Are you interested in qualitative or quantitative research?
Here are a couple of good references that might help you:
Pilgrim J, Robertson S, Kremer P. A qualitative investigation into the role of the caddie in elite-level golf. International Journal of Sports Science & Coaching. 2016 Aug;11(4):599-609. (One focus of this study was to better understand 'optimum' pre-shot routine).
Lagos L, Vaschillo E, Vaschillo B, Lehrer P, Bates M, Pandina R. Heart rate variability biofeedback as a strategy for dealing with competitive anxiety: A case study. Biofeedback. 2008 Sep 1;36(3):109. (An interesting case-study that discusses breath regulation as part of optimizing performance).
Here are some references dealing with the relationship between caffeine, skill level and respiratory rates in golfers. It may not be exactly what you are looking for but they might be useful to help you get started.
All the best,
G
Mumford PW, Tribby AC, Poole CN, et al. Effect of Caffeine on Golf Performance and Fatigue during a Competitive Tournament. Med Sci Sports Exerc. 2016;48(1):132–138. doi:10.1249/MSS.0000000000000753
Neumann DL, Thomas PR. The relationship between skill level and patterns in cardiac and respiratory activity during golf putting. Int J Psychophysiol. 2009;72(3):276–282. doi:10.1016/j.ijpsycho.2009.01.001