Q&A: Cosmology

Q:
What is the hot subject/topic in particle physics these days?

A:
The answer to this question depends on what type of particle physics you are interested in.

In theoretical high-energy particle physics, which is the name usually given to theories attempting to unify the force of gravity with the other 3 known forces (electromagnetic, strong and weak forces), the hottest theories are string theory:
http://superstringtheory.com/

In astronomy/cosmology, a hot topic is the search for the identity of dark matter, which makes up approximately 25% of the "stuff" of the Universe.

Particularly relevant to your question is "The Dark Universe" link, the fifth link on his list. He describes the candidates for dark matter particles there. The Chandra Q&A pages also touch on this subject, for example:
http://chandra.harvard.edu/resources/faq/dmatter/dmatter-9.html