ABSTRACT
One of the crucial windows for distinguishing astrophysical black holes from primordial black holes is through the redshift evolution of their respective merger rates. The low redshift ...population of black holes of astrophysical origin is expected to follow the star formation rate. The corresponding peak in their merger rate peaks at a redshift smaller than that of the star formation rate peak (zp ≈ 2), depending on the time delay between the formation and mergers of black holes. Black holes of primordial origin are going to be present before the formation of the stars, and the merger rate of these sources at high redshift is going to be large. We propose a joint estimation of a hybrid merger rate from the stochastic gravitational wave background, which can use the cosmic history of merger rates to distinguish between the two populations of black holes. Using the latest bounds on the amplitude of the stochastic gravitational wave background amplitude from the third observation run of LIGO/Virgo, we obtain weak constraints at $68{{\ \rm per\ cent}}$ C.L. on the primordial black hole merger rate index $2.56_{-1.76}^{+1.64}$ and astrophysical black hole time delay $6.7_{-4.74}^{+4.22}$ Gyr. We should be able to distinguish between the different populations of black holes with the forthcoming O5 and A+ detector sensitivities.
Abstract
The astrophysical stochastic gravitational wave background (SGWB) is mostly produced from unresolved stellar binary mergers, and the number of events at any moment of time is expected to be ...Poisson-distributed. The event rate is governed by several astrophysical processes. The Poisson nature leads to variation in the number of sources and this causes temporal variations in the SGWB. The intrinsic temporal fluctuations of the SGWB are a rich source of astrophysical information that can be explored via ongoing and future gravitational wave experiments to classify the sources of the SGWB signal. Along with several other methods to estimate the GW event rates from individual sources, the study of the temporal variations of the SGWB signal provides an independent method for estimating the event rates of the GW sources that contribute to the SGWB. Along with direct estimates of event rates, this approach can also distinguish between different sources contributing to the SGWB signal and will be a useful probe of its evolution over a vast cosmic volume. On averaging over observation times, the SGWB will be statistically invariant under time translation. Statistical time translation symmetry of the SGWB is expected due to the negligible evolution of the relevant cosmological and astrophysical phenomena over the observation time-scales over which the data is collected.
ABSTRACT
Alternative theories of gravity predict modifications in the propagation of gravitational waves (GW) through space–time. One of the smoking-gun predictions of such theories is the change in ...the GW luminosity distance to GW sources as a function of redshift relative to the electromagnetic (EM) luminosity distance expected from EM probes. We propose a multimessenger test of the theory of general relativity from the propagation of GWs by combining EM and GW observations to resolve these issues from GW sources without EM counterparts (which are also referred to as dark standard sirens). By using the relation between the geometric distances accessible from baryon acoustic oscillation measurements, and luminosity distance measurements from the GW sources, we can measure any deviation from the general theory of relativity via the GW sources of unknown redshift that will be detectable by networks of GW detectors such as LIGO, Virgo, and KAGRA. Using this technique, the fiducial value of the frictional term can be measured to a precision $\Xi _0=0.98^{+0.04}_{-0.23}$ after marginalizing over redshift dependence, cosmological parameters, and GW bias parameters with ∼3500 dark standard sirens of masses $30\, \rm M_\odot$ each distributed up to redshift z = 0.5. For a fixed redshift dependence, a value of $\Xi _0=0.99^{+0.02}_{-0.02}$ can be measured with a similar number of dark sirens. Application of our methodology to the far more numerous dark standard sirens detectable with next-generation GW detectors, such as LISA, Einstein Telescope and Cosmic Explorer, will allow achievement of higher accuracy than possible from use of bright standard sirens.
Abstract
Using the novel semi-numerical code for reionization AMBER, we model the patchy kinetic Sunyaev–Zel’dovich (kSZ) effect by directly specifying the reionization history with the redshift ...midpoint
z
mid
, duration Δ
z
, and asymmetry
A
z
. We further control the ionizing sources and radiation through the minimum halo mass
M
h
and the radiation mean free path
λ
mfp
. AMBER reproduces the free-electron number density and the patchy kSZ power spectrum of radiation–hydrodynamic simulations at the target resolution (1 Mpc
h
−1
) with matched reionization parameters. With a suite of (2 Gpc/
h
)
3
simulations using AMBER, we first constrain the redshift midpoint 6.0 <
z
mid
< 8.9 using the Planck 2018 Thomson optical depth result (95% CL). Then, assuming
z
mid
= 8, we find that the amplitude of
D
ℓ
=
3000
pkSZ
scales linearly with the duration of reionization Δ
z
and is consistent with the 1
σ
upper limit from South Pole Telescope (SPT) results up to Δ
z
< 5.1 (Δ
z
encloses 5%–95% ionization). Moreover, a shorter
λ
mfp
can lead to a ∼10% lower
D
ℓ
=
3000
pkSZ
and a flatter slope in the
D
ℓ
=
3000
pkSZ
−
Δ
z
scaling relation, thereby affecting the constraints on Δ
z
at
ℓ
= 3000. Allowing
z
mid
and
λ
mfp
to vary simultaneously, we get spectra consistent with the SPT result (95% CL) up to Δ
z
= 12.8 (but
A
z
> 8 is needed to ensure the end of reionization before
z
= 5.5). We show that constraints on the asymmetry require ∼0.1
μ
k
2
measurement accuracy at multipoles other than
ℓ
= 3000. Finally, we find that the amplitude and shape of the kSZ spectrum are only weakly sensitive to
M
h
under a fixed reionization history and radiation mean free path.
