Book contents
- Frontmatter
- Contents
- Frequently used symbols
- Preface
- 1 Overview
- Part I Relativity
- Part II The Universe after the first second
- Part III Field theory
- Part IV Inflation and the early Universe
- 18 Slow-roll inflation
- 19 Inflation with modified gravity
- 20 Multi-field dynamics
- 21 Reheating and phase transitions
- 22 Thermal equilibrium and the origin of baryon number
- 23 Cold dark matter and dark energy
- 24 Generating field perturbations at horizon exit
- 25 Generating ζ at horizon exit
- 26 Generating ζ after horizon exit
- 27 Generating primordial isocurvature perturbations
- 28 Slow-roll inflation and observation
- 29 Perspective
- Appendix A Spherical functions
- Appendix B Constants and parameters
- Index
22 - Thermal equilibrium and the origin of baryon number
from Part IV - Inflation and the early Universe
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Frequently used symbols
- Preface
- 1 Overview
- Part I Relativity
- Part II The Universe after the first second
- Part III Field theory
- Part IV Inflation and the early Universe
- 18 Slow-roll inflation
- 19 Inflation with modified gravity
- 20 Multi-field dynamics
- 21 Reheating and phase transitions
- 22 Thermal equilibrium and the origin of baryon number
- 23 Cold dark matter and dark energy
- 24 Generating field perturbations at horizon exit
- 25 Generating ζ at horizon exit
- 26 Generating ζ after horizon exit
- 27 Generating primordial isocurvature perturbations
- 28 Slow-roll inflation and observation
- 29 Perspective
- Appendix A Spherical functions
- Appendix B Constants and parameters
- Index
Summary
In this chapter we study thermal equilibrium in the early Universe. Then we look at possible mechanisms for the creation of baryon number (baryogenesis). We pay particular attention to baryogenesis mechanisms that directly involve a scalar field, because they offer the best chance of a primordial isocurvature perturbation.
Thermal equilibrium before the electroweak phase transition
In this section we show that electroweak symmetry is likely to be restored in the early Universe, with every particle of the Standard Model in thermal equilibrium.
Electroweak symmetry is restored if the temperature is bigger than a critical temperature TEW. The critical temperature is of order a few hundred GeV, the precise value depending on the parameters of the Standard Model, or an extension like the Minimal Supersymmetric Standard Model (MSSM).
A particle species is in thermal equilibrium if the rate per particle for all relevant interactions exceeds the Hubble rate H. The dominant interactions are (i) decays and two-body scattering and (ii) the sphaleron transitions that violate B and L conservation. As we are interested in the case that electroweak symmetry is restored, particle masses vanish except for the masses of two Higgs particles which are roughly of order 100 GeV and hence less than the temperature. As a result, T is the only relevant dimensionful parameter.
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- The Primordial Density PerturbationCosmology, Inflation and the Origin of Structure, pp. 358 - 368Publisher: Cambridge University PressPrint publication year: 2009