Effective Hadronic Theories Research Articles

Thermal modification of open heavy-flavor mesons from an effective hadronic theory

We have developed a self-consistent theoretical approach to study the modification of the properties of heavy mesons in hot mesonic matter which takes into account chiral and heavy-quark spin-flavor symmetries. The heavylight meson-meson unitarized scattering amplitudes in coupled channels incorporate thermal corrections by using the imaginary-time formalism, as well as the dressing of the heavy mesons with the self-energies. We report our results for the ground-state thermal spectral functions and the implications for the excited mesonic states generated dynamically in the heavy-light molecular model. We have applied these to the calculation of meson Euclidean correlators and transport coefficients for D mesons and summarize here our findings.

Vector and axial-vector mesons in nuclear matter

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.

Properties of heavy mesons at finite temperature

We study the properties of heavy mesons using a unitarized approach in a hot pionic medium, based on an effective hadronic theory. The interaction between the heavy mesons and pseudoscalar Goldstone bosons is described by a chiral Lagrangian at next-to-leading order in the chiral expansion and leading order in the heavy-quark mass expansion so as to satisfy heavy-quark spin symmetry. The meson-meson scattering problem in coupled channels with finite-temperature corrections is solved in a self-consistent manner. Our results show that the masses of the ground-state charmed mesons D(0^-)D(0−) and D_s(1^-)Ds(1−) decrease in a pionic environment at T\neq 0T≠0 and they acquire a substantial width. As a consequence, the behaviour of excited mesonic states (D_{s0}^*(2317)^\pmDs0*(2317)± and D_0^*(2300)^{0,\pm}D0*(2300)0,±), generated dynamically in our heavy-light molecular model, is also modified at T\neq 0T≠0. The aim is to test our results against Lattice QCD calculations in the future.

Non-perturbative Heavy-Flavor Transport at RHIC and LHC

We calculate open heavy-flavor (HF) transport in relativistic heavy-ion collisions by applying a strong-coupling treatment in both macro- and microscopic dynamics (hydrodynamics and non-perturbative diffusion interactions). The hydrodynamic medium evolution is quantitatively constrained by bulk and multi-strange hadron spectra and elliptic flow. The heavy quark transport coefficient is evaluated from a non-perturbative T-matrix approach in the Quark–Gluon Plasma which, close to the critical temperature, leads to resonance formation and feeds into the recombination of heavy quarks on a hydrodynamic hypersurface. In the hadronic phase, the diffusion of HF mesons is obtained from effective hadronic theory. We compute observables at RHIC and LHC for non-photonic electrons and HF mesons, respectively.

Dilepton Spectroscopy of QCD Matter at Collider Energies

Low-mass dilepton spectra as measured in high-energy heavy-ion collisions are a unique tool to obtain spectroscopic information about the strongly interacting medium produced in these reactions. Specifically, in-medium modifications of the vector spectral function, which is well known in the vacuum, can be deduced from the thermal radiation off the expanding QCD fireball. This, in particular, allows to investigate the fate of theρresonance in the dense medium and possibly infer from it signatures of the (partial) restoration of chiral symmetry, which is spontaneously broken in the QCD vacuum. After briefly reviewing calculations of thermal dilepton emission rates from hot QCD matter, utilizing effective hadronic theory, lattice QCD, or resummed perturbative QCD, we focus on applications to dilepton spectra at heavy-ion collider experiments at RHIC and LHC. This includes invariant-mass spectra at full RHIC energy with transverse-momentum dependencies and azimuthal asymmetries, as well as a systematic investigation of the excitation function down to fixed-target energies, thus making contact to previous precision measurements at the SPS. Furthermore, predictions for the energy frontier at the LHC are presented in both dielectron and dimuon channels.

Electromagnetic corrections to ππ scattering lengths: Some lessons for the construction of effective hadronic field theories

Using the framework of effective chiral Lagrangians, we show that, in order to correctly implement electromagnetism (EM), as generated from the Standard Model, into effective hadronic theories (such as meson-exchange models) it is insufficient to consider only graphs in the low-energy effective theory containing explicit photon lines. The Standard Model requires the presence of contact interactions in the effective theory with are electromagnetic in origin, but which involve no photons in the effective theory. We illustrate the problems which can result from a “standard” EM subtraction: i.e., from assuming that removing all contributions in the effective theory generated by graphs with explicit photon lines fully removes EM effects, by considering the case of the s-wave ππ scattering lengths. In this case it is shown that such a subtraction proceedure would lead to the incorrect conclusion that the strong interaction isospin-breaking contributions to these quantities were large when, in fact, they are known to vanish at leading order in m d-m u . The leading EM contact corrections for the channels employed in the extraction of the I = 0.2 s-wave ππ scattering lengths from experiment are also evaluated.

Effective field theory description of the pion form factor

Using our present knowledge on effective hadronic theories, short-distance QCD information, the $1/N_C$ expansion, analyticity and unitarity, we derive an expression for the pion form factor, in terms of $m_\pi, m_K, M_\rho$ and $f_\pi$. This parameter-free prediction provides a surprisingly good description of the experimental data up to energies of the order of 1 GeV.

Quark momentum distribution of hadronic matter in a simple confining quark model.

Exact calculation of the quark momentum distribution of a one-dimensional confining quark model of hadronic matter and comparison with approximations based on an effective hadronic theory provide an instructive, controlled test of the approximations commonly used in describing quark degrees of freedom in nuclei. The hadron-hadron correlation function in the effective theory when corrected for quark antisymmetry agrees well with that in the exact ground state. The package or convolution approximation, which approximates the quark wave function by the product of the many-hadron wave function multiplied by the ground-state wave function for the quarks in each hadron, is shown to produce a poor description of the quark momentum distribution and appropriate antisymmetrization of this product is shown to yield an excellent approximation at densities relevant to nuclear matter.