Generation Of Gravitational Wave Detectors Research Articles

Laser frequency noise in next generation gravitational-wave detectors

Future ground-based gravitational-wave detectors are slated to detect black hole and neutron star collisions from the entire stellar history of the universe. To achieve the designed detector sensitivities, frequency noise from the laser source must be reduced below the level achieved in current Advanced LIGO detectors. This paper reviews the laser frequency noise suppression scheme in Advanced LIGO, and quantifies the noise coupling to the gravitational-wave readout. The laser frequency noise incident on the current Advanced LIGO detectors is 8 × 10 − 5 H z / H z at 1~kHz. Future detectors will require even lower incident frequency noise levels to ensure this technical noise source does not limit sensitivity. The frequency noise requirement for a gravitational wave detector with arm lengths of 40~km is estimated to be 7 × 10 − 7 H z / H z . To reach this goal a new frequency noise suppression scheme is proposed, utilizing two input mode cleaner cavities, and the limits of this scheme are explored. Using this scheme the frequency noise requirement is met, even in pessimistic noise coupling scenarios.

Environmental noises in current and future gravitational-wave detectors

Gravitational–wave (GW) detectors are very sensitive instruments that suffer from a huge number of noises. If we aim to observe gravitational waves with earthbound detectors, we need to take care of every source that can prevent the observation. Seismic noise poses a huge challenge to the sensitivity in the the low-frequency band and it is tackled with suspensions and active controls. The low–frequency band can also be threatened by the so–called Newtonian noise, generated by the fluctuations of the gravity field. If this has not been a problem in the first generation gravitational-wave detectors, it will be so in the next runs and especially in the third–generation detectors, like the Einstein Telescope. We need then to be prepared to suppress as much as possible these noises, otherwise they might become the last wall for the sensitivity of our detectors. This manuscript will explore environmental noises with a particular detail on Newtonian and seismic noise and the techniques that we can employ to reduce their effects.

Were recently reported MHz events planet mass primordial black hole mergers?

A bulk acoustic wave cavity as high frequency gravitational wave antenna has recently detected two rare events at 5.5MHz. Assuming that the detected events are due to gravitational waves, their characteristic strain amplitude lies at about h_capprox 2.5 times 10^{-16}. While a cosmological signal is out of the picture due to the large energy carried by the high frequency waves, the signal could be due to the merging of two planet mass primordial black holes (approx 4times 10^{-4} M_odot ) inside the Oort cloud at roughly 0.025 pc (5300 AU) away. In this short note, we show that the probability of one such event to occur within this volume per year is around 1:10^{24}, if such Saturn-like mass primordial black holes are 1% of the dark matter. Thus, the detected signal is very unlikely to be due the merger of planet mass primordial black holes. Nevertheless, the stochastic background of saturn mass primordial black holes binaries might be seen by next generation gravitational wave detectors, such as DECIGO and BBO.

Gravitational-wave propagation and polarizations in the teleparallel analog of Horndeski gravity

Gravitational waves (GWs) have opened a new window on fundamental physics in a number of important ways. The next generation of GW detectors may reveal more information about the polarization structure of GWs. Additionally, there is growing interest in theories of gravity beyond GR. One such theory which remains viable within the context of recent measurements of the speed of propagation of GWs is the teleparallel analogue of Horndeski gravity. In this work, we explore the polarization structure of this newly proposed formulation of Horndeski theory. In curvature-based gravity, Horndeski theory is almost synonymous with extensions to GR since it spans a large portion of these possible extensions. We perform this calculation by taking perturbations about a Minkowski background and consider which mode propagates. The result is that the polarization structure depends on the choice of model parameters in the teleparallel Horndeski Lagrangian with a maximum of seven propagating degrees of freedom. While the curvature-based Horndeski results follows as a particular limit within this setup, we find a much richer structure of both massive and massless cases which produce scalar--vector--tensor propagating degrees of freedom. We also find that the GW polarization that emerges from the teleparallel analogue of Horndeski gravity results in analogous massive and massless modes which take on at most four polarizations in the massless sector and two scalar ones in the massive sector. In none of the cases do we find vector polarizations.

