  Giving rise to a new and exciting research field, observations of the last 13
years established the accelerated expansion of the Universe. This is a strong
indication of new physics, either in the form of a new energy component of the
Universe -- dark energy -- or of theories of gravity beyond general relativity.
A powerful approach to this problem is the study of complementary cosmological
probes in large optical galaxy surveys such as the Dark Energy Survey (DES). We
present the expectations for dark energy physics based on the combination of
four fundamental probes: galaxy clusters, weak lensing, large scale structure
and supernovae. We show that DES data have constraining power to improve
current measurements of the dark energy equation-of-state parameter by a factor
of 3--5 and to distinguish between general relativity and modified gravity
scenarios.
