Bubble coalescence in breathing DNA: Two vicious walkers in opposite potentials T. Novotný, J. N. Pedersen, T. Ambjörnsson, M. S. Hansen and R. Metzler EPL, 77 4 (2007) 48001 Published online: 25 January 2007 DOI: 10.1209/0295-5075/77/48001