6,169 research outputs found
Vacuum structure of a modified MIT Bag
An alternative to introducing and subsequently renormalizing classical
parameters in the expression for the vacuum energy of the MIT bag for quarks is
proposed in the massless case by appealing to the QCD trace anomaly and scale
separation due to asymptotic freedom. The explicit inclusion of gluons implies
an unrealistically low separation scale.Comment: 5 pages, 2 figure
Magnetic moments of S-shell pentaquarks in the constituent quark model
We discuss the magnetic moments of the recently discovered exotic baryons
Theta(+) and Xi(--) and their multiplet partners in the framework of a naive
additive quark model. These baryons are set up as pentaquark states where four
quarks and a single antiquark are located in their ground state orbit. The
pentaquark states are classified as members of the flavor SU(3) octet and
antidecuplet with spin-parity J^P = (1/2)^- and (3/2)^-, where we determine the
magnetic moments of these pentaquark states.Comment: 13 pages, 2 figures, elsart; publication version, 8 pages, 1 figure,
ptptex; upload miss correcte
Electromagnetic structure of the nucleon and the Roper resonance in a light-front quark approach
A relativistic light-front quark model is used to describe both the elastic
nucleon and nucleon-Roper transition form factors in a large Q2 range, up to 35
GeV2 for the elastic and up to 12 GeV2 for the resonance case. Relativistic
three-quark configurations satisfying the Pauli exclusion principle on the
light-front are used for the derivation of the current matrix elements. The
Roper resonance is considered as a mixed state of a three-quark core
configuration and a molecular N+sigma hadron component. Based on this ansatz we
obtain a realistic description of both processes, elastic and inelastic, and
show that existing experimental data are indicative of a composite structure of
the Roper resonance.Comment: 19 page
Radiative proton-antiproton annihilation and isospin mixing in protonium
A detailed analysis of the radiative annihilation is made in the
framework of a two-step formalism, the annihilates into meson
channels containing a vector meson with a subsequent conversion into a photon
via the vector dominance model (VDM). Both steps are derived from the
underlying quark model. First, branching ratios for radiative protonium
annihilation are calculated and compared with data. Then, details of the
isospin interference are studied for different models of the initial protonium
state and also for different kinematical form factors. The isospin interference
is shown to be uniquely connected to the mixing in the
protonium state. Values of the interference terms directly deduced from data
are consistent with theoretical expectations, indicating a dominant
component for the and a sizable component for the
protonium state. The analysis is extended to the
transition, where the large observed branching ratio remains unexplained in the
VDM approach.Comment: 34 pages, RevTeX, 2 figures, to appear in Phys. Rev. C; typos
correcte
Pion dominance in RPV SUSY induced neutrinoless double beta decay
At the quark level there are basically two types of contributions of R-parity
violating SUSY (RPV SUSY) to neutrinoless double beta decay: the short-range
contribution involving only heavy virtual superpartners and the long-range one
with the virtual squark and neutrino. Hadronization of the effective operators,
corresponding to these two types of contributions, may in general involve
virtual pions in addition to the close on-mass-shell nucleons. It is known that
the short-range contribution is dominated by the pion exchange. In the present
paper we show that this is also true for the long-range RPV SUSY contribution
and, therefore, the RPV SUSY contributes to the neutrinoless double beta decay
dominantly via charged pion exchange between the decaying nucleons.Comment: 7 pages, 1 figure. Minor corrections, several comments and references
adde
Charmed baryon Sigmac(2800) as a ND hadronic molecule
The isotriplet Sigmac(2800) baryon with possible quantum numbers J(P) =
1/2(+), 1/2(-) or 3/2(+), 3/2(-) is considered as a hadronic molecule composed
of a nucleon and a D meson. We determine the strong two-body decay widths
Sigmac to Lambdac + pi which are shown to be consistent with current data for
the J(P) = 1/2(+) and J(P) = 3/2(-) assignments.Comment: 8 pages, 2 figure
Effect of the channel and interference phenomena in the two-pion transitions of charmonia and bottomonia
The basic shape of di-pion mass spectra in the two-pion transitions of both
charmonia and bottomonia states is explained by an unified mechanism based on
contributions of the , and coupled channels
including their interference. The role of the individual resonances in
shaping the di-pion mass distributions in the charmonia and bottomonia decays
is considered.Comment: 8 pages, 4 figures, Talk at the XXIII International Baldin Seminar on
High Energy Physics Problems "Relativistic Nuclear Physics \& Quantum
Chromodynamics" (Dubna, Russia, 19--24 September 2016). arXiv admin note:
text overlap with arXiv:1610.0789
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