[en] Newton’s gravitational constant G is the least known fundamental constant of nature, partly because the gravity signal produced in the laboratory is extremely weak and difficult to measure accurately. There also seem to be unknown systematics in many G measurements. Since Cavendish made the first measurement of G with a torsion balance over two hundred years ago, torsion balances have been used in many G experiments, but uncorrected anelasticity of torsion fibers make the results questionable. We present a new method of G measurement by using a superconducting gravity gradiometer constructed with levitated test masses, which is free from the irregularities of mechanical suspension. The detector is rotated to null the gravity field from the source mass by centrifugal acceleration, forming an artificial planetary system. We show that this experiment can potentially measure G with accuracy better than 10 ppm. (paper)

[en] Terrestrial gravity noise produced by ambient seismic and infrasound fields poses one of the main sensitivity limitations in low-frequency ground-based gravitational-wave (GW) detectors. This noise needs to be suppressed by 3-5 orders of magnitude in the frequency band 10 mHz to 1 Hz, which is extremely challenging. We present a new approach that greatly facilitates cancellation of gravity noise in full-tensor GW detectors. It makes explicit use of the direction of propagation of a GW, and can therefore either be implemented in directional searches for GWs or in observations of known sources. We show that suppression of the Newtonian-noise foreground is greatly facilitated using the extra strain channels in full-tensor GW detectors. Only a modest number of auxiliary, high-sensitivity environmental sensors is required to achieve noise suppression by a few orders of magnitude. (paper)

[en] Newton’s gravitational constant G is the least known fundamental constant of nature. Since Cavendish made the first measurement of G with a torsion balance over two hundred years ago, the best results of G have been obtained by using torsion balances. However, the uncorrected anelasticity of torsion fibers makes the results questionable. We present a new method of G measurement by using a superconducting gravity gradiometer constructed with levitated test masses, which is free from the irregularities of mechanical suspension. The superconducting gravity gradiometer is rotated to generate a centrifugal acceleration that nulls the gravity field of the source mass, forming an artificial planetary system. This experiment has a potential accuracy of G better than 10 ppm. (paper)

[en] Because the Moon is much quieter seismically than the Earth, science to be performed on the Moon using seismology is currently limited by the best available seismometer. We describe the development of a lunar seismometer with sensitivity at least 100 times higher than current state of the art. Analysis of the fundamental noise of this seismometer shows that at frequency below ∼1 Hz the noise will be dominated by Brownian motion of the test mass. Above ∼1 Hz, it will be dominated by thermal noise in the electronic readout. The electronic noise corresponds to ∼10^-13 m Hz^-1/2. A way to reduce the Brownian motion noise of the test mass using electrostatic force is also discussed

[en] Terrestrial gravitational-wave (GW) detectors are mostly based on Michelson-type laser interferometers with arm lengths of a few km and signal bandwidths of tens of Hz to a few kHz. Many conceivable sources would emit GWs below 10 Hz. A low-frequency tensor GW detector can be constructed by combining six magnetically levitated superconducting test masses. Seismic noise and Newtonian gravity noise are serious obstacles in constructing terrestrial GW detectors at such low frequencies. By using the transverse nature of GWs, a full tensor detector, which can in principle distinguish GWs from near-field Newtonian gravity, can be constructed. Such a tensor detector is sensitive to GWs coming from any direction with any polarization; thus a single antenna is capable of resolving the source direction and polarization. We present a design concept of a tensor GW detector that could reach a strain sensitivity of 10"−"1"9–10"−"2"0 Hz"−"1"/"2 at 0.2–10 Hz, compute its intrinsic detector noise, and discuss procedures of mitigating the seismic and Newtonian noise. (paper)

[en] Strange quark matter made of up, down and strange quarks has been postulated by Witten [E. Witten, Phys. Rev D 30 (1984) 279]. Strange quark matter would be nearly charge neutral and would have density of nuclear matter (10¹⁴ gm/cm³). Witten also suggested that nuggets of strange quark matter, or strange quark nuggets (SQNs), could have formed shortly after the Big Bang, and that they would be viable candidates for cold dark matter. As suggested by de Rujula and Glashow [A. de Rujula and S. Glashow, Nature 312 (1984) 734], an SQN may pass through a celestial body releasing detectable seismic energy along a straight line. The Moon, being much quieter seismically than the Earth, would be a favorable place to search for such events. We review previous searches for SQNs to illustrate the parameter space explored by using the Moon as a low-noise detector of SQNs. We also discuss possible detection schemes using a single seismometer, and using an International Lunar Seismic Network