Future Gravitational Wave Detectors Research Articles

Primordial-tensor-induced stochastic gravitational waves

Cosmological stochastic gravitational waves (GWs) induced by a spectator field are usually expected to have an amplitude very small compared with those generated by the curvature perturbation, or equivalently by a field dominating the universe. On the contrary to this expectation, we show that a spectator field that provides a tensor perturbation, on top of the metric tensor perturbation, can generate a significant amount of GWs. The amplitude and frequency of the generated GWs may lie within the sensitivity range of future GW detectors. In particular, if the sound velocities of the two tensor perturbations coincide, the induced GW amplitude may become very large due to resonance by forced oscillation, even in the limit of small coupling between them. A distinct feature of this scenario is that, since tensor modes can hardly lead to the formation of primordial black holes (PBHs), we expect no presence of PBHs, in contrast to the usual scalar-induced case, in which the detection of strong enough induced GWs suggests the existence of PBHs.

Single and coupled cavity mode sensing schemes using a diagnostic field.

Precise optical mode matching is of critical importance in experiments using squeezed-vacuum states. Automatic spatial-mode matching schemes have the potential to reduce losses and improve loss stability. However, in quantum-enhanced coupled-cavity experiments, such as gravitational-wave detectors, one must also ensure that the sub-cavities are also mode matched. We propose what we believe to be a new mode sensing scheme, which works for simple and coupled cavities. The scheme requires no moving parts, nor tuning of Gouy phases. Instead a diagnostic field tuned to the HG20/LG10 mode frequency is used. The error signals are derived to be proportional to the difference in waist position, and difference in Rayleigh ranges, between the sub-cavity eigenmodes. The two error signals are separable by 90 degrees of demodulation phase. We demonstrate reasonable error signals for a simplified Einstein Telescope optical design. This work will facilitate routine use of extremely high levels of squeezing in current and future gravitational-wave detectors.

Scalar-induced gravitational wave interpretation of PTA data: the role of scalar fluctuation propagation speed

Pulsar timing arrays gathered evidence of the presence of a gravitational wave background around nHz frequencies. If the gravitational wave background was induced by large and Gaussian primordial fluctuations, they would then produce too many sub-solar mass primordial black holes. We show that if at the time of gravitational wave generation the universe was dominated by a canonical scalar field, with the same equation of state as standard radiation but a higher propagation speed of fluctuations, one can explain the gravitational wave background with a primordial black hole counterpart consistent with observations. Lastly, we discuss possible ways to test this model with future gravitational wave detectors.

Unraveling the CMB lack-of-correlation anomaly with the cosmological gravitational wave background

Since the very first observations, the Cosmic Microwave Background (CMB) has revealed on large-scales unexpected features known as anomalies, which challenge the standard Λ cold dark matter (ΛCDM) cosmological model. One such anomaly is the “lack-of-correlation”, where the measured two-point angular correlation function of CMB temperature anisotropies is compatible with zero, differently from the predictions of the standard model. This anomaly could indicate a deviation from the standard model, unknown systematics, or simply a rare realization of the model itself. In this study, we explore the possibility that the lack-of-correlation anomaly is a consequence of living in a rare realization of the standard model, by leveraging the potential information provided by the cosmological gravitational wave background (CGWB) detectable by future gravitational wave (GW) interferometers. We analyze both constrained and unconstrained realizations of the CGWB to investigate the extent of information that GWs can offer. To quantify the impact of the CGWB on the lack-of-correlation anomaly, we employ established estimators and introduce a new estimator that addresses the “look-elsewhere” effect. Additionally, we consider three different maximum multipoles, denoted as ℓ max, to account for the anticipated capabilities of future GW detectors (ℓ max = 4, 6, 10). Summarizing our findings for the case of ℓ max = 4, we identify the angular range [63∘ - 180∘] as the region where future observations of the CGWB maximize the probability of rejecting the standard model. Furthermore, we calculate the expected significance of this observation, demonstrating that 98.81% (81.67%) of the constrained GW realizations enhance the current significance of the anomaly when considering the full-sky (masked) Planck SMICA map as our CMB sky.

