分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Both ultralight dark matter and exploring the quantum nature of black holes are all topics of great interest in gravitational wave astronomy at present. The superradiant instability allows an exotic compact object (ECO) to be surrounded by an ultralight boson cloud, which leads to the emission of gravitational waves and further triggers rich dynamical effects. In this paper, we study the gravitational effects of superradiant instabilities by calculating the energy fluxes of gravitational waves emitted from ultralight scalar dark matter fields by solving the Teukolsky equation in the background of a massive ECO phenomenologically described by a Kerr geometry with a reflective boundary condition at its physical boundary. We find that both the amplitude and phase of the reflectivity will either suppress or enhance the energy flux of GWs by several orders of magnitude if $M\mu \gtrsim 0.5$ where $M$ and $\mu$ are the mass of ECO and boson, respectively. However, the modifications to energy flux are negligible if $M \mu \lesssim 0.5$. Our results suggest that reflectivity will play a significant role in the near-horizon physics of ECO.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Parity violation is expected to generate an asymmetry between the amplitude of left and right-handed gravitational-wave modes which leads to a circularly polarized stochastic gravitational-wave background (SGWB). Due to the three independent baselines in the LIGO-Virgo network, we focus on the amplitude difference in strain power characterized by Stokes' parameters and do maximum-likelihood estimation to constrain the polarization degree of SGWB. Our results indicate that there is no evidence for the circularly polarized SGWB in the data. Furthermore, by modeling the SGWB as a power-law spectrum, we place upper limit on the normalized energy density $\Omega_\text{gw}(25\,\text{Hz})<5.3\times10^{-9}$ at $95\%$ confidence level after marginalizing over the polarization degree and spectral index.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yu-Mei Wu
Zu-Cheng Chen
Qing-Guo Huang
Xingjiang Zhu
N. D. Ramesh Bhat
Yi Feng
George Hobbs
Richard N. Manchester
Christopher J. Russell
R. M. Shannon
摘要： Composed of ultralight bosons, fuzzy dark matter provides an intriguing solution to challenges that the standard cold dark matter model encounters on sub-galactic scales. The ultralight dark matter with mass $m\sim10^{-23} \rm{eV}$ will induce a periodic oscillation in gravitational potentials with a frequency in the nanohertz band, leading to observable effects in the arrival times of radio pulses from pulsars. Unlike scalar dark matter, pulsar timing signals induced by the vector dark matter are dependent on the oscillation direction of the vector fields. In this work, we search for ultralight vector dark matter in the mass range of $[2\times 10^{-24}, 2\times 10^{-22}]{\rm{eV}}$ through its gravitational effect in the Parkes Pulsar Timing Array (PPTA) second data release. Since no statistically significant detection is made, we place $95\%$ upper limits on the local dark matter density as $\rho_{\rm{\tiny{VF}}} \lesssim 5{\rm{GeV/cm^{3}}}$ for $m\lesssim 10^{-23}{\rm{eV}}$. As no preferred direction is found for the vector dark matter, these constraints are comparable to those given by the scalar dark matter search with an earlier 12-year data set of PPTA.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Adopting a binned method, we model-independently reconstruct the mass function of primordial black holes (PBHs) from GWTC-3 and find that such a PBH mass function can be explained by a broad red-tilted power spectrum of curvature perturbations. Even though GW190521 with component masses in upper mass gap $(m>65M_\odot)$ can be naturally interpreted in the PBH scenario, the events (including GW190814, GW190425, GW200105, and GW200115) with component masses in the light mass range $(m<3M_\odot)$ are quite unlikely to be explained by binary PBHs although there are no electromagnetic counterparts because the corresponding PBH merger rates are much smaller than those given by LIGO-Virgo. Furthermore, we predict that both the gravitational-wave (GW) background generated by the binary PBHs and the scalar-induced GWs accompanying the formation of PBHs should be detected by the ground-based and space-borne GW detectors and pulsar timing arrays in the future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Parity violation is expected to generate an asymmetry between the amplitude of left and right-handed gravitational-wave modes which leads to a circularly polarized stochastic gravitational-wave background (SGWB). Due to the three independent baselines in the LIGO-Virgo network, we focus on the amplitude difference in strain power characterized by Stokes' parameters and do maximum-likelihood estimation to constrain the polarization degree of SGWB. Our results indicate that there is no evidence for the circularly polarized SGWB in the data. Furthermore, by modeling the SGWB as a power-law spectrum, we place upper limit on the normalized energy density $\Omega_\text{gw}(25\,\text{Hz})<5.3\times10^{-9}$ at $95\%$ confidence level after marginalizing over the polarization degree and spectral index.