Constraints on axionic fuzzy dark matter from light bending and Shapiro time delay

TL;DR

This paper investigates how ultralight axion-like particles as fuzzy dark matter could influence gravitational phenomena like light bending and Shapiro delay, setting bounds on axion properties based on observational data.

Contribution

It provides new constraints on axion decay constant and mass by analyzing their effects on gravitational experiments, especially from light bending and Shapiro delay observations.

Findings

Upper bound on axion decay constant: f_a ≲ 9.85×10^6 GeV

Upper bound on axion mass: m_a ≲ 10^{-18} eV

ALPs likely do not couple to nucleons if they are FDM

Abstract

Ultralight axion like particles (ALPs) of mass $m_a\in (10^{-21}\rm{eV}-10^{-22}\rm{eV})$ with axion decay constant $f_a\sim 10^{17}\rm{GeV}$ can be candidates for fuzzy dark matter (FDM). If celestial bodies like Earth and Sun are immersed in a low mass axionic FDM potential and if the ALPs have coupling with nucleons then the coherent oscillation of the axionic field results a long range axion hair outside of the celestial bodies. The range of the axion mediated Yukawa type fifth force is determined by the distance between the Earth and the Sun which fixes the upper bound of the mass of axion as $m_a\lesssim10^{-18}\rm{eV}$. The long range axionic Yukawa potential between the Earth and Sun changes the gravitational potential between them and contribute to the light bending and the Shapiro time delay. From the observational uncertainties of those experiments, we put an upper bound on the axion decay constant as $f_a\lesssim 9.85\times 10^{6}\rm{GeV}$, which is the stronger bound obtained from Shapiro time delay. This implies if ALPs are FDM, then they do not couple to nucleons.