How to explore Physics research as an undergraduate, keeping in mind the ever increasing weight on publications? I am currently 3rd year Physics UG and have been working on Cosmology for past 3 years.

I want to explore different areas like QFT, Quantum Gravity and maybe a bit of basic Math research as well, before I enter into PhD.(I have 2 more years of MS education)

However, with an ever increasing stress on Publications for PhD applications, it's very hard. I can try get 1-2 publications if I continue in Cosmology, as I already know the bare minimum and can start my projects with comparatively less reading. But if choose a new field I'll first have to do a lot of preliminary readings and only then start my research projects. Thus lower chance of good publications.

So how should a Physics student go about exploring different fields?

Note: [I am not considering doing a course in QFT, Math as exploring the topic]

PS: I am from India where it is much less common for UG students to get publications compared US/Europe. So, if possible, please do consider this.
It would be amazing for you to get 2-3 publications before you enter PhD.  Maybe it’s just the semantics of what is meant by “getting 2-3 publications” but just participating as co-author in one publication in first- or second-quartile journal is not that common, and it’s extremely unlikely that this would be “your” publication, i.e. that you would be the major contributor to this. 

It is not easy to publish original work in a mature field like cosmology: the low-hanging fruits have long been picked.  In other words, all the easy work has already have been done by current researchers or their graduate students or their undergraduate students, or by the generation before them.  Rejection rates in well-recognized journals are generically above 70% of submissions, and these are submissions by authors who considered their work sufficient good to submit to those journals in the first place, i.e. the rejection rate would be much higher if it weren’t for a significant self-filtering of submission to good journals.

I recommend students not to play it safe at the undergraduate level, i.e. if they would like to learn about cryptography then take a crypto course rather than some other “safe” topic which might narrow rather than expand their expertise.  

There is this nice article published in the NYTimes which makes a similar point, although in a the context of students obsessed by grades and from a more “dealing with failure” perspective.