Chiral Symmetry In Nuclear Matter Research Articles

Open strange meson $K^\pm_1$ in hot and dense nuclear matter

Using the unification of the chiral SU(3) model and QCD sum rules, we deduce the in-medium properties of K^\pm_1K1± meson. Within the chiral SU(3) model, medium modified gluon and quark condensates are evaluated through their interactions with the scalar fields (\sigmaσ, \zetaζ, \deltaδ, and \chiχ). These condensates are further used as input in the Borel transformed equations of QCD sum rules to evaluate the in-medium mass of strange K^\pm_1K1± meson. The in-medium property of the above meson can be used to study the restoration of chiral symmetry in nuclear matter.

Examination of N*(1535) as a probe to observe the partial restoration of chiral symmetry in nuclear matter

We investigate modifications of mass and decay width of $N^*(1535)$ in nuclear matter in a chiral symmetric way. The nucleon and $N^*(1535)$ are introduced by a parity doublet model, and nuclear matter is constructed by one-loop diagrams of the nucleon and $N^*(1535)$. The decay width of $N^*(1535)$ is studied respecting chiral symmetry. Our calculations show that the partial width of $\Gamma_{N^*\to N\pi}$ is slightly broadened by a collisional broadening, and that of $\Gamma_{N^*\to N\eta}$ is drastically suppressed at density. As a result, the total decay width $\Gamma_{\rm tot}$ gets small at density. These modifications, especially the drastic narrowing of partial width of $\Gamma_{N^*\to N\eta}$, together with the dropping of mass of $N^*(1535)$ provide experiments for observing the partial restoration of chiral symmetry in nuclear matter by means of $N^*(1535)$ resonance with useful information.

Spectral functions for D¯ and D¯0* mesons in nuclear matter with partial restoration of chiral symmetry

We investigate the in-medium masses of a $\bar{D} (0^-)$ meson and a $\bar{D}_0^* (0^+)$ meson and spectral functions for $\bar{D}$ and $\bar{D}_0^*$ meson channels in nuclear matter. These mesons are introduced as chiral partner in the chiral symmetry broken vacuum, hence they are useful to explore the partial restoration of the broken chiral symmetry in nuclear matter. We consider the linear sigma model to describe the chiral symmetry breaking. Our study shows that the loop corrections to $\bar{D}$ and $\bar{D}_0^*$ meson masses provide a smaller mass splitting at finite density than that in vacuum, whose result indicates a tendency of the restoration of the chiral symmetry. We investigate also the spectral function for $\bar{D}_0^*$ meson channel, and find three peaks. The first peak which corresponds to the resonance of $\bar{D}_0^*$ meson is broadened by collisions with nucleons in medium, and the peak position shifts to lower mass due to the partial restoration of chiral symmetry as the density increases. The second peak is identified as a threshold enhancement which shows a remarkable enhancement as the density increase. The third peak is Landau damping. The obtained properties of $\bar{D}$ and $\bar{D}_0^*$ mesons in nuclear matter will provide useful information for experiments.

Nuclear equation of state in a relativistic independent quark model with chiral symmetry and dependence on quark masses

We have calculated the properties of nuclear matter in a self-consistent manner with a quark-meson coupling mechanism incorporating the structure of nucleons in vacuum through a relativistic potential model; where the dominant confining interaction for the free independent quarks inside a nucleon is represented by a phenomenologically average potential in equally mixed scalar-vector harmonic form. Corrections due to spurious center of mass motion as well as those due to other residual interactions, such as the one gluon exchange at short distances and quark-pion coupling arising out of chiral symmetry restoration, have been considered in a perturbative manner to obtain the nucleon mass in vacuum. The nucleon-nucleon interaction in nuclear matter is then realized by introducing additional quark couplings to $\ensuremath{\sigma}$ and $\ensuremath{\omega}$ mesons through mean field approximations. The relevant parameters of the interaction are obtained self-consistently while realizing the saturation properties such as the binding energy, pressure, and compressibility of the nuclear matter. We also discuss some implications of chiral symmetry in nuclear matter along with the nucleon and nuclear $\ensuremath{\sigma}$ term and the sensitivity of nuclear matter binding energy with variations in the light quark mass.