Measuring the Hubble Constant with Dark Neutron Star–Black Hole Mergers

Detection of gravitational waves (GWs) from neutron star-black hole (NSBH) standard sirens provides local measurements of the Hubble constant (H 0), regardless of the detection of an electromagnetic (EM) counterpart, given that matter effects can be exploited to break the redshift degeneracy of the GW waveforms. The distinctive merger morphology and the high-redshift detectability of tidally disrupted NSBH make them promising candidates for this method. Also, the detection prospects of an EM counterpart for these systems will be limited to z < 0.8 in the optical, in the era of future GW detectors. Using recent constraints on the equation of state of NSs from multi-messenger observations of NICER and LIGO/Virgo/KAGRA, we show the prospects of measuring H 0 solely from GW observation of NSBH systems, achievable by the Einstein telescope (ET) and Cosmic Explorer (CE) detectors. We first analyze individual events to quantify the effect of high-frequency (≥500 Hz) tidal distortions on the inference of NS tidal deformability parameter (Λ) and hence on H 0. We find that disruptive mergers can constrain Λ up to more precisely than nondisruptive ones. However, this precision is not sufficient to place stringent constraints on the H 0 from individual events. By performing Bayesian analysis on simulated NSBH data (up to N = 100 events, corresponding to a day of observation) in the ET+CE detectors, we find that NSBH systems enable unbiased 4%–13% precision on the estimate of H 0 (68% credible interval). This is a similar measurement precision found in studies analyzing NSBH mergers with EM counterparts in the LVKC O5 era.

Gravitational-Wave Phasing of Quasicircular Compact Binary Systems to the Fourth-and-a-Half Post-Newtonian Order.

The inspiral phase of gravitational waves emitted by spinless compact binary systems is derived through the fourth-and-a-half post-Newtonian (4.5PN) order beyond quadrupole radiation, and the leading amplitude mode (ℓ,m)=(2,2) is obtained at 4PN order. We also provide the radiated flux, as well as the phase in the stationary phase approximation. Rough numerical estimates for the contribution of each PN order are provided for typical systems observed by current and future gravitational wave detectors.

UV Signatures of Magnetar Formation and Their Crucial Role for GW Detection

The emission from shock breakouts (SBOs) represents the earliest electromagnetic (EM) signal emitted by cataclysmic events involving the formation or the merger of neutron stars (NSs). As such, SBOs carry unique information on the structure of their progenitors and on the explosion energy. The characteristic SBO emission is expected in the UV range, and its detection is one of the key targets of the ULTRASAT satellite. Among SBO sources, we focus on a specific class involving the formation of fast-spinning magnetars in the core-collapse of massive stars. Fast-spinning magnetars are expected to produce a specific signature in the early UV supernova light curve, powered by the extra spin energy quickly released by the NS. Moreover, they are considered as optimal candidates for the emission of long-transient gravitational wave (GW) signals, the detection of which requires early EM triggers to boost the sensitivity of dedicated GW search pipelines. We calculate early supernova UV light curves in the presence of a magnetar central engine, as a function of the explosion energy, ejecta mass, and magnetar parameters. We then estimate the ULTRASAT detection horizon (z < 0.15) as a function of the same physical parameters, and the overall expected detection rate, finding that magnetar-powered SBOs may represent up to 1/5 of the total events detected by ULTRASAT. Moreover, at the expected sensitivity of the LIGO/Virgo/Kagra O5 science run, one such event occurring within 5 Mpc will provide an ideal trigger for a GW long-transient search. Future GW detectors like the Einstein Telescope will push the horizon for joint EM-GW detections to 35–40 Mpc.

Multiple beam coherent combination via an optical ring resonator.

Future gravitational wave detectors (GWDs) require low noise, single frequency, continuous wave lasers with excellent beam quality and powers in excess of 500 W. Low noise laser amplifiers with high spatial purity have been demonstrated up to 300 W. For higher powers, coherent beam combination can overcome scaling limitations. In this Letter we introduce a new, to the best of our knowledge, combination scheme that uses a bow-tie resonator to combine three laser beams with simultaneous spatial filtering performance.

