Spin polarization of holographic baryon in strongly coupled fluid

The spin polarization for a baryon in a hydrodynamic medium has been extensively studied in the weakly coupled regime using quantum kinetic theory. As a first study of this problem in the strongly coupled regime, we investigate holographically the spectral function of a probe baryon in the fluid-gravity background. This is done by carefully performing gradient expansion of the Dirac equation in the fluid-gravity background. Different contributions in the expansion are understood in terms of density matrices of the probe baryon and the medium. The resulting spectral functions indicate that the holographic baryon is polarized as responses to fluid acceleration, shear stress, and vorticity. The structures of the responses are similar to those found in weakly coupled studies.