Enhanced black hole formation by multiple winding cosmic strings
  Primordial black hole formation by cosmic string collapse is reconsidered when the winding number of the string is larger than the unity. The line energy density of the multiple winding string becomes greater than that of the single winding string so that the probability of the black hole formation by the string collapse during the loop oscillation would be strongly enhanced. Although the production of the multiple winding defect is suppressed and its number density should be small, the enhancement of the black hole formation by the increased energy density may provide a large number of evaporating black holes in the present universe which gives more stringent constraint on the string model compared to the ordinary string scenario. 
Nagasawa Michiyasu