Speaker
Description
Under the framework of thermal field theory, we calculate the tensor polarization and the resulted spin alignment of a generic vector meson in local equilibrium up to the first order in the hydrodynamic gradients.
At the zeroth order, the spin alignment of the vector meson emerges mainly due to the degeneracy breaking between the transverse and longitudinal spectral functions.
At the first order, the tensor polarization can be induced by the hydrodynamic gradients allowed by symmetry, including a shear-induced tensor polarization (SITP) contribution. The corresponding coefficients are calculated using linear response theory up to the order of one loop, and turns out sensitive to the in-medium spectral properties of vector bosons, e.g., the width and in-medium mass-shift. Moreover, within the framework of relativistic hydrodynamics, we find that the SITP together with other contributions could generate substantial spin alignment in heavy-ion collisions, which is within the relevant range of experimental measurements. These results suggest that the spin alignment could be utilized as a new probe revealing the in-medium spectral properties and the microscopic interactions of the medium constituents. The newly discovered SITP effect is universal in both relativistic and non-relativistic cases, and may therefore also be observed in the low energy systems, such as plasma at relatively low energy and cold atomic gases.
