Energy and momentum losses in the process of neutrino scattering on plasma electrons in the presence of a magnetic field

The neutrino-electron scattering in a dense degenerate magnetized plasma under the conditions μ ² > 2eB ≫ μE is investigated. The volume density of the neutrino energy and momentum losses due to this process are calculated. The results we have obtained demonstrate that plasma in the presence of an external magnetic field is more transparent for neutrino than for non-magnetized plasma. It is shown that neutrino scattering under conditions considered does not lead to the neutrino force acting on plasma.     

A Possibility for Studying Gravitational Properties of the Neutrino

We consider the effect that the gravitational field of a neutrino pulse radiated in the collapse of presupernova nuclei has on the observable optical radiation spectra of atoms at the supernova surface. We show that at the modern level of development of experimental methods, neutrino monitoring supplemented by optical monitoring of supernova candidates provides a unique possibility to check whether the Einstein equivalence principle is satisfied for neutrinos of each of the three types (electron, muon, and tau-lepton) and their antiparticles, to estimate the change of the gravitational potential at the surface of the star at the instant of the neutrino radiation pulse, and to obtain upper limits on the mass values of these neutrinos in a new way.     

用HI-13串列加速器质谱装置测量182Hf的研究

¹⁸²Hf的半衰期为(8.90±0.09)Ma, 是一个接近灭绝的放射性核素. 超新星爆炸是自然界中已知的惟一能产生¹⁸²Hf的途径. 因此¹⁸²Hf是研究近1亿年来在地球附近可能发生的超新星事件的理想核素. 另外, ¹⁸²Hf是核工程中特别感兴趣的一个长寿命放射性核素. 精确测量超痕量的¹⁸²Hf对反应堆的设计和核天体物理学以及其他研究领域都是非常重要的. 用加速器质谱有可能实现对超低含量¹⁸²Hf的测量. 在中国原子能科学研究院的HI-13加速器质谱装置上对¹⁸²Hf的测量方法以及样品的化学去钨方法进行了研究, 分别得到了空白样品以及系列标准样品的¹⁸²Hf和¹⁸³W的能量-飞行时间双维谱. ¹⁸²W对¹⁸²Hf计数的贡献是通过测量¹⁸³W的计数归一扣除的. 目前本工作对¹⁸²Hf的测量灵敏度为4.15±10^－11 (¹⁸²Hf/¹⁸⁰Hf比值).     

Relevance of thermally populated first excited state of 44Ti to the abundance problem of cassiopiea A: A model study

We examine the possible role of electron-capture on the thermally populated first 2⁺ excited state of ⁴⁴Ti in hot astrophysical environments pertaining to post explosive nucleosynthesis supernova debris. We find in a simple schematic model that the astrophysical weak interaction rate for electron-capture decay of ⁴⁴Ti can depend considerably on temperature and hence on time. We propose a time varying decay rate for the evolving supernova debris and demonstrate its consequence for the ⁴⁴Ti mass yield of the supernova Cas A, observed through the measured 1.157 MeV γ-ray flux from the electron-capture decay of ⁴⁴Ti.     

Determination of cosmological parameters: An introduction for non-specialists

I start by defining the cosmological parameters H ₀, Θ _m and Θ_A. Then I show how the age of the universe depends on them, followed by the evolution of the scale parameter of the universe for various values of the density parameters. Then I define strategies for measuring them, and show the results for the recent determination of these parameters from measurements on supernovas of type 1a. Implications for particle physics is briefly discussed at the end.     

超新星的前身星阶段fp壳层的电子俘获

基于核的壳层模型，本文讨论了大质量恒星的超新星前身星阶段核的fp壳层电子俘获，分析中引入了一高斯函数来表征Gamow-Teller跃迁强度分布，结果表明，由于这一修正，在高密度下，电子俘获率较前人给出的结果有较大幅度的增加。     

