Gravitational Wave Bar Detector Research Articles

Signatures of Noncommutativity in Bar Detectors of Gravitational Waves

The comparison between the noncommutative length scale √θ and the length variation δL = hL, detected in the GW detectors, indicates that there is a strong possibility to detect the noncommutative structure of space in the GW detector setup. Therefore, we explore how the response of a bar detector gets affected due to the presence of a noncommutative structure of space keeping terms up to the second order in a gravitational wave perturbation (h) in the Hamiltonian. Interestingly, the second-order term in h shows a transition between the ground state and one of the perturbed second excited states that was absent, when the calculation was restricted only to the first order in h.

Dark matter searches using gravitational wave bar detectors: Quark nuggets and newtorites

Many experiments have searched for supersymmetric WIMP dark matter, with null results. This may suggest to look for more exotic possibilities, for example compact ultra-dense quark nuggets, widely discussed in literature with several different names. Nuclearites are an example of candidate compact objects with atomic size cross section. After a short discussion on nuclearites, the result of a nuclearite search with the gravitational wave bar detectors Nautilus and Explorer is reported. The geometrical acceptance of the bar detectors is 19.5 m2 sr, that is smaller than that of other detectors used for similar searches. However, the detection mechanism is completely different and is more straightforward than in other detectors. The experimental limits we obtain are of interest because, for nuclearites of mass less than 10−5 g, we find a flux smaller than that one predicted considering nuclearites as dark matter candidates. Particles with gravitational only interactions (newtorites) are another example. In this case the sensitivity is quite poor and a short discussion is reported on possible improvements.

Quark nuggets search using gravitational waves aluminum bar detectors

Up to now there is no evidence of supersymmetric WIMPS dark matter. This may suggests to look for more exotic possibilities, for example compact ultra-dense quark nuggets. Nuclearites are an example of compact objects that could be constituent of the dark matter. After a short discussion on nuclearites, the result of a nuclearite search with the gravitational wave bar detectors NAUTILUS and EXPLORER is reported.

Investigation on Planck scale physics by the AURIGA gravitational bar detector

We have recently shown that the very low mechanical energy achieved and measured in the main vibration mode of gravitational wave bar detectors can set an upper limit to possible modifications of the Heisenberg uncertainty principle that are expected as an effect of gravity. Here we give more details on the data analysis procedure that allows one to deduce the energy of the bar mode (i.e., the meaningful parameter for our purpose). Furthermore, we extend the analysis of our results, discussing their implication for physical models that face quantum gravity from different points of view, e.g., proposing modified commutation relations or exploring spacetime discreteness.

Results of the IGEC-2 search for gravitational wave bursts during 2005

The network of resonant bar detectors of gravitational waves resumed coordinated observations within the International Gravitational Event Collaboration (IGEC-2). Four detectors are taking part in this Collaboration: ALLEGRO, AURIGA, EXPLORER and NAUTILUS. We present here the results of the search for gravitational wave bursts over 6 months during 2005, when IGEC-2 was the only gravitational wave observatory in operation. The implemented network data analysis is based on a time coincidence search among AURIGA, EXPLORER and NAUTILUS; ALLEGRO data was reserved for follow-up studies. The network amplitude sensitivity to bursts improved by a factor ≈3 over the 1997-2000 IGEC observations; the wider sensitive band also allowed the analysis to be tuned over a larger class of waveforms. Given the higher single-detector duty factors, the analysis was based on threefold coincidence, to ensure the identification of any single candidate of gravitational waves with high statistical confidence. The false detection rate was as low as 1 per century. No candidates were found.

New suspension system for the gravitational wave bar detector AURIGA

We report on the design of the new suspension system for the gravitational wave bar detector AURIGA. The system was designed with the aid of finite element modeling simulations with the goal of achieving at least −240dB of vibration reduction at 900Hz in a cryogenic environment, while preserving a high mechanical quality factor. We report room temperature measurements of the suspension core stage, mode frequencies, and attenuation and we discuss them on the basis of the simulation predictions. The suspension system is currently installed in the detector, which is properly working at the operating temperature of 4.2K. The observed improvements related to the suspension design are reported and discussed.

