Chiral symmetry and light resonances in hot and dense matter

Abstract

Abstract. We present a study of the ππ scattering amplitude in the σ and ρ channels at finite temperature and nuclear density within a chiral unitary framework. Meson resonances are dynamically generated in our approach, which allows us to analyze the behavior of their associated scattering poles when the system is driven towards chiral symmetry restoration. Medium effects are incorporated in three ways: (a) by thermal corrections of the unitarized scattering amplitudes, (b) by finite nuclear density effects associated to a renormalization of the pion decay constant, and complementarily (c) by extending our calculation of the scalar-isoscalar channel to account for finite nuclear density and temperature effects in a microscopic many-body implementation of pion dynamics. Our results are discussed in connection with several phenomenological aspects relevant for nuclear matter and Heavy-Ion Collision experiments, such as ρ mass scaling vs broadening from dilepton spectra and chiral restoration signals in the σ channel. We also elaborate on the molecular nature of ππ resonances. PACS

Transport coefficients and resonances for a meson gas in chiral perturbation theory

“…We see that the mass shift is small remaining far from the threshold near the temperature of the chiral phase transition, and the width increases instead. This behavior is compatible with the dilepton data from heavy ion collisions (see details in [33,34]). …”

“…This approach only takes into account a limited class of contributions, but we reproduce several aspects of the expected chiral symmetry restoration behavior at finite density. We have recently [34] improved the implementation of nuclear density effects for the f 0 (600) resonance by considering a microscopic calculation of many-body pion dynamics and unitarizing by solving the Bethe-Salpeter equation, obtaining in this way results qualitatively compatible with this simpler method we analyze here. In Fig.…”

“…8 that density effects also drive it faster toward the real axis and to the threshold. In this case however, after crossing the threshold, the pole becomes a pair virtual state-bound state located at almost the same value of mass and width, indicating a clearqq nature for this resonance [34].…”

From controversy to precision on the sigma meson: A review on the status of the non-ordinary f0(500) resonance

“…On the other hand, chiral partners in the scalar-pseudoscalar sector are understood through degeneration of correlators and susceptibilities [357] which is also compatible with the behavior of the lattice thermal masses in the corresponding channels [348]. In addition, introducing nuclear density effects combined with temperature reveals new in-medium decay channels for the σ state, which in particular accelerate the migration of the pole to the two-pion threshold [356]. The latter analysis extends previous work on ππ scattering at finite density in this channel [358].…”

“…whose trajectory in the complex plane as T varies shows some interesting features [355,356]. Thus, the sudden drop of M p (T ) towards the two-pion threshold can be interpreted in terms of CSR, as opposed for instance to the I = J = 1 ρ(770)-channel where the mass drop is much softer.…”