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we propose a model in which a spectator field non-minimally couples to an inflaton field and the power spectrum of the perturbation of the 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 $\sim10^{-12}M_\odot$ 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.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves offer a new window to probe the nature of gravity, including answering if the mediating particle, graviton, has a non-zero mass or not. Pulsar timing arrays measure stochastic gravitational wave background (SGWB) at $\sim1-100$~nanohertz. Recently, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration reported an uncorrelated common-spectrum process in their 12.5-year data set with no substantial evidence that the process comes from the SGWB predicted by general relativity. In this work, we explore the possibility of an SGWB from massive gravity in the data set and find that a massless graviton is preferred because of the relatively larger Bayes factor. Without statistically significant evidence for dispersion-related correlations predicted by massive gravity, we place upper limits on the amplitude of the SGWB for graviton mass smaller than $10^{-23}$~eV as $A_{\rm{MG}}<3.21\times 10^{-15}$ at $95\%$ confidence level.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： String cosmology models predict a relic background of gravitational-wave (GW) radiation in the early universe. The GW energy spectrum of radiated power increases rapidly with the frequency, and therefore it becomes a potential and meaningful observation object for high-frequency GW detector. We focus on the stochastic background generated by superinflation in string theory and search for such signal in the observing data of Advanced LIGO and Virgo O1$\sim$O3 runs in a Bayesian framework. We do not find the existence of the signal, and thus put constraints on the GW energy density. Our results indicate that at $f=100\,\text{Hz}$, the fractional energy density of GW background is less than $1.7\times10^{-8}$ and $2.1\times10^{-8}$ for dilaton-string and dilaton only cases respectively, and further rule out the parameter space restricted by the model itself due to the non-decreasing dilaton and stable cosmology background ($\beta$ bound).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We search for a first-order phase transition (PT) gravitational wave (GW) signal from Advanced LIGO and Advanced Virgo's first three observing runs. Due to the large theoretical uncertainties, four GW energy spectral shapes from bubble and sound wave collisions widely adopted in literature are investigated, separately. Our results indicate that there is no evidence for the existence of such GW signals, and therefore we give the upper limits on the amplitude of GW energy spectrum $\Omega_\text{pt}(f_*)$ in the peak frequency range of $f_*\in [5,500]$ Hz for these four theoretical models, separately. We find that $\Omega_\text{pt}(f_*\simeq 40\ \text{Hz})<1.3\times10^{-8}$ at $95\%$ credible level, and roughly $H_*/\beta\lesssim 0.1$ and $\alpha\lesssim 1$ at $68\%$ credible level in the peak frequency range of $20\lesssim f_*\lesssim 100$ Hz corresponding to the most sensitive frequency band of Advanced LIGO and Advanced Virgo's first three observing runs, where $H_*$ is the Hubble parameter when PT happens, $\beta$ is the bubble nucleation rate and $\alpha$ is the ratio of vacuum and relativistic energy density.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves offer a new window to probe the nature of gravity, including answering if the mediating particle, graviton, has a non-zero mass or not. Pulsar timing arrays measure stochastic gravitational wave background (SGWB) at $\sim1-100$~nanohertz. Recently, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration reported an uncorrelated common-spectrum process in their 12.5-year data set with no substantial evidence that the process comes from the SGWB predicted by general relativity. In this work, we explore the possibility of an SGWB from massive gravity in the data set and find that a massless graviton is preferred because of the relatively larger Bayes factor. Without statistically significant evidence for dispersion-related correlations predicted by massive gravity, we place upper limits on the amplitude of the SGWB for graviton mass smaller than $10^{-23}$~eV as $A_{\rm{MG}}<3.21\times 10^{-15}$ at $95\%$ confidence level.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The current observational constraints still leave a substantial mass window $\sim [10^{-16},10^{-14}] \cup [10^{-13},10^{-12}] M_\odot$ for primordial black holes (PBHs) representing all of dark matter (DM) in our Universe. The gravitational waves (GWs) induced by the curvature perturbations are inevitably generated during the formation of these PBHs, and fall in the frequency band of LISA. Such scalar induced gravitational waves (SIGWs) are supposed to be definitely detected by LISA even when the second-order local-type non-Gaussianity characterized by the parameter $F_{\rm NL}$ is taken into account. In this letter, we give a comprehensive analysis of the GWs induced by the local-type non-Gaussian curvature perturbations up to the third-order denoted by the non-linear parameter $G_{\rm NL}$, and find that a log-dependent slope of SIGWs in the infrared region is generically predicted and the amplitude of SIGWs can be further suppressed by several orders of magnitude. Therefore, the null-detection of SIGWs by LISA cannot rule out the possibility of PBHs making up all of DM.