Presentaci

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VECTOR models for DARK ENERGY
Antonio L. MAROTO and Jose BELTRÁN JIMÉNEZ
Universidad Complutense de Madrid
arXiv0801.1486 astro-ph
43rd Recontres de Moriond , March 15-22 (2008)
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The Dark Energy Coincidence Problem
Why rDE rM today ?
Dark Energy models (L, 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 LCDM,
• with natural initial conditions,
• with good fits to SNIa data

Vector models can do the job !
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The model
Vector-tensor action

• G only dimensional scale in the model
• No free parameters
• No potential terms (Kiselev, Armendariz, 04,
  Boehmer, Harko 07, Mota, Koivisto
  07)

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The model
Equations of motion
Flat Robertson-Walker metric
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The model
Explicit solutions radiation and matter eras
Radiation
Matter
Scaling during radiation era
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Energy densities
Radiation
Final singularity
Vector dark energy
Matter
Cosmological constant
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Equation of state
Vector field evolution (MP units)
W1/3
W -0.457
phantom line
Radiation
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Fitting SNe type Ia data
Luminosity distance
Distance modulus
Data sets
SNLS (Astier et al. 06) zlt1
Gold (Riess et al 04) zlt1.7
157 (previous) 16 (HST zgt1) 173 SNe
44 (previous) 71 (new zlt1) 115 SNe
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Fitting SNe type Ia data VCDM vs. LCDM
Gold set
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Other parametrizations with the Gold set
VCDM
Vector dark energy best fit to Gold dataset to
date
Lazkoz, Nesseris, Perivolaropoulos, 05
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Initial conditions and the end of the universe
Natural initial conditions
Imminent final singularity
Type III Big-freeze singularity
tend t0 690 million years (h0.7)
earliest fossils
Nojiri, Odintsov, Tsujikawa, 05 Bouhmadi,
González, Martin, 07
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Problems at small scales?
PPN parameters
Static parameters agree with GR
Preferred frame effects
Will, 81, Nordtvedt
Present bounds
Quantum instabilities Ghosts
Negative energies for perturbations at sub-Hubble
scales,
but can be gauged away in this model
(preliminary)
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Conclusions

• Vector model for dark energy with
• No potential terms
• No dimensional scales (apart from G)
• No free parameters
• Standard kinetic terms

Scaling behaviour during radiation and natural
initial conditions (No coincidence problem)
Excellent fit to Gold dataset and compatible
with SNLS definite predictions for cosmological
parameters
Phantom dark energy today BAO, CMB?