arXiv subjects

Qing-Guo Huang

Publications and source records attributed to Qing-Guo Huang.

At least 91 records · Page 5Linked to original sources

arXiv2020

Searching for primordial black holes with stochastic gravitational-wave background in the space-based detector frequency band

Assuming that primordial black holes compose a fraction of dark matter, some of them may accumulate at the center of galaxy and perform a prograde or retrograde orbit against the gravity pointing towards the center exerted by the central massive black hole. If the mass of primordial black holes is of the order of stellar mass or smaller, such extreme mass ratio inspirals can emit gravitational waves and form a background due to incoherent superposition of all the contributions of the Universe. We investigate the stochastic gravitational-wave background energy density spectra from the directional source, the primordial black holes surrounding Sagittarius A$^\ast$ of the Milky Way, and the isotropic extragalactic total contribution, respectively. As will be shown, the resultant stochastic gravitational-wave background energy density shows different spectrum features such as the peak positions in the frequency domain for the above two kinds of sources. Detection of stochastic gravitational-wave background with such a feature may provide evidence for the existence of primordial black holes. Conversely, a null searching result can put constraints on the abundance of primordial black holes in dark matter.

astro-ph.CO↗

arXiv2020

Log-dependent slope of scalar induced gravitational waves in the infrared regions

We analytically calculate the scalar induced gravitational waves (SIGWs) and find a log-dependent slope of SIGW in the infrared regions $(f<f_c)$, namely $n_{\mathrm{GW}}(f)=3-2/\ln(f_c/f)$, and $n_{\mathrm{GW}}(f)=2-2/\ln(f_c/f)$ near the peak if the power spectrum of scalar curvature perturbation is quite narrow, where $f_c$ is roughly the frequency at the peak of SIGW. Such a log-dependent slope can be taken as a new template for distinguishing SIGW from other sources.

astro-ph.CO↗

arXiv2020

Scalar Induced Gravitational Waves in Different Gauges

In this letter we calculate the scalar induced gravitational waves (SIGWs) accompanying the formation of primordial black hole during the radiation dominated era in three different gauges, i.e. synchronous gauge, Newton gauge and uniform curvature gauge, and we find that the energy density spectra of SIGWs, $\ogw(k)$, are identical in these three different gauges.

astro-ph.CO↗

arXiv2019

Measuring $H_0$ from low-$z$ datasets

Adopting the low-redshift observational datasets, including the Pantheon sample of Type Ia supernovae, baryon acoustic oscillation measurements, and the tomographic Alcock-Paczynski method, we determine the Hubble constant to be $67.95^{+0.78}_{-1.03}$ , $69.81^{+2.22}_{-2.70}$ and $66.75^{+3.42}_{-4.23}$ km s$^{-1}$ Mpc$^{-1}$ at 68\% confidence level in the $Λ$CDM, $w$CDM and $w_0w_a$CDM models, respectively. Compared to the Hubble constant given by Riess et al. in 2019, we conclude that the new physics beyond the standard $Λ$CDM model is needed if all of these datasets are reliable.

astro-ph.CO↗

arXiv2019

Stochastic Gravitational-Wave Background from Axion-Monodromy Oscillons in String Theory During Preheating

Axion monodromy is a generic phenomenon in string compactifications. We investigate the production of gravitational-wave background from axion monodromy inflation during preheating. By performing lattice simulations using pseudo-spectral methods, we find that significant single-peak stochastic gravitational-wave backgrounds are generated during preheating for asymptotic linear $|ϕ|$ and $ϕ^{2/3}$ potentials in axion monodromy inflation and cuspy potentials. This may allow us to explore string compactifications through gravitational waves.

astro-ph.CO↗

arXiv2019

Impact of a Spinning Supermassive Black Hole on the Orbit and Gravitational Waves of a Nearby Compact Binary

Recent theoretical studies suggest that stellar-mass binary black holes (BBHs) would merge more efficiently due to the Kozai-Lidov mechanism if these binaries form in the vicinity of supermassive black holes (SMBHs). Since SMBHs are likely rotating rapidly, we continue our earlier study on the generalization of the Kozai-Lidov formalism to include the spin of the SMBH and study the evolution of a nearby BBH. We find that the eccentricity and orbital inclination of the BBH is significantly affected, because the spin (i) forces the orbital plane of the center-of-mass of the BBH around the SMBH to precess (the Lense-Thirring effect) and (ii) imposes an additional gravitomagnetic force on the BBH. As a result, the merger time of the BBH could be significantly different. We calculate the waveform from the BBH in one representative example and study its detectability by a milli-Hertz GW detector, such as the Laser Interferometer Space Antenna (LISA). We find that the signal is distinguishable from that in the case without spin. Our results imply that the BBHs in the LISA band could potentially be used to probe the spin of the SMBHs in galaxy centers.

