The impact of energy conservation in transport models on the π−/π+\pi^-/\pi^+ multiplicity ratio in heavy-ion collisions and the symmetry energy

The charged pion multiplicity ratio in intermediate energy central heavy-ion collisions has been proposed as a suitable observable to constrain the high density dependence of the isovector part of the equation of state, with contradicting results. Using an upgraded version of the T\"ubingen QMD transport model, which allows the conservation of energy at a local or global level by accounting for the potential energy of hadrons in two-body collisions and leading thus to particle production threshold shifts, we demonstrate that compatible constraints for the symmetry energy stiffness can be extracted from pion multiplicity and elliptic flow observables. Nevertheless, pion multiplicities are proven to be highly sensitive to the yet unknown isovector part of the in-medium $\Delta$(1232) potential which hinders presently the extraction of meaningful information on the high density dependence of the symmetry energy. A solution to this problem together with the inclusion of contributions presently neglected, such as in-medium pion potentials and retardation effects, are needed for a final verdict on this topic.Comment: 12 pages, 7 figure

Feasability of constraining the curvature parameter of the symmetry energy using elliptic flow data

A QMD type transport model supplemented by a phase-space coalescence model fitted to FOPI experimental multiplicities of free nucleons and light clusters has been used to study the density dependence of the symmetry energy above the saturation point by a comparison with experimental elliptic flow ratios measured by the FOPI-LAND and ASYEOS collaborations in $^{197}$Au+$^{197}$Au collisions at 400 MeV/nucleon impact energy. A previous calculation has proven that neutron-to-proton and neutron-to-charged particles elliptic flow ratios probe on average different densities allowing in principle the extraction of both the slope $L$ and curvature $K_{sym}$ parameters of the symmetry energy. Consequently a Gogny interaction inspired potential has been modified to allow independent changes of $L$ and $K_{sym}$. Comparing theoretical predictions with experimental data for neutron-to-proton and neutron-to-charged particles elliptic flow ratios the following constraints have been extracted: $L$=85$\pm$22(exp)$\pm$20(th)$\pm$12(sys) MeV and $K_{sym}$=96$\pm$315(exp)$\pm$170(th)$\pm$166(sys) MeV. Residual model dependence is accounted for in the magnitude of the quoted theoretical error. Systematical uncertainties are generated by the inability of the transport model to reproduce experimental light-cluster-to-proton multiplicity ratios. A value for $L$, free of systematical theoretical uncertainties, can be extracted from the neutron-to-proton elliptic flow ratio alone: $L$=84$\pm$30(exp)$\pm$19(th) MeV. It has also been demonstrated that elliptic flow ratios reach a maximum sensitivity on the $K_{sym}$ parameter in heavy-ion collisions of about 250 MeV/nucleon impact energy, allowing a reduction of the experimental component of uncertainty to about 150 MeV for this parameter.Comment: 22 pages, 13 figure

Dilepton production at HADES: theoretical predictions

Dileptons represent a unique probe for nuclear matter under extreme conditions reached in heavy-ion collisions. They allow to study meson properties, like mass and decay width, at various density and temperature regimes. Present days models allow generally a good description of dilepton spectra in ultra-relativistic heavy ion collision. For the energy regime of a few GeV/nucleon, important discrepancies between theory and experiment, known as the DLS puzzle, have been observed. Various models, including the one developed by the T\"{u}bingen group, have tried to address this problem, but have proven only partially successful. High precision spectra of dilepton emission in heavy-ion reactions at 1 and 2 GeV/nucleon will be released in the near future by the HADES Collaboration at GSI. Here we present the predictions for dilepton spectra in C+C reactions at 1 and 2 GeV/nucleon and investigate up to what degree possible scenarios for the in-medium modification of vector mesons properties are accessible by the HADES experiment.Comment: 12 pages, 4 figures; submitted to Phys.Lett.

Towards a model-independent constraint of the high-density dependence of the symmetry energy

Neutron-proton elliptic flow difference and ratio have been shown to be promising observables in the attempt to constrain the density dependence of the symmetry energy above the saturation point from heavy-ion collision data. Their dependence on model parameters like microscopic nucleon-nucleon cross-sections, compressibility of nuclear matter, optical potential, and symmetry energy parametrization is thoroughly studied. By using a parametrization of the symmetry energy derived from the momentum dependent Gogny force in conjunction with the T\"{u}bingen QMD model and comparing with the experimental FOPI/LAND data for 197Au+197Au collisions at 400 MeV/nucleon, a moderately stiff, x=-1.35 +/- 1.25, symmetry energy is extracted, a result that agrees with that of a similar study that employed the UrQMD transport model and a momentum independent power-law parametrization of the symmetry energy. This contrasts with diverging results extracted from the FOPI $\pi^{-}/\pi^{+}$ ratio available in the literature.Comment: 18 pages, 3 figures, accepted for publication in Phys. Rev.

In-medium Δ(1232)\Delta(1232) potential, pion production in heavy-ion collisions and the symmetry energy

Using the dcQMD transport model, the isoscalar and isovector in-medium potentials of the $\Delta$(1232) baryon are studied and information regarding their effective strength is obtained from a comparison to experimental pion production data in heavy-ion collisions below 800 MeV/nucleon impact energy. The best description is achieved for an isoscalar potential moderately more attractive than the nucleon optical potential and a rather small isoscalar relative effective mass m$^*_\Delta \approx$ 0.45. For the isovector component only a constraint between the potential's strength at saturation and the isovector effective mass difference can be extracted, which depends on quantities such as the slope of the symmetry energy and the neutron-proton effective mass difference. These results are incompatible with the usual assumption, in transport models, that the $\Delta$(1232) and nucleon potentials are equal. The density dependence of symmetry energy can be studied using the high transverse momentum tail of pion multiplicity ratio spectra. Results are however correlated with the value of neutron-proton effective mass difference. This region of spectra is shown to be affected by uncertain model ingredients such as the pion potential or in-medium correction to inelastic scattering cross-sections at levels smaller than 10$\%$. Extraction of precise constraints for the density dependence of symmetry energy above saturation will require experimental data for pion production in heavy-ion collisions below 800 MeV/nucleon impact energy and experimental values for the high transverse momentum tail of pion multiplicity ratio spectra accurate to better than 5$\%$.Comment: 22 pages, 13 figure

Salivary cortisol and α-amylase: subclinical indicators of stress as cardiometabolic risk

Currently, the potential for cardiovascular (CV) stress-induced risk is primarily based on the theoretical (obvious) side effects of stress on the CV system. Salivary cortisol and α-amylase, produced respectively by the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic-adrenomedullary (SAM) system during stress response, are still not included in the routine evaluation of CV risk and require additional and definitive validation. Therefore, this article overviews studies published between 2010 and 2015, in which salivary cortisol and α-amylase were measured as stress biomarkers to examine their associations with CV/CMR (cardiometabolic risk) clinical and subclinical indicators. A comprehensive search of PubMed, Web of Science and Scopus electronic databases was performed, and 54 key articles related to the use of salivary cortisol and α-amylase as subclinical indicators of stress and CV/CMR factors, including studies that emphasized methodological biases that could influence the accuracy of study outcomes, were ultimately identified. Overall, the biological impact of stress measured by salivary cortisol and α-amylase was associated with CV/CMR factors. Results supported the use of salivary cortisol and α-amylase as potential diagnostic tools for detecting stress-induced cardiac diseases and especially to describe the mechanisms by which stress potentially contributes to the pathogenesis and outcomes of CV diseases