Relativistic Celestial Metrology: Dark Matter as an Inertial Gauge Effect

In canonical tetrad gravity, it is possible to identify the gauge variables, describing relativistic inertial effects, in Einstein general relativity. One of these is the York time, the trace of the extrinsic curvature of the instantaneous non‐Euclidean 3‐spaces (global Euclidean 3‐spaces are forbidden by the equivalence principle). The extrinsic curvature depends both on gauge variables and on dynamical ones like the gravitational waves after linearization. The fixation of these gauge variables is done by relativistic metrology with its identification of time and space. Till now, the International Celestial Reference Frame ICRF uses Euclidean 3‐spaces outside the Solar System. It is shown that York time and non‐Euclidean 3‐spaces may explain the main signatures of dark matter in ordinary space‐time before using cosmology. Also dark energy may be connected to these inertial gauge effects, because both red‐shift and luminosity distance depend on them

A quasi-complete mechanical model for a double torsion pendulum

We present a dynamical model for the double torsion pendulum nicknamed PETER, where one torsion pendulum hangs in cascade, but off-axis, from the other. The dynamics of interest in these devices lies around the torsional resonance, that is at very low frequencies (mHz). However, we find that, in order to properly describe the forced motion of the pendulums, also other modes must be considered, namely swinging and bouncing oscillations of the two suspended masses, that resonate at higher frequencies (Hz). Although the system has obviously 6+6 Degrees of Freedom, we find that 8 are sufficient for an accurate description of the observed motion. This model produces reliable estimates of the response to generic external disturbances and actuating forces or torques. In particular, we compute the effect of seismic floor motion (tilt noise) on the low frequency part of the signal spectra and show that it properly accounts for most of the measured low frequency noise.Comment: 15 pages, 6 figure

The 2 Degrees of Freedom Facility in Firenze for the study of Weak Forces

The LISA test-mass (TM) is sensitive to weak forces along all 6 Degrees of Freedom (DoFs). Extensi ve ground test ing is required in order to evaluate the influence of cross-talks of read-outs and actuators operating on different DoFs. To best represent the flight conditions, we developed in Firenze a facility with 2 soft DoFs. Using this facility we measure the forces and stiffnesses acting simultaneously along the 2 soft DoFs, and, more specifically, we will be able to de b ug residual couplings between the TM and the capacitive position sensor that reads the TM position, and to measure actuation cross talks with closed feedback loop. The facility is now ready, and here we report on the co mmi ssioning test s, and on the first measurements

Thermal noise reduction for present and future gravitational wave detectors

Thermal noise in mirror suspension is and will be the most severe fundamental limit to the low-frequency sensitivity of interferometric gravitational wave detectors currently under construction. The technical solutions, adopted in the Virgo detector, optimize the current suspension scheme, but new materials and new designs are needed to further reduce the suspension thermal noise. Silicon fibers are promising candidates both for room temperature advanced detectors and for future cryogenic interferometric detectors

Erratum: "Northern JHK Standard Stars for Array Detectors" [Astron. J. 115, 2594 (1998)]

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Northern JHK Standard Stars for Array Detectors

We report J, H and K photometry of 86 stars in 40 fields in the northern hemisphere. The fields are smaller than or comparable to a 4x4 arcmin field-of-view, and are roughly uniformly distributed over the sky, making them suitable for a homogeneous broadband calibration network for near-infrared panoramic detectors. K magnitudes range from 8.5 to 14, and J-K colors from -0.1 to 1.2. The photometry is derived from a total of 3899 reduced images; each star has been measured, on average, 26.0 times per filter on 5.5 nights. Typical errors on the photometry are about 0.012

The LARASE Spin Model of the two LAGEOS and LARES satellites

Satellite Laser Ranging (SLR) represents a very important technique of the observational space geodesy. In fact, Lunar Laser Ranging, Very Long Baseline Interferometry, Global Navigation Satellite Systems, Doppler Orbitography and Radiopositioning Integrated by Satellite, together with SLR constitute the Global Geodetic Observing System (GGOS). In the context of the GGOS activities, improvements in technology and in modeling will produce advances in Geodesy and Geophysics as well as in General Relativity (GR) measurements. Therefore, these important research fields are not independent, but tightly related to each other. The LARASE (LAser RAnged Satellites Experiment) research program has its main objectives in tests and measurements of Einstein's theory of GR via Precise Orbit Determination (POD) of a set of geodetic satellites. In order to reach such goals by means of very precise measurements of a number of relativistic parameters (and, at the same time, to provide a robust and unassailable error budget of the main systematic effects), we are also reviewing previous models and we are developing new models for the main perturbations (both gravitational and non-gravitational) that act on the orbits of the two LAGEOS and on that of LARES satellites. Within this paper we focus on modeling the spin vector of these satellites. The spin knowledge, both in orientation and rate, is of fundamental importance in order to correctly model the thermal effects acting on the surface of these satellites. These are very important non-gravitational perturbations (NGP) that produce long-term effects on the orbit of the cited satellites, especially for the two LAGEOS, and improvements in their modeling will be very useful both in the field of GR measurements and in those of space geodesy and geophysical applications. Indeed, the current RMS value of the range residuals of the LAGEOS satellites, obtained by the Analysis Centers of the International Laser Ranging Service, is at the level of a few cm since 1992, down to a cm or less during the last years. However, because of the incompleteness in current knowledge of dynamical models, empirical accelerations have been heavily employed to obtain such results. In this context, any step forward in the models developed for the NGP will be useful to reduce the use of empirical accelerations; it also represents an essential prerequisite to reach a sub-mm precision in the RMS of the SLR range residuals and the corresponding benefits in Geophysics and Geodesy, regarding e.g. stations coordinates knowledge, Earth's geocenter and reference frame realization. The paper will focus upon the improvements we obtained with respect on previous models of the spin of the two LAGEOS satellites based on averaged equations for the external torques in the rapid-spin approximation, as well as in a new general model that we developed and based on the solution of the full set of Euler equations

Monocrystalline fibres for low thermal noise suspension in advanced gravitational wave detectors

Thermal noise in mirror suspension will be the most severe fundamental limit to the low-frequency sensitivity of future interferometric gravitational wave detectors. We propose a new type of materials to realize low thermal noise suspension in such detectors. Monocrystalline suspension fibres are good candidates both for cryogenic and for ambient temperature interferometers. Material characteristics and a production facility are described in this paper

Noise parametric identification and whitening for LIGO 40-meter interferometer data

We report the analysis we made on data taken by Caltech 40-meter prototype interferometer to identify the noise power spectral density and to whiten the sequence of noise. We concentrate our study on data taken in November 1994, in particular we analyzed two frames of data: the 18nov94.2.frame and the 19nov94.2.frame. We show that it is possible to whiten these data, to a good degree of whiteness, using a high order whitening filter. Moreover we can choose to whiten only restricted band of frequencies around the region we are interested in, obtaining a higher level of whiteness.Comment: 11 pages, 15 figures, accepted for publication by Physical Review