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Both ultralight dark matter and exploring the quantum nature of black holes are all topics of great interest in gravitational wave astronomy at present. The superradiant instability allows an exotic compact object (ECO) to be surrounded by an ultralight boson cloud, which leads to the emission of gravitational waves and further triggers rich dynamical effects. In this paper, we study the gravitational effects of superradiant instabilities by calculating the energy fluxes of gravitational waves emitted from ultralight scalar dark matter fields by solving the Teukolsky equation in the background of a massive ECO phenomenologically described by a Kerr geometry with a reflective boundary condition at its physical boundary. We find that both the amplitude and phase of the reflectivity will either suppress or enhance the energy flux of GWs by several orders of magnitude if $M\mu \gtrsim 0.5$ where $M$ and $\mu$ are the mass of ECO and boson, respectively. However, the modifications to energy flux are negligible if $M \mu \lesssim 0.5$. Our results suggest that reflectivity will play a significant role in the near-horizon physics of ECO.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we propose a model in which a spectator field non-minimally couples to an inflaton field and the power spectrum of the perturbation of the 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 $\sim10^{-12}M_\odot$ 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.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We perform the first search for an isotropic non-tensorial gravitational-wave background (GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse (ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is $107\pm 7$, but no statistically significant evidence for the tensor transverse, vector longitudinal and scalar longitudinal polarization modes. The median and the $90\%$ equal-tail amplitudes of ST mode are $\mathcal{A}_{\mathrm{ST}}= 1.06^{+0.35}_{-0.28} \times 10^{-15}$, or equivalently the energy density parameter per logarithm frequency is $\Omega_{\mathrm{GW}}^{\mathrm{ST}} = 1.54^{+1.21}_{-0.71} \times 10^{-9}$, at frequency of 1/year.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves (GWs) from compact binary coalescences provide an independent probe of the cosmic expansion history other than electromagnetic waves. In this work, we assume the binary black holes (BBHs) detected by LIGO-Virgo-KAGRA (LVK) collaborations are of primordial origin and constrain the population parameters of primordial black holes (PBHs) and Hubble parameter $H(z)$ using $42$ BBHs from third LVK GW transient catalog (GWTC-3). Three PBH mass models are considered: lognormal, power-law, and critical collapse PBH mass functions. By performing a hierarchical Bayesian population analysis, the Bayes factor strongly disfavors the power-law PBH mass function against the other two in GWTC-3. The constraints on standard $\Lambda{\rm CDM}$ cosmological parameters are rather weak and in agreement with current results. When combining the multi-messenger standard siren measurement from GW170817, the Hubble constant $H_0$ is constrained to be $69^{+19}_{-8}\, \mathrm{km}\, \mathrm{s}^{-1}\, \mathrm{Mpc}^{-1}$ and $70^{+26}_{-8}\, \mathrm{km}\, \mathrm{s}^{-1}\, \mathrm{Mpc}^{-1}$ at $68\%$ confidence for the lognormal and critical collapse mass models, respectively. Furthermore, we consider a mixed ABH+PBH model, in which we assume LVK BBHs can come from both the astrophysical black hole (ABH) and PBH channels. We find that the ABH+PBH model can better describe the mass distribution in GWTC-3 than any single ABH or PBH model, thus improving the precision to constrain the Hubble constant. With the increased BBH events, the mixed ABH+PBH model provides a robust statistical inference for both the population and cosmological parameters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We search for the isotropic stochastic gravitational-wave background, including the nontensorial polarizations that are allowed in general metric theories of gravity, in the Parkes Pulsar Timing Array (PPTA) second data release (DR2). We find no statistically significant evidence that the common-spectrum process reported by the PPTA collaboration has the tensor transverse, scalar transverse, vector longitudinal, or scalar longitudinal correlations in PPTA DR2. Therefore, we place a $95\%$ upper limit on the amplitude of each polarization mode, as $\mathcal{A}_{\mathrm{TT}} \lesssim 3.2\times 10^{-15}$, $\mathcal{A}_{\mathrm{ST}} \lesssim 1.8\times 10^{-15}$, $\mathcal{A}_{\mathrm{VL}}\lesssim 3.5\times 10^{-16}$ and $\mathcal{A}_{\mathrm{SL}}\lesssim 4.2\times 10^{-17}$; or, equivalently, a $95\%$ upper limit on the energy density parameter per logarithm frequency, as $\Omega_{\mathrm{GW}}^{\mathrm{TT}} \lesssim 1.4\times 10^{-8}$, $\Omega_{\mathrm{GW}}^{\mathrm{ST}} \lesssim 4.5\times 10^{-9}$, $\Omega_{\mathrm{GW}}^{\mathrm{VL}} \lesssim 1.7\times 10^{-10}$ and $\Omega_{\mathrm{GW}}^{\mathrm{SL}} \lesssim 2.4\times 10^{-12}$, at a frequency of 1/yr.