New dynamical tide constraints from current and future gravitational wave detections of inspiralling neutron stars

New dynamical tide constraints from current and future gravitational wave detections of inspiralling neutron stars

Conceptual design of a sorption-based cryochain for the ETpathfinder

Next-generation gravitational wave detectors, including the Einstein Telescope [1][2], aim to achieve amplitude-spectral-density strain sensitivities on the order 10−24m/Hz[3]. In the low-frequency band such sensitivities can only be obtained when thermal noise, mainly stemming from the mirror coating, is reduced by employing cryogenic cooling techniques for the mirrors. The optical surface of the mirror should not vibrate with strain noise amplitude spectral densities above 10−20m/Hz for the cryogenic mirrors in the Einstein Telescope [3]. The ETpathfinder research facility [4][5], aims to facilitate the development and testing of critical new technologies required for the design and operation of future gravitational wave detectors. A key enabling technology for the design and operation of such advanced interferometers is the cryogenic system that cools the main optics to a temperature of approximately 10 K. Given the stringent requirements on vibrational noise for these optics, the cryogenic cooling under continuous operation should be essentially vibration free. Joule-Thomson cryocoolers using sorption compressors are known to generate an absolute minimum of vibrational noise during operation. We propose a modular cryochain design comprised of a system of sorption compressors and Joule-Thomson cold stages fitting the ETpathfinder project requirements. In this paper, we present the conceptual design of the cooler chain that is based on a parallel cascade arrangement of a 40 K neon stage, a 15 K hydrogen stage and a 8 K helium stage. The operating parameters of the sorption-based cooler chain are selected via a hybrid modeling workflow, aiming to optimize performance and other design considerations within an envelope of acceptable design parameters.

Prospects for future binary black hole gravitational wave studies in light of PTA measurements

NANOGrav and other Pulsar Timing Arrays (PTAs) have discovered a common-spectrum process in the nHz range that may be due to gravitational waves (GWs): if so, they are likely to have been generated by black hole (BH) binaries with total masses &gt; 109 M⊙. Using the Extended Press-Schechter formalism to model the galactic halo mass function and a simple relation between the halo and BH masses suggests that these binaries have redshifts z = 𝒪(1) and mass ratios ≳10, and that the GW signal at frequencies above 𝒪(10) nHz may be dominated by relatively few binaries that could be distinguished experimentally and would yield observable circular polarization. Extrapolating the model to higher frequencies indicates that future GW detectors such as LISA and AEDGE could extend the PTA observations to lower BH masses ≳103 M⊙.

Detection Prospects of Fast-merging Gravitational Wave Sources in M31

It is widely accepted that quite a number of double compact objects (DCOs) in the Milky Way can be identified by future space-based gravitational wave (GW) detectors, while systematic investigations on the detection of the GW sources in nearby galaxies are still lacking. In this paper, we present calculations of potential populations of GW sources for all types of DCOs in the Local Group galaxy M31. For M31, we use an age-dependent model for the evolution of the metallicity and the star formation rate. By varying assumptions of common-envelope ejection efficiencies and supernova-explosion mechanisms during binary evolution, we make predictions on the properties of DCOs that can be detected by the Laser Interferometer Space Antenna (LISA). Our calculations indicate that a few (a dozen) DCOs are likely to be observed by LISA during its 4 (10) yr mission. We expect that the sources with black hole components are more likely to be first identified during a 4 yr mission since these binaries have relatively large chirp masses, while the systems with white-dwarf components dominate the overall population of detectable GW sources during a 10 yr mission. LISA can only detect very tight fast-merging systems in M31, corresponding to the peak of orbital period distribution from ∼2 minutes for double white dwarfs to ∼20 minutes for double black holes.

