1603412
Chiral perturbation theory Success and challenge
Chiral perturbation theory is the effective field theory of the strong interactions at low energies. We will give a short introduction to chiral perturbation theory for mesons and will discuss, as an example, the electromagnetic polarizabilities of the pion. These have recently been extracted from an experiment on radiative π photoproduction from the proton (γp → γπn) at the Mainz Microtron MAMI. Next we will turn to the one-baryon sector of chiral perturbation theory and will address the issue of a consistent power counting scheme. As examples of the heavy-baryon framework we will comment on the extraction of the axial radius from pion electroproduction and will discuss the generalized polarizabilities of the proton. Finally, we will discuss two recently proposed manifestly Lorentz-invariant renormalization schemes and illustrate their application in a calculation of the nucleon electromagnetic form factors. PACS. 11.10.Gh Renormalization – 11.30.Rd Chiral symmetries – 13.40.-f Electromagnetic processes and properties – 13.40.Gp Electromagnetic form factors – 13.60.Fz Elastic and Compton scattering – 13.60.Le Meson production
119340330
Infrared and extended on-mass-shell renormalization of two-loop diagrams
Abstract Using a toy model Lagrangian we demonstrate the application of both infrared and extended on-mass-shell renormalization schemes to multiloop diagrams by considering as an example a two-loop self-energy diagram. We show that in both cases the renormalized diagrams satisfy a straightforward power counting.
15270133
BARYON CHIRAL PERTURBATION THEORY IN MANIFESTLY LORENTZ-INVARIANT FORM
A successful effective field theory program requires besides the most general effective Lagrangian a perturbative expansion scheme for observables in terms of a consistent power counting method. We discuss a renormalization scheme for manifestly Lorentz-invariant baryon chiral perturbation theory generating a simple and consistent power counting for renormalized diagrams. The approach may be used in an iterative procedure to renormalize higher-order loop diagrams and also allows for implementing a consistent power counting when vector mesons are explicitly included.
119365626
Introduction to Chiral Perturbation Theory
This article provides a pedagogical introduction to the basic concepts of chiral perturbation theory and is designed as a text for a two-semester course on that topic. Section 1 serves as a general introduction to the empirical and theoretical foundations which led to the development of chiral perturbation theory. Section 2 deals with QCD and its global symmetries in the chiral limit; the concept of Green functions and Ward identities reflecting the underlying chiral symmetry is elaborated. In Section 3 the idea of a spontaneous breakdown of a global symmetry is discussed and its consequences in terms of the Goldstone theorem are demonstrated. Section 4 deals with mesonic chiral perturbation theory and the principles entering the construction of the chiral Lagrangian are outlined. Various examples with increasing chiral orders and complexity are given. Finally, in Sect. 5 the methods are extended to include the interaction between Goldstone bosons and baryons in the single-baryon sector, with the main emphasis put on the heavy-baryon formulation. At the end, the method of infrared regularization in the relativistic framework is discussed.
13532458
Pion polarizabilities: No conflict between dispersion theory and ChPT
Recent attempts to determine the pion polarizability by dispersion relations yield values that disagree with the predictions of chiral perturbation theory. These dispersion relations are based on specific forms for the absorptive part of the Compton amplitudes. The analytic properties of these forms are examined, and the strong enhancement of intermediate-meson contributions is shown to be connected to non-analytic structures
122955732
Chiral Perturbation Theory for Baryons
So far we have considered the purely mesonic sector of chiral perturbation theory, involving the interaction of Goldstone bosons with each other and with external fields. However, ChPT can be extended to also describe the dynamics of baryons at low energies. Here we will concentrate on matrix elements with a single baryon in the initial and final states. As in the mesonic sector, Green functions are calculated in an effective-Lagrangian approach in combination with a power counting. The symmetries of QCD and the pattern of their breaking again constrain the possible interaction terms appearing in the effective Lagrangian, and we will discuss several approaches to obtain a consistent power counting.
201855044
Parton Recombination And Fluctuations Of Conserved Charges
We study various fluctuation and correlation signals of the d econfined state using a dynamical recombination approach (quark Molecular Dynamics, qMD). We a nalyse charge ratio fluctuations, charge transfer fluctuations and baryon-strangeness corre lations as a function of the center of mass energy with a set of central Pb+Pb/Au+Au events from AGS energies on ( Elab = 4 AGeV) up to the highest RHIC energy available ( √ sNN = 200 GeV) and as a function of time with a set of central Au+Au qMD events at √ sNN = 200 GeV with and without applying our hadronization procedure. For all studied quantities, the results start fr om values compatible with a weakly coupled QGP in the early stage and end with values compatible wit h the hadronic result in the final state. We show that the loss of the signal occurs at the same ti me as hadronization and trace it back to the dynamical recombination process implemented in our model.
118819388
Hadron ratios: Chiral symmetry restauration vs. nonequilibrium quark dynamics
Hadron production in recent nucleus-nucleus collisions experiments at the SPS and at RHIC have been analyzed in various thermal model fits. Here it is shown that the fit cannot be unique: the chemical freeze-out close to the phase transition to a QGP should be accompanied by shifting baryon masses in medium, which can yield considerably smaller break-up temperatures. Also a simple microscopic quark molecular dynamics model yields hadron ratios in nice agreement with those data. Hence, additional information, e.g., from HBT, is needed to determine the freeze-out parameters from data.