Einstein’s other gravity and the acceleration of the Universe

Spacetime curvature plays the primary role in general relativity but Einstein later considered a theory where torsion was the central quantity. Just as the Einstein-Hilbert action in the Ricci curvature scalar R can be generalized to f (R) gravity, we consider extensions of teleparallel, or torsion scalar T, gravity to f (T) theories. The field equations are naturally second order, avoiding pathologies, and can give rise to cosmic acceleration with unique features.