Large-scale Structure in f(T) Gravity
  In this work we study the cosmology of the general f(T) gravity theory. We
express the modified Einstein equations using covariant quantities, and derive
the gauge-invariant perturbation equations in covariant form. We consider a
specific choice of f(T), designed to explain the observed late-time
accelerating cosmic expansion without including an exotic dark energy
component. Our numerical solution shows that the extra degree of freedom of
such f(T) gravity models generally decays as one goes to smaller scales, and
consequently its effects on scales such as galaxies and galaxies clusters are
small. But on large scales, this degree of freedom can produce large deviations
from the standard LCDM scenario, leading to severe constraints on the f(T)
gravity models as an explanation to the cosmic acceleration.