ABSTRACT
Primordial black holes (PBHs) are dark matter candidates that span broad mass ranges from 10−17 M⊙ to ∼100 M⊙. We show that the stochastic gravitational wave background can be a powerful ...window for the detection of subsolar 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 subsolar mass PBHs ≤1 M⊙ in the form of dark matter $f_\mathrm{PBH}\le 1{{\ \rm per\ cent}}$ at $68{{\ \rm per\ cent}}$ C.L. even for a pessimistic value of a binary suppression factor. In the absence of any suppression of the merger rate, constraints on fPBH will be less than $0.001{{\ \rm per\ cent}}$. Furthermore, we will be able to measure the redshift evolution of the PBH merger rate with about $1{{\ \rm per\ cent}}$ accuracy, making it possible to uniquely distinguish between the Poisson and clustered PBH scenarios.
Gravitational wave (GW) sources are an excellent probe of the luminosity distance and offer a novel measure of the Hubble constant,
H
0
. This estimation of
H
0
from standard sirens requires an ...accurate estimation of the cosmological redshift of the host galaxy of the GW source after correcting for its peculiar velocity. The absence of an accurate peculiar velocity correction affects both the precision and accuracy of the measurement of
H
0
, particularly for nearby sources. Here, we propose a framework to incorporate such a peculiar velocity correction for GW sources. A first implementation of our method to the event GW170817, combined with observations taken with Very Large Baseline Interferometry (VLBI), leads to a revised value of
H
0
= 68.3
−4.5
+4.6
km s
−1
Mpc
−1
. While this revision is minor, it demonstrates that our method makes it possible to obtain unbiased and accurate measurements of
H
0
at the precision required for the standard siren cosmology.
ABSTRACT
Strong lensing of gravitational waves (GWs) is more likely for distant sources but predicted event rates are highly uncertain with many astrophysical origins proposed. Here, we open a new ...avenue to estimate the event rate of strongly lensed systems by exploring the amplitude of the stochastic gravitational wave background (SGWB). This method can provide a direct upper bound on the high-redshift binary coalescing rates, which can be translated into an upper bound on the expected rate of strongly lensed systems. We show that from the ongoing analysis of the Laser Interferometer Gravitational-wave Observatory (LIGO)-Virgo and in the future from the LIGO–Virgo design sensitivity stringent bounds on the lensing event rate can be imposed using the SGWB signal. Combining measurements of loud GW events with an unresolved stochastic background detection will improve estimates of the numbers of lensed events at high redshift. The proposed method is going to play a crucial in understanding the population of lensed and unlensed systems from GW observations.
The large-scale cosmic microwave background (CMB) B-mode polarization is the direct probe to the low-frequency primordial gravitational wave signal. However, unambiguous measurement of this signal ...requires a precise understanding of the possible contamination. One such potential contamination arises from the patchiness in the spatial distribution of free electrons during the epoch of reionization. We estimate the B-mode power spectrum due to patchy reionization using a combination of photon-conserving seminumerical simulation and analytical calculation, and compare its amplitude with the primordial B-mode signal. For a reionization history which is in agreement with several latest observations, we find that a stronger secondary B-mode polarization signal is produced when the reionization is driven by the sources in massive haloes and its amplitude can be comparable to the recombination bump for tensor to scalar ratio (r) ≲ 5 × 10^−4. If contamination from patchy reionization is neglected in the analysis of B-mode polarization data, then for the models of reionization considered in this analysis, we find a maximum bias of about |$30{{\ \rm per\ cent}}$| in the value of |$r=\, 10^{-3}$| when spatial modes between ℓ ∈ 50, 200 are used with a delensing efficiency of |$50{{\ \rm per\ cent}}$|. The inferred bias from patchy reionization is not a severe issue for the upcoming ground-based CMB experiment Simons Observatory, but can be a potential source of confusion for proposed CMB experiments which target to detect the value of r < 10^−3. However, this obstacle can be removed by utilizing the difference in the shape of the power spectrum from the primordial signal.
ABSTRACT
The expected event rate of lensed gravitational wave sources scales with the merger rate at redshift z ≥ 1, where the optical depth for lensing is high. It is commonly assumed that the ...merger rate of the astrophysical compact objects is closely connected with the star formation rate, which peaks around redshift z ∼ 2. However, a major source of uncertainty is the delay time between the formation and merger of compact objects. We explore the impact of delay time on the lensing event rate. We show that as the delay time increases, the peak of the merger rate of gravitational wave sources gets deferred to a lower redshift. This leads to a reduction in the event rate of the lensed events which are detectable by the gravitational wave detectors. We show that for a delay time of around 10 Gyr or larger, the lensed event rate can be less than one per year for the design sensitivity of LIGO/Virgo. We also estimate the merger rate for lensed sub-threshold for different delay time scenarios, finding that for larger delay times the number of lensed sub-threshold events is reduced, whereas for small-delay time models they are significantly more frequent. This analysis shows for the first time that lensing is a complementary probe to explore different formation channels of binary systems by exploiting the lensing event rate from the well-detected events and sub-threshold events which are measurable using the network of gravitational wave detectors.
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