
• Figure 2: Diagrams of the interaction of $f$ with photons.
• Figure 3: Constraints on the parameters of our model. The black area is excluded by Cavendish-type experiments, and the grey area by the astrophysical constraint (\ref{['N1']}). The dashed line corresponds to $v=\mu$, and the dot to $v=\mu\simeq 1$ meV.