Room temperature gravitational wave bar detector with optomechanical readout

We present the full implementation of a room-temperature gravitational wave bar detector equipped with an optomechanical readout. The bar mechanical vibrations are read by a Fabry–Pérot interferometer whose length changes are compared with a stable reference optical cavity by means of a resonant laser. The detector performance is completely characterized in terms of spectral sensitivity and statistical properties of the fluctuations in the system output signal. This kind of readout technique allows for wide-band detection sensitivity and we can accurately test the model of the coupled oscillators for thermal noise. Our results are very promising for cryogenic operation and represent an important step towards significant improvements in the performance of massive gravitational wave detectors.

Effect of cosmic rays on the resonant gravitational wave detector Nautilus at temperature T=1.5 K

The interaction between cosmic rays and the gravitational wave bar detector Nautilus is experimentally studied with the aluminum bar at temperature of T=1.5 K. The results are compared with those obtained in the previous runs when the bar was at T=0.14 K. The results of the run at T=1.5 K are in agreement with the thermo-acoustic model; no large signals at unexpected rate are noticed, unlike the data taken in the run at T=0.14 K. The observations suggest a larger efficiency in the mechanism of conversion of the particle energy into vibrational mode energy when the aluminum bar is in the superconductive status.

Search for gravitational wave bursts by the network of resonant detectors

The groups operating cryogenic bar detectors of gravitational waves are performing a coordinated search for short signals within the International Gravitational Event Collaboration (IGEC). We review the most relevant aspects of the data analysis, based on a time-coincidence search among triggers from different detectors, and the properties of the data exchanged by each detector under a recently-upgraded agreement. The IGEC is currently analysing the observations from 1997 to 2000, when up to four detectors were operating simultaneously. 10% and 50% of this time period were covered by simultaneous observations, respectively, of at least three or at least two detectors. Typical signal search thresholds were in the range 2–6 10−21/Hz. The coincidences found are within the estimated background, hence improved upper limits on incoming GW (gravitational wave) bursts have been set.

Charge effects on gravitational wave detectors

We show that the mean-square displacement of a charged oscillator due to the zero point oscillations of the radiation field is unique in the sense that it is very sensitive to the value of the bare mass of the charge. Thus, a controlled experiment using gravitational wave detectors could lead to a determination of the electron bare mass and shed some light on quantum electrodynamic theory. We also speculate that the irregular signals of non-gravitational origin often observed in gravitational wave bar detectors could be caused by stray charges and that such charges could also adversely affect LIGO and other such detectors.

Resonant detectors for gravitational waves

For the first time a number of cryogenic resonant bar detectors of gravitational waves — ALLEGRO, AURIGA, EXPLORER, NAUTILUS, NIOBE — are on the air, in a continuous search for impulsive events. We present their capabilities, the foreseen upgrades and their role in a future global network with interferometric detectors.

Optical transduction chain for gravitational wave bar detectors

A new signal extraction chain for gravitational wave bar detectors is proposed. Signal transduction is made by means of a Fabry–Perot cavity. Using a reference cavity for frequency comparison a sensitivity of hmin=3×10−20 with a bandwidth of about 50 Hz is estimated for an ultracryogenic bar detector. The first prototype implementation as well as room-temperature measurements on it are reported.

Coincidence experiments between interferometric and resonant bar detectors of gravitational waves

Gravitational wave coincidence experiments between bars and interferometers may be an attractive option once the new generation of full scale interferometers begins taking data. We discuss various ways in which these disparate types of data can be compared in searches for bursts (from supernovae, for example), for pulsar signals, and for a stochastic background. Comparison of broadband interferometer data with narrowband bar data is appropriate in most searches for bursts, but in many cases the results---especially null results (upper limits)---are difficult to interpret. By narrowbanding the interferometer data to the bandwidth of the bar detector, one produces data sets that may give much clearer information in certain burst searches and that are appropriate for searches for a stochastic background of gravitational waves. We suggest, in fact, that there are circumstances where searches for a stochastic background could be more efficiently performed between a bar and an interferometer than between two interferometers. We examine, in some detail, the effect of narrowbanding the interferometer data. We apply this method to a real interferometer and bar data and assess its signal-to-noise performance for different classes of gravitational wave signals.

Measurement of energy transfer in a five-mode gravitational wave bar detector

A 1400-kg five-mode bar detector has been constructed and tested at room temperature. Detailed calculations and computer simulations have been performed to optimize the design and study the dynamics of the system. The tests have confirmed the analytical prediction that a large fraction (67% in this experiment) of the energy deposited into the bar is transferred to the last resonator. The rise time of the energy at the last resonator is short (≂2 ms), and corresponds to an effective detector bandwidth of ≂500 Hz.