Effect of Dust Rotational Disruption by Radiative Torques and
  Implications for F-corona decrease revealed by the Parker Solar Probe
  The first-year results from the Parker Solar Probe (PSP) reveal a gradual
decrease of F-coronal dust from distances of $D=0.166-0.336$ AU (or the inner
elongations of $\sim 9.22- 18.69~R_{\odot}$) to the Sun (Howard et al. 2019).
Such a F-corona decrease cannot be explained by the dust sublimation scenario
of the popular silicate composition that implies a dust-free-zone of boundary
at heliocentric radius $R\lesssim 4-5R_{\odot}$, but may be explained by
appealing to various dust compositions with different sublimation fronts. In
this paper, we present an additional explanation for the F-corona decrease
using our newly introduced mechanism of dust destruction so-called Radiative
Torque Disruption (RATD) mechanism. We demonstrate that RATD rapidly breaks
large grains into nanoparticles so that they can be efficiently destroyed by
nonthermal sputtering induced by bombardment of energetic protons from slow
solar winds, which extends the dust-free-zone established by thermal
sublimation to $R_{dfz}\sim 8R_{\odot}$. Beyond this extended dust-free-zone,
we find that the dust mass decreases gradually from $R\sim 42R_{\odot}$ toward
the Sun due to partial removal of nanodust by nonthermal sputtering. The joint
effect of RATD and nonthermal sputtering can successfully reproduce the gradual
decrease of the F-corona between $19-9R_{\odot}$ observed by the PSP. Finally,
the RATD mechanism can efficiently produce nanoparticles usually observed in
the inner solar system.
