分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We study the effect of baryons on the cosmic web -- halos, filaments, walls, and voids. To do so, we apply a modified version of NEXUS, a cosmic web morphological analysis algorithm, to the IllustrisTNG simulations. We find that halos lose more than $10\%$ of their mass due to baryons, mostly to filaments and a small portion to walls and voids. However, the mass transfer does not significantly shift the boundaries of structures, leaving the volume fractions of the cosmic structures largely unaffected. We quantify the effects of baryonic feedback on the power spectrum and the probability density function (PDF) of the density field for individual cosmic structures. For the power spectrum, most suppression due to feedback can be accounted for by including $M\ge10^{12}~M_\odot/h$ halos, without considering other cosmic structures. However, when examining the PDF of the density field, we find nearly $100\%$ suppression of the emptiest regions and $10\%$-level effects (boost or suppression) in the remaining regions of filaments, walls, and voids. Our results indicate the importance of modeling the effects of baryons in the whole cosmic web, not just halos, for cosmological analysis beyond two-point statistics or field-based inferences.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dark photon as an ultralight dark matter candidate can interact with the Standard Model particles via kinetic mixing. We propose to search for the ultralight dark photon dark matter using radio telescopes with solar observations. The dark photon dark matter can efficiently convert into photons in the outermost region of the solar atmosphere, the solar corona, where the plasma mass of photons is close to the dark photon rest mass. Due to the strong resonant conversion and benefiting from the short distance between the Sun and the Earth, the radio telescopes can lead the dark photon search sensitivity in the mass range of $4 \times 10^{-8} - 4\times 10^{-6} \, \rm{eV}$, corresponding to the frequency $10 - 1000 \, {\rm MHz}$. As a promising example, the operating radio telescope LOFAR can reach the kinetic mixing $\epsilon \sim 10^{-13}$ ($10^{-14}$) within 1 (100) hour solar observations. The future experiment SKA phase 1 can reach $\epsilon \sim 10^{-16} - 10^{-14}$ with $1$ hour solar observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ultralight axions and dark photons are well-motivated dark matter (DM) candidates. The axion DM and dark photon DM (DPDM) can resonantly convert into electromagnetic (EM) waves in the solar corona when their mass is equal to the solar plasma frequency. The resultant EM waves are mono-chromatic in the radio-frequency range with an energy equal to the DM mass, which can be detected via radio telescopes for solar observations. We search for converted mono-chromatic signals in the observational data of the high-sensitivity Low Frequency Array (LOFAR) telescope. We find the upper limit on the kinetic mixing coupling between DPDM and photon can reach $10^{-13}$ in the frequency range $30-80$ MHz, which is about one order of magnitude better than the existing constraint from the cosmic microwave background (CMB) observation. In addition, we also get the upper limit on the axion-photon coupling in the same frequency range, which is better than the constraints from Light-Shining-through-a-Wall experiments but does not exceed the CAST or other astrophysical bounds.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The weakly interacting massive particles (WIMPs) have been the most popular particle dark matter (DM) candidate for the last several decades, and it is well known that WIMP can be probed via the direct, indirect and collider experiments. However, the direct and indirect signals are highly suppressed in some scalar-mediated DM models, e.g. the lepton portal model with a Majorana DM candidate. As a result, collider searches are considered as the only hope to probe such models. In this white paper, we propose that the gravitational wave (GW) astronomy also serves as a powerful tool to probe such scalar mediated WIMP models via the potential first-order phase transition GW signals. An example for the lepton portal dark matter is provided, showing the complementarity between collider and GW probes.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ultralight axions and dark photons are well-motivated dark matter (DM) candidates. The axion DM and dark photon DM (DPDM) can resonantly convert into electromagnetic (EM) waves in the solar corona when their mass is equal to the solar plasma frequency. The resultant EM waves are mono-chromatic in the radio-frequency range with an energy equal to the DM mass, which can be detected via radio telescopes for solar observations. We search for converted mono-chromatic signals in the observational data of the high-sensitivity Low Frequency Array (LOFAR) telescope. We find the upper limit on the kinetic mixing coupling between DPDM and photon can reach $10^{-13}$ in the frequency range $30-80$ MHz, which is about one order of magnitude better than the existing constraint from the cosmic microwave background (CMB) observation. In addition, we also get the upper limit on the axion-photon coupling in the same frequency range, which is better than the constraints from Light-Shining-through-a-Wall experiments but does not exceed the CAST or other astrophysical bounds.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dark photon can be the ultralight dark matter candidate, which can interact with the Standard Model particles via the kinetic mixing. We propose to look for ultralight dark photon dark matter (DPDM) with local absorption at the radio telescope. The DPDM induces an harmonic oscillation of the electrons in the antenna of a radio telescope, which induces a monochromatic radio signal, and will be recorded by the telescope detectors. We show that with this method, the upper limit from the observation data of the FAST telescope on the kinetic mixing can already reach $10^{-12}$ for DPDM with oscillation frequency range $1-1.5$ GHz, stronger than the CMB constraint by about one order of magnitude. We also show that with large scale interferometric arrays the LOFAR and SKA1 telescopes can achieve extraordinary sensitivities for DPDM from 10 MHz to 10 GHz, and provide a competing and complementary method to search for DPDM directly.