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It is theoretically and experimentally argued that there may exist bubble or toroid-shaped configurations in some nucleus systems. Based on the isospin-dependent transport model of nucleus-nucleus collisions, here we propose a method to probe the bubble configuration in the nucleus. That is, one could use the value of the $ \pi^{-} / \pi^{+}$ ratio especially its kinetic energy distribution in head-on collision at intermediate energies to probe whether there is bubble configuration or not in projectile and target nuclei. Due to different maximum compressions and the effect of symmetry energy, the value of the $\pi^{-} / \pi^{+}$ ratio in the collision of bubble nuclei is evidently larger than that in the collision of normal nuclei. [ABSTRACT FROM AUTHOR]

Based on the isospin-dependent transport model IBUU and on the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross-sections on $ \pi^{{-}}_{}$/ $ \pi^{{+}}_{}$ in the neutron-rich reaction Ca + Ca at a beam energy of 400MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect $ \Delta_{{1232}}^{}$ , $ \pi^{{-}}_{}$ and $ \pi^{{+}}_{}$ productions as well as the value of $ \pi^{{-}}_{}$/ $ \pi^{{+}}_{}$ . [ABSTRACT FROM AUTHOR]

The proposed protophobic fifth force in Phys. Rev. Lett. 117, 071803 (2016) has recently attracted much attention. To confirm or refute the existence of this new interaction, here I propose a method to probe the protophobic fifth force in dense matter that forms in nucleus-nucleus collisions. As expected, the protophobic fifth force has negligible effects on the usual observables in nucleus-nucleus collisions. While the protophobic fifth force evidently affects the value of the final positively and negatively charged pions ratio at very high kinetic energies. The signal thus could be used to probe the protophobic fifth force in dense matter by nucleus-nucleus collisions experiments at current experimental facilities worldwide. [ABSTRACT FROM AUTHOR]