  The distribution of bubble lengths in double-stranded DNA is presented for
segments of varying guanine-cytosine (GC) content, obtained with Monte Carlo
simulations using the Peyrard-Bishop-Dauxois model at 310 K. An analytical
description of the obtained distribution in the whole regime investigated,
i.e., up to bubble widths of the order of tens of nanometers, is available. We
find that the decay lengths and characteristic exponents of this distribution
show two distinct regimes as a function of GC content. The observed
distribution is attributed to the anharmonic interactions within base pairs.
The results are discussed in the framework of the Poland-Scheraga and the
Peyrard-Bishop (with linear instead of nonlinear stacking interaction) models.
