Quark pair production in a rapid chiral phase transition

In very energetic heavy ion collisions it is expected that chiral symmetry is temporarily restored. If the underlying QCD vacuum changes its structure rather suddenly, the transition is accompanied by a spontaneous and nonperturbative production of quark pairs. If gluons are already present they may assist additively to the overall production: As a particularly interesting nonequilibrium phenomena, real gluons are partially decaying during such a chiral transition. The total number of produced quarks is calculated and found to be quite sizeable. For the future collider experiments such effects could give rise to a significant contribution to the total number of quark pairs created in the preequilibrium stage of the reaction.     

N = ∞ phase transition in a class of exactly soluble model lattice gauge theories

An exactly soluble class of model U(N) lattice gauge theories is considered. The ground state is discussed as a separable N-fermion problem solved by mathieu functions. Some exact correlation functions are presented. The N = ∞ limit exhibits a third order phase transition demarcating the strong and weak phases at (g²N)^?1 ≈ 0.55.     

A new large N phase transition in YM2

Inspired by the interpretation of two-dimensional Yang–Mills theory on a cylinder as a random walk on the gauge group, we point out the existence of a large N transition which is the gauge theory analogue of the cutoff transition in random walks. The transition occurs in the strong coupling region, with the 't Hooft coupling scaling as $\alpha \log N$, at a critical value of α ($\alpha =4$ on the sphere). The two phases below and above the transition are studied in detail. The effective number of degrees of freedom and the free energy are found to be proportional to $N^{2-\frac{\alpha }{2}}$ below the transition and to vanish altogether above it. The expectation value of a Wilson loop is calculated to the leading order and found to coincide in both phases with the strong coupling value.     

D=1+2 phase diagram forZ N with a variational method

Trial ground state are constructed which forZ _N gauge theories inD=1+2 dimensions lead to phase diagrams which are in agreement both with theoretical expectations and Monte Carlo results. The nature of the phase transition is correctly predicted for eachN.     

Lepton pair emission as a probe for the spacetime scenario of quark-hadron phase transition

The correlation between thermal lepton pair emission and hadronic multiplicity is explored to clear up the spacetime picture of quark matter hadronization phase transition in ultrarelativistic nuclear collisions.     

NiS2-xSex在x=1.00附近的反铁磁量子相变

针对NiS2-xSe,系统在x=1.00附近发生的反铁磁量子相变,制备了一系列NiS2-xSex(x=0.96,0.98,1.00,1.05,1.10和1.20)多晶样品,对其结构、磁性质和电阻率进行了系统的观测.结果发现:样品磁化率-温度关系呈现典型的强关联电子系统特征;与铜氧化物超导体相类似,它们的电阻率-温度关系在很宽的温区内(50--300 K)呈现线性行为;对于x=0.98,1.00样品,低温下(3-30 K)电阻率满足p(T)∝T3/2,呈现非费米液体行为,而在x=1,10,1.20样品中的ρ(T)又呈现费米液体预言的T2关系.根据与量子相变行为相关的反铁磁量子涨落对结果进行了讨论.     

An unusual structural phase transition in Rb2HfF6

An unusual structural phase transition in the crystalline compound Rb₂HfF₆ near room temperature has been observed from perturbed angular correlation (PAC) spectroscopy. Our measurements in this compound produce two different crystalline configurations characterized by ω_Q=74.1(1) Mrad/s, η~0, δ~0 and ω_Q=24.7(2) Mrad/s, η=0.53(1), and δ=4(2)%. From PAC measurements in different samples, it is found that crystal structure corresponding to ω_Q=74 Mrad/s, η~0 transforms to the other quite arbitrarily with temperature and no definite temperature corresponding to this transition has been observed. This can possibly be attributed to displacive phase transition.     

