摘要:

There has been substantial progress in recent years in the quantitative understanding of the nonequilibrium time evolution of quantum fields. Important topical applications, in particular in high energy particle physics and cosmology, involve dynamics of quantum fields far away from the ground state or thermal equilibrium. In these cases, standard approaches based on small deviations from equilibrium, or on a sufficient homogeneity in time underlying kinetic descriptions, are not applicable. A particular challenge is to connect the far‐from‐equilibrium dynamics at early times with the approach to thermal equilibrium at late times. Understanding the “link” between the early‐ and the late‐time behavior of quantum fields is crucial for a wide range of phenomena. For the first time questions such as the explosive particle production at the end of the inflationary universe, including the subsequent process of thermalization, can be addressed in quantum field theory from first principles. The progress in this field is based on efficient functional integral techniques, so‐calledn‐particle irreducible effective actions, for which powerful nonperturbative approximation schemes are available. Here we give an introduction to these techniques and show how they can be applied in practice. Though we focus on particle physics and cosmology applications, we emphasize that these techniques can be equally applied to other nonequilibrium phenomena in complex many body systems. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843591

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

These lectures are a brief introduction to some of the weak coupling techniques used to decribe the physics of the quark‐gluon plasma at high temperature. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843592

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We summarize the theory and phenomenology of the Color Glass Condensate reviewed previously by E. Iancu and the author in hep‐ph/0303204. We discuss some of the subsequent developments in the past year both in theory and in phenomenological applications. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843593

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The functional integral for QCD is reformulated by introducing explicitly an integration over the fluctuations of composite quark‐antiquark bound states. Chiral symmetry breaking by the color singlet scalar field induces masses for the fermions. Our formulation with scalar fluctuations may be useful for lattice gauge theories by modifying the spectrum of the Dirac operator in the vacuum and permitting a simple connection to chiral perturbation theory. We propose that a “condensate” of quark‐antiquark bound states in the color octet channel generates masses of the gluons by the Higgs mechanism. A simple effective action for quarks, gluons and (composite) scalars yields a surprisingly good description of the charges, masses and interactions of all low mass physical excitations — baryons, pseudoscalars and vector mesons. Dressed quarks appear as baryons and dressed gluons as vector mesons. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843594

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Ideal hydroynamics provides an excellent description of all aspects of the single‐particle spectra of all hadrons with transverse momenta below about 1.5‐2 GeV/cat RHIC. This is shown to require rapid local thermalization at a time scale below 1 fm/cand at energy densities which exceed the critical value for color deconfinement by an order of magnitude. The only known thermalized state at such energy densities is the quark‐gluon plasma (QGP). The rapid thermalization indicates that the QGP is a strongly interacting liquid rather than the weakly interacting gas of quarks and gluons that was previously expected. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843595

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We review the experimental evidence on firstly, strangeness production as a signature for the QCD phase transition and secondly, pentaquarks, the latest and most exotic manifestations of strangeness in hadrons. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843596

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We study as function of energy strangeness created in relativistic heavy ion collisions. We consider statistical hadronization with chemical freeze‐out in both equilibrium and nonequilibrium. We present strangeness per baryon and per entropy in the energy range of SPS and RHIC. A baryon density independent evaluation of the kaon to pion ratio is presented. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843597

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The density corrections, in terms of the isospin chemical potential &mgr;1to the mass of the pions are studied in the framework of theSU(2) low energy effective chiral lagrangian in the two phases: The normal phase |&mgr;1| <m&pgr;and the condensed phase |&mgr;1| >m&pgr;. The pion decay constantf&pgr;(T,&mgr;1) is also analyzed in the first phase. As a function of temperature for &mgr;1= 0, the mass remains quite stable, starting to grow for very high values ofT, confirming previous results. However, there are interesting corrections to the mass when both effects (temperature and chemical potential) are simultaneously present. At zero temperature the &pgr;±should condense when &mgr;1= ±m&pgr;. This is not longer valid anymore at finiteT. The mass of the &pgr;0acquires also a non trivial dependence on &mgr;1due to the finite temperature. In the second phase we are able to calculate the thermal and density evolution of masses in the limits where |&mgr;1| ≫mand where |&mgr;1| ∼m. We also identified the phase transition curve. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843598

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

After referring to some basic features of chiral models for baryons, with quarks and mesons, we describe how to construct model states representing physical baryons. We consider soliton models such as the Linear Sigma Model or the Chromodielectric Model, and bag models such as the Cloudy Bag Model. These models are solved approximately using variational approaches whose starting point is a mean‐field description. We go beyond the mean‐field description by introducing quantum fluctuations in the mesonic degrees of freedom. This is achieved, in a first step, by using a quantum state to represent meson clouds and, secondly, by performing an angular momentum and isospin projection from the mean‐field state (actually a coherent state). Model states for baryons (nucleon, Delta, Roper) constructed in this way are used to determine several physical properties. I this seminar we paid a particular attention to the nucleon‐delta electromagnetic and weak transition, presenting the model predictions for the electromagnetic and axial amplitudes. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843599

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present a numerical study of the running coupling constant in four‐dimensional pure‐SU(2) lattice gauge theory. The running coupling is evaluated by fitting data for the gluon and ghost propagators in minimal Landau gauge. Following Refs. [1, 2], the fitting formulae are obtained by a simultaneous integration of the &bgr; function and of a function coinciding with the anomalous dimension of the propagator in the momentum subtraction scheme. We consider these formulae at three and four loops. The fitting method works well, especially for the ghost case, for which statistical error and hyper‐cubic effects are very small. Our present result for &Lgr;MSis200−40+60MeV, where the error is purely systematic. We are currently extending this analysis to five loops in order to reduce this systematic error. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1843600

出版商:AIP    

年代:1904

数据来源: AIP