  A theory is presented for low-frequency current and voltage correlators of a
mesoscopic conductor embedded in a macroscopic electromagnetic environment.
This Keldysh field theory evaluated at its saddle-point provides the
microscopic justification for our earlier phenomenological calculation (using
the cascaded Langevin approach). The nonlinear feedback from the environment
mixes correlators of different orders, which explains the unexpected
temperature dependence of the third moment of tunneling noise observed in a
recent experiment. At non-zero temperature, current and voltage correlators of
order three and higher are no longer linearly related. We show that a Hall bar
measures voltage correlators in the longitudinal voltage and current
correlators in the Hall voltage. We go beyond the saddle-point approximation to
consider the environmental Coulomb blockade. We derive that the leading order
Coulomb blockade correction to the n-th cumulant of current fluctuations is
proportional to the voltage derivative of the (n+1)-th cumulant, generalizing
to any n the earlier results for n=1,2.