Measuring inflaton couplings via primordial gravitational waves

We investigate the reach of future gravitational wave (GW) detectors in probing inflaton couplings with visible sector particles that can either be bosonic or fermionic in nature. Assuming reheating takes place through perturbative quantum production from vacuum in presence of classical inflaton background field, we find that the spectral energy density of the primordial GW generated during inflation becomes sensitive to inflaton-matter coupling. We conclude, obeying bounds from Big Bang Nucleosysthesis and Cosmic Microwave Background, that, e.g., inflaton-scalar couplings of the order of ~ \U0001d4aa(10−20) GeV fall within the sensitivity range of several proposed GW detector facilities. However, this prediction is sensitive to the size of the inflationary scale, nature of the inflaton-matter interaction and shape of the potential during reheating. Having found the time-dependent effective inflaton decay width, we also discuss its implications for dark matter (DM) production from the thermal plasma via UV freeze-in during reheating. It is shown, that one can reproduce the observed DM abundance for its mass up to several PeVs, depending on the dimension of the operator connecting DM with the thermal bath and the associated scale of the UV physics. Thus we promote primordial GW to observables sensitive to feebly coupled inflaton, which is very challenging if not impossible to test in conventional particle physics laboratories or astrophysical measurements.

A Novel Closed-Loop Structure for Drag-Free Control Systems with ESKF and LQR.

Space-borne gravitational wave detection satellite confronts many uncertain perturbations, such as solar pressure, dilute atmospheric drag, etc. To realize an ultra-static and ultra-stable inertial benchmark achieved by a test-mass (TM) being free to move inside a spacecraft (S/C), the drag-free control system of S/C requires super high steady-state accuracies and dynamic performances. The Active Disturbance Rejection Control (ADRC) technique has a certain capability in solving problems with common perturbations, while there is still room for optimization in dealing with the complicated drag-free control problem. When faced with complex noises, the steady-state accuracy of the traditional control method is not good enough and the convergence speed of regulating process is not fast enough. In this paper, the optimized Active Disturbance Rejection Control technique is applied. With the extended state Kalman filter (ESKF) estimating the states and disturbances in real time, a novel closed-loop control structure is designed by combining the linear quadratic regulator (LQR) and ESKF, which can satisfy the design targets competently. The comparative analysis and simulation results show that the LQR controller designed in this paper has a faster response and a higher accuracy compared with the traditional nonlinear state error feedback (NSEF), which uses a deformation of weighting components of classical PID. The new drag-free control structure proposed in the paper can be used in future gravitational wave detection satellites.

Erratum: Outlook for detecting the gravitational-wave displacement and spin memory effects with current and future gravitational-wave detectors [Phys. Rev. D 107 , 064056 (2023)

Erratum: Outlook for detecting the gravitational-wave displacement and spin memory effects with current and future gravitational-wave detectors [Phys. Rev. D <b>107</b> , 064056 (2023)

Parameter estimation for Einstein-dilaton-Gauss-Bonnet gravity with ringdown signals* *Supported by the National Key R & D Program of China (2022YFC2204602), and the Natural Science Foundation of China (11925503)

Future space-based gravitational-wave detectors will detect gravitational waves with high sensitivity in the millihertz frequency band, providing more opportunities to test theories of gravity than ground-based detectors. The study of quasinormal modes (QNMs) and their application in gravity theory testing have been an important aspect in the field of gravitational physics. In this study, we investigate the capability of future space-based gravitational wave detectors, such as LISA, TaiJi, and TianQin, to constrain the dimensionless deviating parameter for Einstein-dilaton-Gauss-Bonnet (EdGB) gravity with ringdown signals from the merger of binary black holes. The ringdown signal is modeled by the two strongest QNMs in EdGB gravity. Considering time-delay interferometry, we calculate the signal-to-noise ratio of different space-based detectors for ringdown signals to analyze their capabilities. The Fisher information matrix is employed to analyze the accuracy of parameter estimation, with particular focus on the dimensionless deviating parameter for EdGB gravity. The impact of the parameters of gravitational wave sources on the estimation accuracy of the dimensionless deviating parameter is also studied. We find that the constraint ability of EdGB gravity is limited because the uncertainty of the dimensionless deviating parameter increases with a decrease in the dimensionless deviating parameter. LISA and TaiJi offer more advantages in constraining the dimensionless deviating parameter to a more accurate level for massive black holes, whereas TianQin is more suited to less massive black holes. The Bayesian inference method is used to perform parameter estimation on simulated data, which verifies the reliability of the conclusion.