γ射线暴的最新研究进展:火球模型、余辉及前身星

γ射线暴（称简γ暴）的研究在最近几年里有了巨大的突破。观测上，人们发现了γ暴的低能余辉以及与γ射线发同时的光学爆发，还发现了它位于宇学距离的寄主星系。越来越多的观测证据还表明长时标γ暴与恒星形成区、甚至可能与超新星成协。在γ暴的相对论火球模型框架下，人们对γ暴以及余辉的产生机制的认识也有了进展。进而人们对γ暴的前身星以及环境效应等有了新的认识。本文旨在对这些进展和认识给一个扼要的评述。     

Model flames in the Boussinesq limit: Rising bubbles

Using the Boussinesq buoyancy approximation, we study a bubble of reaction products rising in the reactant fluid under the influence of gravity. Reaction on the surface of the bubble (the flame) results in an increase of the volume of the bubble. We consider fluids with low Prandtl and high Froude numbers (heat diffusion dominates over viscous dissipation, and burning dominates over gravitational effects). We show that, under these conditions, all initially small bubbles follow the same growth pattern, regardless of the flame speed, the reaction type, the gravity, the viscosity, the initial size, and, to some extent, the initial shape of the bubble. In the initial stage of this similarity solution a bubble grows radially in an essentially motionless fluid until it reaches some critical size, which is determined by the laminar flame speed, the gravitational acceleration, and the Atwood number. Once the bubble reaches the critical size, convection becomes significant and the bubble evolves into a more complicated, mushroom-like shape. The similarity solution is expressed using the critical bubble size for the unit length and the critical size divided by the laminar flame speed as the unit time.     

Anisotropy Effects and Observational Data on the Constraints of Evolution Dark Energy Models

We investigate cosmological dark energy models where the accelerated expansion of the universe is driven by a field with an anisotropic universe. The constraints on the parameters are obtained by maximum likelihood analysis using observational of 194 Type Ia supernovae(SNIa) and the most recent joint light-curve analysis(JLA) sample. In particular we reconstruct the dark energy equation of state parameter w(z) and the deceleration parameter q(z). We find that the best fit dynamical w(z) obtained from the 194 SNIa dataset does not cross the phantom divide line w(z) =-1 and remains above and close to w(z)≈-0.92 line for the whole redshift range 0 ≤ z ≤ 1.75 showing no evidence for phantom behavior. By applying the anisotropy effect on the ΛCDM model, the joint analysis indicates that ?_(σ0)= 0.0163 ± 0.03,with 194 SNIa, ?_(σ0)=-0.0032 ± 0.032 with 238 the SiFTO sample of JLA and ?_(σ0)= 0.011 ± 0.0117 with 1048 the SALT2 sample of Pantheon at 1σ′confidence interval. The analysis shows that by considering the anisotropy, it leads to more best fit parameters in all models with JLA SNe datasets. Furthermore, we use two statistical tests such as the usual χ_(min)~2/dof and p-test to compare two dark energy models with ΛCDM model. Finally we show that the presence of anisotropy is confirmed in mentioned models via SNIa dataset.     

Exploring the latest Pantheon SN Ia dataset by using three kinds of statistics techniques

In this work, we explore the cosmological consequences of the latest Type Ia supernova (SN Ia)dataset, Pantheon, by adopting the wCDM model. The Pantheon dataset currently contains the largest number of SN Ia samples, which contains 1048 supernovae on the redshift range0 z 2.3. Here we take into account three kinds of SN Ia statistics techniques, including:(1) magnitude statistics (MS), which is the traditional SN Ia statistics technique;(2) flux statistics(FS), which is based on the flux-averaging (FA) method; and (3) improved flux statistics (IFS),which combines the advantages of MS and FS. It should be mentioned that the IFS technique needs to scan the (zcut,Δz) parameters plane, where zcutandΔz are redshift cut-off and redshift interval of FA, respectively. The results are as follows.(1) Using the SN dataset only, the best FA recipe for IFS is (zcut,Δz)=(0.1, 0.08);(2) comparing to the old SN dataset, JLA, adopting the Pantheon dataset can reduce the 2σerror bars of equation of state w by 38%, 47%and 53%for MS, FS and IFS, respectively;(3) FS gives closer results to other observations, such as Baryon acoustic oscillations and cosmic microwave background;(4) compared with FS and IFS,MS more favors a Universe that will end in a ‘big rip’.