Quark droplets stability induced by external magnetic field

The influence of a constant homogeneous external magnetic field $H$ on the formation and stability of quark droplets is investigated within a simple Nambu -- Jona-Lasinio model by using a thermodynamic approach. For a vanishing magnetic field stable quark droplets, which are schematically the bags of massless quarks, are allowed to exist only at $G>G_{bag}$, where $G$ is the quark coupling constant, $G_{bag}=1.37G_{crit}$, and $G_{crit}$ is the value of the coupling constant above which chiral symmetry is spontaneously broken down. On the other hand, a nonvanishing external magnetic field can induce the stability of quark droplets so that they may exist even at $G<G_{bag}$. In this case, depending on the value of $H$, quark droplets are composed either of massive or massless quarks.