Constraining parameters of coalescing stellar mass binary black hole systems with the Einstein Telescope alone

The Einstein Telescope (ET) is the future third generation gravitational wave detector consisting of three independent interferometers arranged in a triangular configuration, with the sensitivity large enough to be able to detect stellar mass black holes even beyond the redshift of 10. In this paper, we analyze the capabilities of ET as a standalone instrument and not part of a network. We show that the analysis of detection of binary coalescences in the three individual interferometers of the ET allow us to weakly constrain the sky location of the source. We present the analysis that leads to the constraints on the redshift and source frame chirp mass of detected binaries. We show that these values can be estimated with the accuracy comparable to the one expected from networks of gravitational wave interferometers. Thus, we show that the ET as a single instrument is able to break the redshift - chirp mass degeneracy and is therefore a valuable tool to explore properties of populations of merging compact object binaries.

Merging stellar and intermediate-mass black holes in dense clusters: implications for LIGO, LISA, and the next generation of gravitational wave detectors

Context.The next generation of gravitational wave (GW) observatories would enable the detection of intermediate-mass black holes (IMBHs), an elusive type of BH expected to reside in the centres of massive clusters, dwarf galaxies, and possibly the accretion discs of active galactic nuclei. Intermediate-mass ratio inspirals (IMRIs), which are composed of an IMBH and a compact stellar object, constitute one promising source of GWs detectable by this new generation of instruments.Aims.We study the formation and evolution of IMRIs triggered by interactions between two stellar BHs and an IMBH inhabiting the centre of a dense star cluster, with the aim of placing constraints on the formation rate and detectability of IMRIs.Methods.We exploit directN-body models varying the IMBH mass, the stellar BH mass spectrum, and the star cluster properties. Our simulations take into account the host cluster gravitational field and general relativistic effects via post-Newtonian terms up to order 2.5. These simulations are coupled with a semi-analytic procedure to characterise the evolution of the remnant IMBH after the IMRI phase.Results.Generally, the IMRI formation probability attains values of ∼5−50%, with larger values corresponding to larger IMBH masses. Merging IMRIs tend to map out the stellar BH mass spectrum, suggesting that IMRIs could be used to unravel the role of dynamics in shaping BH populations in star clusters harbouring an IMBH. After the IMRI phase, an initially almost maximal(almost non-rotating) IMBH tends to significantly decrease(increase) its spin. Under the assumption that IMBHs grow mostly via repeated IMRIs, we show that only sufficiently massive (Mseed > 300 M⊙) IMBH seeds can grow up toMIMBH > 103 M⊙in dense globular clusters (GCs). Assuming that these seeds form at a redshift ofz ∼ 2−6, we find that around 1−5% of them would reach typical masses of ∼500−1500 M⊙at redshiftz = 0 and would exhibit low spins, generallySIMBH < 0.2. Measuring the mass and spin of IMBHs involved in IMRIs could help to unravel their formation mechanism. We show that LISA can detect IMBHs in Milky Way GCs with a signal-to-noise ratioS/N = 10−100, or in the Large Magellanic Cloud, for which we get aS/N = 8−40. More generally, we provide the IMRI merger rate for different detectors, namely LIGO (ΓLIGO = 0.003−1.6 yr−1), LISA (ΓLISA = 0.02−60 yr−1), ET (ΓET = 1−600 yr−1), and DECIGO (ΓDECIGO = 6−3000 yr−1).Conclusions.Our simulations explore one possible channel for IMBH growth, namely via merging with stellar BHs in dense clusters. We find that the mass and spin of the IMRI components and the merger remnant encode crucial information about the mechanisms that regulate IMBH formation. Our analysis suggests that the future synergy among GW detectors will enable us to fully unravel IMBH formation and evolution.

