  Ouyed et al. (1998) proposed Deuterium (DD) fusion at the core-mantle
interface of giant planets as a mechanism to explain their observed heat
excess. But rather high interior temperatures (~10^5 K) and a stratified D
layer are needed, making such a scenario unlikely. In this paper, we re-examine
DD fusion, with the addition of screening effects pertinent to a deuterated
core containing ice and some heavy elements. This alleviates the extreme
temperature constraint and removes the requirement of a stratified D layer. As
an application, we propose that, if their core temperatures are a few times
10^4 K and core composition is chemically inhomogeneous, the observed inflated
size of some giant exoplanets ("hot Jupiters") may be linked to screened DD
fusion occurring deep in the interior. Application of an analytic evolution
model suggests that the amount of inflation from this effect can be important
if there is sufficient rock-ice in the core, making DD fusion an effective
extra internal energy source for radius inflation. The mechanism of screened DD
fusion, operating in the above temperature range, is generally consistent with
the trend in radius anomaly with planetary equilibrium temperature $T_{\rm
eq}$, and also depends on planetary mass. Although we do not consider the
effect of incident stellar flux, we expect that a minimum level of irradiation
is necessary to trigger core erosion and subsequent DD fusion inside the
planet. Since DD fusion is quite sensitive to the screening potential inferred
from laboratory experiments, observations of inflated hot Jupiters may help
constrain screening effects in the cores of giant planets.
