Power Corrections and Renormalons in $e^+e^-$ Fragmentation Functions
  We estimate the power corrections (infrared renormalon contributions) to the coefficient functions for the transverse, longitudinal and asymmetric fragmentation functions in $e^+e^-$ annihilation, using a method based on the analysis of one-loop Feynman graphs containing a massive gluon. The leading corrections have the expected $1/Q^2$ behaviour, but the gluonic coefficients of the longitudinal and transverse contributions separately have strong singularities at small $x$, which cancel in their sum. This leads to $1/Q$ corrections to the longitudinal and transverse parts of the annihilation cross section, which cancel in the total cross section. 
M. Dasgupta and B.R. Webber