Abstract
As a first step towards a realistic phenomenological description of vector and axial-vector mesons in nuclear matter, we calculate the spectral functions of the $\ensuremath{\rho}$ and the ${a}_{1}$ meson in a chiral baryon-meson model as a low-energy effective realization of QCD, taking into account the effects of fluctuations from scalar mesons, nucleons, and vector mesons within the functional renormalization group (FRG) approach. The phase diagram of the effective hadronic theory exhibits a nuclear liquid-gas phase transition as well as a chiral phase transition at a higher baryon-chemical potential. The in-medium $\ensuremath{\rho}$ and ${a}_{1}$ spectral functions are calculated by using the previously introduced analytically-continued FRG (aFRG) method. Our results show strong modifications of the spectral functions---in particular near the critical endpoints of both phase transitions---which may well be of relevance for electromagnetic rates in heavy-ion collisions or neutrino emissivities in neutron-star merger events.
Highlights
The properties of matter under extreme conditions in temperature and/or density, the core of neutron stars, and binary neutron star mergers are in the focus of ongoing theoretical as well as experimental and observational efforts
As a first step towards a realistic phenomenological description of vector and axial-vector mesons in nuclear matter, we calculate the spectral functions of the ρ and the a1 meson in a chiral baryon-meson model as a low-energy effective realization of quantum chromodynamics (QCD), taking into account the effects of fluctuations from scalar mesons, nucleons, and vector mesons within the functional renormalization group (FRG) approach
Our results show strong modifications of the spectral functions—in particular near the critical endpoints of both phase transitions—which may well be of relevance for electromagnetic rates in heavy-ion collisions or neutrino emissivities in neutron-star merger events
Summary
The properties of matter under extreme conditions in temperature and/or density (as encountered for instance in the early Universe), the core of neutron stars, and binary neutron star mergers are in the focus of ongoing theoretical as well as experimental and observational efforts. To construct an effective low-energy description for nuclear matter that is consistent with chiral symmetry and its breaking pattern, the notion of parity-partners in the bosonic sector has to be extended to massive fermions This is accomplished in the parity-doublet model (PDM), or mirror-baryon model [22,23,24]. Just like ρ and a1, the nucleon Nð938Þ and its parity partner, commonly assigned to the 1=2− NÃð1535Þ resonance become (almost) degenerate at this transition, with a common and chirally invariant finite baryon mass m0;N from the scale anomaly This model serves as a suitable effective theory to describe a chiral phase transition inside nuclear matter entirely in terms of hadronic degrees of freedom.
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