Cosmology constraints from shear peak statistics in Dark Energy Survey
  Science Verification data
  Shear peak statistics has gained a lot of attention recently as a practical
alternative to the two point statistics for constraining cosmological
parameters. We perform a shear peak statistics analysis of the Dark Energy
Survey (DES) Science Verification (SV) data, using weak gravitational lensing
measurements from a 139 deg$^2$ field. We measure the abundance of peaks
identified in aperture mass maps, as a function of their signal-to-noise ratio,
in the signal-to-noise range $0<\mathcal S / \mathcal N<4$. To predict the peak
counts as a function of cosmological parameters we use a suite of $N$-body
simulations spanning 158 models with varying $\Omega_{\rm m}$ and $\sigma_8$,
fixing $w = -1$, $\Omega_{\rm b} = 0.04$, $h = 0.7$ and $n_s=1$, to which we
have applied the DES SV mask and redshift distribution. In our fiducial
analysis we measure $\sigma_{8}(\Omega_{\rm m}/0.3)^{0.6}=0.77 \pm 0.07$, after
marginalising over the shear multiplicative bias and the error on the mean
redshift of the galaxy sample. We introduce models of intrinsic alignments,
blending, and source contamination by cluster members. These models indicate
that peaks with $\mathcal S / \mathcal N>4$ would require significant
corrections, which is why we do not include them in our analysis. We compare
our results to the cosmological constraints from the two point analysis on the
SV field and find them to be in good agreement in both the central value and
its uncertainty. We discuss prospects for future peak statistics analysis with
upcoming DES data.
