578 research outputs found
Improvement of the Theta+ width estimation method on the Light Cone
Recently, Diakonov and Petrov have suggested a formalism in the Relativistic
Mean Field Approximation allowing one to derive the 3-, 5-, 7-,... quark
wavefunctions for the octet, decuplet and antidecuplet. They have used this
formalism and many strong approximations in order to estimate the exotic Theta+
width. The latter has been estimated to ~4 MeV. Besides they obtained that the
5-quark component of the nucleon is about 50% of its 3-quark component meaning
that relativistic effects are not small. We have improved the technique by
taking into account some relativistic corrections and considering the
previously neglected 5-quark exchange diagrams. We also have computed all
nucleon axial charges. It turns out that exchange diagrams affect very little
Diakonov's and Petrov's results while relativistic corrections reduce the
Theta+ width to ~2 MeV and the 5- to 3-quark component of the nucleon ratio to
30%.Comment: 28 pages, 15 figures; typo corrected and few comments adde
Fermionic determinant for dyons and instantons with nontrivial holonomy
We calculate exactly the functional determinant for fermions in fundamental
representation of SU(2) in the background of periodic instanton with
non-trivial value of the Polyakov line at spatial infinity. The determinant
depends on the value of the holonomy v, the temperature, and the parameter
r_12, which at large values can be treated as separation between the
Bogomolny--Prasad--Sommerfeld monopoles (or dyons) which constitute the
periodic instanton. We find a compact expression for small and large r_12 and
compute the determinant numerically for arbitrary r_12 and v.Comment: 17 pages, published version, references adde
Collective coordinates of the Skyrme model coupled with fermions
The problem of construction of fiber bundle over the moduli space of the
Skyrme model is considered. We analyse an extension of the original Skyrme
model which includes the minimal interaction with fermions. An analogy with
modili space of the fermion-monopole system is used to construct a fiber bundle
structure over the skyrmion moduli space. The possibility of the non-trivial
holonomy appearance is considered. It is shown that the effect of the fermion
interaction turns the -skyrmion moduli space into a real vector bundle with
natural connection.Comment: 10 page
Baryon vector and axial content up to the 7Q component
We have used the light-cone formulation of Chiral-Quark Soliton Model to
investigate the vector and axial content of octet, decuplet and the
hypothetical antidecuplet in the flavor SU(3) symmetry limit. We have extended
previous works by computing the 7Q contribution to vector and axial charges for
the octet and antidecuplet but stayed at the 5Q sector for the decuplet where
the full computation needs much more time. As expected the 7Q component has a
weaker impact on the quantities but still changes them by a few percent. We
give also a detailed decomposition of those charges into flavor, valence quark,
sea quark and antiquark contributions. Many of them are of course not (yet)
measured or estimated and constitute then a theoretical estimation. Among the
different interesting observations made in this work are the explicit
quadrupole deformation of decuplet baryons due to the pion field and the sum of
quark spins larger than the pentaquark one.Comment: 34 pages, 7 figures and 17 tables, revised and more explicit versio
The pion mass dependence of the nucleon form-factors of the energy momentum tensor in the chiral quark-soliton model
The nucleon form factors of the energy-momentum tensor are studied in the
large-Nc limit in the framework of the chiral quark-soliton model for model
parameters that simulate physical situations in which pions are heavy. This
allows for a direct comparison to lattice QCD results.Comment: 17 pages, 12 figure
Screening of Fractional Charges in (2+1)-dimensional QED
We show that the logarithmically rising static potential between
opposite-charged sources in two dimensions is screened by dynamical fields even
if the probe charges are fractional, in units of the charge of the dynamical
fields. The effect is due to quantum mechanics: the wave functions of the
screening charges are superpositions of two bumps localized both near the
opposite- and the same-charge sources, so that each of them gets exactly
screened.Comment: 17 pages, 4 figures, Latex, typo corrected and reference adde
The Neutron Electric Dipole Moment in the Instanton Vacuum: Quenched Versus Unquenched Simulations
We investigate the role played by the fermionic determinant in the evaluation
of the CP-violating neutron electric dipole moment (EDM) adopting the Instanton
Liquid Model. Significant differences between quenched and unquenched
calculations are found. In the case of unquenched simulations the neutron EDM
decreases linearly with the quark mass and is expected to vanish in the chiral
limit. On the contrary, within the quenched approximation, the neutron EDM
increases as the quark mass decreases and is expected to diverge as (1/m)**Nf
in the chiral limit. We argue that such a qualitatively different behavior is a
parameter-free, semi-classical prediction and occurs because the neutron EDM is
sensitive to the topological structure of the vacuum. The present analysis
suggests that quenched and unquenched lattice QCD simulations of the neutron
EDM as well as of other observables governed by topology might show up
important differences in the quark mass dependence, for mq < Lambda(QCD).Comment: 8 pages, 3 figures, 2 table
Gauge invariant effective action for the Polyakov line in the SU(N) Yang--Mills theory at high temperatures
We integrate out fast varying quantum fluctuations around static A_4 and A_i
fields for the SU(N) gauge group. By assuming that the gluon fields are slowly
varying but allowing for an arbitrary amplitude of A_4 we obtain two variants
of the effective high-temperature theory for the Polyakov line. One is the
effective action for the gauge-invariant eigenvalues of the Polyakov line, and
it is explicitly Z(N) symmetric. The other is the effective action for the
Polyakov line itself as an element of the SU(N). In this case the theory
necessarily includes the spatial components A_i to ensure its gauge invariance
under spatial gauge transformations. We derive the 1-loop effective action in
the `electric' and `magnetic' sectors, summing up all powers of A_4.Comment: RevTex4, 2 figure
Estimates of higher-dimensional vacuum condensates from the instanton vacuum
We calculate the values of non-factorizable dimension-7 vacuum condensates in
the instanton vacuum. We comment on a method, recently proposed by Oganesian,
to estimate the dimension-7 condensates by factorization of dimension-10
condensates in various inequivalent ways. The instanton estimates could be used
to analyze the stability of QCD sum rules with increasing dimensions.Comment: 8 pages, Late
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