# Gaussian vs. non-Gaussian fluctuations

1. Jan 27, 2016

### Einj

Hello everyone,
I know this is a very basic question but I was wondering, in the context of inflation, what does it mean to have gaussian or non-gaussian fluctuations.
First of all, are we talking about the fluctuations of the inflation?
Second of all, how is the nature of the fluctuations related to the mechanism of inflation, say e.g. the inflaton potential?

Thanks!

2. Jan 28, 2016

### Chronos

Gaussian, wrt to the CMB, refers to a distribution of CMB photons that is consistent with a gaussian probability curve [i.e., random]. A non-guassian distribution suggests a preferred distribution of CMB photons [i.e., corresponding to topological defects in the universe]. Most cosmologists are suspicious of non gaussianity because it violates the cosmological principle.

3. Jan 28, 2016

### Einj

Thanks for the reply! How can non-gaussianity be generated at the level of inflation?

4. Jan 28, 2016

### Chronos

5. Jan 28, 2016

### bapowell

All sorts of ways: multiple fields, non-slow roll evolution, strong higher-order couplings, non-trivial vacuum/initial state, non-canonical kinetic terms (e.g. DBI inflation), etc....

6. Jan 28, 2016

### bapowell

Nongaussianity can also arise in the distribution of the amplitude of fluctuations (the $a_{\ell m}$) in the temperature power spectrum. I believe this can happen without violating isotropy.