We show that in collisions with neutron-rich heavy ions at energies around the production threshold K0 and K+ yields probe the isospin-dependent part of the nuclear equation of state at high baryon densities. In particular, we suggest the K0/K+ ratio as a promising observable. Results obtained in a covariant relativistic transport approach are presented for Au+Au collisions at 0.8-1.8A GeV. The focus is put on the equation of state influence which goes beyond the collision-cascade picture. The isovector part of the in-medium interaction affects the kaon multiplicities via two mechanisms: (i) a symmetry potential effect, i.e., a larger neutron repulsion in n-rich systems, and (ii) a threshold effect, due to the change in the self-energies of the particles involved in inelastic processes. Genuine relativistic contributions are revealed that could allow one to directly "measure" the Lorentz structure of the effective isovector interaction.

Carbon grains in the interstellar medium evolve through exposure to UV photons, heat, gas, and cosmic rays. Understanding their formation, evolution, and destruction is an essential component of evaluating the composition of the dust available for newly forming planetary systems. The 3.4 lm absorption band, attributed to the aliphatic C"H stretch vibration, is a useful probe of the degree to which energetic processing affects hydrogenated carbon grains. Here we report on the effects of ion bombardment of two different kinds of nano-size hydrogenated carbon grains with different hydrogen content. Grain samples, both with and without a mantle of H 2 O ice, were irradiated with 30 keV He + to simulate cosmic-ray processing in both diffuse and dense interstellar medium conditions. The ion fluences ranged between 1:5 Â 10 13 and 7:9 Â 10 15 ions cm À2 . Infrared and Raman spectroscopy were used to study the effects of ion irradiation on grains. In both the dense and diffuse interstellar medium simulations, ion bombardment led to a reduction of the 3.4 lm band intensity. To discuss the effects of cosmic-ray irradiation of interstellar hydrogenated carbon materials we adopt the approximation of 1 MeV monoenergetic protons. An estimate of the C"H bond destruction cross section by 1 MeV protons was made based on experiments using 30 keV He + ions and model calculations. In combination with results from our previous studies, which focused on UV irradiation and thermal H atom bombardment, the present results indicate that the C"H bond destruction by fastcolliding charged particles is negligible with respect to that of UV photons in the diffuse ISM. However, in dense cloud regions, cosmic-ray bombardment is the most significant C"H bond destruction mechanism when the optical depth corresponds to values of the visual extinction larger than $5 mag. The results presented here strengthen the new interpretation of the evolution of the interstellar aliphatic component (i.e., the C"H bonds in the CH 2 and CH 3 groups) as evidenced by the presence of the 3.4 lm absorption band in the diffuse medium and the absence of such a signature in the dense cloud environment. The evolutionary transformation of carbon grains, induced by H atoms, UV photons, and cosmic rays, indicates that C"H bonds are readily formed, in situ, in the diffuse interstellar medium and are destroyed in the dense cloud environment.

The production/absorption rate of particles in compressed and heated asymmetric matter is studied using a Relativistic Mean Field (RM F ) transport model with an isospin dependent collision term. Just from energy conservation in the elementary production/absorption processes we expect to see a strong dependence of the yields on the basic Lorentz structure of the isovector effective interaction, due to isospin effects on the scalar and vector self-energies of the hadrons. This will be particularly evident for the ratio of the rates of particles produced with different charges: results are shown for π + /π − , K + /K 0 yields. In order to simplify the analysis we perform RM F cascade simulations in a box with periodic boundary conditions. In this way we can better pin down all such fine relativistic effects in particle production, that could likely show up even in realistic heavy ion collisions. In fact the box properties are tuned in order to reproduce the heated dense matter formed during a nucleus-nucleus collision in the few AGeV beam energy region. In particular, K +,0 production is expected to be directly related to the high density behaviour of the symmetry energy, since kaons are produced very early during the high density stage of the collision and their mean free path is rather large. We show that the K + /K 0 ratio reflects important isospin contributions on the production rates just because of the large sensitivity around the threshold. The results are very promising for the possibility of a direct link between particle production data in exotic Heavy Ion Collisions (HIC) and the isospin dependent part of the Equation of State (EoS) at high baryon densities.