Kilonova Emission from Black Hole–Neutron Star Mergers. II. Luminosity Function and Implications for Target-of-opportunity Observations of Gravitational-wave Triggers and Blind Searches

Abstract We present detailed simulations of the kilonova and gamma-ray burst (GRB) afterglow and kilonova luminosity function from black hole–neutron star (BH–NS) mergers, and discuss the detectability of an electromagnetic (EM) counterpart in connection with gravitational wave (GW) detections, GW-triggered target-of-opportunity observations, and time-domain blind searches. The predicted absolute magnitude of BH–NS kilonovae at 0.5 days after the merger falls in the range [−10, −15.5]. The simulated luminosity function contains potential information on the viewing-angle distribution of the anisotropic kilonova emission. We simulate the GW detection rates, detectable distances, and signal duration for future networks of 2nd/2.5th/3rd generation GW detectors. BH–NSs tend to produce brighter kilonovae and afterglows if the BH has a higher aligned spin, and a less massive NS with a stiffer equation of state. The detectability of kilonovae is especially sensitive to the BH spin. If BHs typically have low spins, the BH–NS EM counterparts are hard to discover. For 2nd generation GW detector networks, a limiting magnitude of m limit ∼ 23–24 mag is required to detect kilonovae even if high BH spin is assumed. Thus, a plausible explanation for the lack of BH–NS-associated kilonova detection during LIGO/Virgo O3 is that either there is no EM counterpart (plunging events) or the current follow-ups are too shallow. These observations still have the chance to detect the on-axis jet afterglow associated with a short GRB or an orphan afterglow. Follow-up observations can detect possible associated short GRB afterglows, from which kilonova signatures may be studied. For time-domain observations, a high-cadence search in redder filters is recommended to detect more BH–NS-associated kilonovae and afterglows.

The neutrino gravitational memory from a core collapse supernova: phenomenology and physics potential

General Relativity predicts that the passage of matter or radiation from an asymmetrically-emitting source should cause a permanent change in the local space-time metric. This phenomenon, called the gravitational memory effect, has never been observed, however supernova neutrinos have long been considered a promising avenue for its detection in the future. With the advent of deci-Hertz gravitational wave interferometers, observing the supernova neutrino memory will be possible, with important implications for multimessenger astronomy and for tests of gravity. In this work, we develop a phenomenological (analytical) toy model for the supernova neutrino memory effect, which is overall consistent with the results of numerical simulations. This description is then generalized to several case studies of interest. We find that, for a galactic supernova, the dimensionless strain, h(t), is of order ∼ 10-22 - 10-21, and develops over a typical time scale that varies between ∼ 0.1 - 10 s, depending on the time-evolution of the anisotropy of the neutrino emission. The characteristic strain, h c(f), has a maximum at a frequency f max ∼ \U0001d4aa(10-1) - \U0001d4aa(1) Hz. The detailed features of the time- and frequency-structure of the memory strain will inform us of the matter dynamics near the collapsed core, and allow to distinguish between different stellar collapse scenarios. Next generation gravitational wave detectors like DECIGO and BBO will be sensitive to the neutrino memory effect for supernovae at typical galactic distances and beyond; with Ultimate DECIGO exceeding a detectability distance of 10 Mpc.

Ternary quarter wavelength coatings for gravitational wave detector mirrors: Design optimization via exhaustive search

Multimaterial optical coatings are a promising viable option to meet the challenging requirements (in terms of transmittance, absorbance and thermal noise) of next generation gravitational wave detector mirrors. In this paper we focus on ternary coatings consisting of quarter-wavelength thick layers, where a third material (H') is added to the two presently in use, namely Silica (L) and Titania-doped Tantala (H), featuring higher dielectric contrast (against Silica), and lower thermal noise (compared to Titania-doped Tantala), but higher optical losses. We seek the optimal material sequences, featuring minimal thermal (Brownian) noise under prescribed transmittance and absorbance constraints, by exhaustive simulation over all possible configurations, for different values (in a meaningful range) of the optical density and extinction coefficient of the third material. In all cases studied, the optimal designs consist of a stack of (H'|L) doublets topped by a stack of (H|L) doublets, confirming previous heuristic assumptions, and the achievable coating noise power spectral density reduction factor is \sim 0.5. The robustness of the found optimal designs against layer thickness deposition errors and uncertainties and/or fluctuations in the optical losses of the third material is also investigated. Possible margins for further thermal noise reduction by layer thickness optimization, and strategies to implement it, are discussed.

