Design and implementation of a seismic Newtonian-noise cancellation system for the Virgo gravitational-wave detector

Terrestrial gravity perturbations caused by seismic fields produce the so-called Newtonian noise in gravitational-wave detectors, which is predicted to limit their sensitivity in the upcoming observing runs. In the past, this noise was seen as an infrastructural limitation, i.e., something that cannot be overcome without major investments to improve a detector's infrastructure. However, it is possible to have at least an indirect estimate of this noise by using the data from a large number of seismometers deployed around a detector's suspended test masses. The noise estimate can be subtracted from the gravitational-wave data; a process called Newtonian-noise cancellation (NNC). In this article, we present the design and implementation of the first NNC system at the Virgo detector as part of its AdV+ upgrade. It uses data from 110 vertical geophones deployed inside the Virgo buildings in optimized array configurations. We use a separate tiltmeter channel to test the pipeline in a proof-of-principle. The system has been running with good performance over months

Measurement of gravitational and thermal effects in a liquid-actuated torsion pendulum

We describe a proof-of-principle experiment aiming to investigate the inverse-square law of gravitation at the centimeter scale. The sensor is a two-stage torsion pendulum, while actuation is accomplished by a variable liquid mass. The time-varying gravitational force is related to the level of the circulating fluid in one or two containers at a short distance from the test mass, with all moving mechanical parts positioned at a large distance. We provide a description of the apparatus and present the first results. We identified a systematic effect of thermal origin, producing offsets of few fNm in torque and of about 10 pN in force. When this effect is neutralized, the measurements agree well with the predictions of simulations. We also discuss the upcoming instrument upgradations and the expected sensitivity improvement that will allow us to perform measurements with adequate accuracy to investigate the unexplored regions of the α−λ parameter space of a Yukawa-like deviation from the Newtonian potential

L’ASTRONOMIA GRAVITAZIONALE: IN ASCOLTO DEI SUSSURRI DELL’UNIVERSO

GRAVITATIONAL\ud ASTRONOMY: LISTENING TO THE\ud WHISPERS OF THE UNIVERSE\ud It was about 10 am,\ud Greenwich time, on\ud September 14th 2015 when\ud scientists detected\ud something which had never\ud been detected before: the\ud “sound” of two colliding\ud black holes which, after\ud orbiting around each\ud other for billion years,\ud approached closer and\ud closer until colliding,\ud giving rise to a single\ud huge black hole. A tiny\ud fraction of second before\ud the collision, they sent\ud a signal towards the rest\ud of the universe, their\ud “swansong”, a vibration\ud which propagated in space\ud and time at the speed of\ud light, getting to the Earth 1.4 billion years later. A gravitational wave. A hundred years after\ud the publication of the General Relativity, the Gravitational Waves detection confirms once again\ud the validity of Einstein’s Theory, and paves the way for a completely new research field. Spacetime\ud ripples poorly interacting with matter and giving rise to extremely tiny effects,\ud Gravitational Waves need very sophisticated instruments to be detected. In this paper we will\ud retrace the history of this discovery, starting from the breath of revolution of General Relativity\ud which carries along the theorization of Gravitational Wave. We will then go through the analysis of\ud the effect that Gravitational Waves induce on the matter, and we will describe the basic principles\ud of the instrument which detected them, to finally get to the first discovery which opens the way to\ud a completely new era for astronomy

Towards optomechanical parametric instabilities prediction in ground-based gravitational wave detectors

International audienceIncreasing the laser power is essential to improve the sensitivity of interferometric gravitational wave detectors. However, optomechanical parametric instabilities can set a limit to that power. It is of major importance to understand and characterize the many parameters and effects that influence these instabilities. Here, we model with a high degree of precision the optical and mechanical modes that are involved in these parametric instabilities, such that our model can become predictive. As an example, we perform simulations for the Advanced Virgo interferometer (O3 configuration). In particular we compute mechanical modes losses by combining both on-site measurements and finite element analysis with unprecedented level of detail and accuracy. We also study the influence on optical modes and parametric gains of mirror finite size effects, and mirror deformations due to thermal absorption. We show that these effects play an important role if transverse optical modes of order higher than four are involved in the instability process

Temperature Control for an Intra-Mirror Etalon in Interferometric Gravitational Wave Detector Fabry–Perot Cavities

International audienceThe sensitivity of interferometric gravitational wave detectors is optimized, in part, by balanced finesse in the long Fabry–Perot arm cavities. The input test mass mirrors of Advanced Virgo feature parallel faces, which creates an etalon within the substrate, adding variability in the total mirror reflectivity, in order to correct imbalanced finesse due to manufacturing tolerances. Temperature variations in mirror substrate change the optical path length primarily through varying the index of refraction and are tuned to correct for a finesse imbalance of up to 2.8% by a full etalon fringe of 0.257 K. A negative feedback control system was designed to control the mirror temperature by using an electrical resistive heating belt actuator for a heat transfer process modeled as a two-pole plant. A zero controller filter was designed which achieves temperature control within 2.3% of the etalon fringe and recovers to within 10% of the working point within 32 hours after a step input of one etalon fringe. A preliminary unlock condition control designed to compensate when the interferometer unlocks shows that the control remains stable even after a drastic change in the plant due to the absence of the laser heating. Further improvements to the control must also consider the full heat transfer mechanisms by using modern control state space models

Speech discrimination is impaired in parkinsonian patients: Expanding the audiologic findings of Parkinson's disease

Background and objectives: Hearing impairment (HI) has been previously demonstrated in patients with Parkinson's disease (PD). Pure Tone Audiometry (PTA) gives no information about patients' ability to hear and understand speech. To find out hearing ability and speech discrimination of PD patients, we expanded audiological evaluation by means of speech audiometry (SA). Patients and methods: We screened a series of consecutive PD patients. Severity of motor symptoms and staging were measured by the UPDRS-III and the H&Y scales. Audiometric evaluation consisted of a standardized audiological examination, PTA and SA. Healthy age- and sex-matched subjects were selected as controls. Results: 45 PD patients and 45 healthy controls were enrolled. PTA confirmed our previous finding of high-frequency HI in PD patients. The mean values for the Speech Recognition Threshold were higher in PD patients as compared with controls. PD patients were more likely to have impaired speech discrimination profiles and higher disease stages. Neither the patients nor the controls showed a significant speech-tone dissociation and rollover phenomenon. Conclusion: Our results confirmed sensorineural HI in PD patients. Moreover, SA showed impaired speech discrimination abilities in PD patients as compared with control group thus expanding the audiologic findings of PD

Results of Measuring the Influence of Casimir Energy on Superconducting Phase Transitions

The ALADIN experiment aims at observing how the critical magnetic field of a superconducting aluminum film is modified, when it constitutes one of the reflecting surfaces of a Casimir cavity. If successful, such an observation would reveal the influence of vacuum energy on the superconducting phase transition. In this paper, a rigorous analysis of experimental data is reported, the results are discussed and compared with theoretical predictions based on Lifshitz theory of dispersion forces, and the BCS formula for the optical conductivity of superconductors. Thanks to this rigorous analysis, it can now be asserted that in the region of energy where it is expected that Casimir energy is comparable with condensation energy and the deviations of critical field from BCS formula to be not negligible, an anomalous behavior is found

Large and extremely low loss: the unique challenges of gravitational wave mirrors

International audienceThis paper describes the making of large mirrors for laser interferometer gravitational wave detectors. These optics, working in the near infrared, are among the best optics ever created and played a crucial role in the first direct detection of gravitational waves from black holes or neutron star fusions