The current acceleration of the Universe is one of the most challenging open questions of modern cosmology, dubbed the "dark energy" problem. Intense efforts over the last years have shown that its explanation calls for the introduction of new "fifth forces" beyond the standard model of particle physics and General Relativity. Fifth forces leave their imprints at different scales in the Universe: from cosmological scales to astrophysical gravitational waves and stellar interiors. Their observational detection are of paramount importance for understanding the nature of dark energy, while offering us an exciting opportunity to challenge the fundamentals of the standard model of particles and forces in Nature.
The student will work on the development of novel theoretical and numerical tools that will allow to accurately test the framework of Newtonian gravity and/or General Relativity at astrophysical scales and the implications for cosmology. A key direction in this context will be the theoretical modelling of stellar interiors and stellar pulsations of main sequence stars such as our Sun, white dwarfs or neutron stars [1,2] through state-of-the-art analytical and numerical tools, and the confrontation against the most accurate observations available. Other possible directions include the study of astrophysical gravitational waves in the context of general dark energy theories  and their implications for upcoming missions such as the LISA or Euclid satellite.
References 1. I. D. Saltas & I. Lopes, PRL 123 (2019) no.9, 091103 - arXiv:1909.02552 2. I. D. Saltas, I. Sawicki & I. Lopes, JCAP 1805 (2018) 028 - arXiv:1803.00541 3. I. D. Saltas, L. Amendola, M. Kunz & I. Sawicki (2018) - arXiv:1812.03969