Probing gravity and growth of structure with gravitational waves and galaxies’ peculiar velocity

The low-redshift velocity field is a unique probe of the growth of cosmic structure and gravity. We propose to use distances from gravitational wave (GW) detections, in conjunction with the redshifts of their host galaxies from wide field spectroscopic surveys (e.g. DESI, 4MOST, TAIPAN), to measure peculiar motions within the local Universe. Such measurement has the potential to constrain the growth rate $f\sigma_8$ and test gravity through determination of the gravitational growth index $\gamma$, complementing constraints from other peculiar velocity measurements. We find that binary neutron star mergers with associated counterpart at $z\lesssim 0.2$ that will be detected by the Einstein Telescope (ET) will be able to constrain $f\sigma_8$ to $\sim 3\%$ precision after $10$ years of operations when combined with galaxy overdensities from DESI and TAIPAN. If a larger network of third generation GW detectors is available (e.g. including the Cosmic Explorer), the same constraints can be reached over a shorter timescale ($\sim 5$ years for a 3 detectors network). The same events (plus information from their hosts' redshifts) can constrain $\gamma$ to $\sigma_\gamma\lesssim 0.04$. This constraint is precise enough to discern General Relativity from other popular gravity models at $3\sigma$. This constraint is improved to $\sigma_\gamma\sim 0.02-0.03$ when combined with galaxy overdensities. The potential of combining galaxies' peculiar velocities with gravitational wave detections for cosmology highlights the need for extensive optical to near--infrared follow--up of nearby gravitational wave events, or exquisite GW localization, in the next decade.

Point absorbers in Advanced LIGO.

Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry-Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.

Observation of eccentric binary black hole mergers with second and third generation gravitational wave detector networks

[Abridged] We introduce an improved version of the Eccentric, Non-spinning, Inspiral-Gaussian-process Merger Approximant (ENIGMA) waveform model. We find that this ready-to-use model can: (i) produce physically consistent signals when sampling over 1M samples chosen over the $m_{\{1,\,2\}}\in[5M_{\odot},\,50M_{\odot}]$ parameter space, and the entire range of binary inclination angles; (ii) produce waveforms within 0.04 seconds from an initial gravitational wave frequency $f_{\textrm{GW}} =15\,\textrm{Hz}$ and at a sample rate of 8192 Hz; and (iii) reproduce the physics of quasi-circular mergers. We utilize ENIGMA to compute the expected signal-to-noise ratio (SNR) distributions of eccentric binary black hole mergers assuming the existence of second and third generation gravitational wave detector networks that include the twin LIGO detectors, Virgo, KAGRA, LIGO-India, a LIGO-type detector in Australia, Cosmic Explorer, and the Einstein Telescope. In the context of advanced LIGO-type detectors, we find that the SNR of eccentric mergers is always larger than quasi-circular mergers for systems with $e_0\leq0.4$ at $f_{\textrm{GW}} =10\,\textrm{Hz}$, even if the timespan of eccentric signals is just a third of quasi-circular systems with identical total mass and mass-ratio. For Cosmic Explorer-type detector networks, we find that eccentric mergers have similar SNRs than quasi-circular systems for $e_0\leq0.3$ at $f_{\textrm{GW}} =10\,\textrm{Hz}$. Systems with $e_0\sim0.5$ at $f_{\textrm{GW}} =10\,\textrm{Hz}$ have SNRs that range between 50%-90% of the SNR produced by quasi-circular mergers, even if these eccentric signals are just between a third to a tenth the length of quasi-circular systems. For Einstein Telescope-type detectors, we find that eccentric mergers have similar SNRs than quasi-circular systems for $e_0\leq0.4$ at $f_{\textrm{GW}} =5\,\textrm{Hz}$.

