分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2023-06-01
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmological observations of cosmic microwave background and large-scale structure indicate that our universe has a nearly scaling invariant power spectrum of the primordial perturbation. However, the exact origin for this primordial spectrum is still unclear. Here, we propose the Weyl scaling invariant $R^2+R^3$ gravity that gives rise to inflation that is responsible for the primordial perturbation in the early universe. We develop both analytic and numerical treatments on inflationary observables, and find this model gives a distinctive scalar potential that can support two different patterns of inflation. The first one is similar to that occurs in the pure $R^2$ model, but with a wide range of tensor-to-scalar ratio $r$ from $\mathcal O(10^{-4})$ to $\mathcal O(10^{-2})$. The other one is a new situation with not only slow-roll inflation but also a short stage of oscillation-induced accelerating expansion. Both patterns of inflation have viable parameter spaces that can be probed by future experiments on cosmic microwave background and primordial gravitational waves.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmological observations of cosmic microwave background and large-scale structure indicate that our universe has a nearly scaling invariant power spectrum of the primordial perturbation. However, the exact origin for this primordial spectrum is still unclear. Here, we propose the Weyl scaling invariant $R^2+R^3$ gravity that gives rise to inflation that is responsible for the primordial perturbation in the early universe. We develop both analytic and numerical treatments on inflationary observables, and find this model gives a distinctive scalar potential that can support two different patterns of inflation. The first one is similar to that occurs in the pure $R^2$ model, but with a wide range of tensor-to-scalar ratio $r$ from $\mathcal O(10^{-4})$ to $\mathcal O(10^{-2})$. The other one is a new situation with not only slow-roll inflation but also a short stage of oscillation-induced accelerating expansion. Both patterns of inflation have viable parameter spaces that can be probed by future experiments on cosmic microwave background and primordial gravitational waves.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dark matter and inflation are two key elements to understand the origin of cosmic structures in modern cosmology, and yet their exact physical models remain largely uncertain. The Weyl scaling invariant theory of gravity may provide a feasible scheme to solve these two puzzles jointly, which contains a massive gauge boson playing the role of dark matter candidate, and allows the quadratic scalar curvature term, namely $R^2$, to realize a viable inflationary mechanism in agreement with current observations. We ponder on the production of dark matters in the Weyl $R^2$ model, including the contribution from the non-perturbative production due to the quantum fluctuations from inflationary vacuum and perturbative ones from scattering. We demonstrate that there are generally three parameter ranges for viable dark matter production: (1) If the reheating temperature is larger than $10^3~\mathrm{GeV}$, the Weyl gauge boson as dark matter can be produced abundantly with mass larger than the inflation scale $\sim 10^{13}~\mathrm{GeV}$. (2) Small mass region with $3\times10^{-13}~\mathrm{GeV}$ for a higher reheating temperature. (3) Annihilation channel becomes important in the case of higher reheating temperature, which enables the Weyl gauge boson with mass up to $4\times10^{16}~\mathrm{GeV}$ to be produced through freeze-in.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The galaxy luminosity function and galaxy stellar mass function are fundamental statistics in the testing of galaxy formation models. Theoretical predictions based on cosmological simulations can deviate from observations, especially at the bright and faint ends. In this case, the mismatch may come from missing physics, oversimplified or inaccurate model recipes, or inappropriate methods of extracting basic astrophysical quantities from simulations. The latter is a crucial aspect to consider to avoid misleading conclusions when comparing simulations with observations. In this paper, we have applied a new method to produce `observed' galaxies identified in mock imaging of hydrodynamical simulations. We generate low-redshift mock galaxies from the TNG100-1 simulation of IllustrisTNG and analyse them using standard `observational' techniques to extract their main structural parameters. We show that our technique can produce realistic surface-brightness distributions of the simulated galaxies, including classical morphological substructures, such as spiral arms and bars. In particular, we find a very good agreement of the total luminosity and stellar mass versus halo mass relationships, and the galaxy stellar mass versus size relationship between mock observations and real galaxies. We also compare the luminosity function and the mass function of the mock galaxy sample with literature data and find a good agreement at all luminosity and mass scales. In particular, we find no significant tension at the bright end of the galaxy luminosity function, as reported in many analyses using simplified recipes to identify galaxy haloes, which in fact miscount the contribution of the extended galaxy haloes around large galaxies. This demonstrates the critical impact of using observational driven approaches to the simulation analyses to produce realistic predictions to compare to observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The dispersion measure(DM) of fast radio burst encodes important information
such as its distance, properties of intervening medium. Based on simulations in
the Illustris and IllustrisTNG projects, we analyze the DM of FRBs contributed
by the interstellar medium and circumgalactic medium in the hosts,
$\rm{DM_{host}}$. We explore two population models - tracing the star formation
rate (SFR), and the stellar mass, i.e. young and old progenitors respectively.
