Scientific Synergy Between LSST and Euclid
  Euclid and the Large Synoptic Survey Telescope (LSST) are poised to
dramatically change the astronomy landscape early in the next decade. The
combination of high cadence, deep, wide-field optical photometry from LSST with
high resolution, wide-field optical photometry and near-infrared photometry and
spectroscopy from Euclid will be powerful for addressing a wide range of
astrophysical questions. We explore Euclid/LSST synergy, ignoring the political
issues associated with data access to focus on the scientific, technical, and
financial benefits of coordination. We focus primarily on dark energy
cosmology, but also discuss galaxy evolution, transient objects, solar system
science, and galaxy cluster studies. We concentrate on synergies that require
coordination in cadence or survey overlap, or would benefit from pixel-level
co-processing that is beyond the scope of what is currently planned, rather
than scientific programs that could be accomplished only at the catalog level
without coordination in data processing or survey strategies. We provide two
quantitative examples of scientific synergies: the decrease in photo-z errors
(benefitting many science cases) when high resolution Euclid data are used for
LSST photo-z determination, and the resulting increase in weak lensing
signal-to-noise ratio from smaller photo-z errors. We briefly discuss other
areas of coordination, including high performance computing resources and
calibration data. Finally, we address concerns about the loss of independence
and potential cross-checks between the two missions and potential consequences
of not collaborating.
