  Recently data from PAMELA, ATIC, FERMI-LAT and HESS show that there are
$e^{\pm}$ excesses in the cosmic ray energy spectrum. PAMELA observed excesses
only in $e^+$, but not in anti-proton spectrum. ATIC, FERMI-LAT and HESS
observed excesses in $e^++e^-$ spectrum, but the detailed shapes are different
which requires future experimental observations to pin down the correct data
set. Nevertheless a lot of efforts have been made to explain the observed
$e^\pm$ excesses, and also why PAMELA only observed excesses in $e^+$ but not
in anti-proton. In this brief review we discuss one of the most popular
mechanisms to explain the data, the dark matter annihilation. It has long been
known that about 23% of our universe is made of relic dark matter. If the relic
dark matter was thermally produced, the annihilation rate is constrained
resulting in the need of a large boost factor to explain the data. We will
discuss in detail how a large boost factor can be obtained by the Sommerfeld
and Briet-Wigner enhancement mechanisms. Some implications for particle physics
model buildings will also be discussed.