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ultralight bosons, as important candidates of dark matter, can condense around spinning black holes (BHs) to form long-lived ``boson clouds'' due to superradiance instability. The boson-BH system can be observed through gravitational wave detection and may become a new window to find traces of ultralight bosons. In this letter we explore the effects on the superradiant instability of BHs from the near-horizon microstructure. By introducing the reflection parameter near a BH horizon, we derived analytical results on the corrections to both energy levels of bosonic cloud and its characteristic frequencies of superradiance instability. Our results imply that the evolution of a boson-BH system and gravitational waves it emits would be influenced by the near-horizon physics of a BH.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yu-Mei Wu
Zu-Cheng Chen
Qing-Guo Huang
Xingjiang Zhu
N. D. Ramesh Bhat
Yi Feng
George Hobbs
Richard N. Manchester
Christopher J. Russell
R. M. Shannon
摘要： Composed of ultralight bosons, fuzzy dark matter provides an intriguing solution to challenges that the standard cold dark matter model encounters on sub-galactic scales. The ultralight dark matter with mass $m\sim10^{-23} \rm{eV}$ will induce a periodic oscillation in gravitational potentials with a frequency in the nanohertz band, leading to observable effects in the arrival times of radio pulses from pulsars. Unlike scalar dark matter, pulsar timing signals induced by the vector dark matter are dependent on the oscillation direction of the vector fields. In this work, we search for ultralight vector dark matter in the mass range of $[2\times 10^{-24}, 2\times 10^{-22}]{\rm{eV}}$ through its gravitational effect in the Parkes Pulsar Timing Array (PPTA) second data release. Since no statistically significant detection is made, we place $95\%$ upper limits on the local dark matter density as $\rho_{\rm{\tiny{VF}}} \lesssim 5{\rm{GeV/cm^{3}}}$ for $m\lesssim 10^{-23}{\rm{eV}}$. As no preferred direction is found for the vector dark matter, these constraints are comparable to those given by the scalar dark matter search with an earlier 12-year data set of PPTA.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We put constraints on the normalized energy density in gravitaional waves from cosmic domain walls (DWs) by searching for the stochastic gravitational-wave background (SGWB) in the data of Advanced LIGO and Virgo's first three observing runs. By adopting a phenomenological broken power-law model, we obtain the upper limit of normalized energy density of SGWB generated by DWs in the peak frequency band $10\sim200$ Hz, and get the most stringent limitation at the peak frequency $f_*=35$ Hz, namely $\Omega_\text{DW}(f_*=35\,\text{Hz})<1.4\times10^{-8}$ at $95\%$ confidence level (CL). Subsequently, we work out the constraints on the parameter space in the appealing realization of DW structure -- the heavy axion model which can avoid the so-called quality problem.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves (GWs) from compact binary coalescences provide an independent probe of the cosmic expansion history other than electromagnetic waves. In this work, we assume the binary black holes (BBHs) detected by LIGO-Virgo-KAGRA (LVK) collaborations are of primordial origin and constrain the population parameters of primordial black holes (PBHs) and Hubble parameter $H(z)$ using $42$ BBHs from third LVK GW transient catalog (GWTC-3). Three PBH mass models are considered: lognormal, power-law, and critical collapse PBH mass functions. By performing a hierarchical Bayesian population analysis, the Bayes factor strongly disfavors the power-law PBH mass function against the other two in GWTC-3. The constraints on standard $\Lambda{\rm CDM}$ cosmological parameters are rather weak and in agreement with current results. When combining the multi-messenger standard siren measurement from GW170817, the Hubble constant $H_0$ is constrained to be $69^{+19}_{-8}\, \mathrm{km}\, \mathrm{s}^{-1}\, \mathrm{Mpc}^{-1}$ and $70^{+26}_{-8}\, \mathrm{km}\, \mathrm{s}^{-1}\, \mathrm{Mpc}^{-1}$ at $68\%$ confidence for the lognormal and critical collapse mass models, respectively. Furthermore, we consider a mixed ABH+PBH model, in which we assume LVK BBHs can come from both the astrophysical black hole (ABH) and PBH channels. We find that the ABH+PBH model can better describe the mass distribution in GWTC-3 than any single ABH or PBH model, thus improving the precision to constrain the Hubble constant. With the increased BBH events, the mixed ABH+PBH model provides a robust statistical inference for both the population and cosmological parameters.
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