Pseudoscalar

About: Pseudoscalar is a research topic. Over the lifetime, 4967 publications have been published within this topic receiving 106530 citations. The topic is also known as: pseudo-scalar.

Quark structure of pseudoscalar mesons

Abstract: I review to which extent the properties of pseudoscalar mesons can be understood in terms of the underlying quark (and eventually gluon) structure. Special emphasis is put on the progress in our understanding of η–η′ mixing. Process-independent mixing parameters are defined, and relations between different bases and conventions are studied. Both, the low-energy description in the framework of chiral perturbation theory and the high-energy application in terms of light-cone wave functions for partonic Fock states, are considered. A thorough discussion of theoretical and phenomenological consequences of the mixing approach will be given. Finally, I will discuss mixing with other states (π0, ηc, …).

The U(1) Problem

Abstract: A detailed analysis of the problems associated with the conserved U(1) axial-vector current in quark-gluon models is presented. It is shown that such models involve a light isoscalar pseudoscalar boson, with a mass less than $\sqrt{3}{m}_{\ensuremath{\pi}}$. The existence of this boson would produce a strong off-shell variation in the $\ensuremath{\eta}\ensuremath{\rightarrow}3\ensuremath{\pi}$ matrix element, thus invalidating the usual conclusions about the rate and energy dependence of this decay. Following Kogut and Susskind, it is proposed that the light Goldstone boson is actually a dipole, with positive- and negative-metric parts, which cancel in matrix elements of gluon-gauge-invariant operators but not in operators such as the U(1) current. It is shown that the masses of the observable pseudoscalar bosons and the $\ensuremath{\eta}$ decay rate are then just as they would be in a theory without the U(1) symmetry, and in fair agreement with experiment. The application of current algebra to theories with charmed quarks is briefly discussed.

Theoretical update of pseudoscalar meson distribution amplitudes of higher twist: the nonsinglet case

Abstract: We discuss the two and three particle light-cone distribution amplitudes (DAs) of pseudoscalar nonsinglet mesons of twist 3 and 4. Using nonlocal operator identities and conformal expansion, we derive closed expressions for several DAs. We also include meson-mass corrections which prove to be dominant in the twist 4 DAs of K and η mesons. Explicit parametrizations for the DAs of π, K and η mesons are given, with the numerical input parameters determined from QCD sum rules.