Quintessence Dark Energy & Acceleration of the Universe

BURIN GUMJUDPAI

The Tah Poe Academia Institute for Theoretical Physics & Cosmology

Department of Physics - Naresuan University - Phitsanulok

Invited seminar given @ Department of Physics, Chiang Mai University, Chiang Mai, ThailandSeptember 6, 2006

Fundamental Physics & Cosmology Research Unit

3405159 B.S. (Physics), Chiang Mai University

1996Now, back home!

Outlines

1. Observation of acceleration2. What causes acceleration ?3. Quintessence dark energy

• exponential potential• scaling solution

4. Fate of the universe5. Comments and conclusion

Join the DARK SIDE !

1. Observation of acceleration

1.1 type IA supernovae (discovered in 1998)

A. G. Riess et al. [Supernova Search

Team Collaboration], Astrophys. J. 607 , 665 (2004)

1.2 Cosmic Microwave Background anisotropies (WMAP) combined with Hubble Space Telescope

J. L. Sievers et al., Astrophys. J. 591, 599 (2003)

1.3 WMAP combined with large scale galaxy surveys

N. A. Bahcall, J. P. Ostriker, S. Perlmutter and P. J. Steinhardt, Science 284, 1481 (1999)

COBE 1990

WMAP 2003

the surface of last scattering

2. What causes acceleration ?

2.1 Dark energy (scalar field & cosmological constant)

For review see E. J. Copeland, M. Sami and S. Tsujikawa, hep-th/0603057

Cosmological constant might be coming back! Favored by recent CMB result!

2.2 Modification of gravity (including braneworld models) many authors

2.3 Backreaction of cosmological perturbations E. W. Kolb, S. Matarrese, A. Notari and A. Riotto, hep-th/0503117

3. Quintessence dark energy

There are (too) many models of dark energy • Cosmological constant (w = -1)• Scalar fields:

– Quintessence– K-essence– Tachyon field– Phantom field– Dilaton field– Chaplygin gasand many more...

• Fune-tunning problem

Astrophysics measures

Particle physics predicts

121 order of magnitude difference!

3.1 Motivation- Solution of fine-tunning problem

3.2 Fundamental physics supports• Supergravity inspired models• - - Pseudo Nambu Goldstone models

3.3 The Quintessence model Quintessence scalar field action

Variation of action gives Klein-Gordon field equation

The Eq. can also be obtained from

using

Acceleration eq.

Friedmann eq.: energy+matter BALANCE with geometry :

How it affect expansion

With scalar field domination

Eq. of state

From fluid eq., solution is

Value within a range

However, to attain acceleration, we need

Then

where

• Exponential potential

Expressed in tern of Hubble parameter so that Dark Mattercan be taken into account.

• Scaling solution

E nergy density of the scalar field mimics the background fluid energy density.

When scaling solution is the attractor, any initial conditions, the field sooner or later enter the scaling regime

Possibility of solving f ine tuning problem of dark energy.

Single exponential suffering from the density exit i.e. it does have scaling behavior but cannotdominate the universe.

There are many newer and more complicated models of quintessence potentials.

There are many more other models of dark energy.

4. Fate of the Universe

The universe will end up with some types of future singularities e.g.

• Big Rip at finite time, size & p & energy density infinity, • Sudden at finite time, size is finite, p is finite but energy density infinity and others...

• Dark energy is real• Scaling solution can help solving the fine-tunning problem• Exponential model is the earliest, simplest and give scaling

solution but unviable due to being unable to dominate matter.

• There are many other models• The universe will end up with more and more acceleration• Attempting for avoidance of future singularities is one of our

current work. Doing this, we are working on Loop Quantum Cosmology background with a dark energy dubbed “phantom field”

5. Conclusion & comments

Acknowledgement

• R. Maartens & D. Wands (Ph.D. supervisors) • M. Sami & S. Tsujikawa (collaborators) • F.P.C. Research Unit of the TPTP

• The Thailand Research Fund• Home institute: Naresuan University• The host: Prof. Thirapat Vilaithong & Dept. of Phys. Chiang Mai

University

Gratitude to my beloved parents