Testing Inflation with the Cosmic Microwave Background

Cosmic microwave background (CMB) anisotropy may result from both scalar and tensor perturbations. For a sufficiently narrow range of angular scales, CMB perturbations can be characterized by four parameters. Results from the Cosmic Background Explorer fix one combination of the parameters, reducing the parameters to three. If CMB perturbations are from inflation, there is an additional relation, reducing the parameters to two. An appropriate combination of a medium-angle and a small-angle CMB observation can test the inflation hypothesis because inflation cannot explain a high signal in one experiment and a low signal in the other.