Vortical susceptibility of finite-density QCD matter

The susceptibility of finite-density QCD matter to vorticity is introduced, as an analog of magnetic susceptibility. It describes the spin polarization of quarks and antiquarks in finite-density QCD matter induced by rotation. We estimate this quantity in the chirally broken phase using the mixed gauge-gravity anomaly at finite baryon density. It is proposed that the vortical susceptibility of QCD matter is responsible for the polarization of $\Lambda$ and ${\bar \Lambda}$ hyperons observed recently in heavy ion collisions at RHIC by the STAR Collaboration.