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We study the parametric decay instability of parallel propagating Alfv\'enwave in a low-beta plasma using one-dimensional fully kinetic simulations. Wefocus for the first time on the conversion of the energy stored in the initialAlfv\'en wave into particle internal energy, and on its partition betweenparticle species. We show that compressible fluctuations generated by the decayof the pump wave into a secondary ion-acoustic mode and a reflected Alfv\'enwave contribute to the gain of internal energy via two distinct mechanisms.First, the ion-acoustic mode leads nonlinearly to proton trapping and protonphase space mixing, in agreement with previous work based on hybridsimulations. Second, during the nonlinear stage, a compressible front of thefast type develops at the steepened edge of the backward Alfv\'en wave leadingto a field-aligned proton beam propagating backwards at the Alfv\'en speed. Wefind that parametric decay heats preferentially protons, which gain about 50%of the pump wave energy in the form of internal energy. However, we find thatelectrons are also energized and that they contribute to the total energybalance by gaining 10% of the pump wave energy. By investigating energypartition and particle heating during parametric decay, our results contributeto determine the role of compressible and kinetic effects in wave-driven modelsof the solar wind.

Particle-in-cell simulations of Alfv\'en wave parametric decay in a low-beta plasma