  The Majorana representation of spin operators allows for efficient
field-theoretical description of spin-spin correlation functions. Any N-point
spin correlation function is equivalent to a 2N-point correlator of Majorana
fermions. For a certain class of N-point spin correlation functions (including
"auto" and "pair-wise" correlations) a further simplification is possible, as
they can be reduced to N-point Majorana correlators. As a specific example we
study the Bose-Kondo model. We develop a path-integral technique and obtain the
spin relaxation rate from a saddle point solution of the theory. Furthermore,
we show that fluctuations around the saddle point do not affect the correlation
functions as long as the latter involve only a single spin projection. For
illustration we calculate the 4-point spin correlation function corresponding
to the noise of susceptibility.
