Year: 2008
Type: article
Abstract: We used a torsion pendulum containing $\ensuremath{\approx}{10}^{23}$ polarized electrons to search new interactions that couple to electron spin. We limit $CP$-violating interactions between the pendulum's electrons and unpolarized matter in the Earth or the Sun, test for rotation and boost-dependent preferred-frame effects using the Earth's rotation and velocity with respect to the entire cosmos, and search for exotic velocity-dependent potentials between polarized electrons and unpolarized matter in the Sun and Moon. We find $CP$-violating parameters $|{g}_{\mathrm{P}}^{e}{g}_{\mathrm{S}}^{N}|/(\ensuremath{\hbar}c)<9.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}37}$ and $|{g}_{\mathrm{A}}^{e}{g}_{\mathrm{V}}^{N}|/(\ensuremath{\hbar}c)<1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}56}$ for $\ensuremath{\lambda}>1\text{ }\text{ }\mathrm{AU}$. We test for preferred-frame interactions of the form $V=\ensuremath{-}{\mathbit{\ensuremath{\sigma}}}^{e}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{A}$, $V=\ensuremath{-}B{\mathbit{\ensuremath{\sigma}}}^{e}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{v}/c$, or $V=\ensuremath{-}\ensuremath{\sum}_{}^{}{\ensuremath{\sigma}}_{i}^{e}{C}_{ij}{v}_{j}/c$, where $\mathbit{v}$ is the velocity of the Earth with respect to the cosmic microwave background restframe and $i$, $j$ represent the equatorial inertial coordinates $X$, $Y$, and $Z$. We constrain all 3 components of $A$, obtaining $1\ensuremath{\sigma}$ upper limits $|{\mathbit{A}}_{X,Y}|\ensuremath{\le}1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}$ and $|{\mathbit{A}}_{Z}|\ensuremath{\le}4.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\text{ }\text{ }\mathrm{eV}$ that may be compared to the benchmark value ${m}_{e}^{2}/{M}_{\mathrm{Planck}}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\text{ }\text{ }\mathrm{eV}$. Interpreting our constraint on $\mathbit{A}$ in terms of noncommutative geometry, we obtain an upper bound of $(355{l}_{\mathrm{GUT}}{)}^{2}$ on the minimum observable area, where ${l}_{\mathrm{GUT}}=\ensuremath{\hbar}c/({10}^{16}\text{ }\text{ }\mathrm{GeV})$ is the grand unification length. We find that $|B|\ensuremath{\le}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{eV}$. All 9 components of $\mathbit{C}$ are constrained at the ${10}^{\ensuremath{-}17}$ to ${10}^{\ensuremath{-}18}\text{ }\text{ }\mathrm{eV}$ level. We determine 9 linear combinations of parameters of the standard model extension; rotational-noninvariant and boost-noninvariant terms are limited at roughly the ${10}^{\ensuremath{-}31}\text{ }\text{ }\mathrm{GeV}$ and ${10}^{\ensuremath{-}27}\text{ }\text{ }\mathrm{GeV}$ levels, respectively. Finally, we find that the gravitational mass of an electron spinning toward the galactic center differs by less than about 1 part in ${10}^{21}$ from an electron spinning in the opposite direction. As a byproduct of this work, the density of polarized electrons in $\mathrm{Sm}\text{ }\text{ }{\mathrm{Co}}_{5}$ was measured to be $(4.19\ifmmode\pm\else\textpm\fi{}0.19)\ifmmode\times\else\texttimes\fi{}{10}^{22}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ at a field of 9.6 kG.
Institution: University of Washington
Language: Latvian
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2174246649