  In the core accretion scenario, a massive core forms first and then accretes
an envelope. When discussing how this core forms some divergences appear. First
scenarios of planet formation predict the accretion of km-sized bodies, called
planetesimals, while more recent works suggest growth by accretion of pebbles,
which are cm-sized objects. These two accretion models are often discussed
separately and we aim here at comparing the outcomes of the two models with
identical initial conditions. We use two distinct codes: one computing
planetesimal accretion, the other pebble accretion. Using a population
synthesis approach, we compare planet simulations and study the impact of the
two solid accretion models, focussing on the formation of single planets. We
find that the planetesimal model predicts the formation of more giant planets,
while the pebble accretion model forms more super-Earth mass planets. This is
due to the pebble isolation mass concept, which prevents planets formed by
pebble accretion to accrete gas efficiently before reaching Miso. This
translates into a population of planets that are not heavy enough to accrete a
consequent envelope but that are in a mass range where type I migration is very
efficient. We also find higher gas mass fractions for a given core mass for the
pebble model compared to the planetesimal one caused by luminosity differences.
This also implies planets with lower densities which could be confirmed
observationally. Focusing on giant planets, we conclude that the sensitivity of
their formation differs: for the pebble accretion model, the time at which the
embryos are formed, as well as the period over which solids are accreted
strongly impact the results, while for the planetesimal model it depends on the
planetesimal size and on the splitting in the amount of solids available to
form planetesimals.
