In standard general relativity, spacetime is described by a Levi-Civita connection that is torsion-free. However, in more advanced frameworks like string theory and certain quantum gravity approaches, torsion (represented by the 3-form H̄_μλρ) becomes physically meaningful.
Physically, torsion represents a twisting of spacetime that occurs when parallel transport around closed loops fails to preserve the orientation of vectors. While the Riemannian curvature tells us how vectors change direction during parallel transport, torsion tells us about the failure of parallelograms to close.
In string theory specifically, torsion arises naturally from the antisymmetric Kalb-Ramond B-field, where H = dB represents the field strength. This B-field couples to the worldsheet of strings, similar to how the electromagnetic potential couples to point particles. The presence of H-flux in strin