Constraints on monopole-dipole potential from the tests of gravity

Abstract

Ultralight Axion Like Particle (ALP) can mediate a long range monopole-dipole macroscopic force between Earth and Sun if Earth is treated as a polarized source. There are about $10^{42}$ number of polarized electrons in Earth due to the presence of the geomagnetic field. The monopole-dipole interactions between electrons in Earth and nucleons in Sun can influence the perihelion precession of Earth, gravitational light bending and Shapiro time delay. The contribution of monopole-dipole potential is limited to be no larger than the measurement uncertainty. We obtain the first bound on monopole-dipole strength from single astrophysical observations. The perihelion precession of Earth puts the stronger bound on monopole-dipole coupling strength as $g_Sg_P\lesssim 1.75\times 10^{-16}$ for the ALP of mass $m_a\lesssim 1.35\times 10^{-18}~\rm{eV}$. We also obtain constraints on monopole-dipole coupling strength as $g_Sg_P\lesssim 5.61\times 10^{-38}$ from two different astrophysical observations such as the perihelion precession of the planet and the red giant branch. The bound is three orders of magnitude stronger than the E\"ot-Wash experiment and one order of magnitude stronger than the $(\rm{Lab})^N_S\times (\rm{Astro})^e_P$ limit.