The distribution of $\rm{DM_{host}}$ shows significant differences at $z=0$
between two populations: the stellar mass model exhibits an excess at the low
DM end with respect to the SFR model. The SFR (stellar mass) model has a median
value of $\rm{DM_{host}}$=179 (63) $\rm{pc\, cm^{-3}}$ for galaxies with
$M_*=10^{8-13}\,M_{\odot}$ in the TNG100-1. Galaxies in the Illustris-1 have a
much smaller $\rm{DM_{host}}$. The distributions of $\rm{DM_{host}}$ deviate
from log-normal function for both models. Furthermore, two populations differ
moderately in the spatial offset from host galaxy's center, in the stellar mass
function of hosts. $\rm{DM_{host}}$ increases with the stellar mass of hosts
when $M_*<10^{10.5}\,M_{\odot}$, and fluctuate at higher mass. At $0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The dispersion measure(DM) of fast radio burst encodes important information
such as its distance, properties of intervening medium. Based on simulations in
the Illustris and IllustrisTNG projects, we analyze the DM of FRBs contributed
by the interstellar medium and circumgalactic medium in the hosts,
$\rm{DM_{host}}$. We explore two population models - tracing the star formation
rate (SFR), and the stellar mass, i.e. young and old progenitors respectively.
The distribution of $\rm{DM_{host}}$ shows significant differences at $z=0$
between two populations: the stellar mass model exhibits an excess at the low
DM end with respect to the SFR model. The SFR (stellar mass) model has a median
value of $\rm{DM_{host}}$=179 (63) $\rm{pc\, cm^{-3}}$ for galaxies with
$M_*=10^{8-13}\,M_{\odot}$ in the TNG100-1. Galaxies in the Illustris-1 have a
much smaller $\rm{DM_{host}}$. The distributions of $\rm{DM_{host}}$ deviate
from log-normal function for both models. Furthermore, two populations differ
moderately in the spatial offset from host galaxy's center, in the stellar mass
function of hosts. $\rm{DM_{host}}$ increases with the stellar mass of hosts
when $M_*<10^{10.5}\,M_{\odot}$, and fluctuate at higher mass. At $0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Hydrodynamical interaction in circumbinary discs (CBDs) plays a crucial role in various astrophysical systems, ranging from young stellar binaries to supermassive black hole binaries in galactic centers. Most previous simulations of binary-disc systems have adopted locally isothermal equation of state. In this study, we use the grid-based code $\texttt{Athena++}$ to conduct a suite of two-dimensional viscous hydrodynamical simulations of circumbinary accretion on a cartesian grid, resolving the central cavity of the binary. The gas thermodynamics is treated by thermal relaxation towards an equilibrium temperature (based on the constant$-\beta$ cooling ansatz, where $\beta$ is the cooling time in units of the local Keplerian time). Focusing on equal mass, circular binaries in CBDs with (equilibrium) disc aspect ratio $H/R=0.1$, we find that the cooling of the disc gas significantly influences the binary orbital evolution, accretion variability, and CBD morphology, and the effect depends sensitively on the disc viscosity prescriptions. When adopting a constant kinematic viscosity, a finite cooling time ($\beta \gtrsim 0.1$) leads to binary inspiral as opposed to outspiral and the CBD cavity becomes more symmetric. When adopting a dynamically varying $\alpha-$viscosity, binary inspiral only occurs within a narrow range of cooling time (corresponding to $\beta$ around 0.5).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Hydrodynamical interaction in circumbinary discs (CBDs) plays a crucial role in various astrophysical systems, ranging from young stellar binaries to supermassive black hole binaries in galactic centers. Most previous simulations of binary-disc systems have adopted locally isothermal equation of state. In this study, we use the grid-based code $\texttt{Athena++}$ to conduct a suite of two-dimensional viscous hydrodynamical simulations of circumbinary accretion on a cartesian grid, resolving the central cavity of the binary. The gas thermodynamics is treated by thermal relaxation towards an equilibrium temperature (based on the constant$-\beta$ cooling ansatz, where $\beta$ is the cooling time in units of the local Keplerian time). Focusing on equal mass, circular binaries in CBDs with (equilibrium) disc aspect ratio $H/R=0.1$, we find that the cooling of the disc gas significantly influences the binary orbital evolution, accretion variability, and CBD morphology, and the effect depends sensitively on the disc viscosity prescriptions. When adopting a constant kinematic viscosity, a finite cooling time ($\beta \gtrsim 0.1$) leads to binary inspiral as opposed to outspiral and the CBD cavity becomes more symmetric. When adopting a dynamically varying $\alpha-$viscosity, binary inspiral only occurs within a narrow range of cooling time (corresponding to $\beta$ around 0.5).