Scale-independent R² inflation

Weyl (scale)-invariant theories of scalars and gravity can generate all mass scales spontaneously. In this paper, we study a particularly simple version—scale-invariant R² gravity—and show that, during an inflationary period, it leads to fluctuations which, for a particular parameter choice, are almost indistinguishable from normal R² inflation. Current observations place tight constraints on the primary coupling constant of this theory and predict a tensor to scalar ratio, 0.0033 > r > 0.0026, which is testable with the next generation of cosmic microwave background experiments.