14,548 research outputs found
Dynamical coupled-channels: the key to understanding resonances
Recent developments on a dynamical coupled-channels model of hadronic and
electromagnetic production of nucleon resonances are summarized.Comment: Invited Plenary talk at the 20th European Conference on Few-Body
Problems in Physics (EFB20), September 10-14 2007, Pisa, Italy. To appear in
the proceedings in Few-Body System
Universality for conditional measures of the sine point process
The sine process is a rigid point process on the real line, which means that
for almost all configurations , the number of points in an interval is determined by the points of outside of . In addition, the
points in are an orthogonal polynomial ensemble on with a weight
function that is determined by the points in . We prove a
universality result that in particular implies that the correlation kernel of
the orthogonal polynomial ensemble tends to the sine kernel as the length
tends to infinity, thereby answering a question posed by A.I. Bufetov.Comment: 26 pages, no figures, revised version with Appendix
The role of components in the nucleon and the N(1440) resonance
The role of components in the nucleon and the N(1440) resonance is
studied by explicit coupling of the lowest positive parity state
to the components in the harmonic oscillator quark model. The lowest
energy component, where the 4-quark subsystem has the flavor-spin
symmetry , is close in energy to the lowest positive
parity excitation of the nucleon in the quark model. The confining
interaction leads to a strong mixing of the system and the
positive parity excited state of the system. This result is in line with
the phenomenological indications for a two-component structure of the N(1440)
resonance. The presence of substantial components in the N(1440) can
bring about a reconciliation of the constituent quark model with the large
empirical decay width of the N(1440).Comment: Accepted for publication in Nucl. Phys.
Curvature function and coarse graining
A classic theorem in the theory of connections on principal fiber bundles
states that the evaluation of all holonomy functions gives enough information
to characterize the bundle structure (among those sharing the same structure
group and base manifold) and the connection up to a bundle equivalence map.
This result and other important properties of holonomy functions has encouraged
their use as the primary ingredient for the construction of families of quantum
gauge theories. However, in these applications often the set of holonomy
functions used is a discrete proper subset of the set of holonomy functions
needed for the characterization theorem to hold. We show that the evaluation of
a discrete set of holonomy functions does not characterize the bundle and does
not constrain the connection modulo gauge appropriately.
We exhibit a discrete set of functions of the connection and prove that in
the abelian case their evaluation characterizes the bundle structure (up to
equivalence), and constrains the connection modulo gauge up to "local details"
ignored when working at a given scale. The main ingredient is the Lie algebra
valued curvature function defined below. It covers the holonomy
function in the sense that .Comment: 34 page
A microscopic NN to NN*(1440) potential
By means of a NN to NN*(1440) transition potential derived in a
parameter-free way from a quark-model based NN potential, we determine
simultaneously the and coupling constants.
We also present a study of the target Roper excitation diagram contributing to
the reaction.Comment: Talk presented at the Fourth International Conference on Perspectives
in Hadronic Physics (ICTP, Trieste, Italy, May 2003). To appear in EPJA. 6
pages, 9 figures, needs svepj.clo and svjour.cl
Saturation properties of helium drops from a Leading Order description
Saturation properties are directly linked to the short-range scale of the
two-body interaction of the particles. The case of helium is particular, from
one hand the two-body potential has a strong repulsion at short distances. On
the other hand, the extremely weak binding of the helium dimer locates this
system very close to the unitary limit allowing for a description based on an
effective theory. At leading order of this theory a two- and a three-body term
appear, each one characterized by a low energy constant. In a potential model
this description corresponds to a soft potential model with a two-body term
purely attractive plus a three-body term purely repulsive constructed to
describe the dimer and trimer binding energies. Here we analyse the capability
of this model to describe the saturation properties making a direct link
between the low energy scale and the short-range correlations. We will show
that the energy per particle, , can be obtained with reasonable accuracy
at leading order extending the validity of this approximation, characterizing
universal behavior in few-boson systems close to the unitary limit, to the
many-body system.Comment: 5 pages, 3 figure
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