Qianhang Ding 丁乾航 To Understand To Find
Superradiant Bosons Driving Supermassive Black Hole Mergers [PDF]
Qianhang Ding, Minxi He, Volodymyr Takhistov, Hui-Yu Zhu
Abstract:
Ultralight bosons (ULBs) can form macroscopic superradiant clouds around spinning black holes. We show that for scalar ULB masses μ∼10^(−22)−10^(−21) eV boson cloud dynamical friction drives supermassive black hole (SMBH) final-parsec evolution in ≲1 Gyr and suppresses the nanohertz gravitational wave background with turnover. Considering century-monitored OJ287 system, we place novel bounds restricting ULB mass range μ≃(8.5−22)×10^(−22) eV independent of any dark matter assumptions and show ULB drag can also efficiently reconcile any future confirmations of the debated orbital decay excess. Forthcoming pulsar timing array data and precise SMBH orbital timings will decisively test this scenario.
Primordial Black Hole Mergers as Probes of Dark Matter in Galactic Center [PDF]
Qianhang Ding, Minxi He, Volodymyr Takhistov
Abstract:
Primordial black holes (PBHs) from the early Universe that can contribute to dark matter (DM) abundance have been linked to gravitational wave observations. Super-massive black holes (SMBHs) at the centers of galaxies are expected to modify distribution of DM in their vicinity, and can result in highly concentrated DM spikes. We revisit PBH merger rates in the presence of DM spikes, tracking their history. We find novel peaked structure in the redshift-evolution of PBH merger rates at low redshifts around z∼5. These effects are generic and are present for distinct PBH mass functions and spike profiles, and also can be linked to peaked structure in redshift evolution of star formation rate. Redshift evolution characteristics of PBH merger rates can be distinguished from astrophysical black hole contributions and observable with gravitational waves, enabling them to serve as probes of DM in galactic centers.
The merger rate of primordial black hole binaries as a probe of Hubble parameter [PDF]
Qianhang Ding
Abstract:
We propose that the merger rate of primordial black hole (PBH) binaries can be a probe of Hubble parameter by constraining PBH mass function in the redshifted mass distribution of PBH binaries. In next-generation gravitational wave (GW) detectors, the GWs from PBH binaries would be detected at high redshifts, which gives their redshifted mass and luminosity distances. From a number of detected events, the redshifted mass distribution of PBH binaries can be statistically obtained, and it depends on PBH mass function and redshift distribution of detected PBH binaries. The PBH mass function can be inversely solved by applying the gradient descent method in the relation between redshifted mass distribution and redshift distribution. However, the construction of redshift distribution requires an assumed Hubble parameter in a background cosmology to extract redshift from luminosity distances, which causes solved PBH mass function also depends on assumed Hubble parameter. To determine the Hubble parameter, the merger rate of PBH binaries constrains on this Hubble parameter-dependent PBH mass function by comparing calculated merger rate distribution with observed one, and the best-fit result produces an approximate mass distribution of the physical PBH mass function and pins down the Hubble parameter.
A Dark Matter Probe in Accreting Pulsar-Black Hole Binaries [PDF]
Ali Akil, Qianhang Ding
Abstract:
The accretion of dark matter (DM) into astrophysical black holes slowly increases their mass. The rate of this mass accretion depends on the DM model and the model parameters. If this mass accretion effect can be measured accurately enough, it is possible to rule out some DM models, and, with the sufficient technology and the help of other DM constraints, possibly confirm one model. We propose a DM probe based on accreting pulsar-black hole binaries, which provide a high-precision measurement on binary orbital phase shifts induced by DM accretion into black holes, and can help rule out DM models and study the nature of DM.
Reconciling cosmic dipolar tensions with a gigaparsec void [PDF]
Tingqi Cai, Qianhang Ding, Yi Wang
Abstract:
Recent observations indicate a 4.9σ tension between the CMB and quasar dipoles. This tension challenges the cosmological principle. We propose that if we live in a gigaparsec scale void, the CMB and quasar dipolar tension can be reconciled. This is because we are unlikely to live at the center of the void. And a within 10% offset from the center will impact the quasars and CMB differently in their dipolar anisotropies. As we consider a large and thick void, our setup can also ease the Hubble tension.
Cosmological Standard Timers from Primordial Black Hole Binaries [PDF]
Qianhang Ding
Abstract:
We propose that primordial black hole (PBH) binary systems can work as standard timers in tracking the evolution of the Universe. Through gravitational waves from monochromatic PBH binaries, the probability distribution on major axis and eccentricity from the same redshift is obtained. By studying the dynamical evolution of PBH binaries from the initial probability distribution to observed redshifted ones, the redshift-time calibration can be extracted, which can constrain cosmological models. A general formalism of the standard timer is further concluded based on the evolution of statistical distribution in dynamical systems.
