  The standard theory of plasma emission is based on kinetic couplings between
a single beam of energetic electrons and unmagnetized thermal plasmas,
involving multi-step nonlinear wave-particle and wave-wave interactions. The
theory has not yet been completely verified with fully-kinetic electromagnetic
particle-in-cell (PIC) simulations. Earlier studies, greatly limited by
available computational resources, are controversial regarding whether the
fundamental emission can be generated according to the standard theory. To
resolve the controversy, we conducted PIC simulations with a large domain of
simulation and a large number of macroparticles, among the largest ones of
similar studies. We found significant fundamental emission if the relative beam
density is small enough (say, $\le$ 0.01), in line with earlier study with a
much-smaller domain; the relative intensity (normalized by the total initial
beam energy) of all modes, except the mode associated with the
beam-electromagnetic Weibel instability, decreases with increasing relative
density of the beam. We also found significant transverse magnetic component
associated with the superluminal Langmuir turbulence, which has been mistakenly
regarded as evidence of the F emission in earlier study. Further investigations
are required to reveal their origin.
