  Three-dimensional strong topological insulators (TIs) guarantee the existence
of a 2-D conducting surface state which completely covers the surface of the
TI. The TI surface state necessarily wraps around the TI's top, bottom, and two
sidewalls, and is therefore topologically distinct from ordinary 2-D electron
gases (2DEGs) which are planar. This has several consequences for the
magnetoconductivity $\Delta \sigma$, a frequently studied measure of weak
antilocalization which is sensitive to the quantum coherence time $\tau_\phi$
and to temperature. We show that conduction on the TI sidewalls systematically
reduces $\Delta \sigma$, multiplying it by a factor which is always less than
one and decreases in thicker samples. In addition, we present both an
analytical formula and numerical results for the tilted-field
magnetoconductivity which has been measured in several experiments. Lastly, we
predict that as the temperature is reduced $\Delta \sigma$ will enter a wrapped
regime where it is sensitive to diffusion processes which make one or more
circuits around the TI. In this wrapped regime the magnetoconductivity's
dependence on temperature, typically $1/T^2$ in 2DEGs, disappears. We present
numerical and analytical predictions for the wrapped regime at both small and
large field strengths. The wrapped regime and topological signatures discussed
here should be visible in the same samples and at the same temperatures where
the Altshuler-Aronov-Spivak (AAS) effect has already been observed, when the
measurements are repeated with the magnetic field pointed perpendicularly to
the TI's top face.
