膨胀QGP的热双轻子产生(英文)

研究了QGP中次级热双轻子的产生。在RHIC能区, 次级热双轻子的产生在低质量范围0.2 GeV     

The effects of interactions between photon and the quark-gluon plasma on production of soft dileptons

We investigate the effects of interactions of the intermediate photons with the quark-gluon plasma on dilepton productions. The singular behaviour at the photon mass shell in the case of free photon is removed by the interactions. Instead, we find double resonance peaks near the photon mass shell due to the transverse and longitudinal modes. The effects of interactions further away fromM ²=0 is negligible and the photons effectively propagate as free particles in the plasma. The result of resummation is the enhancement of dilepton production rate, except in an extremely narrow region around each resonance peak, where its effect is to reduce the peak. The net result is more dilepton pairs come out of the plasma than in the one loop case. Both enhancement and reduction are partly due to Landau damping. Whereas the former is true over most range of the energy-momentum of the photon and is particularly prominent in region close to but not too close to the resonance peaks, the latter is effectively only true at the peaks.     

Electromagnetic low-energy constants in χPT

We investigate three-flavour chiral perturbation theory including virtual photons in the limit in which the strange quark mass is much larger than the external momenta and the up and down quark masses, and where the external fields are those of two-flavour chiral perturbation theory. In particular, we work out the strange quark mass dependence of the electromagnetic two-flavour low-energy constants C and k_i. We expect that these relations will be useful for a more precise determination of the electromagnetic low-energy constants. PACS 11.30.Rd; 12.39.Fe; 13.40.Dk; 13.40.Ks     

Hard photon production from unsaturated quark–gluon plasma at two-loop level

The hard photon production from bremsstrahlung and annihilation with scattering that arise at two-loop level are estimated for a chemically non-equilibrated quark–gluon plasma in the framework of Hard Thermal Loop (HTL) resummed effective field theory. The rate of photon production is found to be suppressed due to unsaturated phase space compared to equilibrated plasma. For an unsaturated plasma, unlike the effective one-loop case, the reduction in the effective two-loop processes is found to be independent of gluon fugacity, due to an additional collinear enhancement arising from the decrease in thermal quark mass but strongly depends on quark and antiquark fugacities. It is also found that the photon production is dominated by bremsstrahlung mechanism, since the phase space suppression is higher for annihilation with scattering, in contrast to the equilibrated plasma where annihilation with scattering dominates the photon production.     

Non-perturbative aspects of screening phenomena in abelian and non-abelian gauge theories

When computed to one-loop order in resummed perturbation theory, the non-abelian Debye mass appears to be logarithmically sensitive to the magnetic scale g²T. More generally, we show that in higher orders power-like infrared divergences forbid the use of perturbation theory to calculate the corrections to Debye screening. A similar infrared problem occurs in the determination of the mass-shell behaviour for the scalar propagator in (2+1)-dimensional scalar electrodynamics. In this context, we provide a non-perturbative approach which solves the infrared problems and allows for an accurate calculation of the scalar propagator in the vicinity of the mass shell.     

化学非平衡夸克-胶子物质中等质量双轻子的产生

研究了正在进行化学平衡的富重子夸克-胶子物质的双轻子产生，发现由于产生在RHIC能量 的化学非平衡的富重子夸克-胶子物质冷却慢和高的初始温度，导致中等质量双轻子产生重 大增强.因此，中等质量双轻子的增强可以是夸克-胶子物质形成的信号.同时，这个增强能 补偿由于初始夸克化学势增加引起的双轻子抑制，因而双轻子产额的抑制不再是夸克-胶子 物质产生的信号. 关键词： 化学非平衡夸克-胶子物质 热粲夸克 双轻子     

膨胀的热夸克胶子物质的中等质量双轻子的增强

基于一个描述夸克胶子火柱演化的相对论流体力学模型,研究了夸克相、强子相互作用以及非热过程(DrellYan对、粲强子衰变)的中等质量双轻子的产生.发现由于相边对夸克胶子物质演化的影响和RHIC能量核碰撞产生的夸克胶子物质具有高的初始温度,夸克相对双轻子的贡献显著增强,比那些来自强子相互作用的贡献重要,甚至能与来自非热的贡献比较.表明中等质量双轻子的增强是一个在核碰撞中产生了夸克胶子物质的可能信号. 关键词： 夸克-胶子物质 双轻子增强 相对论流体力学模型     

Hard-thermal-loop QED thermodynamics

The weak-coupling expansion for thermodynamic quantities in thermal field theories is poorly convergent unless the coupling constant is tiny.We discuss the calculation of the free energy for a hot gas of electrons and photons to three-loop order using hard-thermal-loop perturbation theory (HTLpt).We show that the hard-thermal-loop perturbation reorganization improves the convergence of the successive approximations to the QED free energy at large coupling,e ～ 2.The reorganization is gauge invariant by construction,and due to the cancellations among various contributions,we obtain a completely analytic result for the resummed thermodynamic potential at three loops.     

Large mass dilepton production from jet-dilepton conversion in the quark-gluon plasma

We calculate the production of large mass dileptons from the passage of jets passing through the quark-gluon plasma. Using the relativistic kinetic theory, we rigorously derive the production rate for the jet-dilepton conversion in the hot medium. The jet-dilepton conversion is compared with the thermal dilepton emission and the Drell-Yan process. The contribution of the jet-dilepton conversion is not prominent for all values of the invariant mass M, and the Drell-Yan process is found to dominate over the thermal dilepton emission and the jet-dilepton conversion for M>2.5 GeV at RHIC. The jet-dilepton conversion is the dominant source of large mass dileptons in the range of 4 GeV<M<10 GeV at LHC.     

