Z. Aouissat

Dropping sigma-meson mass and in-medium s-wave pion-pion correlations

The influence of a dropping sigma-meson mass on previously calculated in-medium pion-pion correlations in the J=I=0 (sigma-meson) channel is investigated. It is found that the invariant-mass distribution around the vacuum threshold experiences a further strong enhancement with respect to standard many-body effects. The relevance of this result for the explanation of recent

Single boson images via an extended Holstein-Primakoff mapping

A(\pi,2\pi)X

Chiral fluctuations in nuclei

data is pointed out.

Symmetry conserving non-perturbative s-wave renormalization of the pion in hot and baryonic dense medium

The Holstein-Primakoff mapping for pairs of bosons is extended in order to accommodate single boson mapping. The proposed extension allows a variety of applications and especially puts the formalism at finite temperature on firm ground. The new mapping is applied to the

Symmetry conserving dynamical mappings

O(N+1)

Importance of single boson and single fermion mappings in the thermal boson expansion

anharmonic oscillator with global symmetry broken down to

Extended Holstein-Primakoff mapping for the next-to-leading order of the 1/N expansion at finite temperature

O(N).

Self-consistent random phase approximation in a schematic field theoretical model

It is explicitly demonstrated that N-Goldstone modes appear. This result generalizes the Holstein-Primakoff mapping for interacting bosons as developed by Aouissat, Schuck, and Wambach [Nucl. Phys. A618, 402 (1997)].

Symmetry conserving 1/N expansion and extended Holstein-Primakoff mapping for anharmonic O(N + 1) oscillator model

The near-threshold enhancement in the π+π− invariant mass distribution in nuclei, observed by CHAOS collaboration [1] and for ππ pairs by the Crystal Ball collaboration [2], offers the interesting possibility of directly observing a signal for partial restoration of chiral symmetry in a dense medium. There seems to be theoretical consensus on a strong in-medium reshaping of the s-wave isoscalar pion-pair correlations as a direct consequence of increased fluctuations of the chiral order parameter. This translates into a significant downward shift of the strength in the ππ T -matrix in the scalar-isoscalar channel as seen in Fig. 1.

Anharmonic O(N) oscillator model in next-to-leading order of the 1/N expansion

A non-perturbative s-wave renormalization of the pion in a hot and baryon rich medium is presented. This approach proceeds via a mapping of the canonical pion into the axial Noethers charge. The mapping was made dynamical in the Hartree-Fock-Bogoliubov random phase approximation (HFB-RPA). It is shown that this approach, while order mixing, is still symmetry conserving both in the baryon free and baryon rich sectors, at zero as well as finite temperature. The systematic character of this approach is emphasized and it is particularly argued that it may constitute an interesting alternative for the non-perturbative assessment of the nuclear matter saturation properties.