Baryonic strangeness and related susceptibilities in QCD

The ratios of off-diagonal to diagonal conserved charge susceptibilities, e.g., ${\chi }_{\mathrm{BS}}/{\chi }_S,{\chi }_{\mathrm{QS}}/{\chi }_S$, related to the quark flavor susceptibilities, have proven to be discerning probes of the flavor carrying degrees of freedom in hot strongly interacting matter. Various constraining relations between the different susceptibilities are derived based on the Gell-Mann-Nishijima formula and the assumption of isospin symmetry. Using generic models of deconfined matter and results from lattice quantum chromodynamics, it is demonstrated that the flavor-carrying degrees of freedom at a temperature above $1.5T_c$ are quarklike quasiparticles. A new observable related by isospin symmetry to $C_{\mathrm{BS}}=-3{\chi }_{\mathrm{BS}}/{\chi }_S$ and equal to it in the baryon free regime is identified. This new observable, which is blind to neutral and nonstrange particles, carries the potential of being measured in relativistic heavy-ion collisions.