The proposed research aims to constrain the energy spectrum of accelerated particles in pulsar wind nebulae (PWNe), and their contribution to the recently measured primary cosmic-ray positron spectrum. To this end, observations of synchrotron emission from the inner wind tori of young PWNe, in particular in the infrared domain, will be modeled using relativistic magnetohydrodynamic (MHD) numerical simulations developed at the host institute (Arcetri). The radiative and adiabatic energy losses of the accelerated electrons and positrons prior to their escape into the interstellar medium will be computed using relativistic MHD simulations of PWNe in their later, bow-shock phase, when they are most likely to contribute to the leptonic cosmic ray spectrum. The combination of these two parts of the project will allow more precise predictions of the contribution of PWNe to the primary cosmic-ray positron spectrum, and help quantify the potential necessity for additional, alternative sources of positrons such as the annihilation of dark matter particles.The proposed mobility will give Dr. Gallant the opportunity to reach higher levels and a greater balance of theoretical and observational expertise, through collaboration in state-of-the-art theoretical research, as well as interaction with experts in infrared observation, at Arcetri. The skills acquired, and the longer-term collaborations at the European level which his mobility will foster, will allow Dr. Gallant to continue to play a leading role in the scientific exploitation of future high-energy astrophysical experiments, and in particular the planned ground-based gamma-ray observatory CTA, in which European groups are deeply invested.