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On the degeneracy between w 0 and w a

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On the degeneracy between w 0 and w a

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On the degeneracy between w0 and wa

Yungui Gong

Huazhong Univ of Science and Tech

华中科技大学

龚云贵

The 7th Aegean Summer School, Paros, Greece, 2013.9.27

- Motivations: General Property of Scalar Field dynamics
- Dark energy parametrizations
- The degeneracy between w0 and wa
- The consequence of the derived degeneracy

- General Property of scalar field dynamics
- scalar field as dark energy: Tracking solutions
- Tracker fields (Steinhardt etal, PRD 1999)

- Almost independent of initial conditions
- Relation
- Common Dynamics for scalar fields

- Dark energy parametrization: capture the main dynamics of scalar field

MNRAS 383, 879 (1999)

- Approximation

E. Linder

astro-ph/0210217

- w0 and wa is degenerated
- What is the degeneracy? related with ?

- Dark energy parametrization: capture the main dynamics of scalar field
- Efstathiou 1999, MNRAS 310, 842
- CPL, Chevallier & Polarski 2001, IJMPD 10, 213; Linder 2003, PRL 90, 091301
- JBP, Jassal, Bagla & Padmanabhan, MNRAS 356, L11
- Wetterich 2004, PLB 594, 17

- Cosmological equations

- Take the (Slow-roll) approximation
- For Thawing scalar field

Scherrer & Sen 2008, PRD 77, 083515

- Approximate w(z)

dotted curve

short dash curve

long dash curve

- Relation
- 0th order approximation

Scherrer and Sen 2008, PRD 78, 067303

- Taylor Expansion

Gong etal., Int. J. Mod. Phys. 22 (2013) 1350035, 1301.1224

- Take approximation

- Self-consistency

- The dynamics of scalar fields has some common features
- The exists an approximate relation between w and
- For thawing models, the dynamics can be approximated by CPL parametrization with degenerated relation between w0 and wa
- The reduced degeneracy helps improve the constraint on w(z)