  Statistical properties of turbulent magnetic fields in radio-synchrotron
sources should imprint on the statistics of polarimetric observables. In search
of these imprints, we calculate correlation and cross-correlation functions
from a set of observables containing the total intensity I, the polarized
intensity P and the Faraday depth phi. The correlation functions are evaluated
for all combinations of observables up to fourth order in the magnetic field B.
We derive these as far as possible analytically and from first principles only
using some basic assumptions such as Gaussian statistics of the underlying
magnetic field in the observed region and statistical homogeneity. We further
assume some simplifications to reduce the complexity of the calculations, as
for a start we were interested in a proof of concept. Using this statistical
approach, we show that it is in principle possible to gain information about
the helical part of the magnetic power spectrum, namely via the correlation
functions <P(k)phi(k')phi(k")> and <I(k)phi(k')phi(k")>. Using this insight, we
construct an easy-to-use test for helicity, called LITMUS (Local Inference Test
for Magnetic fields which Uncovers heliceS). For now, all calculations are
given in a Faraday-free case, but set up in a way so that Faraday rotational
effects could be included later on.
