arXiv subjects

Hongbo Cai

Publications and source records attributed to Hongbo Cai.

26 records · Page 2Linked to original sources

arXiv2023

Impact of Anisotropic Birefringence on Measuring Cosmic Microwave Background Lensing

The power spectrum of cosmic microwave background lensing is a powerful tool for constraining fundamental physics such as the sum of neutrino masses and the dark energy equation of state. Current lensing measurements primarily come from distortions to the microwave background temperature field, but the polarization lensing signal will dominate upcoming experiments with greater sensitivity. Cosmic birefringence refers to the rotation of the linear polarization direction of microwave photons propagating from the last scattering surface to us, which can be induced by parity-violating physics such as axion-like dark matter or primordial magnetic fields. We find that, for an upcoming CMB-S4-like experiment, if there exists the scale-invariant anisotropic birefringence with an amplitude corresponding to the current $95\%$ upper bound, the measured lensing power spectrum could be biased by up to a factor of few at small scales, $L\gtrsim 1000$. We show that the bias scales linearly with the amplitude of the scale-invariant birefringence spectrum. The signal-to-noise of the contribution from anisotropic birefringence is larger than unity even if the birefringence amplitude decreases to $\sim 5\%$ of the current upper bound. Our results indicate that a measurement and characterization of the anisotropic birefringence is important for lensing analysis in future low-noise polarization experiments.

astro-ph.CO↗

arXiv2022

The Bias to Cosmic Microwave Background Lensing Reconstruction from the Kinematic Sunyaev-Zel'dovich Effect at Reionization

The power spectrum of reconstructed cosmic microwave background (CMB) lensing maps is a powerful tool for constraints on cosmological parameters like the sum of the neutrino masses and the dark energy equation of state. One possible complication is the kinematic Sunyaev-Zel'dovich (kSZ) effect, due to the scattering of CMB photons by moving electrons, which can bias the reconstruction of the CMB lensing power spectrum through both kSZ-lensing correlations and the non-Gaussianity of the kSZ temperature anisotropies. We investigate for the first time the bias to CMB lensing reconstruction from temperature anisotropies due to the reionization-induced kSZ signal and show that it is negligible for both ongoing and upcoming experiments based on current numerical simulations of reionization. We also revisit the bias induced by the late-time kSZ field, using more recent kSZ simulations. We find that it is potentially twice as large as found in earlier studies, reaching values as large as several percent of the CMB lensing power spectrum signal, indicating that this bias will have to be mitigated in upcoming data analyses.

astro-ph.CO↗

arXiv2021

Computing Microwave Background Polarization Power Spectra from Cosmic Birefringence

We present a new publicly available code, $\texttt{class_rot}$, which modifies $\texttt{class}$ to enable fast non-perturbative calculation of cosmic microwave background polarization power spectra due to both isotropic and anisotropic polarization rotation from cosmic birefringence. Cosmic birefringence can arise from new parity-violating physics such as axion dark matter with a Chern-Simons coupling to photons or Faraday rotation due to a primordial magnetic field. Constraints on these effects can be obtained by comparing measurements to precise numerical calculations of the polarization power spectra. We describe the implementation of $\texttt{class_rot}$ in terms of both mathematical formalism and coding architecture. We also provide usage examples and demonstrate the accuracy of the code by comparing with simulations.

astro-ph.CO↗

arXiv2021

Intermittent excitation of parametric instabilities enhanced by synergistic effect in broadband laser plasma interaction

A new evolution pattern for parametric instabilities in the non-linear stage driven by a broadband laser is studied with kinetic particle-in-cell simulations. It is found that an intermittent excitation of parametric instabilities caused by the high-intensity pulses, which are generated by the laser intensity variation of the broadband laser. The synergism between these high-intensity pulses reduces the Landau damping through the co-propagation of the electron-plasma waves and hot electrons, promoting the transition from convective to absolute stimulated Raman scattering. These intermittently excited parametric instabilities, especially absolute instability, will produce over-expected hot electrons compared with linear theory. However, comparisons between the energy of scattered lights for various bandwidth lasers indicate suppression of parametric instabilities with large laser bandwidths. Our works provided an opportunity to advance the understanding of the broadband laser-plasma interaction.

physics.plasm-ph↗

arXiv2021

An Automatic Observation Management System of the GWAC Network I: System Architecture and Workflow

