What is primordial non gaussianity?

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• Avi Nandi
In summary, Primordial non-Gaussianity is simply a term for the non-Gaussian distribution detected in the temperature anisotropy of the cosmic microwave background. It has some interesting mathematical properties which make understanding the statistics of the CMB really easy, but it's possible that there are significant deviations from Gaussianity in some more complex inflation models.

Avi Nandi

Can anyone give an idea about primordial non gaussianity in a popular way??

Where did you see this expression, or did you make it up?

Primordial non-Gaussianity is simply a term fo the non Guassian distribution detected in the temperature anisotropy of the cosmic microwave background. One of the better known discussions of this phenomenon is probably https://arxiv.org/abs/0712.1148, Detection of primordial non-Gaussianity (fNL) in the WMAP 3-year data at above 99.5% confidence.

Avi Nandi said:
Can anyone give an idea about primordial non gaussianity in a popular way??
The super short version is that it's all about the statistical properties of the temperature variations in the CMB.

Those temperature variations are sound waves, and at each frequency and direction of motion, if they are Gaussian, the amplitude of the resulting wave is drawn from an independent Gaussian distribution (also known as a Normal distribution). Deviations from this strict Gaussianity come in two ways:
1. The amplitudes of the waves can be correlated with one another.
2. The distribution of amplitudes differs from a Gaussian distribution (typically having fatter tails, meaning large deviations are more frequent than expected from a pure Gaussian).

The benefit of having Gaussian-distributed waves is that they can be perfectly-described by what is known as the two-point correlation function (which is the statistical variance between two points as a function of distance between the two points, independent of direction). This fact has a lot of really neat mathematical properties which make understanding the statistics of the CMB really easy. It means, for example, that all of the information about the temperature variation of the CMB is encoded in its power spectrum.

But what if this assumption isn't the case? Lots of more complex inflation models predict significant deviations from Gaussian behavior. These deviations can become far more challenging to investigate, just due to the more complex mathematics involved. So far, there is no evidence of deviation from Gaussianity:
https://arxiv.org/abs/1502.01592

Thanks Chronos and Kimbyd.

1. What is primordial non-gaussianity?

Primordial non-gaussianity refers to the statistical distribution of the early universe, particularly the distribution of matter and energy. It describes the degree to which the distribution is non-uniform or irregular, which can provide insight into the processes that shaped the universe during its early stages.

2. How is primordial non-gaussianity measured?

Primordial non-gaussianity can be measured through observations of the cosmic microwave background (CMB) radiation, which is the oldest light in the universe. By analyzing the patterns and fluctuations in the CMB, scientists can determine the level of non-gaussianity in the early universe.

3. What causes primordial non-gaussianity?

The exact cause of primordial non-gaussianity is still unknown, but it is thought to be related to the initial conditions of the universe and the processes that drove inflation, the rapid expansion of the universe in its early stages. Other theories suggest that it may be caused by interactions between different types of particles in the early universe.

4. Why is primordial non-gaussianity important in cosmology?

Studying primordial non-gaussianity can provide valuable insights into the early universe and the processes that shaped it. It can also help test and refine theories about the origins and evolution of the universe, and potentially provide clues about the nature of dark matter and dark energy.

5. What are the implications of a high level of primordial non-gaussianity?

If primordial non-gaussianity is found to be higher than expected, it could challenge our current understanding of the early universe and require a re-evaluation of existing theories. It could also provide new avenues for research and lead to breakthroughs in our understanding of the universe's origins.