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We study the effect of super-sample covariance (SSC) on the power spectrum and higher-order statistics: bispectrum, halo mass function, and void size function. We also investigate the effect of SSC on the cross-covariance between the statistics. We consider both the matter and halo fields. Higher-order statistics of the large-scale structure contain additional cosmological information beyond the power spectrum and are a powerful tool to constrain cosmology. They are a promising probe for ongoing and upcoming high precision cosmological surveys such as DESI, PFS, Rubin Observatory LSST, Euclid, SPHEREx, SKA, and Roman Space Telescope. Cosmological simulations used in modeling and validating these statistics often have sizes that are much smaller than the observed Universe. Density fluctuations on scales larger than the simulation box, known as super-sample modes, are not captured by the simulations and in turn can lead to inaccuracies in the covariance matrix. We compare the covariance measured using simulation boxes containing super-sample modes to those without. We also compare with the Separate Universe approach. We find that while the power spectrum, bispectrum and halo mass function show significant scale- or mass-dependent SSC, the void size function shows relatively small SSC. We also find significant SSC contributions to the cross-covariances between the different statistics, implying that future joint-analyses will need to carefully take into consideration the effect of SSC.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Observation of Interplanetary Scintillation (IPS) provides an important and effective way to study the solar wind and the space weather. A series of IPS observations were conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The extraordinary sensitivity and the wide frequency coverage make FAST an ideal platform for IPS studies. In this paper we present some first scientific results from FAST observations of IPS with the L-band receiver. Based on the solar wind velocity fitting values of FAST observations on September 26-28, 2020, we found that the velocity decreases with increasing frequency linearly, which has not yet been reported in literature. And we have also detected a variation of solar wind velocity on a timescale of 3-5 minutes, which imply the slow change of the background solar wind, a co-existence of high- and low-speed streams, or a reflect of the quasi-periodic electron-density fluctuations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Observations of Interplanetary Scintillation (IPS) are an efficient remote-sensing method to study the solar wind and inner heliosphere. From 2016 to 2018, some distinctive observations of IPS sources like 3C 286 and 3C 279 were accomplished with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single-dish telescope in the world. Due to the 270-1620 MHz wide frequency coverage of the Ultra-Wideband (UWB) receiver, one can use both single-frequency and dual-frequency analyses to determine the projected velocity of the solar wind. Moreover, based on the extraordinary sensitivity owing to the large collecting surface area of FAST, we can observe weak IPS signals. With the advantages of both the wider frequency coverage and high sensitivity, also with our radio frequency interference (RFI) mitigation strategy and an optimized model-fitting method developed, in this paper, we analyze the fitting confidence intervals of the solar wind velocity, and present some preliminary results achieved using FAST, which points to the current FAST system being highly capable of carrying out observations of IPS
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Dang Yao
Yuan-Wei Wu
Bo Zhang
Jing Sun
Yan Sun
Shuang-Jing Xu
Jia Liu
Lang-Ming Ma
Jian-Jun Gong
Ying Yang
Xu-Hai Yang
摘要： In order to measure the Universal Time (UT1) in real time, National Time Service Center (NTSC) has built a VGOS-like (VLBI Global Observing System) broadband VLBI network, which includes three 13-m radio telescopes located in Jilin, Sanya and Kashi, and a data analysis center in Xi'an. Each station is equipped with a highly stable hydrogen atomic clock and a self-developed VLBI backend, and is co-located with two GPS receivers. This VGOS-like VLBI network may play an important role in improving the Chinese broadband VLBI technology and making valuable contributions to domestic VLBI measurements of UT1. In this paper, we introduce the specifications of this VLBI network, and present the UT1 measurements at C-band conducted in 2018 using the Jilin-Kashi baseline of this network. The comparisons between our UT1 estimates and those provided by IERS suggest that the NTSC VLBI network is capable to determine UT1 accurate at the level of 58.8 microseconds.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Dang Yao
Yuan-Wei Wu
Bo Zhang
Jing Sun
Yan Sun
Shuang-Jing Xu
Jia Liu
Lang-Ming Ma
Jian-Jun Gong
Ying Yang
Xu-Hai Yang
摘要： In order to measure the Universal Time (UT1) in real time, National Time Service Center (NTSC) has built a VGOS-like (VLBI Global Observing System) broadband VLBI network, which includes three 13-m radio telescopes located in Jilin, Sanya and Kashi, and a data analysis center in Xi'an. Each station is equipped with a highly stable hydrogen atomic clock and a self-developed VLBI backend, and is co-located with two GPS receivers. This VGOS-like VLBI network may play an important role in improving the Chinese broadband VLBI technology and making valuable contributions to domestic VLBI measurements of UT1. In this paper, we introduce the specifications of this VLBI network, and present the UT1 measurements at C-band conducted in 2018 using the Jilin-Kashi baseline of this network. The comparisons between our UT1 estimates and those provided by IERS suggest that the NTSC VLBI network is capable to determine UT1 accurate at the level of 58.8 microseconds.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Chun-Yu Li
Si-Jia Liu
Bing-Shi Yu
Hai-Jun Wu
Carmelo Rosales-Guzmán
Yijie Shen
Peng Chen
Zhi-Han Zhu
Yan-Qing Lu
摘要： Reciprocal spin-orbit coupling (SOC) via geometric phase with flat optics provides a promising platform for shaping and controlling paraxial structured light. Current devices, from the pioneering q-plates to the recent J-plates, provide only spin-dependent wavefront modulation without amplitude control. However, achieving control over all the spatial dimensions of paraxial SOC states requires spin-dependent control of corresponding complex amplitude, which remains challenging for flat optics. Here, to address this issue, we present a new type of flat-optics elements termed structured geometric phase gratings that is capable of conjugated complex-amplitude control for orthogonal input circular polarizations. By using a microstructured liquid crystal photoalignment technique, we engineered a series of flat-optics elements and experimentally showed their excellent precision in arbitrary SOC control. This principle unlocks the full-field control of paraxial structured light via flat optics, providing a promising way to develop an information exchange and processing units for general photonic SOC states, as well as extra-/intracavity mode convertors for high-precision laser beam shaping.
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