The GWAC-N is an observation network composed of multi-aperture and multi-field of view robotic optical telescopes. The main instruments are the GWAC-A. Besides, several robotic optical telescopes with narrower field of views provide fast follow-up multi-band capabilities to the GWAC-N. The primary scientific goal of the GWAC-N is to search for the optical counterparts of GRB that will be detected by the SVOM. The GWAC-N performs many other observing tasks including the follow-ups of ToO and both the detection and the monitoring of variable/periodic objects as well as optical transients. To handle all of those scientific cases, we designed 10 observation modes and 175 observation strategies, especially, a joint observation strategy with multiple telescopes of the GWAC-N for the follow-up of GW events. To perform these observations, we thus develop an AOM system in charge of the object management, the dynamic scheduling of the observation plan and its automatic broadcasting to the network management and finally the image management. The AOM combines the individual telescopes into a network and smoothly organizes all the associated operations. The system completely meets the requirements of the GWAC-N on all its science objectives. With its good portability, the AOM is scientifically and technically qualified for other general purposed telescope networks. As the GWAC-N extends and evolves, the AOM will greatly enhance the discovery potential for the GWAC-N. In the first paper of a series of publications, we present the scientific goals of the GWAC-N as well as the hardware, the software and the strategy setup to achieve the scientific objectives. The structure, the technical design, the implementation and performances of the AOM will be also described in details. In the end, we summarize the current status of the GWAC-N and prospect for the development plan in the near future.

astro-ph.IM↗

arXiv2020

Hybrid-drive pressure suppressing implosion instabilities and offering nonstagnation hotspot ignition with low convergence ratio for high-gain inertial fusion

In laser-drive ICF, hybrid drive (HD) combined direct drive (DD) and indirect drive (ID) offers a smoothed HD pressure $P_{HD}$, far higher than the ablation pressure in ID and DD, to suppress hydrodynamic instabilities. In this letter, simulations of a new robust HD ignition target show that maximal HD pressure as high as $P_{HD} \sim$ 650 Mbar driven by a novel "bulldozer" effect is achieved, resulting in nonstagnation hotspot ignition at the convergence ratio $C_r \sim $23, and finally, fusion energy gain $\sim$ 10 in total laser energy = 1.42 MJ. Two-dimensional simulations have confirmed that hydrodynamic instabilities are suppressed. A well-fitted scale of maximal HD pressure $P_{HD}$ (Mbar)= $BE_{DD}^{1/4} T_r$ is found from simulations of different targets and laser energies as long as $T_r> 160$ eV, where B is the constant depending on ablator materials, $E_{DD}$ in kJ is DD laser energy and $T_r$ in 100 eV is radiation temperature depending on ID laser energy $E_{ID}$. $P_{HD}\geq$ 450 Mbar is requested for hotspot ignition. This scale from "bulldozer" effect is also available as $E_{DD}$ is reduced to kJ. Experiments have verified $P_{HD}$ about 3.5 times radiation ablation pressure for CH ablator using $E_{ID}=43$ kJ ($T_r \simeq$200 eV) and $E_{DD}$=3.6 kJ, also shown that both backscattering fraction and hot-electron energy fraction for DD laser intensity $\sim 1.8 \times 10^{15} {\rm w\cdot cm^{-2}}$ are about a third of the traditional DD laser-plasma interaction

physics.plasm-ph↗

arXiv2020

The GWAC Data Processing and Management System

GWAC will have been built an integrated FOV of 5,000 $degree^2$ and have already built 1,800 square $degree^2$. The limit magnitude of a 10-second exposure image in the moonless night is 16R. In each observation night, GWAC produces about 0.7TB of raw data, and the data processing pipeline generates millions of single frame alerts. We describe the GWAC Data Processing and Management System (GPMS), including hardware architecture, database, detection-filtering-validation of transient candidates, data archiving, and user interfaces for the check of transient and the monitor of the system. GPMS combines general technology and software in astronomy and computer field, and use some advanced technologies such as deep learning. Practical results show that GPMS can fully meet the scientific data processing requirement of GWAC. It can online accomplish the detection, filtering and validation of millions of transient candidates, and feedback the final results to the astronomer in real-time. During the observation from October of 2018 to December of 2019, we have already found 102 transients.

astro-ph.IM↗

arXiv2020

Effects of Regional Trade Agreement to Local and Global Trade Purity Relationships

In contrast to the rapid integration of the world economy, many regional trade agreements (RTAs) have also emerged since the early 1990s. This seeming contradiction has encouraged scholars and policy makers to explore the true effects of RTAs, including both regional and global trade relationships. This paper defines synthesized trade resistance and decomposes it into natural and artificial factors. Here, we separate the influence of geographical distance, economic volume, overall increases in transportation and labor costs and use the expectation maximization algorithm to optimize the parameters and quantify the trade purity indicator, which describes the true global trade environment and relationships among countries. This indicates that although global and most regional trade relations gradually deteriorated during the period 2007-2017, RTAs generate trade relations among members, especially contributing to the relative prosperity of EU and NAFTA countries. In addition, we apply the network to reflect the purity of the trade relations among countries. The effects of RTAs can be analyzed by comparing typical trade unions and trade communities, which are presented using an empirical network structure. This analysis shows that the community structure is quite consistent with some trade unions, and the representative RTAs constitute the core structure of international trade network. However, the role of trade unions has weakened, and multilateral trade liberalization has accelerated in the past decade. This means that more countries have recently tended to expand their trading partners outside of these unions rather than limit their trading activities to RTAs.

q-fin.GN↗