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The peculiar velocities of dark matter halos are crucial to study many issues in cosmology and galaxy evolution. In this study, by using the state-of-the-art deep learning technique, a UNet-based neural network, we propose to reconstruct the peculiar velocity field from the redshift-space distribution of dark matter halos. Through a point-to-point comparison and examination of various statistical properties, we demonstrate that, the reconstructed velocity field is in good agreement with the ground truth. The power spectra of various velocity field components, including velocity magnitude, divergence and vorticity, can be successfully recovered when $k\lesssim 1.1$ $h/\rm Mpc$ (the Nyquist frequency of the simulations) at about 80% accuracy. This approach is very promising and presents an alternative method to correct the redshift-space distortions using the measured 3D spatial information of halos. Additionally, for the reconstruction of the momentum field of halos, UNet achieves similar good results. Hence the applications in various aspects of cosmology are very broad, such as correcting redshift errors and improving measurements in the structure of the cosmic web, the kinetic Sunyaev-Zel'dovich effect, BAO reconstruction, etc.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The peculiar velocities of dark matter halos are crucial to study many issues in cosmology and galaxy evolution. In this study, by using the state-of-the-art deep learning technique, a UNet-based neural network, we propose to reconstruct the peculiar velocity field from the redshift-space distribution of dark matter halos. Through a point-to-point comparison and examination of various statistical properties, we demonstrate that, the reconstructed velocity field is in good agreement with the ground truth. The power spectra of various velocity field components, including velocity magnitude, divergence and vorticity, can be successfully recovered when $k\lesssim 1.1$ $h/\rm Mpc$ (the Nyquist frequency of the simulations) at about 80% accuracy. This approach is very promising and presents an alternative method to correct the redshift-space distortions using the measured 3D spatial information of halos. Additionally, for the reconstruction of the momentum field of halos, UNet achieves similar good results. Hence the applications in various aspects of cosmology are very broad, such as correcting redshift errors and improving measurements in the structure of the cosmic web, the kinetic Sunyaev-Zel'dovich effect, BAO reconstruction, etc.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Jingsong Gao
Xiang Zhang
Yang Wang
Yiqi Fang
Qi Lu
Zheng Li
Yi Liu
Chengyin Wu
Qihuang Gong
Yunquan Liu
Hongbing Jiang
摘要： Structured light has attracted great interest in scientific and technical fields. Here, we demonstrate the first generation of structured air lasing in N2+ driven by 800 nm femtosecond laser pulses. By focusing a vortex pump beam at 800 nm in N2 gas, we generate a vortex superfluorescent radiation of N2+ at 391 nm, which carries the same photon orbital angular momentum as the pump beam. With the injection of a Gaussian seed beam at 391 nm, the coherent radiation is amplified, but the vorticity is unchanged. A new physical mechanism is revealed in the vortex N2+ superfluorescent radiation: the vortex pump beam transfers the spatial spiral phase into the N2+ gain medium, and the Gaussian seed beam picks up the spatial spiral phase and is then amplified into a vortex beam. Moreover, when we employ a pump beam with a cylindrical vector mode, the Gaussian seed beam is correspondingly amplified into a cylindrical vector beam. Surprisingly, the spatial polarization state of the amplified radiation is identical to that of the vector pump beam regardless of whether the Gaussian seed beam is linearly, elliptically, or circularly polarized. Solving three-dimensional coupled wave equations, we show how a Gaussian beam becomes a cylindrical vector beam in a cylindrically symmetric gain medium. This study provides a novel approach to generating structured light via N2+ air lasing.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ziyong Wu
Zhenyu Zhang
Shuyang Pan
Haitao Miao
Xin Wang
Cristiano G. Sabiu
Jaime Forero-Romero
Yang Wang
Xiao-Dong Li
摘要： We develop a deep learning technique to infer the non-linear velocity field from the dark matter density field. The deep learning architecture we use is an "U-net" style convolutional neural network, which consists of 15 convolution layers and 2 deconvolution layers. This setup maps the 3-dimensional density field of $32^3$-voxels to the 3-dimensional velocity or momentum fields of $20^3$-voxels. Through the analysis of the dark matter simulation with a resolution of $2 {h^{-1}}{\rm Mpc}$, we find that the network can predict the the non-linearity, complexity and vorticity of the velocity and momentum fields, as well as the power spectra of their value, divergence and vorticity and its prediction accuracy reaches the range of $k\simeq1.4$ $h{\rm Mpc}^{-1}$ with a relative error ranging from 1% to $\lesssim$10%. A simple comparison shows that neural networks may have an overwhelming advantage over perturbation theory in the reconstruction of velocity or momentum fields.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yang Wang
