The Need for Purely Laboratory-Based Axion-Like Particle Searches

TL;DR

This work tackles the tension between the PVLAS ALP interpretation and robust astrophysical bounds by proposing environment-dependent ALP parameters, specifically $M$ and $m$, that suppress stellar production. It analyzes dynamical and kinematical suppression mechanisms, quantifying their effects using solar models and showing potential relaxation of CAST and HB constraints. The results imply that near-term laboratory ALP searches could remain viable and that experiments probing environmental variations (e.g., buffer gas in LSW setups) could test the scenario. Overall, the study suggests a path for reconciling PVLAS with astrophysical limits while preserving experimental accessibility in purely laboratory-based searches.

Abstract

The PVLAS signal has led to the proposal of many experiments searching for light bosons coupled to photons. The coupling strength probed by these near future searches is, however, far from the allowed region, if astrophysical bounds apply. But the environmental conditions for the production of axion-like particles in stars are very different from those present in laboratories. We consider the case in which the coupling and the mass of an axion-like particle depend on environmental conditions such as the temperature and matter density. This can relax astrophysical bounds by several orders of magnitude, just enough to allow for the PVLAS signal. This creates exciting possibilities for a detection in near future experiments.

Figures (8)

• Figure 1: Primakoff processes in which a photon turns into an ALP in the electric field of a charged particle like a proton or electron.
• Figure 2: Environmental parameters as a function of the distance to the solar center. Temperature (solid, red), matter density (dashed, blue), Debye screening scale (double dashed, green) and plasma frequency (triple dashed, black), normalized to their values in the solar center, $T_0=1.35$ keV, $\rho_0=1.5\times 10^{2}$ g cm$^{-3}$, $k_{s0}=9$ keV, $\omega_{P0}=0.3$ keV for the solar model BS05(OP) of Bahcall et al.Bahcall:2004pz.
• Figure 3: Coupling as a function of an environmental parameter $\eta$: The simple form used in our calculations (solid line) and a generic, more realistic, dependence (dashed).
• Figure 4: Our spectrum of ALPs at Earth (black solid) agrees reasonably well with that of the CAST collaboration Zioutas:2004hi (dashed orange) for $M=10^{10}\,\rm{GeV}$.
• Figure 5: Suppression of the flux of ALPs $S(\omega_0=1\,\rm{keV},R_{\rm{crit}})$ as a function of $R_{\rm crit}$.