N=2 affine superalgebras and Hamiltonian reduction inN=2 superspace

We constructN=2 affine current algebras for the superalgebrassl(n/n-1)⁽¹⁾ in terms ofN=2 supercurrents subjected to nonlinear constraints and discuss the general procedure of the hamiltonian reduction inN=2 superspace at the classical level. We consider in detail the simplest case ofN=2sl(2/1)⁽¹⁾ and show howN=2 superconformal algebra inN=2 superspace follows via the hamiltonian reduction. Applying the hamiltonian reduction to the case ofN=2sl(3/2)⁽¹⁾, we find two new extendedN=2 superconformal algebras in a manifestly supersymmetricN=2 superfield form. Decoupling of four component currents of dimension 1/2 in them yields, respectively,u(2/1) andu(3) Knizhnik-Bershadsky superconformal algebras. We also discuss how theN=2 superfield formulations ofN=2W ₃ andN=2W ₃ ⁽²⁾ superconformal algebras come out in this framework, as well as some unusual extendedN=2 superconformal algebras containing constrainedN=2 stress tensor and/or spin 0 supercurrents.     

Real Forms of the Complex Twisted N=2 Supersymmetric Toda Chain Hierarchy in Real N=1 and Twisted N=2 Superspaces

Abstract

Three nonequivalent real forms of the complex twisted N=2 supersymmetric Toda chain hierarchy (solv-int/9907021) in real N=1 superspace are presented. It is demonstrated that they possess a global twisted N=2 supersymmetry. We discuss a new superfield basis in which the supersymmetry transformations are local. Furthermore, a representation of this hierarchy is given in terms of two twisted chiral N=2 superfields. The relations to the s-Toda hierarchy by H. Aratyn, E. Nissimov and S. Pacheva (solv-int/9801021) as well as to the modified and derivative NLS hierarchies are established.     

An x-ray study of a possible phase transition in phenanthrene

X-ray diffraction powder patterns from phenanthrene taken between 20°C and 80°C, show positive evidence for a reversible phase transition; shifts and splitting of peaks have been observed.     

Massive N = 2a supergravity in ten dimensions

A new version of the non-chiral N = 2a supergravity in ten dimensions is obtained, in which the two-index tensor field of the theory “eats” the single vector field and acquires a mass in a Higgs-type mechanism. The new theory, although it contains no fundamental vectors, bears many formal resemblances to gauged supergravities (in particular, the recently constructed F(4) theory in six dimensions). The scalar potential has no extrema, but nevertheless the classical equations of motion admit a wide variety of spontaneous compactifications, many to four dimensions.     

Quantum theory of transition radiation and transition pair creation

A theory of the transition radiation and the transition pair creation is developed in the frame of QED. The spectral-angular distributions of probability of the transition radiation and of the transition pair creation are found. The total energy losses of an electron and the total probability of pair creation by a photon are calculated and analyzed. Features of radiation and pair creation processes in a superdense medium (typical for white dwarfs) are discussed.     

Pressure-induced phase transition in ThO2 and PuO2

Abstract

Thorium and plutonium dioxides were studied under pressure by the energy dispersive X-ray diffraction method. A double conical slit assembly was used to collect simultaneously the diffracted radiation at five and seven degrees.

ThO₂ undergoes a phase transformation at 40 GPa. The high-pressure phase remains stable up to 55 GPa, the highest pressure reached in the experiment. For PuO₂, a structural transformation occurs near 39 GPa. The observed high-pressure phases of ThO₂ and PuO₂ exhibit similar diffraction spectra. Like for some other fluorite type compounds, the ThO₂ and PuO₂ high-pressure phase has been indexed in the PbCl₂-type structure. The bulk modulus has been calculated as B₀= 262 GPa with a pressure derivative of B₀' = 6.7 for ThO₂ and as B₀ = 379 GPa with B₀' = 2.4 for PuO₂. The volume decrease at the transition is 12% for PuO₂ and 8% for ThO₂.     

Extended supergravity on the supergroup manifold: N = 3 and N = 2 theories

In this paper I construct the group-manifold first-order formulation of N = 2 and N = 3 supergravity based on the $\text{Osp}\text{(}\text{4}\text{2}\text{)}\text{and Osp}\text{(}\text{4}\text{3}\text{)}$ supergroups, respectively. In the case N = 2, a group manifold version of the theory was already presented in a previous paper. Here a simpler formulation is given which shows exact factorization in the SO(2) subgroup absent in the previous one. Particular attention is paid to the algebraic role played by the $\text{spin}\text{-}\text{1}\text{2}$ field which is the novel feature of the N = 3 case with respect to N = 2. It is shown how the “non-geometrical” term in the gravitino transformation law in the N = 2 theory arises from the rheonomic symmetry mechanism.