Particle Physics in the

Early Universe

An online resource for the course 402-0833-00L given
within the MSc curriculum of the Institute for Theoretical Physics, ETH Zurich

by Achilleas Lazopoulos

Exercises Assistance by Zeno Capatti

Introduction

This course aims to be a review of modern Cosmology, and in particular, of those aspects of modern Cosmology that provide information to Particle Physics.

Cosmology has become, in recent years, a much more quantitative scientific endeavour than it used to be, thanks to the wealth of observational information coming from modern satellite telescopes,like Hubble, Cobe, Planck et al. There is now an equivalent to the Standard Model for Cosmology, a basic narrative of the evolution of the Universe in the past as well as in the future.

This narrative, mostly a product of last one hundred years, puts constraints to fundamental theories of nature that strive to extend the Standard Model (henceforth abbreviated to SM) of particle physics. In fact we have reached the point where the most compelling evidence that there exist other fundamental particles beyond those of the SM (and gravitons) comes from cosmological observations that indicate the existence of Dark Matter.

It is therefore becoming increasingly important for a particle physicist to understand what is the Standard Theory of Cosmology, what are its successes and which constraints are imposed by those successes on fundamental particle theories, as well as which are the open questions that the study of the Universe poses on us.

Contents

  1. 1.

    An overview

    What do we know about the Universe as a whole
  2. 2.

    Input from GR

    the Friedman equation
    The material in this lecture can be found at any introductory book on Cosmology or the Early Universe. For concise versions see
    • Rubakov and Gobrunov: sec. 2.2,3.1,3.2,4.1
    • Weinberg: sec. 1.5
    while a very accessible introduction, without many details, but with the basic concepts elucidated can be found in
    • Zee: VIII.1,VIII.2
  3. 3.

    Thermodynamics and evolution

    The Universe as an expanding soup
    The Matter density vs Dark Energy density discussion can be found at
    • Zee: VIII.2
    but similar material is, once again, present in all GR books in the references.
  4. 4.

    During the first 3 minutes

    Electron decoupling, nucleosynthesis
    • Weinberg, 3.1 and 3.2 are excellent accounts of thermal evolution and BBN, with many further details than we talked about in class.
  5. 5.

    Cosmic Microwave Background

    The moment Photons decoupled
    • Dolgov & Bambi ch. 10
    • Weinberg ch. 2 & 7
    • Gorbunov & Rubakov ch. 6
  6. 6.

    Phase transitions

    First order vs second order EW phase transition
  7. 7.

    Baryogenesis

    Or why is there something instead of nothing
  8. 8.

    Baryogenesis and Leptogenesis

    A possible scenario
  9. 9.

    Dark Matter

    What we know about it
    Both
    • Weinberg: ch 3.4
    • Gorbunov and Rubakov: ch. 9
    have a good discussion of the material. I based most of the lecture on the excellent which is contains many topics beyond the lecture (and the course) and is a very good source for those interested in doing research in DM models.
  10. 10.

    Dark Matter models

    Theorist speculations about what it might be
    The slides shown at class can be found here.
  11. 11.

    Inflation

    The way the Universe is supposed to have turned flat
    Two good reviews are For a recent review by the pioneer of Chaotic Inflation, Andrei Linde see For an (advanced level) review focused on density perturbations see
  12. 12.

    Dark Energy

    The force of accelerated expansion
    I based some of the discussion in class on
    • Bambi and Dolgov, ch. 11
    Also, have a look on the apropriately named You might also want to read the classic, (and greatly enjoyable), if a bit dated, paper by Weinberg (1989), the one which all anthropic wars cite,
  13. 13.

    Axions, ALPs and ULAs

    Ultra light and very elusive.
    Most of the discussion in the class and much more is contained in
  14. #

    Exam questions

    39+1 questions for the exam
    39+1 questions for the exam can be found here.
  15. #

    Exercises

    All the exercise sheets distributed in exercise class, by Zeno Capatti