Conneted sum of representations of knot groups
  When two boundary-parabolic representations of knot groups are given, we introduce the connected sum of these representations and show several natural properties including the unique factorization property. Furthermore, the complex volume of the connected sum is the sum of each complex volumes modulo $i\pi^2$ and the twisted Alexander polynomial of the connected sum is the product of each polynomials with normalization. 
Jinseok Cho
math.GT