2,577 research outputs found
Chiral effective field theory for nuclear matter
We report on the recent developments of a new effective field theory for
nuclear matter [1,2,3]. We present first the nuclear matter chiral power
counting that takes into account both short-- and long--range inter-nucleon
interactions. It also identifies non-perturbative strings of diagrams, related
to the iteration of nucleon-nucleon interactions, which have to be re-summed.
The methods of unitary chiral perturbation theory has been shown to be a useful
tool in order to perform those resummations. Results up to next-to-leading
order for the ground state energy per particle of nuclear matter, the in-medium
chiral quark condensate and pion self-energy are discussed.Comment: Plenary talk at Chiral10 WORKSHOP, 21-24 Jun 2010, Valencia, Spai
Skyrme models and nuclear matter equation of state
We investigate the role of pressure in a class of generalised Skyrme models. We introduce pressure as the trace of the spatial part of the energy-momentum tensor and show that it obeys the usual thermodynamical relation. Then, we compute analytically the mean-field equation of state in the high and medium pressure regimes by applying topological bounds on compact domains. The equation of state is further investigated numerically for the charge one skyrmions. We identify which term in a generalised Skyrme model is responsible for which part in the equation of state. Further, we compare our findings with the corresponding results in the Walecka model
Alternative experimental evidence for chiral restoration in excited baryons
Given existing empirical spectral patterns of excited hadrons it has been
suggested that chiral symmetry is approximately restored in excited hadrons at
zero temperature/density (effective symmetry restoration). If correct, this
implies that mass generation mechanisms and physics in excited hadrons is very
different as compared to the lowest states. One needs an alternative and
independent experimental information to confirm this conjecture. Using very
general chiral symmetry arguments it is shown that strict chiral restoration in
a given excited nucleon forbids its decay into the N \pi channel. Hence those
excited nucleons which are assumed from the spectroscopic patterns to be in
approximate chiral multiplets must only "weakly" decay into the N \pi channel,
(f_{N^*N\pi}/f_{NN\pi})^2 << 1. However, those baryons which have no chiral
partner must decay strongly with a decay constant comparable with f_{NN\pi}.
Decay constants can be extracted from the existing decay widths and branching
ratios. It turnes out that for all those well established excited nucleons
which can be classified into chiral doublets N_+(1440) - N_-(1535), N_+(1710) -
N_-(1650), N_+(1720) - N_-(1700), N_+(1680) - N_-(1675), N_+(2220) - N_-(2250),
N_+(?) - N_-(2190), N_+(?) - N_-(2600), the ratio is (f_{N^*N\pi}/f_{NN\pi})^2
~ 0.1 or much smaller for the high-spin states. In contrast, the only well
established excited nucleon for which the chiral partner cannot be identified
from the spectroscopic data, N(1520), has a decay constant into the N\pi
channel that is comparable with f_{NN\pi}. This gives an independent
experimental verification of the chiral symmetry restoration scenario.Comment: 4 pp. A new footnote with an alternative proof of impossibility of
parity doublet decay into pi + N is added. To appear in Phys. Rev. Let
Nuclear Forces and Few-Nucleon Studies Based on Chiral Perturbation Theory
After a brief review on the status of few--nucleon studies based on
conventional nuclear forces, we sketch the concepts of the effective field
theory approach constrained by chiral symmetry and its application to nuclear
forces. Then first results for few--nucleon observables are discussed.Comment: 8 pages, presented by W. Gloeckle at the International Symposium on
"A New Era of Nuclear Structure Physics", Kurokawa Village (Niigata Pref.),
Japan, Nov. 19-22, 200
Few-Nucleon Systems with Two-Nucleon Forces from Chiral Effective Field Theory
Nucleon-nucleon (NN) forces from chiral perturbation theory at
next-to-leading (NLO) and next-to-next-to-leading order (NNLO) are applied to
systems with two, three and four nucleons. At NNLO, we consider two versions of
the chiral potential which differ in the strength of the two-pion-exchange
(TPE) but describe two nucleon observables equally well. The NNLO potential
leads to unphysical deeply bound states in the low partial waves and effects of
the 3N forces, which appear first at this order, are expected to be large. We
provide arguments for a reduction of the TPE potential and introduce the NNLO*
version of the NN forces. We calculate nd scattering observables as well as
various properties of 3H and 4He with the NNLO* potential and find good
agreement with the data and with predictions based upon the standard
high-precision potentials. We find an improved description of the 3H and 4He
binding energies.Comment: 34 pages, 25 figure
Vector-axialvector mixing from a chiral effective field theory at finite temperature
We study the vector-axialvector mixing in a hot medium and its evolution
toward the chiral phase transition using different symmetry restoration
scenarios based on the generalized hidden local symmetry framework. We show
that the presence of the meson reduces the vector spectral function
around meson mass and enhances it around meson mass. The coupling
strength of to and vanishes at the critical temperature due
to the degenerate - masses. This feature holds rigorously in the
chiral limit and still stays intact to good approximation for the physical pion
mass.Comment: v2:11 pages, 6 figures, reorganized and expanded the text, new plots
and references added, main result and conclusions unchange
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