AST5220/9420 – Course presentation

1. AST5220/9420 – Course presentation Hans Kristian Eriksen 17. januar 2011

2. Fact: The universe has structure Our main question: How did these form?

3. AST5220/9420 in three bullet points • Goal: • Understand the structure formation processes in the early universe • Main method: • Compute numerically and (where possible) analytically the evolution of structure • Main deliverable in the form of a project: • CMB power spectrum code; takes in cosmological parameters, outputs spectrum

4. Main topics to be covered • Short introduction to General Relativity • One of two lectures given by David Mota • Boltzmann equations • How do particles behave in non-equlibrium conditions? • Baryons, photons, dark matter • Recombination; how did the universe become transparent? • Einstein equations • How do space behave when matter is present, and moves around? • Inflation • How were the very first structures generated? • Observables • How can we predict what we will observe, given a theoretical model?

5. Lectures, times etc. • Two lectures per week • Tuesday at 14.15-16.00 in Peisestua • Thursday at 14.15-16.15 in Peisestua • Style will vary: • PowerPoint for review material • Blackboard for derivations • Sometimes I will sit at the computer, ”coding” live • Sometimes the ”lecture” will be a workshop where you either code or do analytic calculations • I will give most of the lectures • David Mota will give one of the GR lectures • If people are interested, we’ll organize a weekend trip to the mountains (Valdres), where we’ll go through the first milestone • We do have internet access there.. 

6. Evaluation • The evaluation will consists of two parts • Written exam – 70% of the grade • Project – 30% of the grade • The project will consist of four milestones, each counting 25% of the project score • Deadlines are February 18th, March 18th, April 29th and June 8th • Date for exam is not settled yet • Open for suggestions from you

7. The project • The project forms the skeleton of the course • What are you supposed to do? • Compute the CMB temperature power spectrum given cosmological parameters! • How will you do it? • Write a computer code that solves the linearized Boltzmann and Einstein equations for photons, baryons and dark matter • Follow step-by-step procedure; the code will be built up piece by piece • Why will you do it? • Completing this project will form an excellent foundation for both theoretical and observations Master and Ph.d. projects

8. More on the project • Four milestones: • ”The background cosmology” (February 24th) • Solve the Friedmann equations, to know how the average, large-scale and uniform space itself behaves • ”Recombination” (March 22th) • Compute the electron density of the universe as a function of time, to know how often photons scatter at any time • Done by solving the Saha and Peebles’ equations • ”Evolution of matter in the universe” (April 14th) • Track the evolution of a single Fourier mode from just after inflation until today, by solving the Boltzmann and Einstein equations in space and time • ”The CMB power spectrum” (May 31st) • Compute the CMB temperature spectrum, by averaging the photon fluctuations over all scales and random realizations, and projecting them onto a sphere

9. Rules for the project • Deliverables: • For each milestone, a short report (~1-2 pages of text, not counting figures) is to be written • Computer code is to be submitted using Mercurial • Collaboration: • No collaboration on ”future” milestones • No restrictions at all on passed milestones; copy codes if you want! • Note that I should be considered a legal aid; do ask me if something doesn’t work or is unclear – I’ll do my best to help! • Grading: • Each milestone can give 25 points • Errors, bad coding practice will lead to lost points • Note: Coding style gives points; write clear and well documented code!

10. Programming language? • You are completely free to choose whatever language you want • However, I only know F90 very well, and if you want help from me, you better choose F90 too. • Recommendations: • If you trust yourself to be an experienced programmer, choose whatever you are most comfortable with • If you are less experienced, choose F90, so that I can help you out if and when you get stuck 

11. Exam • Written exam will be held ~10th to 15th of July • Suggestions? • Problems will be a mix of • analytic calculations • e.g., linearize some equations • interpretation of plots derived during project work • e.g., what does this plot of the visibility function tell us? • questions on physical intuition • e.g., what is the reason that the third peak is higher than the second peak in the CMB spectrum, if the baryon density is high? • Last year’s exam (and test exams) are available online

12. AST5220 vs. AST9420 • Main differences are: • Ph. D. students will have to implement support for neutrinos and polarization in their computer codes • One problem will be different on the final exam • Note that only the AST5220 web pages will be continuously updated, but not the AST9420 pages

13. Textbook, curriculum etc. • The curriculum is defined by • Chapter 1 to 8 in ”Modern cosmology” by Scott Dodelson • The material covered in the project work • In addition, there are several other useful sources of information: • ”How to calculate the CMB spectrum” by P. Callin • ”Numerical recipes”; pdfs are available online at www.nr.com • For those who chooses F90 as their programming language, Bo Einarsson’s online reference is highly recommended • http://www.nsc.liu.se/~boein/f90/ • And you will learn how to use Mercurial for version control

14. Comparison with earlier years • Main differences from earlier years (before 2010): • 30% less material covered in twice as many lectures • Fewer heavy-duty analytic calculations • More numerical calculations • Hopefully tighter interaction between students and teachers • Whenever something is unclear, come and ask me, and we’ll try to figure it out!

15. Tips and hints! • Set up your coding environment (editor, directories, Makefiles, Mercurial etc.) as soon as possible! • You don’t want to struggle with infrastructure problems just before a deadline • Take a quick look at the project summary pages, and keep the various sections there in mind as we go along • If possible, spend a weekend reading through chapter 1 to 8 in ”Modern cosmology” from start to finish, early in the course • You won’t understand everything, but you will get a rough idea of what we are going to do, and even more importantly, why. • As you start programming, you will probably find Callin (2005) even more useful than Dodelson!

16. Practicalities • Email addresses • User accounts at ITA • Exam date? • Laptops? • Mountain trip?