Results from high-frequency all-sky search for continuous gravitational waves from small-ellipticity sources

We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 1700-2000 Hz range from neutron stars with ellipticity of 1e-8. The search employs the Falcon analysis pipeline [citation 5] on LIGO O2 public data. Our results improve by a factor greater than 5 over [citation 11]. This is a huge leap forward: it takes an entirely new generation of gravitational wave detectors to achieve a 10-fold sensitivity increase over the previous generation [citation 12]. Within the probed frequency range and aside from the detected outliers, we can exclude neutron stars with ellipticity of 1e-8 within 65 pc of Earth. We set upper limits on the gravitational wave amplitude that hold even for worst-case signal parameters. New outliers are found, some of which we are unable to associate with any instrumental cause. If any were associated with a rotating neutron star, this would likely be the fastest neutron star today.

Low noise 400 W coherently combined single frequency laser beam for next generation gravitational wave detectors.

Design studies for the next generation of interferometric gravitational wave detectors propose the use of low-noise single-frequency high power laser sources at 1064 nm. Fiber amplifiers are a promising design option because of their high output power and excellent optical beam properties. We performed filled-aperture coherent beam combining with independently amplified beams from two low-noise high-power single-frequency fiber amplifiers to further scale the available optical power. An optical power of approximately 400 W with a combining efficiency of more than 93% was achieved. The combined beam contained 370 W of linearly polarized TEM00-mode and was characterized with respect to the application requirements of low relative power noise, relative beam pointing noise, and frequency noise. The noise performance of the combined beam is comparable to the single amplifier noise. This represents, to our knowledge, the highest measured power in the TEM00-mode of single frequency signals that fulfills the low noise requirements of gravitational wave detectors.

Gravitational Wave Implications for the Parity Symmetry of Gravity in the High Energy Region

Abstract Einstein's general relativity, as the most successful theory of gravity, is one of the cornerstones of modern physics. However, the experimental tests for gravity in the high energy region are limited. The emerging gravitational-wave astronomy has opened an avenue for probing the fundamental properties of gravity in a strong and dynamical field, and in particular, a high energy regime. In this work, we test the parity conservation of gravity with gravitational waves. If the parity symmetry is broken, the left- and right-handed modes of gravitational waves would follow different equations of motion, dubbed as birefringence. We perform full Bayesian inference by comparing the state-of-the-art waveform with parity violation with the compact binary coalescence data released by LIGO and Virgo collaboration. We do not find any violations of general relativity, thus constrain the lower bound of the parity-violating energy scale to be 0.09 GeV through the velocity birefringence of gravitational waves. This provides the most stringent experimental test of gravitational parity symmetry to date. We also find third generation gravitational-wave detectors can enhance this bound to GeV if there is still no violation, comparable to the current energy scale in particle physics, which indicates gravitational-wave astronomy can usher in a new era of testing the ultraviolet behavior of gravity in the high energy region.

Sensitivity of present and future detectors across the black-hole binary gravitational wave spectrum

Black-holes are known to span at least 9 orders of magnitude in mass: from the stellar-mass objects observed by the Laser Interferometer Gravitational-Wave Observatory Scientific Collaboration and Virgo Collaboration, to supermassive black-holes like the one observed by the Event Horizon Telescope at the heart of M87. Regardless of the mass scale, all of these objects are expected to form binaries and eventually emit observable gravitational radiation, with more massive objects emitting at ever lower gravitational-wave frequencies. We present the tool, gwent, for modeling the sensitivities of current and future generations of gravitational wave detectors across the entire gravitational-wave spectrum of coalescing black-hole binaries (BHBs). We provide methods to generate sensitivity curves for pulsar timing arrays (PTAs) using a novel realistic PTA sensitivity curve generator (Hazboun, Romano and Smith 2019 Phys. Rev. D 100 104028), space-based interferometers using adaptive models that can represent a wide range of proposed detector designs (Amaro-Seoane et al 2017 arXiv:1702.00786), and ground-based interferometers using realistic noise models that can reproduce current (Abbott et al 2016 Phys. Rev. Lett. 116 061102), second, and third generation designs (Hild et al 2011 Class. Quantum Grav. 28 094013), as well as novel variations of the essential design parameters. To model the signal from BHBs at any mass scale, we use phenomenological waveforms capable of modeling the inspiral, merger, and ringdown for sources with varying mass ratios and spins (Khan et al 2016 Phys. Rev. D 93 044007; Husa et al 2016 Phys. Rev. D 93 044006). Using this adaptable framework, we produce signal-to-noise ratios (SNR) for the combination of any modeled parameter, associated with either the detector or the source. By allowing variation across each detector and source parameter, we can pinpoint the most important factors to determining the optimal performance for particular instrument designs. The adaptability of our detector and signal models can easily be extended to new detector designs and other models of gravitational wave signals.

