Resonant Gravitational Wave Detectors Research Articles

Analysis of quadrupolar frequencies of the spherical gravitational wave detector by finite element modeling: A study case

The Schenberg detector is a spherical resonant antenna gravitational wave detector with a solid sphere with a diameter of 65 cm and a weight of approximately 1.15 metric tons. It is made of a copper–aluminum alloy with 94% Cu and 6% Al. This work aims to verify the natural frequencies of the Schenberg detector structure. The authors used the finite element method to calculate the quadrupole frequency band and compare it with the value measured in tests during the construction of the antenna at University of Sao Paulo, which was 67.3 Hz. In the modal simulation with the homogenous material, the frequency band of the quadrupole modes was around 35 Hz. Many trials to improve this result were made with no significant improvement. The improvement came when the sphere was considered not homogenous, as to the cooling process of the sphere casting, the alloy that cooled faster (close to the surface sides and in the bottom) can reach a hardness 20% higher than the material that cooled slower (in the center and on the top). Including these characteristics, the band value obtained was close to the one measured during the construction of the antenna, a value of 63.2 Hz was obtained.

Ultra-stable optical clock cavities as resonant mass gravitational wave detectors in search for new physics

We propose using table-top-size ultra-stable optical cavities from state-of-the-art optical atomic clocks as bar gravitational wave detectors for frequencies higher than 2 kHz. We show that the 2-20 kHz range of gravitational waves' spectrum can be accessed with instruments below 2 meters in size. The materials and properties of the proposed cavities are in the grasp of today's technology. The ultra-stable optical cavities allow detection not only predicted gravitational wave signals from such sources as binary neutron star mergers and post-mergers, subsolar-mass primordial black-hole mergers, and collapsing stellar cores, but can also reach new physics beyond the standard model, looking for ultralight bosons such as QCD axions and axion-like particles formed through black hole superradiance.

The laser interferometric gravitational wave detector calibrator suspension: First attempt

AbstractIn 2015 the first detection of gravitational waves (GW) was made; such detection was made by kilometer size interferometer detectors. The calibration of such a detector is still a challenge then a calibrator was proposed. This calibrator is a resonant mass gravitational wave detector that operates at frequencies where the GW have been detected. This work shows part of the challenges of making a suspension for this device. The device has its vibration mode simulated in Finite Element Methods, then the parts of the device which have less movement were chosen to connect the suspension. Other simulations were made with the complete system and the results were analyzed.

Path Integral Action for a Resonant Detector of Gravitational Waves in the Generalized Uncertainty Principle Framework

The Heisenberg uncertainty principle is modified by the introduction of an observer-independent minimal length. In this work, we have considered the resonant gravitational wave detector in the modified uncertainty principle framework, where we have used the position momentum uncertainty relation with a quadratic order correction only. We have then used the path integral approach to calculate an action for the bar detector in the presence of a gravitational wave and then derived the Lagrangian of the system, leading to the equation of motion for the configuration-space position coordinate in one dimension. We then find a perturbative solution for the coordinate of the detector for a circularly polarized gravitational wave, leading to a classical solution of the same for the given initial conditions. Using this classical form of the coordinate of the detector, we finally obtain the classical form of the on-shell action describing the harmonic oscillator–gravitational wave system. Finally, we have obtained the free particle propagator containing the quantum fluctuation term considering gravitational wave interaction.

Modelling a mechanical antenna for a calibrator for interferometric gravitational wave detector using finite elements method

Interferometric gravitational wave detectors (IGWD) are a very complex detector, the need to lock the detector in a dark fringe condition besides the vibrations that affect the mirrors, creates the necessity of using active suspension systems. These active systems make the system reach the desired sensitivity but make the calibration of such detectors much more difficult. To solve this problem a calibrator is proposed, a resonant mass gravitational wave detector could be used to detect the same signal in a narrower band and use the measured amplitude to calibrate the IGWD, as resonant mass gravitational wave detectors are easily calibrated. This work aims to design the mechanical antenna of such a calibrator. The main difficulty is to design the calibrator is the frequencies required to make the detection. These massive detectors usually were made in frequencies close to 1 kHz and the frequency range to operate for better sensitivity is around 100 Hz. The antenna is modelled in finite elements method and a design of such an antenna is presented.

