The poor convergence of quantum field theory at finite temperature has been one of the main obstacles in the practical applications of thermal QCD for decades.Here we briefly review the progress of hard-thermal-loop p...The poor convergence of quantum field theory at finite temperature has been one of the main obstacles in the practical applications of thermal QCD for decades.Here we briefly review the progress of hard-thermal-loop perturbation theory (HTLpt) in reorganizing the perturbative expansion in order to improve the convergence.The quantum mechanical anharmonic oscillator is used as a simple example to show the breakdown of weak-coupling expansion,and variational perturbation theory is introduced as an effective resummation scheme for divergent weak-coupling expansions.We discuss HTLpt thermodynamic calculations for QED,pure-glue QCD,and QCD with N f=3 up to three-loop order.The results suggest that HTLpt provides a systematic framework that can be used to calculate both static and dynamic quantities for temperatures relevant at LHC.展开更多
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...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.展开更多
With the hard thermal loop （HTL） resummation technique, we calculate the dielectric function excited by hard gluon in quark-gluon plasma （QCP）. We find that in a section of the space-like region po/p ∈ [0.78, 0.9...With the hard thermal loop （HTL） resummation technique, we calculate the dielectric function excited by hard gluon in quark-gluon plasma （QCP）. We find that in a section of the space-like region po/p ∈ [0.78, 0.95], there are two extremum structures on the dielectric function curve, while the dielectric function in the HTL approximation decreases monotonously without these properties. Through the analyses of the imaginary part of the dielectric function, we conclude that the character of the dielectric function in this region reflects effects of the Landau damping.展开更多
The light cone gauge with light cone variables is often used in p QCD calculations in relativistic heavyion collision physics. The Hard Thermal Loops（HTL） resummation is an indispensable technique for hot QCD calcul...The light cone gauge with light cone variables is often used in p QCD calculations in relativistic heavyion collision physics. The Hard Thermal Loops（HTL） resummation is an indispensable technique for hot QCD calculation. It was developed in covariant gauges with conventional Minkowski varaiables; we shall extend this method to the light cone gauge. In the real time formalism, using the Mandelstam-Leibbrant prescription of（n·K）-1,we calculate the transverse and longitudinal components of the gluon HTL self energy, and prove that there are no infrared divergences. With this HTL self energy, we derive the HTL resummed gluon propagator in the light cone gauge. We also calculate the quark HTL self energy and the resummed quark propagator in the light cone gauge and find it is gauge independent. As application examples, we analytically calculate the damping rates of hard quarks and gluons with the HTL resummed gluon propagator in the light cone gauge and showed that they are gauge independent. The final physical results are identical to those computed in covariant gauge, as they should be.展开更多
文摘The poor convergence of quantum field theory at finite temperature has been one of the main obstacles in the practical applications of thermal QCD for decades.Here we briefly review the progress of hard-thermal-loop perturbation theory (HTLpt) in reorganizing the perturbative expansion in order to improve the convergence.The quantum mechanical anharmonic oscillator is used as a simple example to show the breakdown of weak-coupling expansion,and variational perturbation theory is introduced as an effective resummation scheme for divergent weak-coupling expansions.We discuss HTLpt thermodynamic calculations for QED,pure-glue QCD,and QCD with N f=3 up to three-loop order.The results suggest that HTLpt provides a systematic framework that can be used to calculate both static and dynamic quantities for temperatures relevant at LHC.
基金N. S.was supported by the Frankfurt International Graduate School for Science. M. S.was supported in part by the Helmholtz International Center for FAIR Landesoffensive zur Entwicklung Wissenschaftlich-konomischer Exzellenz program
文摘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.
基金the National Natural Science Foundation of China under Grant No.10675052
文摘With the hard thermal loop （HTL） resummation technique, we calculate the dielectric function excited by hard gluon in quark-gluon plasma （QCP）. We find that in a section of the space-like region po/p ∈ [0.78, 0.95], there are two extremum structures on the dielectric function curve, while the dielectric function in the HTL approximation decreases monotonously without these properties. Through the analyses of the imaginary part of the dielectric function, we conclude that the character of the dielectric function in this region reflects effects of the Landau damping.
基金Supported by National Natural Science Foundation of China(11375070,11735007,11521064)
文摘The light cone gauge with light cone variables is often used in p QCD calculations in relativistic heavyion collision physics. The Hard Thermal Loops（HTL） resummation is an indispensable technique for hot QCD calculation. It was developed in covariant gauges with conventional Minkowski varaiables; we shall extend this method to the light cone gauge. In the real time formalism, using the Mandelstam-Leibbrant prescription of（n·K）-1,we calculate the transverse and longitudinal components of the gluon HTL self energy, and prove that there are no infrared divergences. With this HTL self energy, we derive the HTL resummed gluon propagator in the light cone gauge. We also calculate the quark HTL self energy and the resummed quark propagator in the light cone gauge and find it is gauge independent. As application examples, we analytically calculate the damping rates of hard quarks and gluons with the HTL resummed gluon propagator in the light cone gauge and showed that they are gauge independent. The final physical results are identical to those computed in covariant gauge, as they should be.
