What is a word for "not well studied"

Solution 1:

I've seen variations on the following:

• little studied
• under-examined
• open field
• unexplored

These are often combined with relatively so the reviewers don't carp.

Solution 2:

If you are asking for single words, "cloudy", "nebulous", "blear", "obscure"

blear - obscure to the view or imagination Merriam-Webster

nebulous - unclear, vague, or ill-defined OED

cloudy - uncertain; nuclear OED

If you are asking for phrases, then you have quite a few good choices

• not completely understood.
• not fully elucidated.
• needing further research.
• not fully clarified.

Examples from scientific papers:

• "Exact mechanisms responsible for this kind of endocrinopathy have not been completely clarified." Autoimmune Diseases
• "The mechanism of pain has not yet been fully understood."
• "The mechanism of cerebral uptake has not been completely elucidated." Nuclear Medicine
• "Its exact mechanism of action needs further research."