Observational verification of CPT invariance with binary black hole gravitational waves in the LIGO-Virgo catalog GWTC-1

A discovery of gravitational waves from binary black holes raises a possibility that measurements of them can provide strict tests of CPT invariance in gravitational waves. When CPT violation exists, if any, gravitational waves with different circular polarizations could gain a slight difference in propagating speeds. Hence, the birefringence of gravitational waves is induced and there should be a rotation of plus and cross modes. For CPT-violating dispersion relation ${\omega^{2}=k^{2}}$ ${\pm 2\zeta k^{3}}$, where a sign ${\pm}$ denotes different circular polarizations, we find no substantial deviations from CPT invariance in gravitational waves by analyzing a compilation of ten signals of binary black holes in the LIGO-Virgo catalog GWTC-1. We obtain a strict constraint on the CPT-violating parameter ${\zeta}$, namely, $\zeta=(0.33\pm0.85)\times10^{-15}\text{m}$, which is one order of magnitude better than the existing one. Therefore, this study stands for the up-to-date strictest tests of CPT invariance in gravitational waves.Comment: 6 pages, 2 figur

Unveiling the Graviton Mass Bounds through Analysis of 2023 Pulsar Timing Array Datasets

Strong evidence for the Helling-Downs correlations have been reported by several pulsar timing array collaborations in middle 2023. In this work, we study the state-of-the-art graviton mass bounds by analyzing the observational data of overlap ruduction functions from NANOGrav 15-year data release and CPTA first data release. The data analysis places upper limits on the graviton mass at 95\% confidence level, namely, $m_{g}\lesssim4.3\times10^{-23}\mathrm{eV}$ for NANOGrav and $m_{g}\lesssim5.7\times10^{-23}\mathrm{eV}$ for CPTA. In addition, we discuss implications of these results for scenarios of ultralight tensor dark matter.Comment: typos are correcte

GW200105 and GW200115 are compatible with a scenario of primordial black hole binary coalescences

Two gravitational wave events, namely GW200105 and GW200115, were observed by the Advanced LIGO and Virgo detectors recently. In this work, we show that they can be explained by a scenario of primordial black hole binaries that are formed in the early Universe. The merger rate predicted by such a scenario could be consistent with the one estimated from LIGO and Virgo, even if primordial black holes constitute a fraction of cold dark matter. The required abundance of primordial black holes is compatible with the existing upper limits from microlensing, caustic crossing and cosmic microwave background observations.Comment: Preprint, 8pages, 1 figur

Bayesian Implications for the Primordial Black Holes from NANOGrav's Pulsar-Timing Data Using the Scalar-Induced Gravitational Waves

Assuming that the common-spectrum process in the NANOGrav 12.5-year dataset has an origin of scalar-induced gravitational waves, we study the enhancement of primordial curvature perturbations and the mass function of primordial black holes, by performing the Bayesian parameter inference for the first time. We obtain lower limits on the spectral amplitude, i.e., $\mathcal{A}\gtrsim10^{-2}$ at 95\% confidence level, when assuming the power spectrum of primordial curvature perturbations to follow a log-normal distribution function with width $\sigma$. In the case of $\sigma\rightarrow0$, we find that the primordial black holes with $2\times10^{-4}-10^{-2}$ solar mass are allowed to compose at least a fraction $10^{-6}$ of dark matter. Such a mass range is shifted to more massive regimes for larger values of $\sigma$, e.g., to a regime of $4\times10^{-3}-0.2$ solar mass in the case of $\sigma=1$. We expect the planned gravitational-wave experiments to have their best sensitivity to $\mathcal{A}$ in the range of $10^{-4}$ to $10^{-7}$, depending on the experimental setups. With this level of sensitivity, we can search for primordial black holes throughout the entire parameter space, especially in the mass range of $10^{-16}$ to $10^{-11}$ solar masses, where they could account for all dark matter. In addition, the importance of multi-band detector networks is emphasized to accomplish our theoretical expectation.Comment: 15 pages, 5 figures, 1 table, version publishe

Standard physics is capable to interpret ∼\sim18 TeV photons from GRB 221009A

It is reported that the Large High Altitude Air Shower Observatory (LHAASO) observed thousands of very-high-energy photons up to $\sim$18 TeV from GRB 221009A. We study the survival rate of these photons by considering the fact that they are absorbed by the extragalactic background light. By performing a set of $10^6$ Monte-Carlo simulations, we explore the parameter space allowed by current observations and find that the probability of predicting that LHAASO observes at least one photons of $\sim$18 TeV from GRB 221009A within 2000 seconds is 80\% and 25\% if assuming the spectral index of photon flux is $-2$ and $-3$, respectively. Hence, it is still possible for the standard physics to interpret the observation of LHAASO in the energy range of several TeV. Our research method can be straightforwardly generalized to study more data sets of LHAASO and other experiments in the future.Comment: 5 pages, 2 figure

Joint implications of BBN, CMB, and PTA Datasets for Scalar-Induced Gravitational Waves of Second and Third orders

Assuming the evidence for gravitational wave background from recent data release of pulsar timing arrays to be interpreted as the scalar-induced gravitational waves (SIGWs), we study the second and third order gravitational waves simultaneously, by jointly analyzing a combination of PTA, big-bang nucleosynthesis (BBN), and cosmic microwave background (CMB) datasets. We obtain the primordial curvature spectral amplitude $0.014<A_\zeta<0.058$ and the spectral peak frequency $10^{-7.4}\ \mathrm{Hz}<f_\ast<10^{-6.4}\ \mathrm{Hz}$at 95\% confidence level, indicating a mass range of primordial black holes (PBHs)$10^{-4.3}M_\odot<m_{\mathrm{pbh}}<10^{-2.3}M_\odot$. We further find that the third order gravitational waves have greater contributions to the integrated energy density than the second order gravitational waves when$A_\zeta\gtrsim0.06$. In addition, we anticipate that future PTA projects can not only test the above results, but also have powerful abilities to explore the origin and evolution of the universe, particularly, the inflation.Comment: 12 pages, 2 figure