Constraints on Possible Monopole-Dipole Interactions of WISPs from the Transverse Relaxation Time of Polarized $^3$He Gas

TL;DR

This paper uses measurements of polarized helium-3 gas relaxation times to set new experimental limits on hypothetical monopole-dipole interactions mediated by light particles, improving constraints in certain range scales.

Contribution

It provides the first constraints on monopole-dipole interactions from polarized helium-3 gas relaxation data, focusing on interaction ranges between 0.01 cm and 1 cm.

Findings

Established new laboratory limits on monopole-dipole interactions for neutrons.

Improved constraints for interaction ranges between 0.01 cm and 1 cm.

Reanalyzed existing data with a theoretical model of spin relaxation in magnetic field gradients.

Abstract

Various theories beyond the Standard Model predict new particles with masses in the sub-eV range with very weak couplings to ordinary matter. A $P$-odd, $T$-odd, spin-dependent interaction between polarized and unpolarized matter is one such possibility. Such a monopole-dipole interaction can be induced by the exchange of spin-$0$ particles. The presence of a possible monopole-dipole interaction between fermion spins and unpolarized matter would cause an decreased transverse spin relaxation time $T_{2}$ for a confined gas of polarized nuclei. By reanalyzing previously existing data on the spin relaxation times of polarized $^3$He in gas cells with pressure in the millibar range and applying the well-established theory of spin relaxation for magnetic field gradients to gradients in a possible monopole-dipole field, we present new laboratory constraints on the strength and range of such an interaction. These constraints represent to our knowledge the best limits on such interactions for the neutron with ranges between $0.01$ cm and 1 cm.