Obtaining the sensitivity of a calibrator for interferometric gravitational wave

Interferometric gravitational wave detectors (IGWD) are a very complex detector, the need to lock the detector in a dark fringe condition besides the vibrations that affect the mirrors, creates the necessity of using active suspension systems. These active systems make the system reach the desired sensitivity but make the calibration of such detectors much more difficult. To solve this problem a calibrator is proposed, a resonant mass gravitational wave detector could be used to detect the same signal in a narrower band and use the measured amplitude to calibrate the IGWD, as resonant mass gravitational wave detectors are easily calibrated. This work aims to obtain the expected sensitivity of such a calibrator by using lumped modelling in such mechanical detectors. The calibrator is modelled as a spring mass system and the sensitivity curve is presented calculated in by a matlab program. The curve shows that using state of art parameters for the detector the final sensitivity is close to the quantum limit and can be used to calibrate the IGWDs.

Gravitational wave driving of a gapped holographic system

This work addresses the response of a holographic conformal field theory to a homogeneous gravitational periodic driving. The dual geometry is the AdS-soliton, which models a strongly coupled quantum system in a gapped phase, on a compact domain. The response is a time-periodic geometry up to a driving amplitude threshold which decreases with the driving frequency. Beyond that, collapse to a black hole occurs, signaling decoherence and thermalization in the dual theory. At some frequencies, we also find a resonant coupling to the gravitational normal modes of the AdS-soliton, yielding a nonlinearly bound state. We also speculate on the possible uses of quantum strongly coupled systems to build resonant gravitational wave detectors.

Resonant bar detector constraints on macro dark matter

The current standard model of cosmology, $\Lambda$CDM, requires dark matter to make up around $25\%$ of the total energy budget of the Universe. Yet, quite puzzlingly, there appears to be no candidate particle in the current Standard Model of particle physics. Assuming the validity of the cold dark matter (CDM) paradigm, dark matter has evaded detection thus far either because it is intrinsically a weakly interacting substance or because its interactions are suppressed by its high constituent mass and low number density. Most approaches to explain dark matter to date assume the former and therefore require beyond-the-Standard-Model particles that have yet to be observed directly or indirectly. Given the dearth of evidence for this class of candidates it is timely to consider the latter possibility, which allows for candidates that may or may not arise from the Standard Model. In this work we extend a recent study of this general class of so-called macro dark matter--candidates with characteristic masses of grams and geometric cross sections of cm$^2$. We consider new bounds that can be set using existing data from the resonant bar gravitational wave detectors NAUTILUS and EXPLORER.

High sensitivity niobium parametric transducer for the Mario Schenberg gravitational wave detector

Parametric transducers can work below the quantum limit of sensitivity for resonant mass gravitational wave detectors. This makes them a promising alternative for electromechanical transductance for such detectors. These transducers consist of a reentrant superconducting niobium cavity coupled to a mass-spring system with three mechanical modes. These cavities have a central post responsible for creating a narrow axial gap between its top and the cavity wall, which is a resonant membrane. Their displacement sensitivity (df/dx) increases as the gap spacing decreases. However, this is not a linear relationship and the dimensioning of the cavity becomes critical if the gap is of the order of a few microns. In this paper, we describe how to obtain a gap spacing of ∼ 3 μ m and also the development of parametric transducers that will be employed in the coming experimental runs of the Schenberg gravitational wave antenna. Mechanical thinning methods were performed followed by mechanical and electrical frequency measurements to tune the device to operate at the required frequencies. The main results present better frequency stability and an improvement of df/dx by one order of magnitude higher than the preceding models. These results will allow us to reach the quantum limit of detector sensitivity of ∼ 10−22 Hz−1/2 in the near future, making it possible to search for gravitational waves around 3.2 kHz.

