263 research outputs found
Chirally symmetric quark description of low energy \pi-\pi scattering
Weinberg's theorem for \pi-\pi scattering, including the Adler zero at
threshold in the chiral limit, is analytically proved for microscopic quark
models that preserve chiral symmetry. Implementing Ward-Takahashi identities,
the isospin 0 and 2 scattering lengths are derived in exact agreement with
Weinberg's low energy results. Our proof applies to alternative quark
formulations including the Hamiltonian and Euclidean space Dyson-Schwinger
approaches. Finally, the threshold \pi-\pi scattering amplitudes are calculated
using the Dyson-Schwinger equations in the rainbow-ladder truncation,
confirming the formal derivation.Comment: 10 pages, 7 figures, Revtex
Repulsive Core of NN S-Wave Scattering in a Quark Model with a Condensed Vacuum
We work in a chiral invariant quark model, with a condensed vacuum,
characterized by only one parameter. Bound state equations for the nucleon and
Delta are solved in order to obtain an updated value of their radii and masses.
Nucleon-nucleon S-Wave scattering is studied in the RGM framework both for
isospin T=1 and T=0. The phase shifts are calculated and an equivalent local
potential, which is consistent with K-N scattering, is derived. The result is a
reasonable microscopic short range repulsion in the nucleon-nucleon
interaction.Comment: 23 pages in latex revtex, 4 Postscript figure
A new Perspective on the Scalar meson Puzzle, from Spontaneous Chiral Symmetry Breaking Beyond BCS
We introduce coupled channels of Bethe-Salpeter mesons both in the boundstate
equation for mesons and in the mass gap equation for chiral symmetry.
Consistency is insured by the Ward Identities for axial currents, which
preserve the Goldstone boson nature of the pion and prevents a systematic shift
of the hadron spectrum. We study the decay of a scalar meson coupled to a pair
of pseudoscalars. We also show that coupled channels reduce the breaking of
chiral symmetry, with the same Feynman diagrams that appear in the coupling of
a scalar meson to a pair of pseudoscalar mesons. Exact calculations are
performed in a particular confining quark model, where we find that the
groundstate meson is the f_0(980) with a partial decay
width of 40MeV. We also find a 30% reduction of the chiral condensate due to
coupled channels.Comment: 17 pages, Revtex, 8 eps figures, and several eps diagrams in
equation
Vacuum replicas in QCD
The properties of the vacuum are addressed in the two- and four-dimensional
quark models for QCD. It is demonstrated that the two-dimensional QCD ('t Hooft
model) possesses only one possible vacuum state - the solution to the mass-gap
equation, which provides spontaneous breaking of the chiral symmetry (SBCS). On
the contrary, the four-dimensional theory with confinement modeled by the
linear potential supplied by the Coulomb OGE interaction, not only has the
chirally-noninvariant ground vacuum state, but it possesses an excited vacuum
replica, which also exhibits SBCS and can realize as a metastable intermediate
state of hadronic systems. We discuss the influence of the latter on physical
observables as well as on the possibility to probe the vacuum background fields
in QCD.Comment: RevTeX4, 26 pages, 8 EPS figures, extended references, corrected some
typos, to appear in Phys.Rev.
The BES f_0(1810): a new glueball candidate
We analyze the f_0(1810) state recently observed by the BES collaboration via
radiative J/\psi decay to a resonant \phi\omega spectrum and confront it with
DM2 data and glueball theory. The DM2 group only measured \omega\omega decays
and reported a pseudoscalar but no scalar resonance in this mass region. A
rescattering mechanism from the open flavored KKbar decay channel is considered
to explain why the resonance is only seen in the flavor asymmetric \omega\phi
branch along with a discussion of positive C parity charmonia decays to
strengthen the case for preferred open flavor glueball decays. We also
calculate the total glueball decay width to be roughly 100 MeV, in agreement
with the narrow, newly found f_0, and smaller than the expected estimate of
200-400 MeV. We conclude that this discovered scalar hadron is a solid glueball
candidate and deserves further experimental investigation, especially in the
K-Kbar channel. Finally we comment on other, but less likely, possible
assignments for this state.Comment: 11 pages, 4 figures. Major substantive additions, including an
ab-initio, QCD-based computation of the glueball inclusive decay width,
evaluation of final state effects, and enhanced discussion of several
alternative possibilities. Our conclusions are unchanged: the BES f_0(1810)
is a promising glueball candidat
D^+ \to K^- \p^+ \p^+ : the low-energy sector
An effective chiral lagrangian, which includes scalar
resonances, is used to describe the process D^+ \rar K^- \p^+ \p^+ at
low-energies. Our main result is a set of five -wave amplitudes, suited to
be used in analyses of production data.Comment: Talk given at SCADRON 70 - Workshop on Scalar Mesons and Related
Topics - Lisbon - February 200
A Espectroscopia na região do Infravermelho e algumas aplicações.
bitstream/item/88969/1/DOC51-2010.pd
Algas e cianobactérias continentais no estado do Pará, Brasil.
Estudos ficológicos no Pará; Compilação dos dados; Diversidade; Cyanophyceae/Cyanobacteria; Chlamydophyceae; Chlorophyceae; Zygnemaphyceae; Oedogoniophyceae; Charophyceae; Euglenophyceae; Dinophyceae; Chrysophyceae; Xanthophyceae; Cryptophyceae; Rhodophyceae; Classe não definida
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