Will it hurt my grad school chances if I don't mention/contact a particular proffessor-potential guide? I'll be applying to Physics grad school in US in the next cycle. Several of my seniors who have entered grad school have suggested me to mail a professor-potential guide before or immediately after applying and maybe even mention this in my application. However, I am not set with my research topic. I confused between 2 closely related fields and want to explore a bit more once I enter grad school before choosing a potential guide. So I don't to get tied with a group right now.
So, if I don't mention a prof or contact them, will it hurt my chances? Even here in Stack I've seen a post saying contacting professors will help my chances. So, I'm worried about how to proceed. Please give me some suggestions.
I am not from US and hence do not know US grad school system very well. So please do let me know if I'm missing something.
If it's a PhD program, very probably yes.
Most PhDs are earned by working closely with one professor.  In experimental physics, you work in their lab space.  If there is not a professor you can work with during your PhD, then you will not be successful.  Admissions committees want to see that you have identified a small number of faculty who would be suitable for you to work with.
Also, some professors may have funding.  If they want to use the funding to pay you, you will probably be admitted.
We cannot tell you who to approach.