Detection of high energy cosmic rays with the resonant gravitational wave detectors NAUTILUS and EXPLORER and comparison with the direct measurements with an aluminum superconductive bar

The cryogenic resonant gravitational wave detectors NAUTILUS and EXPLORER, made of an aluminum alloy bar, can detect cosmic ray showers. At temperatures above 1 K, when the material is in the normal conducting state, the measured signals are in good agreement with the values expected based on the cosmic rays data and on the thermo-acoustic model. When NAUTILUS was operated at the temperature of 0.14 K, in superconductive state, large signals produced by cosmic ray interactions, more energetic than expected, were recorded. The NAUTILUS data in this case are in agreement with the measurements done by a dedicated experiment on a particle beam. The largest event detected up to now has an energy in the first longitudinal mode of ∼ 670 K corresponding to ∼ 360 TeV in the bar.

Experimental study of high energy electron interactions in a superconducting aluminum alloy resonant bar

Peak amplitude measurements of the fundamental mode of oscillation of a suspended aluminum alloy bar hit by an electron beam show that the amplitude is enhanced by a factor ∼3.5 when the material is in the superconducting state. This result is consistent with the cosmic ray observations performed by the resonant gravitational wave detector NAUTILUS, made of the same alloy, when operated in the superconducting state. A comparison of the experimental data with the predictions of the model describing the underlying physical process is also presented.

Detection of high energy cosmic rays with the resonant gravitational wave detectors NAUTILUS and EXPLORER

The cryogenic resonant gravitational wave detectors NAUTILUS and EXPLORER, made of an aluminum alloy bar, can detect cosmic ray showers. At temperatures above 1 K, when the material is in the normal-conducting state, the measured signals are in good agreement with the expected values based on the cosmic rays data and on the thermo-acoustic model. When NAUTILUS was operated at the temperature of 0.14 K, in superconductive state, large signals produced by cosmic ray interactions, more energetic than expected, were recorded. The NAUTILUS data in this case are in agreement with the measurements done by a dedicated experiment on a particle beam. The biggest recorded event was in EXPLORER and excited the first longitudinal mode to a vibrational energy of ∼670 K, corresponding to ∼360 TeV absorbed in the bar. Cosmic rays can be an important background in future acoustic detectors of improved sensitivity. At present, they represent a useful tool to verify the gravitational wave antenna performance.

Effect of energy deposited by cosmic-ray particles on interferometric gravitational wave detectors

We investigated the noise of interferometric gravitational wave detectors due to heat energy deposited by cosmic-ray particles. We derived a general formula that describes the response of a mirror against a cosmic-ray passage. We found that there are differences in the comic-ray responses (the dependence of temperature and cosmic-ray track position) in cases of interferometric and resonant gravitational wave detectors. The power spectral density of vibrations caused by low-energy secondary muons is 100 times smaller than the goal sensitivity of future second-generation interferometer projects, such as LCGT and Advanced LIGO. The arrival frequency of high-energy cosmic-ray muons that generate enough large showers inside mirrors of LCGT and Advanced LIGO is one per a millennium. We also discuss the probability of exotic-particle detection with interferometers.

SQUID Developments for the Gravitational Wave Antenna MiniGRAIL

We designed two different sensor SQUIDs for the readout of the resonant mass gravitational wave detector MiniGRAIL. Both designs have integrated input inductors in the order of 1.5 muH and are planned for operation in the mK temperature range. Cooling fins were added to the shunt resistors. The fabricated SQUIDs show a behavior that differs from standard DC-SQUIDs. We were able to operate a design with a parallel configuration of washers at reasonable sensitivities. The flux noise saturated to a value of 0.84 muPhi0/radicHz below a temperature of 200 mK. The equivalent noise referred to the current through the input coil is 155 fA/radicHz and the energy resolution yields 62 h.

