分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this work, we study the applications of entropy bounds in two toy cosmological models with particle production (annihilation), i.e., radiation-dominated universe and dust-dominated universe. Since entropy bounds are involved in the volume of the thermodynamc system, we need to specify the thermodynamc system in the universe in advance. We consider the co-moving volume and the volume covered by the particle horizon as the target thermodynamic system. With Bekenstein bound and spherical entropy bound, it is found that the cosmological singularity could be avoided and the cosmological particle production (annihilation) may need to be truncated for some special situations. Our study can be extended to other cosmological models with particle production (annihilation).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this work, we study the applications of entropy bounds in two toy cosmological models with particle production (annihilation), i.e., radiation-dominated universe and dust-dominated universe. Since entropy bounds are involved in the volume of the thermodynamc system, we need to specify the thermodynamc system in the universe in advance. We consider the co-moving volume and the volume covered by the particle horizon as the target thermodynamic system. With Bekenstein bound and spherical entropy bound, it is found that the cosmological singularity could be avoided and the cosmological particle production (annihilation) may need to be truncated for some special situations. Our study can be extended to other cosmological models with particle production (annihilation).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We study the influence of running vacuum on the baryon-to-photon ratio in running vacuum models (RVMs). When there exists a non-minimal coupling between photons and other matter in the expanding universe, the energy-momentum tensor of photons is no longer conserved, but the energy of photons could remain conserved. We discuss the conditions for the energy conservation of photons in RVMs. The photon number density and baryon number density, from the epoch of photon decoupling to the present day, are obtained in the context of RVMs by assuming that photons and baryons can be coupled to running vacuum, respectively. Both cases lead to a time-evolving baryon-to-photon ratio. However the evolution of the baryon-to-photon ratio is strictly constrained by observations. It is found that if the dynamic term of running vacuum is indeed coupled to photons or baryons, the coefficient of the dynamic term must be extremely small, which is unnatural. Therefore, our study basically rules out the possibility that running vacuum is coupled to photons or baryons in RVMs.
分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2024-01-09 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： The error propagation among estimated parameters reflects the correlation among the parameters. We study the capability of machine learning of "learning" the correlation of estimated parameters. We show that machine learning can recover the relation between the uncertainties of different parameters, especially, as predicted by the error propagation formula. Gravitational lensing can be used to probe both astrophysics and cosmology. As a practical application, we show that the machine learning is able to intelligently find the error propagation among the gravitational lens parameters (effective lens mass ML and Einstein radius θE) in accordance with the theoretical formula for the singular isothermal ellipse (SIE) lens model.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we use electromagnetic wave data (H0LiCOW, $H(z)$, SNe) and gravitational wave data (Tianqin) to constrain the interacting dark energy (IDE) model and investigate the Hubble tension problem and coincidences problem. By combining these four kinds of data (Tianqin+H0LiCOW+SNe+$H(z)$), we obtained the parameter values at the confidence interval of $1\sigma$: $\Omega_m=0.36\pm0.18$, $\omega_x=-1.29^{+0.61}_{-0.23}$, $\xi=3.15^{+0.36}_{-1.1}$, and $H_0=70.04\pm0.42$ $kms^{-1}Mpc^{-1}$. According to our results, the best valve of $H_0$ show that the Hubble tension problem can be alleviated to some extent. In addition, the $\xi+3\omega_x = -0.72^{+2.19}_{-1.19}(1\sigma)$ of which the center value indicates the coincidence problem is slightly alleviated. However, the $\xi+3\omega_x = 0$ is still within the $1\sigma$ error range which indicates the $\Lambda$CDM model is still the model which is in best agreement with the observational data at present. Finally, we compare the constraint results of electromagnetic wave and gravitational wave on the model parameters and find that the constraint effect of electromagnetic wave data on model parameters is better than that of simulated Tianqin gravitational wave data.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we use electromagnetic wave data (H0LiCOW, $H(z)$, SNe) and gravitational wave data (Tianqin) to constrain the interacting dark energy (IDE) model and investigate the Hubble tension problem and coincidences problem. By combining these four kinds of data (Tianqin+H0LiCOW+SNe+$H(z)$), we obtained the parameter values at the confidence interval of $1\sigma$: $\Omega_m=0.36\pm0.18$, $\omega_x=-1.29^{+0.61}_{-0.23}$, $\xi=3.15^{+0.36}_{-1.1}$, and $H_0=70.04\pm0.42$ $kms^{-1}Mpc^{-1}$. According to our results, the best valve of $H_0$ show that the Hubble tension problem can be alleviated to some extent. In addition, the $\xi+3\omega_x = -0.72^{+2.19}_{-1.19}(1\sigma)$ of which the center value indicates the coincidence problem is slightly alleviated. However, the $\xi+3\omega_x = 0$ is still within the $1\sigma$ error range which indicates the $\Lambda$CDM model is still the model which is in best agreement with the observational data at present. Finally, we compare the constraint results of electromagnetic wave and gravitational wave on the model parameters and find that the constraint effect of electromagnetic wave data on model parameters is better than that of simulated Tianqin gravitational wave data.