astro-ph.HE↗

arXiv2019

Measuring the tilt of primordial gravitational-wave power spectrum from observations

Primordial gravitational waves generated during inflation lead to the B-mode polarization in the cosmic microwave background and a stochastic gravitational wave background in the Universe. We will explore the current constraint on the tilt of primordial gravitational-wave spectrum, and forecast how the future observations can improve the current constraint.

astro-ph.CO↗

arXiv2019

Probing Primordial-Black-Hole Dark Matter with Scalar Induced Gravitational Waves

The possibility that primordial black holes (PBHs) represent all of the dark matter (DM) in the Universe and explain the coalescences of binary black holes detected by LIGO/Virgo has attracted a lot of attention. PBHs are generated by the enhancement of scalar perturbations which inevitably produce the induced gravitational waves (GWs). We calculate the induced GWs up to the third-order correction which not only enhances the amplitude of induced GWs, but also extends the cutoff frequency from $2k_*$ to $3k_*$. Such effects of the third-order correction lead to an around $10\%$ increase of the signal-to-noise ratio (SNR) for both LISA and pulsar timing array (PTA) observations, and significantly widen the mass range of PBHs in the stellar mass window accompanying detectable induced GWs for PTA observations including IPTA, FAST and SKA. On the other hand, the null detections of the induced GWs by LISA and PTA experiments will exclude the possibility that all of the DM is comprised of PBHs and the GW events detected by LIGO/Virgo are generated by PBHs.

astro-ph.CO↗

arXiv2019

Inflation model selection revisited

We update the constraints on the power spectra of primordial curvature perturbation and tensor perturbation including Planck data 2015 (P15) and recently released BICEP2/Keck data (BK15), Baryon Acoustic Oscillation data and the Type Ia supernovae data. We find that the upper limits of tensor-to-scalar ratio are $0.061$, $0.064$ and $0.072$ at $95\%$ confidence level (CL) in the $Λ$CDM+$r$, $Λ$CDM+$r$+$α_s$ and $Λ$CDM+$r$+$α_s$+$β_s$ models respectively, where $α_s$ and $β_s$ are the running of scalar spectral index and running of running. The inflation model with a concave potential is favored at more than $95\%$ CL. In addition, parametrizing the slow-roll parameter $ε\sim 1/N^p$, where $N$ is the e-folding number before the end of inflation and taken in the range of $[50,60]$ and $[14,75]$ respectively, we conclude that the inflation model with a monomial potential $V(ϕ)\sim ϕ^n$ is disfavored at more than $95\%$ CL, and both the Starobinsky inflation model and brane inflation model are still consistent with the data.

astro-ph.CO↗

arXiv2019

Stochastic Gravitational-Wave Background from Binary Black Holes and Binary Neutron Stars and Implications for LISA

The advent of gravitational wave (GW) and multi-messenger astronomy has stimulated the research on the formation mechanisms of binary black holes (BBHs) observed by LIGO/Virgo. In literature, the progenitors of these BBHs could be stellar-origin black holes (sBHs) or primordial black holes (PBHs). In this paper we calculate the Stochastic Gravitational-Wave Background (SGWB) from BBHs, covering the astrophysical and primordial scenarios separately, together with the one from binary neutron stars (BNSs). Our results indicate that PBHs contribute a stronger SGWB than that from sBHs, and the total SGWB from both BBHs and BNSs has a high possibility to be detected by the future observing runs of LIGO/Virgo and LISA. On the other hand, the SGWB from BBHs and BNSs also contributes an additional source of confusion noise to LISA's total noise curve, and then weakens LISA's detection abilities. For instance, the detection of massive black hole binary (MBHB) coalescences is one of the key missions of LISA, and the largest detectable redshift of MBHB mergers can be significantly reduced.

gr-qc↗

arXiv2019

The redshift dependence of Alcock-Paczynski effect: cosmological constraints from the current and next generation observations

