  We compare two widely used models for dephasing in a chaotic quantum dot: The
introduction of a fictitious voltage probe into the scattering matrix and the
addition of an imaginary potential to the Hamiltonian. We identify the limit in
which the two models are equivalent and compute the distribution of the
conductance in that limit. Our analysis explains why previous treatments of
dephasing gave different results. The distribution remains non-Gaussian for
strong dephasing if the coupling of the quantum dot to the electron reservoirs
is via ballistic single-mode point contacts, but becomes Gaussian if the
coupling is via tunneling contacts.
