分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We quantitatively study how the primordial density fluctuations are imprinted on the anisotropy of the phase transition gravitational wave (PTGW). Generated long before recombination and free from Silk damping, the anisotropic PTGW might reveal the density perturbation seeded from inflation or alternatives. We find new behaviors of the PTGW anisotropy power spectrum. The PTGW anisotropy is stronger than the anisotropy of the cosmic microwave background temperature at all scales, and the high-$\ell$ multiples are enhanced about 1 order due to the early integrated Sachs-Wolfe effect. Furthermore, differences in primordial power spectra at small scales manifest themselves more significantly on the angular power spectrum of PTGW anisotropy compared to that of the cosmic microwave background. These properties might provide a novel clue to understanding the primordial density perturbation of our early Universe and thereby complete our understanding of inflation theory. Taking nanohertz PTGW from dark matter models as a typical example, we obtain amplitudes of PTGW anisotropy which are about 4 or 3 orders weaker than the isotropic PTGW energy spectra.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The energy budget of cosmological first-order phase transition is essential for the gravitational wave spectra. Most of the previous studies are based on the bag model with same sound velocity in the symmetric and broken phase. We study the energy budget and the corresponding gravitational wave spectra beyond the bag model, where the sound velocities could be different in the symmetric and broken phase. Taking the Higgs sextic effective model as a representative model, we calculate the sound velocities in different phase, the gravitational wave spectra and the signal-to-noise ratio for different combinations of phase transition parameters beyond the bag model. We compare these new results with the ones obtained from the bag model.The proper sound velocities and phase transition parameters at the appropriate temperature are important to obtain more precise predictions.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: A cosmological first-order phase transition gravitational wave could provide a novel approach to studying the early Universe. In most cases, the acoustic gravitational wave from the sound wave mechanism is dominant. Considering different sound velocities in symmetric and broken phases, we study sound velocity effects on the acoustic phase transition gravitational wave spectra in the sound shell model. We demonstrate that different sound velocities could obviously modify the peak frequency and peak amplitude of the gravitational wave power spectra. Therefore, taking more realistic sound velocities might provide more accurate predictions for various gravitational wave experiments.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Manipulating bosonic condensates with electric fields is very challenging as the electric fields do not directly interact with the neutral particles of the condensate. Here we demonstrate a simple electric method to tune the vorticity of exciton polariton condensates in a strong coupling liquid crystal (LC) microcavity with CsPbBr$_3$ microplates as active material at room temperature. In such a microcavity, the LC molecular director can be electrically modulated giving control over the polariton condensation in different modes. For isotropic non-resonant optical pumping we demonstrate the spontaneous formation of vortices with topological charges of +1, +2, -2, and -1. The topological vortex charge is controlled by a voltage in the range of 1 to 10 V applied to the microcavity sample. This control is achieved by the interplay of a built-in potential gradient, the anisotropy of the optically active perovskite microplates, and the electrically controllable LC molecular director in our system with intentionally broken rotational symmetry. Besides the fundamental interest in the achieved electric polariton vortex control at room temperature, our work paves the way to micron-sized emitters with electric control over the emitted light's phase profile and quantized orbital angular momentum for information processing and integration into photonic circuits.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Gating techniques have been widely used for the generation of isolated attosecond pulses(IAPs) by limiting the high harmonics generation(HHG) within one optical cycle of the driving laser. However, as only one optical cycle is taken advantaged, the IAP the energy can hardly be enhanced by using a long driving pulse. In this letter, we present a regime named pumping ionizing gating(PIG) to generate IAPs. Instead of traditional ionizing gating, a long pump dynamically reflected by fast-extending plasma grating(FEPG) is employed to continuously inject the energy to the driving(ionizing) pulse. The overlapping region of the pump reflection and frequency upconversion forms a narrow PIG, which opens a door to transfer the long-pump energy to IAPs. This regime is demonstrated by the particle-in-cell(PIC) simulation, at extremely wide plasma densities(0.02nc-0.5nc) and FEPG modulation depths(10%-60%). The three dimensional(3D) simulation shows a 330 as laser pulse is obtained by a 1.6-ps 1-$\mu$m pump, with the peak intensity 33 times as the pump, and a conversion efficiency around 0.1%.