夸克-胶子等离子体中色屏蔽的时间演化与J/ψ、χ和ψ'压低

本文采用非相对论性禁闭势模型讨论了夸克-胶子等离子体中色屏蔽的时间演化和J/ψ、χ及ψ'的产额压低.     

夸克－胶子等离子体对高能碰撞多重产生的可能描述

以ＱＣＤ袋模型和统计流体力学模型为基础，在二维平衡态近似下得到多重数和质心系能量的关系式，和高能　碰撞非单衍过程产生的多重数实验数据吻合得很好；在三维平衡态近似下得到中心在快度较大区域的产生粒子的源Ⅱ的大小和横动量的关系，关系式和三火球模型计算结果符合．     

CERE实验产生出夸克-胶子等离子体

 ＣＥＡＮ计划于今日（２月１０日）公布“有力的证据”,表明ＣＥＲＮ的科学家们已经创造了预言在大爆炸后不久就一直存在着的物质的夸克－胶子等离子态．如果这一结果得到证实,那将是人类首次在实验室条件下观测到大爆炸之后最初三分钟的情况,那是组成原子核的质子和中子产生的时刻．这样的‘核子’是由两类基本粒子组成的：夸克和将夸克结合在一起的力的载体──胶子．但是,人们从未探测到自由夸克,理论预言它们只存在于一种非约束态中,要么是在这一浪小的时间窗口上,要么是在很高能量的重离子对撞时的能量密度上．量子色动力学预言,在这样的能量上,夸克和胶子非束缚地共同存在于等离子体中．     

夸克–胶子等离子体对高能pp(p)碰撞多重产生的可能描述

以QCD袋模型和统计流体力学模型为基础,在二维平衡态近似下得到多重数和质心系能量的关系式,和高能 碰撞非单衍过程产生的多重数实验数据吻合得很好;在三维平衡态近似下得到中心在快度较大区域的产生粒子的源Ⅱ的大小和横动量的关系,关系式和三火球模型计算结果符合.     

产生在夸克–胶子等离子体中的中等质量双轻子的增强

基于一个相对论流体力学模型,在夸克–胶子等离子体中具有中等质量双轻子的产生被研究.由于相边对夸克–胶子等离子体系统演化的影响和产生在RHIC能量的夸克–胶子等离子体系统有高的初始温度,夸克相的贡献变得比强子相互作用的贡献重要得多,甚至能与本底相比较.它表明这样的增强是夸克–胶子等离子体形成的一种信号.     

化学非平衡夸克–胶子等离子体中的双轻子产生

研究了正在进行化学平衡的具有有限重子密度的夸克–胶子等离子体系统的演化和双轻子产生.结果发现由于夸克相的寿命随初始夸克化学势的增加而增加,以及其他一些因素,如较高的初始温度、较大的胶子密度和较大的胶子聚变和夸克湮没反应截面,导致热粲夸克对双轻子产生提供了占统治的贡献.这个效应造成中等质量双轻子的重大增强.     

夸克-胶子等离子体中的喷注-光子转换机制(英文)

提出了一种夸克 胶子等离子体中的喷注 光子转换机制。 对于热光子而言, 在热夸克 胶子媒介中的喷注 光子转换是一个非常重要的热光子来源。 喷注可以通过次级康普顿散射和湮灭过程来实现喷注 光子转换。 此外, 还考虑了在快光子产生过程中起重要修正作用的胶子 光子贡献, 其中,核遮蔽效应和同位旋效应也被引入到了部分子模型中。We develop a jet photon conversion mechanism in the expanding quark gluon plasma. The jet photon conversion in hot quark gluon medium is a vital source of the thermal photon production. The jet converts into photons via the secondary Compton and annihilation processes in the quark gluon plasma. The gluon photons are also considered in the calculation of prompt photons which includes the effect of the shadowing and isospin of nucleus. We find that the prompt gluon photons are also an important modification to prompt photons.     

热密QED中的德拜质量

从QED中光子传播子的Schweinger-Dyson方程出发,得到一个有用的德拜质量和热力学压强之间的关系.利用这个关系以及有限温度与有限化学势下的相关压强计算了德拜质量的双圈修正.其结果显示双圈修正减少了德拜屏蔽质量.最后还讨论了QED等离子体中的磁质量     

On the chromo-electric permittivity and Debye screening in hot QCD

We study the response functions (chromo-electric susceptibilities) for an interacting quark-gluon plasma. The interaction effects have been encoded in the effective fugacities for quasi-partons which are extracted self-consistently from the two equations of state for hot QCD. The first one is the fully perturbative O(g ⁵) EOS and the second one, which is O(g ⁶ln(1/g)) , incorporates some non-perturbative effects. We find that the response function shows large deviations from the ideal behavior. We further determine the temperature dependence of the Debye mass by fixing the effective coupling constant Q² which appears in the transport equation. We show that our formalism naturally yields the leading-order HTL expression for the Debye mass if we employ the ideal EOS. Employing the Debye mass, we estimate the dissociation temperatures for various charmonium and bottomonium bound states. These results are consistent with the current theoretical studies.     

