Spin-charge induced scalarization of Kerr-Newman black-hole spacetimes

It has recently been demonstrated that Reissner-Nordstr\"om black holes in composed Einstein-Maxwell-scalar field theories can support static scalar configurations with a non-minimal negative coupling to the Maxwell electromagnetic invariant of charged spacetime. We here reveal physically interesting fact {\it positive} spatially-dependent ${\cal F}\equiv F_{\mu\nu}F^{\mu\nu}$ also be supported black-hole spacetimes. Intriguingly, it is explicitly proved positive-coupling spontaneous scalarization phenomenon induced by non-zero combination $a\cdot Q\neq0$ both} spin $a\equiv J/M$ and electric charge $Q$ central supporting hole. Using analytical techniques we prove regime existence Kerr-Newman horizon radius $r_+(M,a,Q)$ (which, principle, may arbitrarily small) determined critical onset line} $(a/r_+)_{\text{critical}}=\sqrt{2}-1$. In particular, spinning theory are spontaneously scalarized positively coupled fields dimensionless $0<{{Q}\over{M}}\leq\sqrt{2\sqrt{2}-2}$ if their parameters lie above line ${{a(Q)}\over{M}}\geq \big[{{a(Q)}\over{M}}\big]_{\text{critical}}={{1+\sqrt{1-2(2-\sqrt{2}){(Q/M)}^2}}\over{2\sqrt{2}}}$.