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Register a new userProspects for probing gravitational waves from primordial black hole binaries
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We study the prospects of future gravitational wave (GW) detectors in probing primordial black hole (PBH) binaries. We show that across a broad mass range from $10^{-5}M_odot$ to $10^7M_odot$, future GW interferometers provide a potential probe of the PBH abundance that is more sensitive than any currently existing experiment. In particular, we find that galactic PBH binaries with masses as low as $10^{-5}M_odot$ may be probed with ET, AEDGE and LISA by searching for nearly monochromatic continuous GW signals. Such searches could independently test the PBH interpretation of the ultrashort microlensing events observed by OGLE. We also consider the possibility of observing GWs from asteroid mass PBH binaries through graviton-photon conversion.
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Primordial black holes (PBHs) have long been suggested as a candidate for making up some or all of the dark matter in the Universe. Most of the theoretically possible mass range for PBH dark matter has been ruled out with various null observations of expected signatures of their interaction with standard astrophysical objects. However, current constraints are significantly less robust in the 20 M_sun < M_PBH < 100 M_sun mass window, which has received much attention recently, following the detection of merging black holes with estimated masses of ~30 M_sun by LIGO and the suggestion that these could be black holes formed in the early Universe. We consider the potential of advanced LIGO (aLIGO) operating at design sensitivity to probe this mass range by looking for peaks in the mass spectrum of detected events. To quantify the background, which is due to black holes that are formed from dying stars, we model the shape of the stellar-black-hole mass function and calibrate its amplitude to match the O1 results. Adopting very conservative assumptions about the PBH and stellar-black-hole merger rates, we show that ~5 years of aLIGO data can be used to detect a contribution of >20 M_sun PBHs to dark matter down to f_PBH<0.5 at >99.9% confidence level. Combined with other probes that already suggest tension with f_PBH=1, the obtainable independent limits from aLIGO will thus enable a firm test of the scenario that PBHs make up all of dark matter.
In this paper, we will give a general introduction to the project of Ali CMB Polarization Telescope (AliCPT), which is a Sino-US joint project led by the Institute of High Energy Physics (IHEP) and has involved many different institutes in China. It is the first ground-based Cosmic Microwave Background (CMB) polarization experiment in China and an integral part of Chinas Gravitational Waves Program. The main scientific goal of AliCPT project is to probe the primordial gravitational waves (PGWs) originated from the very early Universe. The AliCPT project includes two stages. The first stage referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet with an altitude of 5,250 meters. Once completed, it will be the worldwide highest ground-based CMB observatory and open a new window for probing PGWs in northern hemisphere. AliCPT-1 telescope is designed to have about 7,000 TES detectors at 90GHz and 150GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with the number of detectors more than 20,000. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio $r$ by one order of magnitude with 3 years observation. Besides the PGWs, the AliCPT will also enable a precise measurement on the CMB rotation angle and provide a precise test on the CPT symmetry. We show 3 years observation will improve the current limit by two order of magnitude.
Primordial black holes (PBHs) are dark matter candidates that span broad mass ranges from $10^{-17}$ $M_odot$ to $sim 100$ $M_odot$. We show that the stochastic gravitational wave background can be a powerful window for the detection of sub-solar mass PBHs and shed light on their formation channel via third-generation gravitational wave detectors such as Cosmic Explorer and the Einstein Telescope. By using the mass distribution of the compact objects and the redshift evolution of the merger rates, we can distinguish astrophysical sources from PBHs and will be able to constrain the fraction of sub-solar mass PBHs $leq 1$ $M_odot$ in the form of dark matter $f_{PBH}leq 1%$ at $68%$ C.L. even for a pessimistic value of the suppression factor ($f_{sup} sim 10^{-3}$). For $f_{sup} sim 1$, the constraints on $f_{PBH}$ will be less than $0.001%$. Furthermore, we will be able to measure the redshift evolution of the PBH merger rate with about $1%$ accuracy, making it possible to uniquely distinguish between the Poisson and clustered PBH scenarios.
The black hole merging rates inferred after the gravitational-wave detection by Advanced LIGO/VIRGO and the relatively high mass of the progenitors are consistent with models of dark matter made of massive primordial black holes (PBH). PBH binaries emit gravitational waves in a broad range of frequencies that will be probed by future space interferometers (LISA) and pulsar timing arrays (PTA). The amplitude of the stochastic gravitational-wave background expected for PBH dark matter is calculated taking into account various effects such as initial eccentricity of binaries, PBH velocities, mass distribution and clustering. It allows a detection by the LISA space interferometer, and possibly by the PTA of the SKA radio-telescope. Interestingly, one can distinguish this background from the one of non-primordial massive binaries through a specific frequency dependence, resulting from the maximal impact parameter of binaries formed by PBH capture, depending on the PBH velocity distribution and their clustering properties. Moreover, we find that the gravitational wave spectrum is boosted by the width of PBH mass distribution, compared with that of the monochromatic spectrum. The current PTA constraints already rule out broad-mass PBH models covering more than three decades of masses, but evading the microlensing and CMB constraints due to clustering.
Primordial black holes (PBHs) have been proposed to explain at least a portion of dark matter. Observations have put strong constraints on PBHs in terms of the fraction of dark matter which they can represent, $f_{rm PBH}$, across a wide mass range -- apart from the stellar-mass range of $20M_odotlesssim M_{rm PBH}lesssim 100M_odot$. In this paper, we explore the possibility that such PBHs could serve as point-mass lenses capable of altering the gravitational-wave (GW) signals observed from binary black hole (BBH) mergers along their line-of-sight. We find that careful GW data analysis could verify the existence of such PBHs based on the $fitting~factor$ and odds ratio analyses. When such a lensed GW signal is detected, we expect to be able to measure the redshifted mass of the lens with a relative error $Delta M_{rm PBH}/M_{rm PBH}lesssim0.3$. If no such lensed GW events were detected despite the operation of sensitive GW detectors accumulating large numbers of BBH mergers, it would translate into a stringent constraint of $f_{rm PBH}lesssim 10^{-2}-10^{-5}$ for PBHs with a mass larger than $sim10M_odot$ by the Einstein Telescope after one year of running, and $f_{rm PBH}lesssim 0.2$ for PBHs with mass greater than $sim 50M_odot$ for advanced LIGO after ten years of running.
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