The effect of asymmetric beams in the Wilkinson Microwave Anisotropy
  Probe experiment
  We generate simulations of the CMB temperature field as observed by the WMAP
satellite, taking into account the detailed shape of the asymmetric beams and
scanning strategy of the experiment, and use these to re-estimate the WMAP beam
transfer functions. This method avoids the need of artificially symmetrizing
the beams, as done in the baseline WMAP approach, and instead measures the
total convolution effect by direct simulation. We find only small differences
with respect to the nominal transfer functions, typically less than 1%
everywhere, and less than 0.5% at l<400. The net effect on the CMB power
spectrum is less than 0.6%. The effect on all considered cosmological
parameters are negligible. For instance, we find that the spectral index of
scalar perturbations after taking into account the beam asymmetries is n_s =
0.964 +- 0.014, corresponding to a negative shift of -0.1 sigma compared to the
previously released WMAP results. Our CMB sky simulations are made publicly
available, and can be used for general studies of asymmetric beam effects in
the WMAP data.
