  We discuss situations under which Lorentz symmetry is violated in effective
gravitational field theories that arise in the low-energy limit of strings. In
particular, we discuss spontaneous violation of the symmetry by the ground
state of the system. In the flat space-time limit, the effective theory of the
broken Lorentz Symmetry acquires a form that belongs to the general framework
of the so-called Standard Model Extension (SME) formalism. A brief review of
this formalism is given before we proceed to describe a concrete example, where
we discuss a Lorentz-symmetry-Violating (LV) string-inspired cosmological
model. The model is a gravitational field theory coupled to matter, which
contains torsion, arising from the fundamental degrees of freedom of the
underlying string theory. The latter, under certain conditions which we shall
specify, can acquire a LV condensate, and lead, via the appropriate equations
of motion, to solutions that violate Lorentz and CPT
(Charge-Parity-Time-Reversal) symmetry. The model is described by a specific
form of an SME effective theory, with specific LV and CPT symmetry Violating
coefficients, which depend on the microscopic parameters of the underlying
string theory, and thus can be bounded by current-era phenomenology.
