1. Degenerate neutrino as a Dark Energy 12 th Marcel Grossmann Meeting, 12-18 July 2009, Paris Hyung Won Lee, Inje University July 15, 2009 Collaboration with K.Y. Kim, R. Ruffini

2. Contents Introduction Properties of degenerate neutrino Evolution of density parameters Possibility as a dark energy Remarks

3. Introduction Universe is in accelerating expansion Riess & Perlmutter Apparent Bolometric Magnitude m(z)

4. Introduction Universe is in accelerating expansion Riess & Perlmutter

5. Introduction

6. Introduction

7. Introduction The present Universe accelerated expansion supernova type Ia (SN Ia) data EOS (equation of state) Main issue of the present cosmology : How to explain the present accelerating universe? negative pressure : Dark Energy candidate: cosmological constant, quintessence, k- essence, holographic dark energy, phantom matter, MaVaN …

8. Introduction All candidates have weakness No physical explanation is given Can we explain dark energy or accelerating expansion with some physical principle? Can we explain accelerating expansion with neutrinos?

9. Properties of degenerate neutrino Decouple at early time Energy density proportional to degeneracy parameter It may have mass

10. Evolution of density parameters Hubble equation Distance modulus

11. Evolution of density parameters (0.1, 0.9), (0.3, 0.7), (0.5, 0.7), LCDM

12. Possibility as a dark energy Light mass : do not generate structure May dominate energy density with degeneracy Evolution may different from standard cosmology

13. Possibility as a dark energy It is not possible to explain with standard consideration Need to study carefully Boltzmann equation

14. Remarks It seems not possible as a dark energy except mass varying with scalar field coupling Cosmological integration of kinematic equation