Upload
amanda-walters
View
216
Download
1
Tags:
Embed Size (px)
Citation preview
ERE 2008 September 15-19, 2008 1Spanish Relativity Meeting 2008, Salamanca, September 15-19 (2008)
Avoiding the
DARK ENERGY coincidence problem with a
COSMIC VECTOR
Antonio L. MAROTO and Jose BELTRÁN JIMÉNEZ Universidad Complutense de Madrid
Phys. Rev. D 78, 063005 (2008)
ERE 2008 September 15-19, 2008 2
The accelerated expansion of the universe
dL(z) relation from SN Ia data
Supernova Cosmology Project: 42 SNe Ia, z<0.83
High-z Supernova Search Team: 14 SNe Ia, z < 0.62,
Hubble Space Telescope
(Gold Set): 157 SNe Ia, + 16 with z > 1.25.
Deceleration - acceleration transition at z0.46 0.13
SNLS 71 SNe Ia z < 1 Reduced systematics
(single instrument)
1998
2004
2005
AcceleratedDecelerated-acceleratedDecelerated
ERE 2008 September 15-19, 2008 3
The need for dark energy
Friedmann equation
Einstein’s equations in flat FRW backgrounds
Acceleration requires negative pressure:
DARK ENERGY
ERE 2008 September 15-19, 2008 4
Dark energy equation of state pDE = wDE DE
Gold Set
Flat models (M + DE = 1)
Favors wDE < -1
Gold set
SNLS setwDE= const.
The need for dark energy
ERE 2008 September 15-19, 2008 5
Crossing the phantom divide wDE < -1?
Gold Set
ODEP: CMB, BAO, growth factor
Nesseris,Perivolaropoulos, ‘07
wDE= wDE(z)
The need for dark energy
ERE 2008 September 15-19, 2008 6
Cosmological constant p= -
G = (1019 GeV)-2
G8G (Tg)
~ (10 - 3 eV) 4
Coincidenceproblem
The dark energy coincidence problem
ERE 2008 September 15-19, 2008 7
Quintessence: scaling regime
Scaling
M has to be fixed in order to get DE
The dark energy coincidence problem
ERE 2008 September 15-19, 2008 8
The dark energy coincidence problem
Dark Energy models scalar, f(R),… require unnatural dimensional parameters in their
Lagrangians or initial conditions
Our aim is to find a model:• without dimensional scales (apart from G), • with the same number of parameters as CDM, • with natural initial conditions,• with good fits to SNIa data
Vector models can do the job !
Why DE ~ Mtoday ?
ERE 2008 September 15-19, 2008 9
The model
• G only dimensional scale in the model• No free parameters• No potential terms (Kiselev, Armendariz, ’04, Boehmer, Harko ’07,
Mota, Koivisto `07)
Vector-tensor action
ERE 2008 September 15-19, 2008 10
The model
Equations of motion
Flat Robertson-Walker metric
ERE 2008 September 15-19, 2008 11
The model
Explicit solutions: radiation and matter eras
Matter
Radiation
Scaling duringradiation era
ERE 2008 September 15-19, 2008 12
Energy densities
Matter
Radiation
Vector dark energy
Cosmological constant
Final
singularity
Scaling
ERE 2008 September 15-19, 2008 13
Equation of state
Radiation
Vector field evolution (MP units)
W=1/3 W= -0.457
phantom line
ERE 2008 September 15-19, 2008 14
Fitting SNe type Ia data
Distance modulus
Luminosity distance
Data sets
SNLS (Astier et al. ’06) z<1Gold (Riess et al ’04) z<1.7
157 (previous)+ 16 (HST z>1) = 173 SNe 44 (previous)+ 71 (new z<1) = 115 SNe
ERE 2008 September 15-19, 2008 15
Fitting SNe type Ia data: VCDM vs. CDM
Gold set
ERE 2008 September 15-19, 2008 16
Other parametrizations with the Gold set
Lazkoz, Nesseris,Perivolaropoulos, ‘05
VCDM:
Vector dark energy: best fit to Gold dataset to date
ERE 2008 September 15-19, 2008 17
Initial conditions and the end of the universe
Natural initial conditions:
Nojiri, Odintsov, Tsujikawa, ‘05Bouhmadi, González, Martin,
’07
Type III “Big-freeze”
singularity
“Imminent” final singularity:
tend –t0 = 690 million years
(h=0.7)
~ earliest fossils
ERE 2008 September 15-19, 2008 18
Stability and local gravity tests
PPN parameters
Static parametersagree with GR
Preferred frame effects
Present bounds
Classical stability
Will, ’81,Nordtvedt
Real propagation speed for scalar, vector and tensor perturbations
Quantum stability: ghosts?
ERE 2008 September 15-19, 2008 19
Conclusions
Vector model for dark energy with:• No potential terms• No dimensional scales (apart from G)• No free parameters• Standard kinetic terms
Excellent fit to Gold dataset and compatible with SNLS:
definite predictions for cosmological parameters
Scaling behaviour during radiation and natural initial
conditions (No coincidence problem)
Phantom dark energy today: BAO, CMB?
ERE 2008 September 15-19, 2008 20
Evolution of density perturbations
Sub-Hubble modes
Radiation era
Matter era
Matter or radiation eras
Density contrast(matter and radiation)
PRELIMINARY
ERE 2008 September 15-19, 2008 21
Evolution of density perturbations
Super-Hubble modes
Matter and radiation eras
Density contrast(matter and radiation)
PRELIMINARY