Photons,Dileptons and Hadrons Produced by Quark-Gluon Plasma

Altarelli-Parisi equations in perturbative QCD are applied to getting evolution equations of quark-gluon plasma. The equations describe the cooling process of quark-gluon plasma by emitting photons. The numbers of observable photons and dileptons are calculated directly from these equations. The cooled quark-gluon plasma hadronizes and the production rates of hadrons are calculated with separable scalar confinement potentials.     

Curing fermion mass gauge variance in QED

The problem of the gauge dependence of the fermion mass in the Maxwell-Chern-Simons QED is revisited. Using Proca mass term as an intermediate infrared regulator we are demonstrating gauge-invariance of the fermion mass shell in QED in all orders of the perturbation theory.     

Isospin breaking in the pion–nucleon scattering lengths

We analyze isospin breaking through quark mass differences and virtual photons in the pion–nucleon scattering lengths in all physical channels in the framework of covariant baryon chiral perturbation theory.     

A quantum electrodynamic theory of two-centre two-photon circular dichroism

Expressions for the rate of two-photon circular dichroism occurring at two identical oriented or completely randomly oriented centres are calculated using perturbation theory and the Fermi golden rule within the framework of non-relativistic quantum electrodynamics. Circular differential absorption in the two-group model arises from the relative dissymmetric juxtaposition of two inherently achiral functional groups. Inter-chromophore coupling is included through the exchange of virtual photons. Absorption of two circularly polarized photons takes place at each centre, and the interference between the two amplitudes depends on the chromophore separation and on the handedness of the incident radiation. In the near zone, the two-centre two-photon circular dichroism rate is found to depend linearly upon the inter-group separation distance.     

Enhancement of Dileptons with Intermediate Masses Produced in QGP

The production of dileptons in the intermediate mass region in QGP has been studied on the basis of a relativistic hydrodynamic model. Due to the influence of the phase boundary on the evolution of the QGP system and the high initial temperature of the QGP produced at RHIC energies, the quark phase contribution is much more important than that from hadronic interactions and even comparable with that from background sources. It is shown that such an enhancement is a signature for the QGP formation.     

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.     

Quark-matter diagnostics: Dileptons,photons and (JΨ) suppression

The appropriate kinematic window for dileptons and photons, and possible signals of quarkgluon plasma are discussed. A suppression ofJ/Ψ, entirely due to hadronic matteris also discussed.     

Equation of state of hadronic matter and electromagnetic radiation from relativistic heavy ion collisions

We study the radiation of thermal photons and dileptons likely to be produced in relativistic heavy ion collisions. We find that the thermal photon multiplicity scales with the charged pion multiplicity (dN_ch/dy) as (dN_ch/dy)^α with α1.2 for a transversely expanding system, contrary to the general belief of a quadratic dependence. The scaling is shown to be valid, both for real and virtual photons. The coefficient of proportionality at a given energy shows, however, strong dependance on the equation of state of hot hadronic matter produced in such collisions.     

色玻璃凝聚近似下极端相对论重离子碰撞中的双轻子和光子产生(英文)

在色玻璃凝聚胶子饱和框架下,研究了相对论重离子碰撞中的双轻子和光子产生。在胶子饱和区域,在微扰近似(kT-因子化近似) 下低转移动量双轻子和光子的主要产生机制是胶子-胶子相互作用。在RHIC 和LHC 能量区域的相对论重离子碰撞中,饱和动量的值远远大于量子色动力学禁闭标度ΛQCD,这使得αs?1。此时,当转移动量小于饱和动量Qs 时质子和原子核的胶子密度值就会很高,双轻子和光子的不变产生横截面会由于饱效应而得到增强。数值结果给出在RHIC 和LHC 能量区域的pp, pA 和AA碰撞中,来源于色玻璃凝聚的低转移动量双轻子和光子产生贡献是显著的。We investigate inclusive dileptons and photons production in relativistic heavy ion collisions based on the idea of gluon saturation in the color glass condensate (CGC) framework. In the gluon saturation region, the dominant mechanism for low-pT dileptons and photons production in the perturbative approach (the kT-factorization approach) is gluon-gluon interaction. At Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies, the value of saturation momentum becomes larger than the Quantum Chromodynamics (QCD) confinement scale ΛQCD for relativistic heavy ion collisions, which implies that αs?1. In this state, the gluon density for proton and nucleus with transverse momentum less than the saturation momentum Qs will reach a high value, and the invariant cross-section for dileptons and direct photons is further enhanced by saturation effects. The numerical results indicate that the production of low-pT dileptons and photons from the color glass condensate becomes prominent in pp, pA, and AA collisions at RHIC and LHC  Energies.     

Breakdown of the hard thermal loop expansion for quasi-real photons production

We discuss the bremsstrahlung production of soft real and virtual photons in a quark-gluon plasma at thermal equilibrium beyond the Hard Thermal Loop (HTL) resummation. The physics is controlled by the ratio $Q^{2}/q_{0}^{2}$ of the virtuality to the energy. When $Q^{2}/q_{0}^{2} ? g^{2}$ where g is the strong coupling constant, the emission rate is enhanced by a factor 1/g² over the HTL results due to light-cone singularities and the bremsstrahlung is induced by scattering of the quark via both transverse and longitudinal soft gluon exchanges. When $Q^{2}/q_{0}^{2}$ increases, the enhancement factor is given by $q_{0}^{2}/Q^{2}$. When this ratio is near unity, the bremsstrahlung contribution is of the same order as the rate predicted by the HTL resummation. In that case, the bremsstrahlung is induced by both soft and hard gluon exchanges.