Abstract
T Tauri stars, young analogues of Sun-like stars, are surrounded by protoplanetary discs of dust and gas. These stars and their discs are crucial for understanding stellar evolution and planet formation in low-mass systems. These stars exhibit strong variability, notably emitting intense X-ray flares due to magnetic reconnection events. During these events, magnetic energy is transformed into particle kinetic energy. Some of these particles subsequently heat the plasma of the underlying chromosphere to tens of millions of degrees, emitting the observed X-rays. Other particles are believed to escape from the chromosphere and interact with the surrounding circumstellar environment.The issue that arises is to estimate the impact of particles produced by magnetic reconnection events on the discs of young stars.The complex features of protoplanetary discs around T Tauri stars require an interdisciplinary approach to enhance our understanding of these objects. This thesis has contributed to the development of a framework that combines observational methodologies, chemical and dynamical models of protoplanetary discs, and the mechanics of energetic particle acceleration and transport. This synergy aims to demonstrate their collective impact on the disc's dynamics and chemistry and potentially its associated jets.We first introduce the modelling of T Tauri stars and their discs, taking into account current observational constraints, such as the disc's mass distribution and thermal structure. Next, we focus on the role of ionisation in disc dynamics, including its origins from not only standard sources like stellar radiation and Galactic Cosmic Rays (GCRs) but also potential non-thermal ionisation from reconnection events. We then explore magnetic reconnection events in T Tauri flares as an alternate ionisation source, requiring distinct theoretical considerations from solar flares due to their amplified magnetic and luminous properties. Subsequently, we analyse the transport of energetic particles in the accretion disc, introducing two transport models based on particle column density.Following that, we present a study using the ProDiMO code, revealing that particles from magnetic reconnection events could significantly contribute to disc ionisation. Lastly, we introduce a supplementary study considering temporal factors, indicating that accounting for these particles could boost the ionisation rate and influence the disc's chemistry and dynamics, as well as the launching mechanism of winds and jets. In conclusion, this thesis emphasises the possibility that magnetic reconnection events might be pivotal for understanding ionisation in inner protoplanetary discs surrounding young T Tauri stars. Such insights could redefine our understanding of disc dynamics, chemistry, and the early stages of planetary formation.