  Polarization-dependent dynamical properties of light as the spin angular
momentum (SAM), helicity, and chirality are conserved quantities in free-space.
Despite their similarities on account of their relationship with a circular
state of polarization, SAM, helicity, and chirality emerge from distinct
symmetries, which endows them with different physical meanings, properties, and
practical applications. In this work, we investigate the behavior of such
quantities in time-varying media (TVM), i.e., how a temporal modulation impacts
their symmetries and conservation laws. Our results demonstrate that the SAM is
conserved for any time modulation, helicity is only preserved in
impedance-matched time modulations, while chirality is not conserved. In
addition, the continuity equations highlight the dependence of the chirality
with the energy content of the fields. These results provide additional
insights into the similarities and differences between SAM, helicity, and
chirality, as well as their physical meaning. Furthermore, our theoretical
framework provides with a new perspective to analyze polarization-dependent
light-matter interactions in TVM.