Nicola R. Napolitano
Weiguang Cui
Xiao-Dong Li
Alexander Knebe
Chris Power
Frazer Pearce
Lin Tang
Gustavo Yepes
Xi Kang
摘要： The star formation history (SFH) of galaxies is critical for understanding galaxy evolution. Hydrodynamical simulations enable us to precisely reconstruct the SFH of galaxies and establish a link to the underlying physical processes. In this work, we present a model to describe individual galaxies' SFHs from three simulations: TheThreeHundred, Illustris-1 and TNG100-1. This model divides the galaxy SFH into two distinct components: the "main sequence" and the "variation". The "main sequence" part is generated by tracing the history of the $SFR-M_*$ main sequence of galaxies across time. The "variation" part consists of the scatter around the main sequence, which is reproduced by fractional Brownian motions. We find that: 1) The evolution of the main sequence varies between simulations; 2) fractional Brownian motions can reproduce many features of SFHs, however, discrepancies still exist; 3) The variations and mass-loss rate are crucial for reconstructing the SFHs of the simulations. This model provides a fair description of the SFHs in simulations. On the other hand, by correlating the fractional Brownian motion model to simulation data, we provide a 'standard' against which to compare simulations.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Implementation of a twin-field quantum key distribution network faces limitations, including the low tolerance of interference errors for phase-matching type protocols and the strict constraint regarding intensity and probability for sending-or-not-sending type protocols. Here, we propose a two-photon twin-field quantum key distribution protocol inspired by multiplexing in quantum repeaters. We achieve twin-field-type two-photon interference through post-matching phase-correlated single-photon interference events. We exploit the non-interference mode as the code mode to highly tolerate interference errors, and the two-photon interference naturally removes the intensity and probability constraint. Therefore, our protocol can transcend the abovementioned limitations while breaking the secret key capacity of repeaterless quantum key distribution. These features are tailored for scalable quantum networks, under which each node with fixed system parameters can dynamically switch different attenuation links. Simulations show that for a four-user network, the key rates of our protocol for all six links can either exceed or approach the secret key capacity. However, the key rates of all links are lower than the key capacity when using phase-matching type protocols. Additionally, four of the links could not extract the key when using sending-or-not-sending type protocols. We anticipate that our protocol can facilitate the development of practical and efficient quantum networks.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Shuren Zhou
Zhenjie Liu
Qinglin Ma
Yu Liu
Le Zhang
Xiao-Dong Li
Yang Wang
Xin Wang
Yu Yu
Hao-Ran Yu
Yi Zheng
摘要： We investigate impacts of massive neutrinos on the cosmic velocity fields, employing high-resolution cosmological $N$-body simulations provided by the information-optimized CUBE code, where cosmic neutrinos are evolved using collisionless hydrodynamics and their perturbations can be accurately resolved. In this study we focus, for the first time, on the analysis of massive-neutrino induced suppression effects in various cosmic velocity field components of velocity magnitude, divergence, vorticity and dispersion. By varying the neutrino mass sum $M_\nu$ from 0 -- 0.4 eV, the simulations show that, the power spectra of vorticity -- exclusively sourced by non-linear structure formation that is affected by massive neutrinos significantly -- is very sensitive to the mass sum, which potentially provide novel signatures in detecting massive neutrinos. Furthermore, using the chi-square statistic, we quantitatively test the sensitivity of the density and velocity power spectra to the neutrino mass sum. Indeed, we find that, the vorticity spectrum has the highest sensitivity, and the null hypothesis of massless neutrinos is incompatible with both vorticity and divergence spectra from $M_\nu=0.1$ eV at high significance ($p$-value $= 0.03$ and $0.07$, respectively). These results demonstrate clearly the importance of peculiar velocity field measurements, in particular of vorticity and divergence components, in determination of neutrino mass and mass hierarchy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Zijie Yu
Furen Deng
