Evolutionary tracks of massive stars during formation
  A model for massive stars is constructed by piecing together evolutionary
algorithms for the protostellar structure, the environment, the inflow and the
radiation feedback. We investigate specified accretion histories of constant,
decelerating and accelerating forms and consider both hot and cold accretion,
identified with spherical free-fall and disk accretion, respectively.
Diagnostic tools for the interpretation of the phases of massive star formation
and testing the evolutionary models are then developed. Evolutionary tracks
able to fit Herschel Space Telescope data require the generated stars to be
three to four times less massive than in previous interpretations, thus being
consistent with clump star formation efficiencies of $10 -- 15\%$. However, for
these cold Hershel clumps, the bolometric temperature is not a good diagnostic
to differentiate between accretion models. We also find that neither spherical
nor disk accretion can explain the high radio luminosities of many protostars.
Nevertheless, we discover a solution in which the extreme ultraviolet flux
needed to explain the radio emission is produced if the accretion flow is via
free-fall on to hot spots covering less than $10\%$ of the surface area.
Moreover, the protostar must be compact, and so has formed through cold
accretion. We show that these conclusions are independent of the imposed
accretion history. This suggests that massive stars form via gas accretion
through disks which, in the phase before the star bloats, download their mass
via magnetic flux tubes on to the protostar.
