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Theory Seminar
# Potentially Large One-loop Corrections to WIMP Annihilation

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Europe/Berlin

Main-2-313 (MPI fuer Physik)
### Main-2-313

#### MPI fuer Physik

Description

We compute one--loop corrections to the annihilation of
non--relativistic particles $\chi$ due to the exchange of a (gauge
or Higgs) boson $\phi$ with mass $\mu$ in the initial state. In
the limit $m_{\chi} \gg \mu$ this leads to the ``Sommerfeld
enhancement'' of the annihilation cross section. However, here we
are interested in the case $\mu < m_{\chi}$, where the one--loop
corrections are well--behaved, but can still be sizable. We find
simple and accurate expressions for annihilation from both S- and
P-wave initial states; they differ from each other if $\mu$ != 0. In order to apply our results to the calculation of the relic density of Weakly Interacting Massive Particles (WIMPs), we describe
how to compute the thermal average of the corrected cross
sections. We apply this formalism to scalar and Dirac fermion
singlet WIMPs, and show that the corrections are always very small
in the former case, but can be very large in the latter. Moreover,
in the context of the Minimal Supersymmetric Standard Model, these
corrections can decrease the relic density of neutralinos by more
than 1%, if the lightest neutralino is a strongly mixed state.