The electron-cyclotron maser （ECM） emission driven by nonthermal electrons is one of the most crucial mechanisms responsible for radio emissions in magnetized planets, for the interplanetary medium （IPM） and for t...The electron-cyclotron maser （ECM） emission driven by nonthermal electrons is one of the most crucial mechanisms responsible for radio emissions in magnetized planets, for the interplanetary medium （IPM） and for the laboratory microwave generation devices. Major astrophysical observations demonstrate that nonthermal electrons frequently have a negative power-law spectrum with a lower energy cutoff and anisotropic distribution in the velocity space. In this paper, the effects of power-law spectrum behaviors of electrons on a ring-beam maser emission are considered. The results show that the growth rates of O1 and X2 modes decrease rapidly for small A （the dispersion of momentum u）. Because of the lower energy cutoff behavior, the nonthermal electrons with large a still can excite the ECM instability efficiently. The present analysis also includes the effects of parameter β （βu0 is the dispersion of perpendicular momentum ui, u0 the average value of u） on the instability. The growth rate of X2 mode decreases with parameter v0 （v0 = u⊥o/uo, U⊥0 is the average value of u⊥）. But for O1 mode, the relationship between the growth rate and v0 is complicated. It also shows that the growth rates are very sensitive to frequency ratio Ω （frequency ratio of electron cyclotron frequency to plasma frequency）.展开更多
Recently,Riess et al.[1]reported the new result of local measurement of the Hubble constant,H_0=(73.00±1.75)km s^(-1) Mpc^(-1),which is 3.3σhigher than the fit result of ocal measurement of the Hubble constant, ...Recently,Riess et al.[1]reported the new result of local measurement of the Hubble constant,H_0=(73.00±1.75)km s^(-1) Mpc^(-1),which is 3.3σhigher than the fit result of ocal measurement of the Hubble constant, H_0 = (73.00 ± 1.75) km s^(-1) Mpc^(-1), which is 3.3σ higher than the fit result of (66.93±0.62) km s^(-1) Mpc^(-1) derived by the Planck collaboration based on theΛCDM model withmν=0.06 e V using the latest Planck CMB data.The tension between the latest H0measurement and the Planck data has inspired numerous discussions.On one hand,it might be caused by some systematic uncertainties in the measurements.On the other hand,perhaps one has omitted some unknown physical factors in the cosmological model,which leads to some inconsistencies among different data sets.For example,replacing the cosmological constant with a dynamical dark energy[2]and considering the extra relativistic degrees of freedom(i.e.,an additional parameter Neff)[1,3,4]both can help relieve this tension to some extent.It was also shown in ref.[4]that the involvement of light sterile neutrinos in the cosmological model can simultaneously relieve almost all the tensions among the current astrophysical observations,which leads to a new cosmic concordance.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10973043 and 41074107)the Ministry of Science and Technology of China (Grant No. 2011CB811402)the Key Laboratory of Solar Activity at National Astronomical Observatories,CAS
文摘The electron-cyclotron maser （ECM） emission driven by nonthermal electrons is one of the most crucial mechanisms responsible for radio emissions in magnetized planets, for the interplanetary medium （IPM） and for the laboratory microwave generation devices. Major astrophysical observations demonstrate that nonthermal electrons frequently have a negative power-law spectrum with a lower energy cutoff and anisotropic distribution in the velocity space. In this paper, the effects of power-law spectrum behaviors of electrons on a ring-beam maser emission are considered. The results show that the growth rates of O1 and X2 modes decrease rapidly for small A （the dispersion of momentum u）. Because of the lower energy cutoff behavior, the nonthermal electrons with large a still can excite the ECM instability efficiently. The present analysis also includes the effects of parameter β （βu0 is the dispersion of perpendicular momentum ui, u0 the average value of u） on the instability. The growth rate of X2 mode decreases with parameter v0 （v0 = u⊥o/uo, U⊥0 is the average value of u⊥）. But for O1 mode, the relationship between the growth rate and v0 is complicated. It also shows that the growth rates are very sensitive to frequency ratio Ω （frequency ratio of electron cyclotron frequency to plasma frequency）.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11522540, and 11690021)the Top-Notch Young Talents Program of China, and the Provincial Department of Education of Liaoning (Grant No. L2012087)
文摘Recently,Riess et al.[1]reported the new result of local measurement of the Hubble constant,H_0=(73.00±1.75)km s^(-1) Mpc^(-1),which is 3.3σhigher than the fit result of ocal measurement of the Hubble constant, H_0 = (73.00 ± 1.75) km s^(-1) Mpc^(-1), which is 3.3σ higher than the fit result of (66.93±0.62) km s^(-1) Mpc^(-1) derived by the Planck collaboration based on theΛCDM model withmν=0.06 e V using the latest Planck CMB data.The tension between the latest H0measurement and the Planck data has inspired numerous discussions.On one hand,it might be caused by some systematic uncertainties in the measurements.On the other hand,perhaps one has omitted some unknown physical factors in the cosmological model,which leads to some inconsistencies among different data sets.For example,replacing the cosmological constant with a dynamical dark energy[2]and considering the extra relativistic degrees of freedom(i.e.,an additional parameter Neff)[1,3,4]both can help relieve this tension to some extent.It was also shown in ref.[4]that the involvement of light sterile neutrinos in the cosmological model can simultaneously relieve almost all the tensions among the current astrophysical observations,which leads to a new cosmic concordance.
