14365411
A consistent approximation scheme beyond RPA for bosons
Abstract:In this paper, we develop a consistent extension of RPA for bosonic systems. In order to illustrate the method, we consider the case of the anharmonic oscillator. We compare our results with those obtained in mean-field and standard RPA approaches with the exact ones and show that they are very close to these ones.
118415445
How the Polyakov loop and the regularization affect strangeness and restoration of symmetries at finite T
The effects of the Polyakov loop and of a regularization procedure that allows the presence of high momentum quark states at finite temperature is investigated within the Polyakov‐loop extended Nambu‐Jona‐Lasinio model. The characteristic temperatures, as well as the behavior of observables that signal deconfinement and restoration of chiral and axial symmetries, are analyzed, paying special attention to the behavior of strangeness degrees of freedom. We observe that the cumulative effects of the Polyakov loop and of the regularization procedure contribute to a better description of the thermodynamics, as compared with lattice estimations. We find a faster partial restoration of chiral symmetry and the restoration of the axial symmetry appears as a natural consequence of the full recovering of the chiral symmetry that was dynamically broken. These results show the relevance of the effects of the interplay among the Polyakov loop dynamics, the high momentum quark sates and the restoration of the chiral and...
118491126
Scalar-pseudoscalar meson behavior and restoration of symmetries in SU(3) PNJL model
The modification of mesonic observables in a hot medium is analyzed as a tool to investigate the restoration of chiral and axial symmetries in the context of the Polyakov-loop extended Nambu--Jona-Lasinio model. The results of the extended model lead to the conclusion that the effects of the Polyakov loop are fundamental for reproducing lattice findings. In particular, the partial restoration of the chiral symmetry is faster in the PNJL model than in the NJL one, and it is responsible for several effects: the meson-quark coupling constants show a remarkable difference in both models, there is a faster tendency to recover the Okubo-Zweig-Iizuka rule, and finally the topological susceptibility nicely reproduces the lattice results around $T/T_c\approx 1.0$.
17678438
Long distance expansion for the NJL model with SU(3) and UA(1) breaking
This work is a follow up of recent investigations, where we study the implications of a generalized heat kernel expansion, constructed to incorporate non-perturbatively the effects of a non-commutative quark mass matrix in a fully covariant way at each order of the expansion. As underlying Lagrangian we use the Nambu–Jona-Lasinio model of QCD, with SUf(3) and UA(1) breaking, the latter generated by the 't Hooft flavour determinant interaction. The associated bosonized Lagrangian is derived in leading stationary phase approximation (SPA) and up to second order in the generalized heat kernel expansion. Its symmetry breaking pattern is shown to have a complex structure, involving all powers of the mesonic fields allowed by symmetry. The considered Lagrangian yields a reliable playground for the study of the implications of symmetry and vacuum structure on the mesonic spectra, which we evaluate for the scalar and pseudoscalar meson nonets and compare with other approaches and experiment.
16319641
Scalar-pseudoscalar meson spectrum in SU(3) PNJL model
We investigate the modifications of mesonic properties in a hot medium having in mind to use the mesonic modes as a tool to analyze the restoration of chiral and axial symmetries in the context of the SU(3) Polyakov--Nambu--Jona-Lasinio (PNJL) model. The results lead to the conclusion that the effects of the Polyakov loop are fundamental for reproducing lattice findings. It is found that the restoration of chiral symmetry in the PNJL model occurs in a small range of temperature (smaller that in the Nambu--Jona-Lasinio (NJL)), and the topological susceptibility reproduces well the lattice results around $T/T_c^\chi\approx 1.0$.
118426821
Phase transition and critical end point driven by an external magnetic field in asymmetric quark matter
The location of the critical end point (CEP) in the QCD phase diagram is determined under different scenarios. The effect of strangeness, isospin/charge asymmetry and an external magnetic field is investigated. The discussion is performed within the 2+1 flavor Nambu–Jona-Lasinio model with Polyakov loop. It is shown that isospin asymmetry shifts the CEP to larger baryonic chemical potentials and smaller temperatures. At large asymmetries the CEP disappears. However, a strong enough magnetic field drives the system into a first order phase transition.
135763
Landau-Pomeranchuk-Migdal effect for multihundred GeV electrons
Experimental results for the bremsstrahlung energy loss of 149, 207, and 287 GeV electrons in thin Ir, Ta, and Cu targets are presented. For each target and energy, a comparison between simulated values based on the Landau-Pomeranchuk-Migdal (LPM) suppression of incoherent bremsstrahlung is shown. For the electron energies investigated, the LPM effect enters the quantum regime where the recoil imposed on the electron by the emitted photon becomes important. Good agreement between simulations based on Migdal's theory and data from the experiment is found, indicating that the LPM suppression is well understood also in the quantum regime. Results from a comparison between simulations with the "threshold" energy E