Upper limit on the flux of gravitational wave bursts

Summary The data obtained with three highly sensitive gravitational wave antennas have been used to establish an improved observational upper limit on the flux of impulsive gravitational waves. Preliminary results under the assumption of a source located in the center of the Galaxy are also reported. To speed up publication, the proofs were not sent to the authors and were superised by the Scientific Committee.     

String propagation in gravitational wave backgrounds

The Conformal Field Theory of the current algebra of the centrally extended 2-d Euclidean group is analyzed. Its representations can be written in terms of four free fields (without background charge) with signature (-+++). We construct all irreducible representations of the current algebra with unitary base out of the free fields and their orbifolds. This is used to investigate the spectrum and scattering of strings moving in the background of a gravitational wave. We find that all the dynamics happens in the transverse space or the longitudinal one but not both.     

The gravitational wave antenna in Frascati

Summary We report on the cryogenic gravitational detector operating at 1763 Hz in Frascati. The antenna was equipped with a resonant capacitive transducer and a d.c. SQUID as an amplifier. After a test run in 1987, the detector was cooled again in the present configuration and took data for nearly two months in June and July 1988. A preliminary data analysis shows a noise temperature of 115 mK, but we expect to lower it further by applying improved filtering tecniques. During the same period two other cryogenic antennae were operating, and we plan to undertake a correlation analysis between the output of the three detectors. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.     

Data analysis for a gravitational wave antenna with resonant capacitive transducer

Summary We present here a new approach which simplifies considerably the data analysis for gravitational-wave antennas equipped with resonant transducer, based on the representation of the antenna as two independent oscillators. In fact, we can apply to each of the two modes of these antennas the same data analysis procedures already in use for antennas with nonresonant transducer and then compute the coincidences between the outputs of the two modes. The results deduced by such a procedure are in good agreement with the experimental results from the data collected in March 1984 with our 2270 kg 5056 Al bar cooled at liquid-helium temperature (T=4.2 K). The performances of the algorithms are presented in terms of the effective noise temperatures and sensitivity to short bursts of gravitational waves. With our experimental values, obtained by using a FET amplifier, we get an instrumental sensitivityF(v) of 6 J/m² Hz. We have also evaluated the sensitivity of the detector for monochromatic gravitational waves with frequencies in bandwidths of ≏0.4 Hz around the frequenciesv ₋ andv ₊, for one month of observation:h ₀≏3·10⁻²³.

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Riassunto Si presenta un nuovo approccio che semplifica notevolmente l’analisi dei dati per antenne gravitazionali con trasduttore risonante, basato sulla rappresentazione dell’antenna come due oscillatori indipendenti. A ciascuno dei modi di tali antenne si applicano le procedure di analisi dei dati già usati per le antenne con trasduttore risonante e si calcolano quindi le coincidenze tra le uscite dei due modi. I risultati dedotti mediante tale procedura sono in buon accordo con i risultati sperimentali relativi ai dati raccolti nel marzo 1984 con la nostra sbarra di Al 5056 da 2270 kg raffreddata alla temperatura dell’elio liquido (T=4.2 K). Si presentano le prestazioni degli algoritmi in termini delle temperature efficaci di rumore e della sensibilità per brevi fiotti di onde gravitazionali. Con i nostri valori sperimentali, ottenuti usando un amplificatore a FET, si ha una sensibilità strumentaleF(v) di 6 J/m² Hz. Si è anche calcolata la sensibilità del rivelatore per onde gravitazionali monocromatiche in bande di frequenza di circa 0.4 Hz attorno alle frequenzev ₋ ev ₊, per un mese di ossevazione:h ₀≏3.·10⁻²³.

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Резюме Предлагается новый подход, котрый значительно упрощает анализ данных для антенн гравитационных волн с резонансным емкостным датчиком, основанный на представлении антенны в виде двух независимых осцилляторов. Мы можем применить к каждой из двух мод этих антенн процедуры анализа данных, которые ыже использовались для антенн с нерезонансными датчиками, а затем вычислить совпадения между результатами на выходе для двух мод. Результаты, полученные с помощью такой процедуры, хорошо согласуются с экспериментальными результатами, собранными в марте 1984 года с помощью 2270 кг 5056 Al антенны, охлажденной до температуры жидкого гелия (T=4.2 К). Описываются алгоритмы анализа, исходя из эффективных температур шума и чувствительности к коротким вспышкам гравитационных волн. Используя экспериментальные значения, полученные с помощью FET усилителя, мы определяем инструментальную чувствительностьF(v)≈6Дж/M² Гц. Мы также оцениваем чувствительность детектора для монохроматических гравитационных волн в полосе частот 0.4 Гц вблизи частот,v ₋ иv ₊ для одного месяца наблюдения:h ₀≏3·10⁻²³.

