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We study the correlation functions of logarithmic conformal field theories.
First, assuming conformal invariance, we explicitly calculate two- and
three-point functions. This calculation is done for the general case of more
than one logarithmic field in a block, and more than one set of logarithmic
fields. Then we show that one can regard the logarithmic field as a formal
derivative of the ordinary field with respect to its conformal weight. This
enables one to calculate any $n$-point function containing the
logarithmic field in terms of ordinary $n$-point functions. Finally, we
calculate the operator product expansion (OPE) coefficients of a logarithmic
conformal field theory, and show that these can be obtained from the
corresponding coefficients of ordinary conformal theory by a simple
derivation.
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