The tomographic Alcock-Paczynski (AP) test is a robust large-scale structure (LSS) measurement that receives little contamination from the redshift space distortion (RSD). It has placed tight cosmological constraints by using small and intermediate clustering scales of the LSS data. However, previous works have neglected the cross-correlation among different redshift bins, which could cause the statistical uncertainty being underestimated by $\sim$20\%. In this work, we further improve this method by including this multi-redshifts full correlation. We apply it to the SDSS DR12 galaxies sample and find out that, for $Λ$CDM, the combination of AP with the Planck+BAO dataset slightly reduces (within 1-$σ$) $Ω_m$ to $0.304\pm0.007$ (68.3\% CL). This then leads to a larger $H_0$ and also mildly affects $Ω_b h^2$, $n_s$ and the derived parameters $z_*$, $r_*$, $z_{re}$ but not $τ$, $A_s$ and $σ_8$. For the flat $w$CDM model, our measurement gives $Ω_m=0.301\pm 0.010$ and $w=-1.090\pm 0.047$, where the additional AP measurement reduces the error budget by $\sim 25\%$. When including more parameters into the analysis, the AP method also improves the constraints on $Ω_k$, $\sum m_μ$, $N_{\rm eff}$ by $20-30\%$. Early universe parameters such as $dn_s/d{\rm ln}k$ and $r$, however, are unaffected. Assuming the dark energy equation of state $w=w_0+w_a \frac{z}{1+z}$, the Planck+BAO+SNIa+$H_0$+AP datasets prefer a dynamical dark energy at $\approx1.5 σ$ CL. Finally, we forecast the cosmological constraints expected from the DESI galaxy survey and find that combining AP with CMB+BAO method would improve the $w_0$-$w_a$ constraint by a factor of $\sim 10$.

astro-ph.CO↗

arXiv2019

Secular evolution of compact binaries revolving around a spinning massive black hole

The leading order effect of the spin of a distant supermassive black hole (SMBH) on the orbit of compact binary revolving around it appears at the 1.5 post Newtonian (PN) expansion through coupling with the inner and outer orbital angular momenta, and makes an oscillating characteristic contribution to the secular evolution of the compact binary eccentricity over a long time scale compared to the Kozai-Lidov dynamics caused by a non-spinning SMBH.

gr-qc↗

arXiv2018

Constraints on $H_0$ from WMAP and baryon acoustic osillation measurements

We report the constraints of $H_0$ obtained from Wilkinson Microwave Anisotropy Probe (WMAP) combined with the latest baryonic acoustic oscillations (BAO) measurements. We use the BAO measurements from the 6dF Galaxy Survey (6dFGS), the SDSS DR7 main galaxies sample (MGS), the BOSS DR12 galaxies and the eBOSS DR14 quasars. Adding the recent BAO measurements to the cosmic microwave background (CMB) data from WMAP, we constrain cosmological parameters $Ω_m=0.298\pm0.005$, $H_0=68.36^{+0.53}_{-0.52}$ km s$^{-1}$ Mpc$^{-1}$, $σ_8=0.8170^{+0.0159}_{-0.0175}$ in a spatially flat $Λ$ cold dark matter ($Λ$CDM) model, and $Ω_m=0.302\pm0.008$, $H_0=67.63\pm1.30$ km s$^{-1}$ Mpc$^{-1}$, $σ_8=0.7988^{+0.0345}_{-0.0338}$ in a spatially flat $w$CDM model, respectively. The combined constraint on $w$ from CMB and BAO in a spatially flat $w$CDM model is $w=-0.96\pm0.07$. Our measured $H_0$ results prefer a value lower than 70 km s$^{-1}$ Mpc$^{-1}$, consistent with the recent data on CMB constraints from Planck (2018), but in $3.1\sim 3.5σ$ tension with local measurements of Riess et al. (2018) in $Λ$CDM and $w$CDM framework, respectively. Compared with the WMAP alone analysis, the WMPA+BAO analysis reduces the error bar by 75.4% in $Λ$CDM model and 95.3% in $w$CDM model.

astro-ph.CO↗

arXiv2018

Optimistic estimation on probing primordial gravitational waves with CMB B-mode polarization

