Hiding dark energy transitions at low redshift
  We show that it is both observationally allowable and theoretically possible
to have large fluctuations in the dark energy equation of state as long as they
occur at ultra-low redshifts z<0.02. These fluctuations would masquerade as a
local transition in the Hubble rate of a few percent or less and escape even
future, high precision, high redshift measurements of the expansion history and
structure. Scalar field models that exhibit this behavior have a sharp feature
in the potential that the field traverses within a fraction of an e-fold of the
present. The equation of state parameter can become arbitrarily large if a
sharp dip or bump in the potential causes the kinetic and potential energy of
the field to both be large and have opposite sign. While canonical scalar field
models can decrease the expansion rate at low redshift, increasing the local
expansion rate requires a non-canonical kinetic term for the scalar field.
