9,972 research outputs found
Pion Electromagnetic Form Factor in the Factorization Formulae
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC
wavefunction affects the hard and soft contributions substantially. A model for
the twist-3 wavefunction of the pion has been
constructed based on the moment calculation by applying the QCD sum rules,
whose distribution amplitude has a better end-point behavior than that of the
asymptotic one. With this model wavefunction, the twist-3 contributions
including both the usual helicity components () and the
higher helicity components () to the pion form
factor have been studied within the modified pQCD approach. Our results show
that the twist-3 contribution drops fast and it becomes less than the twist-2
contribution at . The higher helicity components in the
twist-3 wavefunction will give an extra suppression to the pion form factor.
When all the power contributions, which include higher order in ,
higher helicities, higher twists in DA and etc., have been taken into account,
it is expected that the hard contributions will fit the present experimental
data well at the energy region where pQCD is applicable.Comment: 4 pages, 2 figures, Prepared for International Conference on QCD and
Hadronic Physics, Beijing, China, 16-20 June 200
Thermodynamics of the Schwarzschild-AdS black hole with a minimal length
Using the mass-smeared scheme of black holes, we study the thermodynamics of
black holes. Two interesting models are considered. One is the self-regular
Schwarzschild-AdS black hole whose mass density is given by the analogue to
probability densities of quantum hydrogen atoms. The other model is the same
black hole but whose mass density is chosen to be a rational fractional
function of radial coordinates. Both mass densities are in fact analytic
expressions of the -function. We analyze the phase structures of the
two models by investigating the heat capacity at constant pressure and the
Gibbs free energy in an isothermal-isobaric ensemble. Both models fail to decay
into the pure thermal radiation even with the positive Gibbs free energy due to
the existence of a minimal length. Furthermore, we extend our analysis to a
general mass-smeared form that is also associated with the -function,
and indicate the similar thermodynamic properties for various possible
mass-smeared forms based on the -function.Comment: v1: 25 pages, 14 figures; v2: 26 pages, 15 figures; v3: minor
revisions, final version to appear in Adv. High Energy Phy
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