  We investigate the low energy continuum limit theory for electrons in a
graphene sheet under strain. We use the quantum field theory in curved spaces
to analyze the effect of the system deformations into an effective gauge field.
We study both in-plane and out-of-plane deformations and obtain a closed
expression for the effective gauge field due to arbitrary nonuniform sheet
deformations. The obtained results reveal a remarkable relation between the
local-pseudo magnetic field and the Riemann curvature, so far overlooked.
