摘要:

A brief account of the achievements of Prof. Augusto Garci´a is presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594311

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A brief account of the achievements of Prof. Arnulfo Zepeda is presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594312

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We study the behavior of the pion dispersion relation in a pion medium at finite density and temperature, introducing a chemical potential to describe the finite pion number density. Such description is particularly important during the hadronic phase of a relativistic heavy‐ion collision, between chemical and thermal freeze‐out, where the pion number changing processes, driven by the strong interaction, can be considered to be frozen. We make use of an effective Lagrangian that explicitly respects chiral symmetry through the enforcement of the chiral Ward identities. The pion dispersion relation is computed through the computation of the pion self‐energy in a non‐perturbative fashion by giving an approximate solution to the Schwinger‐Dyson equation for this self‐energy. The dispersion relation is described in terms of a density and temperature dependent mass and an index of refraction which is also temperature, density as well as momentum dependent. The index of refraction is larger than unity for all values of the momentum for finite &mgr; andT. Given the strong coupling between &rgr; vectors and pions, we argue that the modification of the pion mass due to finite pion density effects has to be taken into account self‐consistently for the description of the in‐medium modifications of &rgr;’s. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594313

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This talk provides a survey of the more recent developments in semi‐inclusive deep inelastic scattering (DIS) processes in high energy collisions from the stand point of perturbative QCD. We discuss the factorization approach and the energy scale dependence of the relevant functions involved in the description of these processes. The central role played by the so called fracture functions to guarantee the correct cancellation of singularities is discussed in detail. We include recent results up to next to leading order with comments on the technical details involved in the calculation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594314

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Quark‐hadron duality is often used to calculate rates of hadronic processes. For heavy mesons duality predicts small differences in lifetimes of theB±,B0and &Lgr;b, in sharp disagreement with experimental results. We embark in a study of quark‐hadron duality in heavy meson decays. Using the ’t Hooft model as a laboratory, we discover violations to duality that scale as one inverse power of the heavy quark mass. In contrast, we find that the heavy quark mass smeared meson and quark widths differ by two inverse powers of the heavy quark mass. In 3 + 1 dimensions an analogous result holds, namely, the heavy meson hadronic decay widths satisfy quark‐hadron duality when smeared over the heavy quark mass to an accuracy of order 1/M2. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594315

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

I make the case that the nucleon excitations do not exist as isolated higher spin states but are fully absorbed byK2, K2 ⊗ 12, 0 ⊕ 0, 12multiplets taking their origin from the rotational and vibrational excitations of an underlying quark‐diquark string. The &Dgr;(1232) spectrum presents itself as the exact replica (up to &Dgr;(1600)) of the nucleon spectrum with theK‐ clusters being shifted upward by about 200 MeV. QCD inspired arguments support legitimacy of the quark‐diquark string. The aboveKmultiplets can be mapped (up to form‐factors) onto Lorentz group representation spaces of the type &psgr;&mgr;1&cellip;&mgr;K, thus guaranteeing covariant description of resonant states. The quantum &psgr;&mgr;1&cellip;&mgr;Kstates are of multiple spins at rest, and of undetermined spins elsewhere. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594316

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

I draw attention to a recent breakthrough in the field of low energy pion physics: the consequences of the hidden symmetry of the QCD Hamiltonian have successfully been incorporated in the general dispersive framework for the &pgr;&pgr; scattering amplitude, which is due to Roy. The meagre experimental information about the imaginary parts at and above 0.8 GeV suffices to unambiguously and accurately pin down the scattering amplitude at lower energies. The recent Brookhaven data on the reactionK→ &pgr;&pgr;evprovide a significant test of the theory. They imply that the Gell‐Mann‐Oakes‐Renner relation is approximately valid — the bulk of the pion mass indeed originates in the quark condensate. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594317

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We discuss the evolution of the bubbles of quark matter which survive from the first‐order confinement phase transition till the increase of the internal pressure stops their contraction. We also show that at low temperature and high pressure a quark matter composition u d s is preferred to u d d. We finally describe the different colour superconducting phases which may be formed inside neutron stars, and the topological defects that can be generated, where the stable strangelets might be originated and perhaps already detected at high‐altitude observatories. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594318

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We review the results of our calculations for the energy spectrum and branching ratios ofV0→P0P0′&ggr; in the context of aU(3) ×U(3) linear sigma model which includes ’t Hooft interaction. The corresponding amplitudes reduce to theO(p4) predictions of CHPT for these processes in the limit of heavy scalars (or equivalently in the low energy region). In this sense our approach extend to the resonance region theO(p4) predictions of CHPT in a chiral invariant way. The measured energy spectrum and branching ratios are well described in this formalism. In particular, the negative interference shown by the data aroundm&pgr;&pgr;= 500MeVin &fgr; → &pgr;0&pgr;0&ggr; arises in a natural way in this framework. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594319

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A summary is presented of the most recent matrix elements for massless 2 → 2 scattering processes calculated at two loops in QCD perturbation theory together with a brief review on the calculational methods and techniques used. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1594320

出版商:AIP    

年代:1903

数据来源: AIP