Preflight 6: Large Scale Structure

Post your response on the course Compass site

Due Friday, April 18, 9am

Reading

Course Texts

The questions are meant to direct you to the main conceptual points; I recommend you first focus on these rather than on the technical details, which can become involved.

Peacock

Chapters 15, 16

Questions

The questions are really meant to help guide your thinking as you read. You may find it helpful to look at the questions first and bear them in mind as you read.

1. Discussion Question. Please go on Compass and answer this week's discussion question.


2. Density Fluctuations and Large-Scale Structure.
   1. Inflation produces density flucuations which are nearly scale invariant, Gaussian, and "adiabatic". In physical terms, what is meant by each of these properties? For each, describe a fluctuation spectrum which would fail to have the property.
   2. To quantify cosmic density fields, a particularly useful statistics the power spectrum. What does this measure? What is its physical significance? What power spectrum does inflation predict? What potentially useful information is not encoded in the power spectrum?
   3. Observationally, how does the amplitude of density fluctuations depend on lengthscale? What is a characteristic scale for fluctuations to be "large," and how is it defined? What is required to theoretically describe the evolution of perturbations on scales above and below this characterstic length?


3. Gravitational Instability.
   1. Describe physical origin of the Jeans instability, the Jeans length, and the Jeans mass.
   2. What is the main qualitative difference between the growth of matter density fluctuations during radiation domination versus growth during matter domination? What is the physical origin of the difference?
   3. What is a transfer function? What does it account for, physically? Why is it a useful?


4. Other questions or comments?