  We theoretically investigated the temperature fluctuations of DNA close to
denaturation and observed a strong enhancement of these fluctuations at the
critical temperature. Although in a much lower frequency range, such a sharp
increase was also reported in the recent experimental work of Nagapriya et al
[Phys. Rev. Lett. 96, 038102 (2006)]. We showed that there is instead no
enhancement of temperature fluctuations when the dissipation coefficient in
Langevin equations is assumed to be larger than a few tens of ps-1, and pointed
out the possible role of the solvent in real experiments. We sought for a
possible correlation between the growth of large bubbles and the enhancement of
temperature fluctuations but found no direct evidence thereof. Finally, we
showed that neither the enhancement of fluctuations nor the 1/f dependence are
observed at the scale of a single base pair, while these properties show up
when summing the contributions of a large number of base pairs. We therefore
conclude that both effects result from collective motions that are facilitated
by the divergence of the correlation length at denaturation.