QGP中夸克静色电波的辐射研究

利用QGP中存在德拜屏蔽现象以及高温极限下QGP中夸克的分布函数和色电势,得到QGP中夸克静色电波的辐射功率. 讨论了夸克静色电波的辐射功率与德拜长度λ_D的关系,有助于利用辐射功率研究德拜屏蔽位势.     

Ionic Debye Screening in Dense Liquid Plasmas Observed for Li+p,d Reactions with Liquid Li Target

Thick target yields of a particles emitted in the ~6Li(d,a)~4 He and ~7Li(p,a)~4 He reactions were measured for Li target in the solid and liquid phase.Observed reaction rates for the liquid Li are always larger than those for the solid.This suggests that the stopping power of hydrogen ion in the liquid Li metal might be smaller than in the solid.Using the empirically obtained stopping power for the liquid Li,we have deduced the screening potentials of the Li+p and Li+d reactions in both phases.The deduced screening potential for the liquid Li is about 500 eV larger than for the solid.This difference is attributed to the effect of liquefied Li~+ ions.It is concluded that the ionic screening is much stronger than the electronic screening in a low-temperature dense plasmas.     

Instability of the plasma oscillations in finite temperature perturbative QCD

We use linear-response dielectric theory to show that the baryon-poor QCD plasma based on the perturbative vacuum is unstable, even at a high temperature. If deconfinement occurs in nuclear collisions or the early universe, it is not accompanied by the restoration of the perturbative vacuum.     

Calculation of the Longitudinal Structure Function from Regge-Like Behaviour of the Gluon Distribution Function in Leading Order Approximation at Low x

We present the calculations of FL longitudinal structure functions from DGLAP evolution equation in leading order （LO） at low-x, assuming the Regge-like behaviour of gluon distribution at this limit. The calculated results are compared with the H1 data and QCD fit. It is shown that the obtained results are very close to the mentioned methods. The proposed simple analytical relation for EL provides a t-evolution equation for the determination of the longitudinal structure function at low-x. All the results can consistently be described within the framework of perturbative QCD, which essentially shows increases as x decreases.     

Effective action in a general chiral model: Next to leading order derivative expansion in the worldline method

We present a formalism to determine the imaginary part of a general chiral model in the derivative expansion. Our formalism is based on the worldline path integral for the covariant current that can be given in an explicit chiral and gauge covariant form. The effective action is then obtained by integrating the covariant current, taking account of the anomaly.     

On the contribution of nonlinear scattering to optical limiting in C60 solution

We present experimental results which bring out the contribution of nonlinear scattering to the energy limiting of 527 nm, 30 ns pulses in C₆₀ solution. To perform these measurements we used a specific experimental arrangement to separate the effects of nonlinear refraction and scattering. Our results show that scattering reduces the output significantly and contributes to limiting in C₆₀ solution.     

A Remark on the Courant-Friedrichs-Lewy Condition in Finite Difference Approach to PDE's

The Courant-Friedrichs-Lewy condition (The CFL condition) is appeared in the analysis of the finite difference method applied to linear hyperbolic partial differential equations. We give a remark on the CFL condition from a view point of stability, and we give some numerical experiments which show instability of numerical solutions even under the CFL condition. We give a mathematical model for rounding errors in order to explain the instability.     

On the generation of nanograins in pure copper through uniaxial single compression

Attempts at generating nanograins through uniaxial single compression were made by deforming copper samples at 298 K and 77 K. At 298 K, dynamically-deformed samples (DDS) become softer, in contrast to quasi-statically deformed samples (QDS), which show a hardness close to the saturation value. The microstructure of DDS is characterised by deformation twins and equiaxed micron-sized grains, and the observed softening is due to the occurrence of recrystallisation (RX). At a reduced temperature of 77 K, nanograins are generated in DDS, whereas QDS show forest dislocations and twins. The generation of nanograins, which evolve through rotational DRX, is associated with the formation of shear bands with an amorphous structure. Compared with twinning, it appears that amorphisation plays a more pronounced role in high strain rate deformation at reduced temperatures (77 K). The hardness of DDS, obtained from compression at 77 K, exceeds the saturation value by 16%, whereas that of QDS corresponds approximately to saturation.