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Search Results: 1 - 10 of 202951 matches for " Ulf-G. Mei?ner "
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The Pion Cloud of the Nucleon: Facts and popular Fantasies
Mei ner, Ulf-G.
High Energy Physics - Phenomenology , 2007, DOI: 10.1063/1.2734299
Abstract: I discuss the concept of the pion cloud surrounding the nucleon and other hadrons - and its limitations.
Recent developments in heavy baryon chiral perturbation theory: Selected topics
Ulf-G. Meiner
Physics , 1997,
Abstract: I review recent results in baryon chiral perturbation theory, in particular related to pion-nucleon scattering and first systematic attempts to go beyond next-to-leading order in the case of three flavors. New insight into the chiral expansion of the baryon masses and magnetic moments is presented.
The role of massive states in chiral perturbation theory
Ulf-G. Meiner
Physics , 1996,
Abstract: I review some basic facts about the chiral limit of QCD. This allows to formulate an effective field theory below the chiral symmetry breaking scale, chiral perturbation theory (CHPT). I show that for threshold reactions, the spectrum of QCD is most economically encoded in a set of coupling constants of operators of higher chiral dimension. A consistent scheme to incorporate the $\Delta(1232)$ is also discussed and some examples are given. It is stressed that more precise low--energy data are needed to further test and sharpen the resonance saturation hypothesis in the presence of baryons.
Status of three flavor baryon chiral perturbation theory
Ulf-G. Meiner
Physics , 1997, DOI: 10.1007/BFb0104906
Abstract: I review the present status of three flavor baryon chiral perturbation theory in the heavy fermion formalism. It is argued that precise calculations have to include all terms quadratic in the quark masses. As examples, I consider the chiral expansion of the octet baryon masses, the baryon magnetic moments and kaon photoproduction off nucleons.
Applied Chiral Perturbation Theory
Ulf-G. Meiner
Physics , 1994,
Abstract: I consider some selected topics in chiral perturbation theory (CHPT) as probed at colliders such as DA$\Phi$NE. Emphasis is put on processes involving pions in the isospin zero S-wave which require multi-loop calculations. These include the scalar form factor of the pion, two--photon fusion into pion pairs and $K_{\ell 4}$--decays. The physics of the chiral anomaly is briefly touched upon
Baryon Chiral Perturbation Theory A.D. 1994
Ulf-G. Meiner
Physics , 1994, DOI: 10.1007/BF01724517
Abstract: In these lectures, the status of baryon chiral perturbation theory is reviewed. Particular emphasis is put on the two--flavor sector and the physics related to electromagnetic probes. I discuss in some detail the structure of the effective Lagrangian at next--to--leading order, the meaning of low--energy theorems in Compton scattering and pion photoproduction and confront the chiral predictions with the existing data. Some remaining problems and challenges are outlined.
Nucleon form factors: From the space-like to the time-like region
Ulf-G. Meiner
Physics , 1996, DOI: 10.1016/S0375-9474(97)00453-3
Abstract: I discuss how dispersion relations can be used to analyse the nucleon electromagnetic form factors, with particular emphasis on the constraints from unitarity and pQCD. Results for nucleon radii, vector-meson couplings, the onset of pQCD and bounds on the strangeness form factors are presented. The em form factors in the time-like region reveal some interesting physics which is not yet understood in full detail. The need for a better data basis at low, intermediate and large momentum transfer and also in the time-like region is stressed.
Recent Developments in Chiral Perturbation Theory
Ulf-G. Meiner
Physics , 1993, DOI: 10.1088/0034-4885/56/8/001
Abstract: I review recent developments in chiral perturbation theory (CHPT) which is the effective field theory of the standard model below the chiral symmetry breaking scale. The effective chiral Lagrangian formulated in terms of the pseudoscalar Goldstone bosons ($\pi, \, K, \, \eta$) is briefly discussed. It is shown how one can gain insight into the ratios of the light quark masses and to what extent these statements are model--independent. A few selected topics concerning the dynamics and interactions of the Goldstone bosons are considered. These are $\pi \pi$ and $\pi K$ scattering, some non--leptonic kaon decays and the problem of strong pionic final state interactions. CHPT also allows to make precise statements about the temperature dependence of QCD Green functions and the finite size effects related to the propagation of the (almost) massless pseudoscalar mesons. A central topic is the inclusion of matter fields, baryon CHPT. The relativistic and the heavy fermion formulation of coupling the baryons to the Goldstone fields are discussed. As applications, photo--nucleon processes, the $\pi N$ $\Sigma$--term and non--leptonic hyperon decays are presented. Implications of the spontaneously broken chiral symmetry on the nuclear forces and meson exchange currents are also described. Finally, the use of effective field theory methods in the strongly coupled Higgs sector and in the calculation of oblique electroweak corrections is touched upon.
Electroweak Reactions in the Non-Perturbative Regime of QCD
Ulf-G. Meiner
Physics , 1993, DOI: 10.1007/BFb0028950
Abstract: In the first part of these lectures, I consider chiral perturbation theory in the presence of matter fields. It allows to systematically work out the consequences of the broken chiral symmetry of QCD. As examples, threshold pion photo- and electroproduction and (spin-flip) nucleon Compton scattering are considered. The second part deals with the quark structure of the nucleon at low energies. The various electromagnetic and weak form factors are discussed. It is shown how parity-violating electron and (anti)neutrino scattering off nucleons and nuclei can be used as a tool to pin down strange matrix elements of the proton. The calculation of QED, QCD and heavy quark corrections to these processes is also touched upon. (Lectures given at the XXXII. Internationale Universit{\"a}tswochen f{\"u}r Kern- und Teilchenphysik, Schladming, Austria, February 24- March 5, 1993).
Thermal Pions
Ulf-G. Meiner
Physics , 1993, DOI: 10.1016/0375-9474(94)90618-1
Abstract: I discuss the absorption and dispersion of pions in hot matter. A two-loop calculation in the framework of chiral perturbation theory is presented and its result is compactly written in terms of the two- and three-particle forward $\pi \pi$ scattering amplitudes. At modest temperatures, $T \le 100$ MeV, the change in the pion mass is small and its dispersion law closely resembles the free space one. At these temperatures, all quantities of interest are given to a good degree of accuracy by the first term in the virial expansion which is linear in the density. (BUTP-93/16, uses espcrc1.sty from North-Holland Publishing)
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