263 research outputs found
Effective short-range interaction for spin-singlet P-wave nucleon-nucleon scattering
Distorted-wave methods are used to remove the effects of one- and two-pion
exchange up to order Q^3 from the empirical 1P1 phase shift. The one divergence
that arises can be renormalised using an order-Q^2 counterterm which is
provided by the (Weinberg) power counting appropriate to the effective field
theory for this channel. The residual interaction is used to estimate the scale
of the underlying physics.Comment: 4 pages, 3 figures (pdf
Three and Four Harmonically Trapped Particles in an Effective Field Theory Framework
We study systems of few two-component fermions interacting via short-range
interactions within a harmonic-oscillator trap. The dominant interactions,
which are two-body, are organized according to the number of derivatives and
defined in a two-body truncated model space made from a bound-state basis.
Leading-order (LO) interactions are solved for exactly using the formalism of
the No-Core Shell Model, whereas corrections are treated as many-body
perturbations. We show explicitly that next-to-LO and next-to-next-to-LO
interactions improve convergence as the model space increases. We present
results at unitarity for three- and four-fermion systems, which show excellent
agreement with the exact solution (for the three-body problem) and results
obtained by others methods (in the four-body case). We also present results for
finite scattering lengths and non-zero range of the interaction, including (at
positive scattering length) observation of a change in the structure of the
three-body ground state and extraction of the atom-dimer scattering length.Comment: 18 pages, 10 figure
The \rho\rho interaction in the hidden gauge formalism and the f_0(1370) and f_2(1270) resonances
We have studied the interaction of vectors mesons within the hidden gauge
formalism and applied it to the particular case of the interaction.
We find a strong attraction in the isospin, spin channels I,S=0,0 and 0,2,
which is enough to bind the system. We also find that the
attraction in the I,S=0,2 channel is much stronger than in the 0,0 case. The
states develop a width when the mass distribution is considered, and
particularly when the decay channel is turned on. Using a
regularization scheme with cut offs of natural size, we obtain results in fair
agreement with the mass and the width of the and meson
states, providing a natural explanation of why the tensor state is more bound
than the scalar and offering a new picture for these states, which would be
dynamically generated from the interaction or, in simpler words,
molecular states.Comment: Version accepted for publicatio
Hidden gauge formalism for the radiative decays of axial-vector mesons
The radiative decay of the axial-vector resonances into a pseudoscalar meson
and a photon is studied using the vector meson Lagrangian obtained from the
hidden gauge symmetry (HGS) formalism. The formalism is well suited to study
this problem since it deals with pseudoscalar and vector mesons in a unified
way, respecting chiral invariance. We show explicitly the gauge invariance of
the set of diagrams that appear in the approach and evaluate the radiative
decay width of the a1(1260) and b1(1235) axial vector meson resonances into pi
gamma. We also include the contribution of loops involving anomalous couplings
and compare the results to those obtained previously within another formalism.Comment: 24 pages, 6 tables, 11 figure
Generalized vector form factors of the pion in a chiral quark model
Generalized vector form factors of the pion, related to the moments of the
generalized parton distribution functions, are evaluated in the
Nambu--Jona-Lasinio model with the Pauli-Villars regularization. The lowest
moments (the electromagnetic and the gravitational form factors) are compared
to recent lattice data, with fair agreement. Predictions for higher-order
moments are also made. Relevant features of the generalized form factors in the
chiral quark models are highlighted and the role of the QCD evolution for the
higher-order GFFs is stressed.Comment: Dedicated to the memory of Manoj K. Banerjee, to appear in a special
issue of the Indian Journal of Physics, 6 pages, 4 figure
Low-energy interaction of composite spin-half systems with scalar and vector fields
We consider a composite spin-half particle moving in spatially-varying scalar
and vector fields. The vector field is assumed to couple to a conserved charge,
but no assumption is made about either the structure of the composite or its
coupling to the scalar field. A general form for the piece of the spin-orbit
interaction of the composite with the scalar and vector fields which is
first-order in momentum transfer and second-order in the fields is
derived.Comment: 10 pages, RevTe
Chiral symmetry and quantum hadro-dynamics
Using the linear sigma model, we study the evolutions of the quark condensate
and of the nucleon mass in the nuclear medium. Our formulation of the model
allows the inclusion of both pion and scalar-isoscalar degrees of freedom. It
guarantees that the low energy theorems and the constrains of chiral
perturbation theory are respected. We show how this formalism incorporates
quantum hadro-dynamics improved by the pion loops effects.Comment: 24 pages, 2 figure
Renormalisation-group analysis of repulsive three-body systems
A coordinate space approach, based on that used by Efimov, is applied to
three-body systems with contact interactions between pairs of particles. In
systems with nonzero orbital angular momentum or with asymmetric spatial wave
functions, the hyperradial equation contains a repulsive 1/r^2 potential. The
resulting wave functions are used in a renormalisation group analysis. This
confirms Griesshammer's power counting for short-range three-body forces in
these systems. The only exceptions are ones like the 4S channel for three
nucleons, where any derivatives needed in the interaction are found to be
already counted by the scaling with the cut-off.Comment: 5 pages, RevTe
A new window on Strange Quark Matter as the ground state of strongly interacting matter
If strange quark matter is the true ground state of matter, it must have
lower energy than nuclear matter. Simultaneously, two-flavour quark matter must
have higher energy than nuclear matter, for otherwise the latter would convert
to the former. We show, using an effective chiral lagrangian, that the
existence of a new lower energy ground state for two-flavour quark matter, the
pion condensate, shrinks the window for strange quark matter to be the ground
state of matter and sets new limits on the current strange quark mass
Effective Nucleon-Nucleon Interaction and Fermi Liquid Theory
We present two novel relations between the quasiparticle interaction in
nuclear matter and the unique low momentum nucleon-nucleon interaction in
vacuum. These relations provide two independent constraints on the Fermi liquid
parameters of nuclear matter. Moreover, the new constraints define two
combinations of Fermi liquid parameters, which are invariant under the
renormalization group flow in the particle-hole channels. Using empirical
values for the spin-independent Fermi liquid parameters, we are able to compute
the major spin-dependent ones by imposing the new constraints as well as the
Pauli principle sum rules.Comment: 4 pages, 5 figures, in Proc. 11th International Conference on Recent
Progress in Many-Body Theories, Manchester, UK, July 9-13, 200
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