Dynamical friction in gravitational atoms

Due to superradiant instabilities, clouds of ultralight bosons can spontaneously grow around rotating black holes, creating so-called “gravitational atoms”. In this work, we study their dynamical effects on binary systems. We first focus on open orbits, showing that the presence of a cloud can increase the cross section for the dynamical capture of a compact object by more than an order of magnitude. We then consider closed orbits and demonstrate that the backreaction of the cloud's ionization on the orbital motion should be identified as dynamical friction. Finally, we study for the first time eccentric and inclined orbits. We find that, while ionization quickly circularizes the binary, it barely affects the inclination angle. These results enable a more realistic description of the dynamics of gravitational atoms in binaries and pave the way for dedicated searches with future gravitational wave detectors.

Dynamical Love numbers for area quantized black holes

We study the tidal deformability of horizonless exotic compact objects, with implications for area quantized black holes. Since, any such horizonless compact object, including an area quantized black hole, possesses a nonzero reflectivity, it follows that they inherit a nonzero tidal Love number which varies as a function of the perturbing frequency. The reflectivity of the horizon for an area quantized black hole has a distinct shape and unmistakable features, which are also present in the frequency-dependent tidal Love numbers, and therefore is a smoking gun test for such quantum black holes. The existence of these features also promotes the dynamical Love number to be a crucial observational tool to not only distinguish area quantized black holes from other models of horizonless compact objects, but also to differentiate between black holes with distinct schemes of area quantization. We further discuss implications of the same for the present and the future gravitational wave detectors.

Effect of solar proton events on test mass for gravitational wave detection in the 24th solar cycle

Free-falling cubic Test Masses (TMs) are a key component of the interferometer used for low-frequency gravitational wave (GW) detection in space. However, exposure to energetic particles in the environment can lead to electrostatic charging of the TM, resulting in additional electrostatic and Lorentz forces that can impact GW detection sensitivity. To evaluate this effect, the high-energy proton data set of the Geostationary Operational Environmental Satellite (GOES) program was used to analyze TM charging due to Solar Proton Events (SPEs) in the 24th solar cycle. Using the Geant4 Monte Carlo toolkit, the TM charging process is simulated in a space environment for SPEs falling into three ranges of proton flux: (1) greater than 10 pfu and less than 100 pfu, (2) greater than 100 pfu and less than 1000 pfu, and (3) greater than 1000 pfu. It is found that SPEs charging can reach the threshold within 535 s to 18.6 h, considering a reasonable discharge threshold of LISA and Taiji. We demonstrate that while there is a somewhat linear correlation between the net charging rate of the TM and the integrated flux of ge 10 MeV SPEs, there are many cases in which the integrated flux is significantly different from the charging rate. Therefore, we investigate the difference between the integral flux and the charging rate of SPEs using the charging efficiency assessment method. Our results indicate that the energy spectrum structure of SPEs is the most important factor influencing the charging rate. Lastly, we evaluate the charging probability of SPEs in the 24th solar cycle and find that the frequency and charging risk of SPEs are highest in the 3rd, 4th, 5th, 6th, and 7th years, which can serve as a reference for future GW detection spacecraft.

Primordial black holes generated by the non-minimal spectator field

We improve and generalize the non-minimal curvaton model originally proposed in arXiv: 2112.12680 to a model in which a spectator field non-minimally couples to an inflaton field and the power spectrum of the perturbation of spectator field at small scales is dramatically enhanced by the sharp feature in the form of non-minimal coupling. At or after the end of inflation, the perturbation of the spectator field is converted into curvature perturbation and leads to the formation of primordial black holes (PBHs). Furthermore, for example, we consider three phenomenological models for generating PBHs with mass function peaked at ~ 10−12Mʘ and representing all the cold dark matter in our universe and find that the scalar induced gravitational waves generated by the curvature perturbation can be detected by the future space-borne gravitational-wave detectors such as Taiji, TianQin, and LISA.