5.3. Perturbation spectrum and other specifics

One clear prediction from the standard picture is the ``nearly scale invariant'' spectrum (_H(k) const.) discussed in section 3.5. Strong deviations (more than several percent) from a scale invariant spectrum would destroy our standard picture. Fortunately for inflation, there current CMB and other cosmological data gives substantial support to the idea that the primordial spectrum was indeed close to scale invariant. Current data is consistent with a nearly scale invariant spectrum, as illustrated for example in Fig. 13.

Figure 13. This is Fig. 2 from [14]. This shows that the Maxima data are consistent with a scale invariant spectrum (n = 1). Other data show a similar level of consistency.

Also, the creation of gravitational waves during inflation is a unique effect [24]. While gravity waves from inflation are only observable with foreseeable experiments for certain inflation models [25], we know of no other source of a similar spectrum of gravity waves. Thus, if we do observe the right gravity wave spectrum this would be strong evidence for inflation.

There are a host of specific details of the perturbations that are not uniquely specified by all ``Standard Picture'' models. Some models have significant contributions form tensor perturbations (gravity waves) while others do not. The inflaton potential specifies the ratio of scalar to tensor amplitudes, but this ratio can be different for different models.