In the measurements of cosmic microwave background polarizations, three frequency channels are necessary for discriminating the primordial B-modes from the polarized dust and the synchrotron emission. We carry out an optimistic estimate on the sensitivity to the detection of primordial gravitational waves using the cosmic microwave background B-modes only, and explore how to reach the thresholds for the tensor-to-scalar ratio $r$ in the theoretically well-motivated inflation models. For example, Lyth bound implies $r \simeq 2\times10^{-3}$, a corrected Lyth bound shows $r \simeq 7\times10^{-4}$, and some typical inflation models gives $r\simeq4\times10^{-5}$. Taking into account the up-to-date constraints on $r$, i.e. $r_{0.05}<0.07$ at $95\%$ confidence, we find that the consistency relation $n_t=-r/8$ in the canonical single-field slow-roll inflation cannot be distinguished from the scale invariance, due to the cosmic variance in the power spectrum of cosmic microwave background B-modes. The cosmic variance places an inevitable limit on the measurements of the tensor spectral index, i.e. $σ_{n_t}\simeq0.01$ for $2\leqslant\ell\leqslant \ell_\text{max}=300$.

astro-ph.CO↗

arXiv2018

Distance Priors from Planck Final Release

We present the distance priors from the finally released $Planck~ \textrm{TT,TE,EE}+\textrm{lowE}$ data in 2018. The uncertainties are around $40\%$ smaller than those from $Planck$ 2015 TT$+$lowP. In order to check the validity of these new distance priors, we adopt the distance priors to constrain the cosmological parameters in different dark energy models, including the $Λ$CDM model, the $w$CDM model and the CPL model, and conclude that the distance priors provide consistent constraints on the relevant cosmological parameters compared to those from the full $Planck$ 2018 data release.

astro-ph.CO↗

arXiv2018

Merger Rate Distribution of Primordial-Black-Hole Binaries

Up to now several gravitational-wave events from the coalescences of black hole binaries have been reported by LIGO/VIRGO, and imply that black holes should have an extended mass function. We work out the merger rate distribution of primordial-black-hole binaries with a general mass function by taking into account the torques by all primordial black holes and linear density perturbations. In the future, many more coalescences of black hole binaries are expected to be detected, and the one-dimensional and two-dimensional merger rate distributions will be crucial for reconstructing the mass function of primordial black holes.

astro-ph.CO↗

arXiv2018

Super-Eddington accreting massive black holes explore high-$z$ cosmology: Monte-Carlo simulations

In this paper, we simulate Super-Eddington accreting massive black holes (SEAMBHs) as the candles to probe cosmology for the first time. SEAMBHs have been demonstrated to be able to provide a new tool for estimating cosmological distance. Thus, we create a series of mock data sets of SEAMBHs, especially in the high redshift region, to check their abilities to probe the cosmology. To fulfill the potential of the SEAMBHs on the cosmology, we apply the simulated data to three projects. The first is the exploration of their abilities to constrain the cosmological parameters, in which we combine different data sets of current observations such as the cosmic microwave background from {\it Planck} and type Ia supernovae from Joint Light-curve Analysis (JLA). We find that the high redshift SEAMBHs can help to break the degeneracies of the background cosmological parameters constrained by {\it Planck} and JLA, thus giving much tighter constraints of the cosmological parameters. The second uses the high redshift SEAMBHs as the complements of the low redshift JLA to constrain the early expansion rate and the dark energy density evolution in the cold dark matter frame. Our results show that these high redshift SEAMBHs are very powerful on constraining the early Hubble rate and the evolution of the dark energy density; thus they can give us more information about the expansion history of our Universe, which is also crucial for testing the $Λ$CDM model in the high redshift region. Finally, we check the SEAMBH candles' abilities to reconstruct the equation of state of dark energy at high redshift. In summary, our results show that the SEAMBHs, as the rare candles in the high redshift region, can provide us a new and independent observation to probe cosmology in the future.

astro-ph.CO↗

arXiv2018

Measuring the spectral running from cosmic microwave background and primordial black holes

We constrain the spectral running by combining cosmic microwave background (CMB) data, baryon acoustic oscillation (BAO) data and the constraint from primordial black holes (PBHs). We find that the constraint from PBHs has a significant impact on the running of running of scalar spectral index, and a power-law scalar power spectrum without running is consistent with observational data once the constraint from PBHs is taken into account. In addition, from the constraints on the slow-roll parameters, the derived tensor spectral index in the single-field slow-roll inflation model is quite small, namely $|n_t|\lesssim 9.3\times 10^{-3}$ which will be very difficult to be measured by CMB data only in the future, and the absolute value of derived running of tensor spectral index is not larger than $2.1\times 10^{-4}$ at 95% confidence level.

astro-ph.CO↗