     

The electric field induced by a gravitational wave in a superconductor: a principle for a new gravitational wave antenna

In this paper we investigate the effect of gravitational waves (GW) on a superconductor. We find that the key properties of a superconductor, namely zero resistance and perfect diamagnetism, give rise to an important new effect, the presence of an induced electric fieldE(r, t) in the interior of the superconductor. TheE field reacts with the ions and superelectrons. We argue, that not only is the finding of the coupled interactions of gravitation, electromagnetism and superconductivity inherently interesting, but that the inducedE field might provide a significantly more sensitive means of detecting gravitational waves. It appears likely that existing resonant-mass superconducting antennas withL - 3m,Q - 10⁸ could be readily modified to detectE fields induced by GWs of dimensionless amplitudeh - 10^–24 This essay received the first award from the Gravity Research Foundation for the year 1989—Ed.     

Experimental study of the dynamic Newtonian field with a cryogenic gravitational wave antenna

We present an experiment performed to study the behaviour of the dynamic gravitational interaction at laboratory scale. We used as field generator a mass quadrupole rotating in the range of 460 Hz and we detected the acceleration field with the cryogenic gravitational wave antenna Explorer of the Rome group. We report the measurements of this interaction as a function of the distance between the field source and the detector. An upper limit on the parameters of a Yukawa-like potential, modeling an hypotetic deviation from the Newtonian law of gravity, is derived. Received: 14 June 1998 / Published online: 16 September 1998     

Evaluation and preliminary measurement of the interaction of a dynamical gravitational near field with a cryogenic gravitational wave antenna

We present a detailed analysis of the effect of the gravitational field generated by a small rotating quadrupole on a graviational wave antenna and we report on the preliminary measurement of this effect on the Explorer 2270 kg cryogenic gravitational wave antenna of the Rome group. The induced signal had an amplitude twenty times larger than the detector noise when the antenna was equipped with an FET amplifier and was easily detected without requiring integration in time. We remark that with this method we were able to make an absolute calibration of a gravitational wave antenna.     

Quantum non-demolition observables for a weber-type gravitational wave antenna coupled to a resonant transducer

We present a general proof of the QND nature of the complex amplitudes for two coupled harmonic oscillators. The possibilities of the QND schemes for the detection of gravitational waves with a Weber-type antenna coupled to a resonant transducer are discussed, as well as their importance for the design of the next generation of gravitational wave antennas.     

Interaction of gravitational waves with a superconducting cylindrical antenna

In this paper we investigate the effects of gravitational waves (GW) on a superconducting cylindrical antenna (S-antenna). We suggest that the electric fields induced by GW of dimensionless amplitudeh - 10^–24 in the interior of existing cylindrical antenna might be detectable.     

Upper limits on the cosmological gravitational wave background and maser clocks in space

We consider the possibility of detecting gravitational waves through the measurement of a time varying phase shift using a hydrogen maser clock on a satellite. Such measurements enable us to put interesting upper limits on the contribution of the gravitational-wave background to the dimensionless density of the Universe. The requirements on residual accelerations and the sensitivity of an accelerometer on the spacecraft are shown to be realistic and could be achieved using the accelerometer technology developed by ONERA for the ARISTOTELES mission. Such an experiment placing upper limits on the cosmological gravitational wave background could be conducted using the proposed Russian satellite Millimetron.On leave from the Astro Space Center, Lebedev Physical Institute, Moscow, Russia     

Remark on a toroidal detector of a gravitational wave

The object of this paper is to review the detector of a gravitational wave that was proposed by Braginsky and Mensky (1971). The derivation of the sensitivity is based on the same assumption as they proposed. It is concluded that the phase difference is linear in time and that the sensitivity of this detector is different from the result claimed by Braginsky and Mensky. The foundation to obtain the phase difference, i.e., the sensitivity, in this paper is not the frequency as they used but rather the movement of the wave front in the detector.     

Interaction of a planar gravitational wave with a scalar field

It is shown that a strong gravitational wave can reflect a flow of scalar particles moving toward it. The particles initially penetrate the forward wave propagation front and only then are reflected.     

Upper limits on a stochastic background of gravitational waves

The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of omega0 < 8.4 x 10(-4) in the 69-156 Hz band is approximately 10(5) times lower than the previous result in this frequency range.     

Interaction of a gravitational wave with an elastic body

The problem concerning the interaction of a weak gravitational wave with an elastic body in the general theory of relativity is solved by the use of the theory of elasticity composed earlier by the author on the basis of a gravitoinertial system of reference (GISR).Translated from Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 67–73, July, 1976.In conclusion, we thank V. I. Rodichev and D. D. Ivanenko for interest in the project and for valuable critical comments.