Tractors, Mass and Weyl Invariance

Understand

Deser and Nepomechie established a relationship between masslessness and rigid conformal invariance by coupling to a background metric and demanding local Weyl invariance, a method which applies neither to massive theories nor theories which rely upon gauge invariances for masslessness.

• We extend this method to describe massive and gauge invariant theories using Weyl invariance.
• The key idea is to introduce a new scalar field which is constant when evaluated at the scale corresponding to the metric of physical interest.
• This technique relies on being able to efficiently construct Weyl invariant theories.