I'm a physics Ph.D student who just complete his first year of classes. I struggled a lot and found this year to be academically the hardest of my life. However in the end I did get excellent grades in all of my core classes. I would really like to take it easy next semester and only take 1 class Relativistic Field Theory and maybe do research in either determining if massive Gravitons can be a good candidate for either cold dark matter or warm dark matter, or perhaps something in AGN black holes. However Cosmology is being offered next semester and one part of me wants to take it because I want to go into theoretical particle Cosmology. The other part says that it will distract me from learning QFT and it would be a waste of time because I took General Relativity and have already read large sections from multiple textbooks on Cosmology. Eventually I want to do my dissertation work in applications of noncommunative QFT and Modified Gravity to cosmological problems such as the accelerated expansion of the universe. Do you think I can get away with not taking Cosmology?