The Rotation Curves Of Galaxies In Modified Gravity Theories

In 1998,the universe was found to go through an accelerated expansion by type Ia supernovae(SNIa),which scientists have tried to explain theoretically.According to the successful cosmological model,the universe contains two major components,namely,dark matter and dark energy.In 1970 s,Rubin and Ford realized that the rotation curves of superluminous galaxies were almost flat on the galactic scale.Soon,both the observational and theoretical researchers agreed that there is a massive dark halo in the peripheral of galaxy,which is made of dark matter.Dark matter was in the mainstream of research for a long time.But many authors suggested that the general relativity is modified on the galactic scale.The modified gravity theories might be able to replace dark matter to explain the flattening of the galaxy's rotation curve.There are a lot of works related to the modified gravity theories.In this work,we are interested in the galactic rotation curves in f(T)theory and Horndeski theory.They are both modified gravity theory,which can reduce to general relativity under suitable conditions.We can obtain the theoretical rotation curves in these two modified gravity theories.Then,we compare them with the observational rotation curves of the Milky way as well as the ones in general relativity,and see whether or not f(T)and Horndeski theories can take the place of dark matter.