Frequency-doubling of continuous laser light in the Laguerre–Gaussian modes LG0,0 and LG3,3

For future generations of gravitational wave detectors, it is proposed to use the helical Laguerre-Gaussian LG3,3 mode to reduce thermal noise, which limits the detector sensitivity. At the same time, this requires the efficient generation of squeezed vacuum states in the LG3,3 mode for quantum noise reduction. Since this technique includes the process of second harmonic generation (SHG), we experimentally compare the conversion efficiency and harmonic output field of the LG0,0 and LG3,3 modes in a cavity-enhanced SHG using the same 7% doped MgO:LiNbO3 crystal. Conversion efficiencies of 96% and 45% are achieved, respectively. The influence of mode mismatches and astigmatism is analyzed to estimate the ratio of the pump mode-dependent effective nonlinearities to be d0,0/d3,3∼5. Furthermore, we show that absorption loss in the crystal is more relevant for the LG3,3 mode.

Low phase noise squeezed vacuum for future generation gravitational wave detectors

Squeezed light has become a standard technique to enhance the sensitivity of gravitational wave detectors. Both optical losses and phase noise in the squeezed path can degrade the achievable improvements. Phase noise can be mitigated by having a high bandwidth servo to stabilize the squeezer phase to the light from the interferometer. In advanced LIGO, this control loop bandwidth is limited by the 4 km arm cavity free spectral range to about ∼15 kHz. Future generation gravitational-wave detectors are designed to employ much longer arm cavities. For cosmic explorer [], a 40 km arm length will limit the bandwidth to ∼1.5 kHz. We propose an alternative controls scheme that will increase the overall phase noise suppression by using the in-vacuum filter cavity as a reference for stabilizing the laser frequency of the squeezed light source. This will allow for rms phase noise of less than a milliradian—a negligible level for all future generations of gravitational-wave detectors [].

Distinguishing primordial black holes from astrophysical black holes by Einstein Telescope and Cosmic Explorer

We investigate how the next generation gravitational-wave (GW) detectors, such as Einstein Telescope (ET) and Cosmic Explorer (CE), can be used to distinguish primordial black holes (PBHs) from astrophysical black holes (ABHs). Since a direct detection of sub-solar mass black holes can be taken as the smoking gun for PBHs, we estimate the detectable limits of the abundance of sub-solar mass PBHs in cold dark matter by the targeted search for sub-solar mass PBH binaries and binaries containing a sub-solar mass PBH and a super-solar mass PBH, respectively. On the other hand, according to the different redshift evolutions of the merger rate for PBH binaries and ABH binaries, we forecast the detectable event rate distributions for the PBH binaries and ABH binaries by ET and CE respectively, which can serve as a method to distinguish super-solar mass PBHs from ABHs.

Exploring Populations of Low Mass Merging Compact Binary Systems with Single Einstein Telescope

AbstractEinstein Telescope (ET), a the future third generation gravitational wave detector will be sensitive to gravitational wave signal down to 1 Hz. We present an algorithm to estimate the parameters of the low mass merging compact binary systems such as localisation, chirp mass, redshift, mass ratios and total mass of the source which are crucial in order to estimate the capability of ET to study various compact binary populations. We analysed the compact binary populations of (i) Pop I and Pop II, (ii) Pop III, and (iii) globular clusters, with single ET.