Several types of neutrinos have been well studied in many
experiments. Their are still some unanswered questions about them
(especially whether or not they have non-zero rest masses) and they have
unusual properties (because of their weak interaction), but they are
routine enough entities for physicists that they are hardly "exotic".
Gravitons are the theoretical quanta of the gravitational field, and
it would be extremely surprising & upsetting to present theories if
they didn't exist. But they have not been detected experimentally yet &
probably won't be for some time, primarily because gravitational
radiation from any conceivable sourceis very weak. Alas, the way
neutrinos & gravitons are invoked on Star Trek in generally nonsense.
There are more exotic theoretical entities which _may_ exist -
"axions", "photinos", "squarks" &c. Some of these _might_ provide some
of the hypothesized cosmological "dark matter", but that, if it exists,
could be more routine stuff. Marcia Bartusiak's _Through a Universe
Darkly_ is a decent popular presentation of the dark matter problem,
with Chapter 9 dealing with some of the more exotic forms of matter.
SHALOM,
George Murphy