• Besov Estimates for Sub-elliptic Equations in the Heisenberg Group

    分类: 数学 >> 应用数学 提交时间: 2024-02-22

    摘要: 本文研究Heisenberg群上非退化散度型次椭圆方程弱解的正则性。基于系数矩阵更一般的假设,本文针对齐次与非齐次两种情形,建立弱解在Besov空间中的水平Calderon-Zygmund估计。本文的研究将丰富发展Heisenberg群上非线性Calderon-Zygmund正则性理论。

  • Constraining light dark matter upscattered by ultrahigh-energy cosmic rays

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Light halo dark matter (DM) particles upscattered by high-energy cosmic rays (CRs) can be energetic, and become detectable by conventional direct detection experiments. The current constraints derived from space-based direct CR measurements can reach $\mathcal{O}(10^{-31})\text{ cm}^{2}$ for a constant DM-nucleon scattering cross section. We show that if the CR energy spectrum follows a power law of type $\sim E^{-3}$, the derived constraints on the scattering cross section will be highly insensitive to DM particle mass. This suggests that ultrahigh-energy CRs (UHECRs) indirectly measured by ground-based detectors can be used to place constraints on ultralight DM particles, as $E^{-3}$ is a very good approximation of the UHECR energy spectrum up to energy $\sim10^{20}\text{ eV}$. Using the recent UHECR flux data, we show that the current constraints derived from space-based CR measurements can in principle be extended to ultralight DM particles far below eV scale.

  • Cavity optomechanical bistability with an ultrahigh reflectivity photonic crystal membrane

    分类: 光学 >> 量子光学 提交时间: 2023-02-19

    摘要: Photonic crystal (PhC) membranes patterned with sub-wavelength periods offer a unique combination of high reflectivity, low mass, and high mechanical quality factor. We demonstrate a PhC membrane that we use as one mirror of a Fabry-Perot cavity with finesse as high as $F=35,000(500)$, corresponding to a record high PhC reflectivity of $R=0.999835(6)$. The fundamental mechanical frequency is 426 kHz, more than twice the optical linewidth, placing it firmly in the resolved-sideband regime. The mechanical quality factor in vacuum is $Q=1.1(1)\times 10^6$, allowing us to achieve values of the single-photon cooperativity as high as ${\cal C}_0=6.6\times10^{-3}$. We easily see optomechanical bistability as hysteresis in the cavity transmission. As the input power is raised well beyond the bistability threshold, dynamical backaction induces strong mechanical oscillation above 1~MHz, even in the presence of air damping. This platform will facilitate advances in optomechanics, precision sensing, and applications of optomechanically-induced bistability.

  • Pseudo-Dirac Sterile Neutrino Dark Matter

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: Sterile neutrino is a promising dark matter (DM) candidate. However the parameter space of this scenario has almost been ruled out by the X-ray observation results whenever the sterile neutrino is solely produced by the Dodelson-Widrow (DW) mechanism in the early Universe. In this letter we propose an extension to the minimal sterile neutrino DM model by introducing the pseudo-Dirac sterile neutrino, which implies the existence of two nearly degenerate Majorana states $\hat N_{1,2}^{}$, and a permutation symmetry. The heavy state $\hat N_1$ is produced via the DW mechanism, and the light state $\hat N_2$, which serves as the DM, is produced from the decay of $\hat N_1$ in the early Universe. The X-ray constraint is avoided by the permutation symmetry, which forbidden the two-body decay of the DM into active neutrinos and photon. A promising signal of this scenario is the effective number of neutrino species, which will be precisely measured in future experiments, such as CMB stage IV. We further study the impact of this model on the cosmological parameters. The Markov Chain Monte Carlo analysis for the Planck + BAO+R19 data gives $H_0=69.2_{-0.59}^{+0.58}$, which may relieve the Hubble tension.

  • Long-range self-interacting dark matter in the Sun

    分类: 物理学 >> 核物理学 提交时间: 2016-09-13

    摘要: We investigate the implications of the long-rang self-interaction on both the self-capture and the annihilation of the self-interacting dark matter (SIDM) trapped in the Sun. Our discussion is based on a specific SIDM model in which DM particles self-interact via a light scalar mediator, or Yukawa potential, in the context of quantum mechanics. Within this framework, we calculate the self-capture rate across a broad region of parameter space. While the self-capture rate can be obtained separately in the Born regime with perturbative method, and the classical limits with the Rutherford formula, our calculation covers the gap between in a non-perturbative fashion. Besides, the phenomelogy of both the Sommerfeld-enhanced s- and p-wave annihilation of the solar SIDM is also involved in our discussion. Moreover, by combining the analysis of the Super-Kamiokande (SK) data and the observed DM relic density, we constrain the nuclear capture rate of the DM particles in the presence of the dark Yukawa potential. The consequence of the long-range dark force on probing the solar SIDM turns out to be significant if the force-carrier is much lighter than the DM particle, and a quantitative analysis is provided.

  • Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要: The origin of water on the Earth is a long-standing mystery, requiring a comprehensive search for hydrous compounds, stable at conditions of the deep Earth and made of Earth-abundant elements. Previous studies usually focused on the current range of pressure-temperature conditions in the Earth's mantle and ignored a possible difference in the past, such as the stage of the core-mantle separation. Here, using ab initio evolutionary structure prediction, we find that only two magnesium hydrosilicate phases are stable at megabar pressures, $\alpha$-Mg$_2$SiO$_5$H$_2$ and $\beta$-Mg$_2$SiO$_5$H$_2$, stable at 262-338 GPa and >338 GPa,respectively (all these pressures now lie within the Earth's iron core). Both are superionic conductors with quasi-one-dimensional proton diffusion at relevant conditions. In the first 30 million years of Earth's history, before the Earth's core was formed, these must have existed in the Earth, hosting much of Earth's water. As dense iron alloys segregated to form the Earth's core, Mg$_2$SiO$_5$H$_2$ phases decomposed and released water. Thus, now-extinct Mg$_2$SiO$_5$H$_2$ phases have likely contributed in a major way to the evolution of our planet.

  • Fully-integrated multipurpose microwave frequency identification system on a single chip

    分类: 光学 >> 量子光学 提交时间: 2023-02-19

    摘要: We demonstrate a fully-integrated multipurpose microwave frequency identification system on silicon-on-insulator platform. Thanks to its multipurpose features, the chip is able to identify different types of microwave signals, including single-frequency, multiple-frequency, chirped and frequency-hopping microwave signals, as well as discriminate instantaneous frequency variation among the frequency-modulated signals. This demonstration exhibits fully integrated solution and fully functional microwave frequency identification, which can meet the requirements in reduction of size, weight and power for future advanced microwave photonic processor.