Cosmological Standard Timers from Unstable Primordial Relics [PDF]
Yi-Fu Cai, Chao Chen, Qianhang Ding, Yi Wang
Abstract:
In this article we study a hypothetical possibility of tracking the evolution of our Universe by introducing a series of the so-called standard timers. Any unstable primordial relics generated in the very early Universe may serve as the standard timers, as they can evolve through the whole cosmological background until their end while their certain time-varying properties could be a possible timer by recording the amount of physical time elapsed since the very early moments. Accordingly, if one could observe these quantities at different redshifts, then a redshift-time relation of the cosmic history can be attained. To illustrate such a hypothetical possibility, we consider the primordial black hole bubbles as a concrete example and analyze the mass function inside a redshifted bubble by investigating the inverse problem of Hawking radiation. To complete the analyses theoretically, the mass distribution can serve as a calibration of the standard timers.
Ultrahigh-energy Gamma Rays and Gravitational Waves from Primordial Exotic Stellar Bubbles [PDF]
Yi-Fu Cai, Chao Chen, Qianhang Ding, Yi Wang
Abstract:
We put forward a novel class of exotic celestial objects that can be produced through phase transitions occurred in the primordial Universe. These objects appear as bubbles of stellar sizes and can be dominated by primordial black holes (PBHs). We report that, due to the processes of Hawking radiation and binary evolution of PBHs inside these stellar bubbles, both electromagnetic and gravitational radiations can be emitted that are featured on the gamma-ray spectra and stochastic gravitational waves (GWs). Our results reveal that, depending on the mass distribution, the exotic stellar bubbles consisting of PBHs provide not only a decent fit for the ultrahigh-energy gamma-ray spectrum reported by the recent LHAASO experiment, but also predict GW signals that are expected to be tested by the forthcoming GW surveys.
Detectability of Primordial Black Hole Binaries at High Redshift [PDF]
Qianhang Ding
Abstract: We show that the gravitational wave signals from primordial black hole (PBH) binaries at high redshift can be detected. The detectability of PBH binaries is enhanced by redshift bias and more PBH binaries at high redshift. The initial clustering of PBHs is also included and enhances the effectively detectable mass ranges of PBHs at high redshift. Future observations on the gravitational wave at high redshift by space-based detectors such as LISA and SKA can constrain the fraction of PBHs in dark matter and PBHs initial distribution.
Gravitational Collider Physics via Pulsar-Black Hole Binaries [PDF]
Qianhang Ding, Xi Tong, Yi Wang
Abstract: We propose to use pulsar-black hole binaries as a probe of gravitational collider physics. Induced by the gravitation of the pulsar, the atomic transitions of the boson cloud around the black hole back-react on the orbital motion. This leads to the deviation of binary period decrease from that predicted by general relativity, which can be directly probed by the Rømer delay of pulsar time-of-arrivals. The sensitivity and accuracy of this approach is estimated for two typical atomic transitions. It is shown that once the transitions happen within the observable window, the pulsar-timing accuracy is almost always sufficient to capture the resonance phenomenon.
A gigaparsec-scale local void and the Hubble tension [PDF]
Qianhang Ding, Tomohiro Nakama, Yi Wang
Abstract: We explore the possibility of using a gigaparsec-scale local void to reconcile the Hubble tension. Such a gigaparsec-scale void can be produced by multi-stream inflation where different parts of the observable universe follow different inflationary trajectories. The impact of such a void for cosmological observations is studied, especially those involving supernovae, Baryon Acoustic Oscillations (BAO) and the kinetic Sunyaev-Zel'dovich (kSZ) effect. As a benchmark model, a 1.7Gpc scale with boundary width 0.7Gpc and density contrast -0.14 may ease the Hubble tension.
Detectability of Gravitational Waves from the Coalescence of Massive Primordial Black Holes with Initial Clustering [PDF]
Qianhang Ding, Tomohiro Nakama, Joseph Silk, Yi Wang
Abstract: We show that the effect of initial non-Gaussian clustering can significantly enhance the event rate for primordial black hole (PBH) coalescence. The impact of such clustering is studied in a specific scenario of multi-stream inflation. Initial clustering enables the possibility of detecting massive PBH coalescence by space-based gravitational wave interferometers such as LISA and DECIGO/BBO. The parameter regime for the ground-based detectors to detect PBH coalescence is also extended.
Imprints of Schwinger Effect on Primordial Spectra [PDF]
Wan Zhen Chua, Qianhang Ding, Yi Wang, Siyi Zhou
Abstract: We study the Schwinger effect during inflation and its imprints on the primordial power spectrum and bispectrum. The produced charged particles by Schwinger effect during inflation can leave a unique angular dependence on the primodial spectra. If such features are observed in future observations, they will be the smoking gun for the existence of the primordial electric field.