Shijie Sun
Chenhui Niu
Jixia Li
Fengquan Wu
Wei-Yang Wang
Yougang Wang
Hui Feng
Lin Shu
Jie Hao
Reza Ansari
Albert Stebbins
Xuelei Chen
摘要： The Tianlai Dish Pathfinder array is a radio interferometer array consisting of 16 six meter dish antennas. The original digital backend integration time is at the seconds level, designed for HI intensity mapping experiment. A new digital backend with millisecond response is added to enable it to search for fast radio burst (FRB) during its observations. The design and calibration of this backend, and the real time search pipeline for it are described in this paper. It is capable of forming 16 digital beams for each linear polarisation, covering an area of 19.6 square degrees. The search pipeline is capable of searching for, recording and classifying FRBs automatically in real time. In commissioning, we succeeded in capturing the signal pulses from the pulsars PSR B0329+54 and B2021+51.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Zijie Yu
Furen Deng
Shijie Sun
Chenhui Niu
Jixia Li
Fengquan Wu
Wei-Yang Wang
Yougang Wang
Hui Feng
Lin Shu
Jie Hao
Reza Ansari
Albert Stebbins
Xuelei Chen
摘要： The Tianlai Dish Pathfinder array is a radio interferometer array consisting of 16 six meter dish antennas. The original digital backend integration time is at the seconds level, designed for HI intensity mapping experiment. A new digital backend with millisecond response is added to enable it to search for fast radio burst (FRB) during its observations. The design and calibration of this backend, and the real time search pipeline for it are described in this paper. It is capable of forming 16 digital beams for each linear polarisation, covering an area of 19.6 square degrees. The search pipeline is capable of searching for, recording and classifying FRBs automatically in real time. In commissioning, we succeeded in capturing the signal pulses from the pulsars PSR B0329+54 and B2021+51.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Xuan Mao
Hong Yang
Dan Long
Min Wang
Peng-Yu Wen
Yun-Qi Hu
Bo-Yang Wang
Gui-Qin Li
Jian-Cun Gao
Gui-Lu Long
摘要： The highly efficient coupling of light from conventional optical components to optical mode volumes lies in the heart of chip-based micro-devices, which is determined by the phase-matching between propagation constants of fiber taper and the whispering-gallery-mode (WGM) of the resonator. Optical gyroscopes, typically realized as fiber-optic gyroscopes and ring-laser gyroscopes, have been the mainstay in diverse applications such as positioning and inertial sensing. Here, the phase-matching is theoretically analyzed and experimentally verified. We observe Sagnac effect in a millimeter-scale wedged resonator gyroscope which has attracted considerable attention and been rapidly promoted in recent years. We demonstrate a bidirectional pump and probe scheme, which directly measures the frequency beat caused by the Sagnac effect. We establish the linear response between the detected beat frequency and the rotation velocity. The clockwise and counterclockwise rotation can also be distinguished according to the value of the frequency beat. The experimental results verify the feasibility of developing gyroscope in WGM resonator system and pave the way for future development.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Yuan-Mei Xie
Yu-Shuo Lu
Chen-Xun Weng
Xiao-Yu Cao
Zhao-Ying Jia
Yu Bao
Yang Wang
Yao Fu
Hua-Lei Yin
Zeng-Bing Chen
摘要： Twin-field quantum key distribution can overcome the secret key capacity of repeaterless quantum key distribution via single-photon interference. However, to compensate for the channel fluctuations and lock the laser fluctuations, the techniques of phase tracking and phase locking are indispensable in experiment, which drastically increase experimental complexity and hinder free-space realization. Inspired by the duality in entanglement, we herein present an asynchronous measurement-device-independent quantum key distribution protocol that can surpass the secret key capacity even without phase tracking and phase locking. Leveraging the concept of time multiplexing, asynchronous two-photon Bell-state measurement is realized by postmatching two interference detection events. For a 1 GHz system, the new protocol reaches a transmission distance of 450 km without phase tracking. After further removing phase locking, our protocol is still capable of breaking the capacity at 270 km. Intriguingly, when using the same experimental techniques, our protocol has a higher key rate than the phase-matching-type twin-field protocol. In the presence of imperfect intensity modulation, it also has a significant advantage in terms of the transmission distance over the sending-or-not-sending type twin-field protocol. With high key rates and accessible technology, our work provides a promising candidate for practical scalable quantum communication networks.
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