  Spin chirality in electron gases is mandated by symmetry to be nonzero
whenever time reversal symmetry (TRS) is broken. In metals, both normal and
superconducting, spin chirality is generated by orbital currents present in the
ground state as a result of TRS breaking. Nonzero chirality is found to emerge
in the absence of any spin-dependent interactions, even when the ground state
remains spin-unpolarized. We present a diagrammatic derivation of the chirality
effect and illustrate its generality for problems such as valley magnetism and
topological superconductivity. Spin chirality results in a chiral three-spin
RKKY interaction between localized spins coupled to carriers by s-d
interaction, an effect that can be detected by local probes such as
spin-sensitive STM. In systems where detecting TRS breaking by macroscopic
measurements is challenging, such as topological superconductors, local
detection of spin chirality can serve as a reliable diagnostic of broken time
reversal symmetry.
