New Limits on Exotic Spin-Dependent Interactions at Astronomical Distances
L. Y. Wu, Kaiyuan Zhang, M. Peng, Jian Gong, H. Yan
Abstract
Exotic spin-dependent interactions involving new light particles address key questions in modern physics. Interactions between polarized neutrons ($n$) and unpolarized nucleons ($N$) occur in three forms: ${g}_{\mathrm{S}}^{N}{g}_{\mathrm{P}}^{n}\mathbit{\ensuremath{\sigma}}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{r}$, ${g}_{\mathrm{V}}^{N}{g}_{\mathrm{A}}^{n}\mathbit{\ensuremath{\sigma}}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{v}$, and ${g}_{\mathrm{A}}^{N}{g}_{\mathrm{A}}^{n}\mathbit{\ensuremath{\sigma}}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{v}\ifmmode\times\else\texttimes\fi{}\mathbit{r}$, where $\mathbit{\ensuremath{\sigma}}$ is the spin and $g$'s are the corresponding coupling constants for scalar, pseudoscalar, vector, and axial-vector vertexes. If such interactions exist, the Sun and Moon could induce sidereal variations of effective fields in laboratories. By analyzing existing data from laboratory measurements on Lorentz and $CPT$ violation, we derive new experimental upper limits on these exotic spin-dependent interactions at astronomical ranges. Our limits on ${g}_{\mathrm{S}}^{N}{g}_{\mathrm{P}}^{n}$ surpass the previous combined astrophysical-laboratory limits, setting the most stringent experimental constraints to date. We also report new constraints on vector-axial-vector and axial-axial-vector interactions at astronomical scales, with vector-axial-vector limits improved by $\ensuremath{\sim}12$ orders of magnitude. We extend our analysis to Hari Dass interactions and obtain new constraints.