The rationale for giving tax cuts to the income brackets is that this money is then invested in new businesses which increases jobs.
If the saved money is being saved/invested instead of being spent, this would increase the amount of lending capital available and decrease interest rates.
Given that changing tax rates is a distinct and frequent occurrence around the world in a variety of contexts, there must be a lot of data available to perform a regression on.
Do tax cuts to higher income brackets cause a subsequent lowering of interest rates?