  We investigate known mechanisms for enhancing nuclear fusion rates at ambient
temperatures and pressures in solid-state environments. In deuterium fusion, on
which the paper is focused, an enhancement of >40 orders of magnitude would be
needed to achieve observable fusion. We find that mechanisms for fusion rate
enhancement up to 30 orders of magnitude each are known across the domains of
atomic physics, nuclear physics, and quantum dynamics. Cascading such
mechanisms could lead to an overall enhancement of 40 orders of magnitude and
more. We present a roadmap with examples of how hypothesis-driven research
could be conducted in -- and across -- each domain to probe the plausibility of
technologically-relevant fusion in the solid state.
