What's the Rb and Rc problems in electroweak theoy?
With respect to hadronic branching fractions into heavy quarks (Rb, Rc), here a two papers.
Electroweak Results from SLD
Authors: Nicolo de Groot
Electroweak and Heavy Flavor Physics at SLD
Authors: Stephane Willocq (for the SLD Collaboration)
This paper may be of interest - http://pdg.ift.unesp.br/2007/reviews/stanmodelrpp.pdf
What does one mean by problem?
Separate names with a comma.