"hot topic" as phrase in thesis

Both “in a nutshell” and “hot topic” are phrases more informal than one expects to find anywhere in a thesis (although language may be more relaxed in places, such as the Acknowledgements section).

Consider rephrasing “in a nutshell” to briefly or in brief or in short. Rather than “hot topic” consider variations using phrases like “a subject undergoing intense study”, “receiving close review”, “of broad and current interest”, etc. Phrases like these add verbosity and weakness if overused but will raise no eyebrows.

If you need a synonym for "hot topic," try "focus point." For "in a nutshell," use "in essence" or "in sum."