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although the spatial curvature has been measured with very high precision, it still suffers from the well known cosmic curvature tension. In this paper, we propose an improved method to determine the cosmic curvature, by using the simulated data of binary neutron star mergers observed by the second generation space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO). By applying the Hubble parameter observations of cosmic chronometers to the DECIGO standard sirens, we explore different possibilities of making measurements of the cosmic curvature referring to a distant past: one is to reconstruct the Hubble parameters through the Gaussian process without the influence of hypothetical models, and the other is deriving constraints on $\Omega_K$ in the framework of non-flat $\Lambda$ cold dark matter model. It is shown that in the improved method DECIGO could provide a reliable and stringent constraint on the cosmic curvature ($\Omega_{K} = -0.007\pm0.016$), while we could only expect the zero cosmic curvature to be established at the precision of $\Delta \Omega_K=0.12$ in the second model-dependent method. Therefore, our results indicate that in the framework of methodology proposed in this paper, the increasing number of well-measured standard sirens in DECIGO could significantly reduce the bias of estimations for cosmic curvature. Such constraint is also comparable to the precision of Planck 2018 results with the newest cosmic microwave background (CMB) observations ($\Delta \Omega_{K} \approx 0.018$), based on the concordance $\Lambda$CDM model.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Polarization detection of X-rays is a non-negligible topic to astrophysical observation. Many polarization detection methods have been well developed for X-rays in the energy range below 10~keV, while the detection at 10-30~keV is rarely discussed. This paper presents a simulation study of a Xe-based gas pixel detector, which can achieve the polarization detection of X-rays at 10-30~keV. To verify the emission angle distribution of photoelectrons, different electromagnetic models in Geant4 were investigated. After a necessary modification by considering the missing factor when sampling the emission angle, a good agreement can be achieved. Moreover, the detection capability of 20~keV polarized photons was discussed and the modulation factor could be 43\%.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Jian Li
Jie Pang
Zhen-dong Yan
Junghoon Jahng
Jin Li
William Morrison
Jing Liang
Qing-Ying Zhang
Xing-Hua Xia
摘要： Tip enhanced IR spectra and imaging have been widely used in cutting-edge studies for the in-depth understanding of the composition, structure and function of interfaces at the nanoscale. However, molecular monolayer sensitivity has only been demonstrated on solid/gas interfaces. In aqueous environment, the reduced sensitivity due to strong damping of the cantilever oscillation and background IR absorption extremely limits the practical applications of tip enhanced IR nanospectroscopy. Here, we demonstrate hypersensitive nanoscale IR spectra and imaging in aqueous environment with the combination of photoinduced force (PiF) microscopy and resonant antennas. The highly confined electromagnetic field inbetween the tip end and antenna extremely amplifies the photoinduced force to the detectable level, while the excitation via plasmon internal reflection mode minimizes the environmental absorption. A polydimethylsiloxane (PDMS) layer (~1-2 nm thickness) functionalized on the AFM tip has been successfully identified in water with antennas of different sizes. Sampling volume of ~604 chemical bonds from PDMS was demonstrated with sub-10 nm spatial resolution confirmed by electric (E) field distribution mapping on antennas, which strongly suggests the desired requirements for interfacial spectroscopy. This platform demonstrates for the first time the application of photoinduced force microscopy in aqueous environments, providing a brand-new configuration to achieve highly enhanced nanoscale IR signals, which is extremely promising for future research of interfaces and nanosystems in aqueous environments.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Bo Chen
Yueguang Zhou
Peinian Huang
Chaochao Ye
Qian Cao
Yang Liu
Chanju Kim
Kresten Yvind
Jin Li
Chunhua Dong
Songnian Fu
Qiwen Zhan
Xuehua Wang
Minhao Pu
Jin Liu
摘要： The explorations of physical degrees of freedom with infinite dimensionalities, such as orbital angular momentum and frequency of light, have profoundly reshaped the landscape of modern optics with representative photonic functional devices including optical vortex emitters and frequency combs. In nanophotonics, whisper gallery mode microresonators naturally support orbital angular momentum of light and have been demonstrated as on-chip emitters of monochromatic optical vortices. On the other hand, whisper gallery mode microresonators serve as a highly-efficient nonlinear optical platform for producing light at different frequencies - i.e., microcombs. Here, we interlace the optical vortices and microcombs by demonstrating an optical vortex comb on an III-V integrated nonlinear microresonator. The angular-grating-dressed nonlinear microring simultaneously emits up to 50 orbital angular momentum modes that are each spectrally addressed to the frequency components ((longitudinal whispering gallery modes) of the generated microcomb. We further show that the integrated vortex comb with varied orbital angular momenta distributed across different frequencies exhibits unprecedented advantages in the synthesis of spatio-temporal optical pulses with time-varying orbital angular momenta. This work may immediately boost the development of integrated nonlinear/quantum photonics for exploring fundamental optical physics and advancing photonic quantum technology.
分类： 核科学技术 >> 核科学与技术 提交时间： 2024-01-06
Huan-Bo Feng
Hong-Bang Liu
Dong Wang
Zi-Li Li
Shu-Lin Liu
Qian Liu
Hang-Zhou Li
Bin-Long Wang
Yan-Jun Xie
Zong-Wang Fan
Hui Wang
Ran Chen
Di-Fan Yi,
Rui-Ting Ma
Fei Xie
Bo Peng
Xiang-Ming Sun
Jin Li
En-Wei Liang
摘要： POLAR-2 is a gamma-ray burst (GRB) polarimeter that is designed to study the polarization in GRB radiation emissions, aiming to improve our knowledge of related mechanisms. POLAR-2 is expected to utilize an on#2;board polarimeter that is sensitive to soft X-rays (210 keV), called low-energy polarization detector (LPD). We have developed a new soft X-ray polarization detector prototype based on gas microchannel plates (GMCPs) and pixel chips (Topmetal). The GMCPs have bulk resistance, which prevents charging-up effects and ensures gain stability during operation. The detector is composed of low-outgassing materials and is gas-sealed using a laser welding technique, ensuring long-term stability. A modulation factor of 41.28% 0.64% is obtained for a 4.5 keV polarized X-ray beam. A residual modulation of 1.96% 0.58% at 5.9 keV is observed for the entire sensitive area.
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