arXiv subjects

Jing-Zhi Zhou

Publications and source records attributed to Jing-Zhi Zhou.

23 records · Page 2Linked to original sources

arXiv2023

Primordial black holes and third order scalar induced gravitational waves

The process of \acp{PBH} formation would be inevitably accompanied by \acp{SIGW}. This strong correlation between \acp{PBH} and \acp{SIGW} signals could be a promising approach to detecting \acp{PBH} in the upcoming \ac{GW} experiments, such as \ac{LISA}. We investigate the third order \acp{SIGW} during a \ac{RD} era in the case of a monochromatic primordial power spectrum $\mathcal{P}_ζ=A_ζk_*δ\left(k-k_*\right)$. For \ac{LISA} observations, the relations between \ac{SNR} and monochromatic primordial power spectrum are studied systematically. It shows that the effects of third order \acp{SIGW} extend the cutoff frequency from $2f_*$ to $3f_*$ and lead to about $200\%$ increase of the \ac{SNR} for frequency band from $10^{-5}$Hz to $1.6\times 10^{-3}$Hz corresponding to \acp{PBH} with mass range $4\times 10^{-12}M_{\odot} \sim 10^{-7}M_{\odot}$. We find that there exists a critical value $A_*=1.76\times 10^{-2}$ for the amplitude of the monochromatic primordial power spectra, such that when $A_ζ>A_*$, the energy density of third order \acp{SIGW} will be larger than the energy density of second order \acp{SIGW}.

astro-ph.CO↗

arXiv2022

Pulsars as candidates of LHAASO sources J2226+6057, J1908+0621 and J1825-1326

The LHAASO Collaboration has observed ultrahigh-energy photons up to $1.4$PeV from $12$ $γ$-ray Galactic sources. In particular, the $γ$-ray spectra of the sources J2226+6057, J1908+0621, J1825-1326 have been published. We investigate the possibility of suggested origin pulsars near the sources as the PeVatrons. The pulsar is described by a rotating magnetic dipole. Assuming protons are uniform distributed out of the light cylinders, we obtain the Lorentz distribution of proton energy spectrum. It is found that the protons around pulsar could be accelerated to PeV at short times. The hadronic $γ$-ray spectra of the suggested origin pulsars are in good agreement with the LHAASO observed $γ$-ray spectra of the sources J2226+6057, J1908+0621, J1825-1326.

astro-ph.HE↗

arXiv2022

Impact of the free-streaming neutrinos to the second order induced gravitational waves

The damping effect of the free-streaming neutrinos on the second order gravitational waves is investigated in detail. We solve the Boltzmann equation and give the anisotropic stress induced by neutrinos to second order. The first order tensor and its coupling with scalar perturbations induced gravitational waves are considered. We give the analytic equations of the damping kernel functions and finally obtain the energy density spectrum. The results show that the free-streaming neutrinos suppress the density spectrum significantly for low frequency gravitational waves and enlarge the logarithmic slope $n$ in the infrared region ($k \ll k_*$) of the spectrum. For the spectrum of $k_*\sim 10^{-7}$Hz, the damping effect in the range of $k<k_*$ is significant. The combined effect of the first and second order could reduce the amplitude by $30\%$ and make $n$ jump from $1.54$ to $1.63$ at $k\sim 10^{-9}$Hz, which may be probed by the pulsar timing arrays (PTA) in the future.

astro-ph.CO↗

arXiv2022

The cosmological vector modes from a monochromatic primordial power spectrum

The cosmological background of higher order vector modes can be generated by the first order scalar perturbations. We investigate the second order and the third order vector modes systematically. The explicit expressions of two point functions $\langle V^{(n),λ}V^{(n),λ'} \rangle$$\left(n=2,3\right)$ and power spectra corresponded are presented. In the case of a monochromatic primordial power spectrum, the second order vector modes do not exist. However, the third order vector modes can be generated by a monochromatic primordial power spectrum. And it is found that the third order vector modes sourced by the second order scalar perturbations dominate the two point function $\langle V^{(3),λ}V^{(3),λ'} \rangle$ and power spectrum corresponded.

astro-ph.CO↗

arXiv2022

The Third Order Scalar Induced Gravitational Waves

Since the gravitational waves were detected by LIGO and Virgo, it has been promising that lots of information about the primordial Universe could be learned by further observations on stochastic gravitational waves background. The studies on gravitational waves induced by primordial curvature perturbations are of great interest. The aim of this paper is to investigate the third order induced gravitational waves. Based on the theory of cosmological perturbations, the first order scalar induces the second order scalar, vector and tensor perturbations. At the next iteration, the first order scalar, the second order scalar, vector and tensor perturbations all induce the third order tensor perturbations. We present the energy density spectrum of the third order gravitational waves for a monochromatic primordial power spectrum. The shape of the energy density spectrum of the third order gravitational waves is different from that of the second order scalar induced gravitational waves. And it is found that the third order gravitational waves sourced by the second order scalar perturbations dominate the energy density spectrum.

astro-ph.CO↗