Motivated by higher-dimensional theories that predict new effects, we tested the gravitational $1/r^2$ law at separations ranging down to $218\mu \mathrm{m}$ using a 10-fold symmetric torsion pendulum and a rotating 10-fold symmetric attractor. We improved previous short-range constraints by up to a factor of 1000 and find no deviations from Newtonian physics.

Motivated by a variety of theories that predict new effects, we tested the gravitational ${1/r}^2$ law at separations between 10.77 mm and $137\mu \mathrm{m}$ using two different 10-fold azimuthally symmetric torsion pendulums and rotating 10-fold symmetric attractors. Our work improves upon other experiments by up to a factor of about 100. We found no deviation from Newtonian physics at the 95% confidence level and interpret these results as constraints on extensions of the standard model that predict Yukawa or power-law forces. We set a constraint on the largest single extra dimension (assuming toroidal compactification and that one extra dimension is significantly larger than all the others) of $R_{*}<~160\mu \mathrm{m},$ and on two equal-sized large extra dimensions of $R_{*}<~130\mu \mathrm{m}.$ Yukawa interactions with $|\alpha |>~1$ are ruled out at 95% confidence for $\lambda >~197\mu \mathrm{m}.$ Extra-dimensions scenarios stabilized by radions are restricted to unification masses $M_{*}>~3.0\mathrm{TeV}{/c}^2,$ regardless of the number of large extra dimensions. We also provide new constraints on power-law potentials $V\left(r\right)\mathrm{}\propto r^{-k}$ with k between 2 and 5 and on the ${\gamma }_5$ couplings of pseudoscalars with $m<~10\mathrm{meV}{/c}^2.$

Cosmic‐ray neutron probes are widely used to monitor environmental water content near the surface. The method averages over tens of hectares and is unrivaled in serving representative data for agriculture and hydrological models at the hectometer scale. Recent experiments, however, indicate that the sensor response to environmental heterogeneity is not fully understood. Knowledge of the support volume is a prerequisite for the proper interpretation and validation of hydrogeophysical data. In a previous study, several physical simplifications have been introduced into a neutron transport model in order to derive the characteristics of the cosmic‐ray probe's footprint. We utilize a refined source and energy spectrum for cosmic‐ray neutrons and simulate their response to a variety of environmental conditions. Results indicate that the method is particularly sensitive to soil moisture in the first tens of meters around the probe, whereas the radial weights are changing dynamically with ambient water. The footprint radius ranges from 130 to 240 m depending on air humidity, soil moisture, and vegetation. The moisture‐dependent penetration depth of 15 to 83 cm decreases exponentially with distance to the sensor. However, the footprint circle remains almost isotropic in complex terrain with nearby rivers, roads or hill slopes. Our findings suggest that a dynamically weighted average of point measurements is essential for accurate calibration and validation. The new insights will have important impact on signal interpretation, sensor installation, data interpolation from mobile surveys, and the choice of appropriate resolutions for data assimilation into hydrological models.

We used a torsion pendulum containing $\approx {10}^{23}$ 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 $|g_{\mathrm{P}}^e{g}_{\mathrm{S}}^N|/(\hslash c)<9.4\times {10}^{-37}$ and $|g_{\mathrm{A}}^e{g}_{\mathrm{V}}^N|/(\hslash c)<1.2\times {10}^{-56}$ for $\lambda >1\mathrm{AU}$. We test for preferred-frame interactions of the form $V=-{\mathit{\sigma }}^e·\mathit{A}$, $V=-B{\mathit{\sigma }}^e·\mathit{v}/c$, or $V=-\sum _{}^{}{\sigma }_i^e{C}_{ij}{v}_j/c$, where $\mathit{v}$ 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 $1\sigma$ upper limits $|{\mathit{A}}_{X,Y}|\le 1.5\times {10}^{-22}\mathrm{eV}$ and $|{\mathit{A}}_Z|\le 4.4\times {10}^{-21}\mathrm{eV}$ that may be compared to the benchmark value $m_e^2/M_{\mathrm{Planck}}=2\times {10}^{-17}\mathrm{eV}$. Interpreting our constraint on $\mathit{A}$ in terms of noncommutative geometry, we obtain an upper bound of $(355l_{\mathrm{GUT}}{)}^2$ on the minimum observable area, where $l_{\mathrm{GUT}}=\hslash c/({10}^{16}\mathrm{GeV})$ is the grand unification length. We find that $|B|\le 1.2\times {10}^{-19}\mathrm{eV}$. All 9 components of $\mathit{C}$ are constrained at the ${10}^{-17}$ to ${10}^{-18}\mathrm{eV}$ level. We determine 9 linear combinations of parameters of the standard model extension; rotational-noninvariant and boost-noninvariant terms are limited at roughly the ${10}^{-31}\mathrm{GeV}$ and ${10}^{-27}\mathrm{GeV}$ 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 $\mathrm{Sm}{\mathrm{Co}}_5$ was measured to be $(4.19\pm 0.19)\times {10}^{22}{\mathrm{cm}}^{-3}$ at a field of 9.6 kG.

We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate that Newton’s inverse square law of gravity is understood at micron distances on an energy scale of $10^{-14}\mathrm{eV}$. At this level of precision, we are able to provide constraints on any possible gravitylike interaction. In particular, a dark energy chameleon field is excluded for values of the coupling constant $\beta >5.8\times 10^8$ at 95% confidence level (C.L.), and an attractive (repulsive) dark matter axionlike spin-mass coupling is excluded for the coupling strength $g_s{g}_p>3.7\times 10^{-16}$ ($5.3\times 10^{-16}$) at a Yukawa length of $\lambda =20\mu \mathrm{m}$ (95% C.L.).

The lunar-ranging test of the equivalence principle for gravitational self-energy is ambiguous. Although the Earth has more gravitational self-energy than the Moon, its sizable Fe/Ni core also gives it a different composition than the Moon. We removed this ambiguity by comparing, in effect, the accelerations of “miniature” earths and moons toward the Sun. Our composition-dependent Earth-Moon acceleration, $\Delta a_{\mathrm{CD}}/a_{\mathrm{s}}=(+0.1\mathrm{}\pm 2.7\pm 1.7)\times {10}^{-13\mathrm{}}$, and lunar-ranging data provide an unambiguous test at the $1.3\times {10}^{-3\mathrm{}}$ level.