On the sensitivity of a hollow sphere as a multi-modal resonant gravitational wave detector

We present a numerical analysis to simulate the response of a spherical resonant gravitational wave detector and to compute its sensitivity. Under the assumption of optimal filtering, we work out the sensitivity curve for a sphere first taking into account only a single transducer, and then using a coherent analysis of the whole set of transducers. We use our model for computing the sensitivity and therefore compare different designs of spherical detectors. In particular, we present the case of 1 m radius bulk and hollow spheres equipped with transducers in a TIGA configuration, and we explore the sensitivity of a hollow sphere as a multi-modal detector.

Response of resonant gravitational wave detectors to damped sinusoid signals

Till date, the search for burst signals with resonant gravitational wave (GW) detectors has been done using the δ-function approximation for the signal, which was reasonable due to the very small bandwidth of these detectors. However, now with increased bandwidth (of the order of 10 or more Hz) and with the possibility of comparing results with interferometric GW detectors (broad-band), it is very important to exploit the resonant detectors' capability to detect also signals with specific wave shapes. As a first step, we present a study of the response of resonant GW detectors to damped sinusoids with given frequency and decay time and report on the development of a filter matched to these signals. This study is a preliminary step towards the comprehension of the detector response and of the filtering for signals such as the excitation of stellar quasi-normal modes.

Measurement of optical response of a detuned resonant sideband extraction gravitational wave detector

We report on the optical response of a suspended-mass detuned resonant sideband extraction (RSE) interferometer with power recycling. The purpose of the detuned RSE configuration is to manipulate and optimize the optical response of the interferometer to differential displacements (induced by gravitational waves) as a function of frequency, independently of other parameters of the interferometer. The design of our interferometer results in an optical gain with two peaks: an RSE optical resonance at around 4 kHz and a radiation pressure induced optical spring at around 41 Hz. We have developed a reliable procedure for acquiring lock and establishing the desired optical configuration. In this configuration, we have measured the optical response to differential displacement and found good agreement with predictions at both resonances and all other relevant frequencies. These results build confidence in both the theory and practical implementation of the more complex optical configuration being planned for Advanced LIGO.

SFERA: the new spherical gravitational wave detector

This paper describes the main properties of gravitational wave detectors of spherical shape, the experimental achievements obtained up to now towards the development of this kind of detectors and the expected sensitivity of SFERA, a 2 meters diameter spherical antenna proposed as the next step in the development of resonant gravitational wave detectors.

Present performance and future upgrades of the AURIGA capacitive readout

The resonant bar gravitational wave detector AURIGA is taking data for its second run at T = 4.5 K. The readout has been largely upgraded with respect to the previous run. In particular, we have realized a 3-mode detection scheme by tuning the high-Q resonance of the electrical readout to the mechanical modes of bar and transducer. Moreover, a low noise two-stage SQUID amplifier has been implemented. Thanks to these improvements, the bandwidth has been largely increased and the strain sensitivity is now better than 10−20 Hz−1/2 over more than 100 Hz. In this paper, we describe a 3-mode model of the detector, which allows us to distinguish between the different noise contributions. Some possible upgrades are discussed.

27ℏ SQUID amplifier operating with high-Q resonant input load

We have extended to ultracryogenic temperatures the complete noise characterization of a low-noise two-stage superconducting quantum interference device (SQUID) amplifier developed for resonant gravitational wave detectors. The additive current noise is evaluated from open input measurements. To evaluate the back action voltage noise, the SQUID is strongly coupled to a high-Q macroscopic electrical resonator operating at 11.7 kHz. From these measurements, we estimate a minimum noise temperature of 15μK, corresponding to 27 times the quantum-limited noise temperature. Implications of this result for the sensitivity of resonant gravitational wave detectors are briefly discussed.