I'm a Greek physics student and I want to study theoretical or mathematical physics in a USA university. Because in our universities we don't have much research opportunities in an undergraduate level. When I get my degree I can enter a math department and in two years I'll have my math degree, something like double major. (I'll do that because I really like math, not because it might boost my chances to get in a prestigious university). But recently, it came to mind that I can do a master's degree here in Greece instead of doing the above, because it will take the same amount of time (2 years), and the GREs seem pretty easy. Should I go for a Master's or not?? Thanks you in advance.