The a1(1260) as a Resonance in Nuclear Matter

We present a theoretical study of the properties of the a1(1260) axial-vector resonance in a cold nuclear medium. In the vacuum, the a1(1260) resonance is generated dynamically from the interactions of a pseudoscalar and vector meson (ρπ and KK*) in a coupled channel chiral unitary approach. Medium effects are implemented through the modification of the ρ and π propagators at finite nuclear density from well established microscopic many-body calculations. The in-medium pion spectral function accounts for the coupling to N-hole and Δ-hole excitations including short range correlations, whereas the in-medium ρ incorporates modifications of its virtual pion cloud as well as direct resonance-hole excitations. The resulting in-medium a1(1260) exhibits significant broadening with increasing density as reflected in the ρπ scattering amplitude. The possible relation of our results with partial restoration of chiral symmetry in nuclear matter is discussed in terms of in-medium Weinberg sum rules.

The [formula omitted] interaction in nuclear matter from a study of the [formula omitted] reactions

The pion-production reactions π+A→π+π±A′ were studied on 2H, 12C, 40Ca, and 208Pb nuclei at an incident pion energy of Tπ+=283 MeV. Pions were detected in coincidence using the CHAOS spectrometer. The experimental results are reduced to differential cross sections and compared to both theoretical predictions and the reaction phase space. The composite ratio CππA between the π+π± invariant masses on nuclei and on the nucleon is also presented. Near the 2mπ threshold pion pairs couple to (ππ)I=J=0 when produced in the π+→π+π− reaction channel. There is a marked near-threshold enhancement of Cπ+π−A which is consistent with theoretical predictions addressing the partial restoration of chiral symmetry in nuclear matter. Furthermore, the behaviour of Cπ+π−A is well described when the restoration of chiral symmetry is combined with standard P-wave renormalization of pions in nuclear matter. On the other hand, nuclear matter only weakly influences Cπ+π+A, which displays a flat behaviour throughout the energy range regardless of A.

ρ-mass modification in3He: Signal of restoration of chiral symmetry or test for nuclear matter models?

Two recent experiments have demonstrated that the effective $\rho$-mass in nuclear medium, as extracted from the $^3He(\gamma, \pi^+ \pi^-)$ reaction, is substantially reduced. This has been advocated as an indication of partial restoration of chiral symmetry in nuclear matter. We show that even in the absence of chiral symmetry, effective mean field nuclear matter models can explain these findings quantitatively.

On scale and chiral symmetry in nuclear matter

We examine the properties of cold matter at transnuclear densities using an effective lagrangian, suggested by QCD, which incorporates broken scale and chiral invariance. Nuclear matter is found to saturate in the mean field approximation with reasonable values of the parameters. Effective nucleon masses at equilibrium are obtained in the range 0.72–0.78, with the larger values favored.

Partial restoration of chiral symmetry in nuclear matter.

Recent work of Cohen, Furnstahl, and Griegel has advanced our understanding of the behavior of quark and gluon condensates in nuclear matter. We make use of their analysis to discuss the role of chiral condensates as they appear in relativistic Brueckner-Hartree-Fock theory. We find some support for assumptions we used to discuss the properties of nuclear matter in our earlier work. We also find that a rather consistent picture emerges from these studies, when we relate the parameters of the boson-exchange model of nuclear forces to an underlying field-theoretic description of nuclear matter.

Chiral symmetry in nuclear matter

We use the chiral σ-ω model at zero temperature to study the role of chiral symmetry in nuclear matter. The central role played by the pion propagator in connection with the energy density of nuclear matter and the problem of chiral phase transitions is pointed out. Results obtained previously are reexamined from the standpoint of chiral symmetry. Consequences of baryon current conservation and the renormalization of the neutral vector boson field in connection with many-body problems are also treated in detail.