1 J. A. S. Lima (IAG/USP) The Accelerating Universe: Dark Energy and Alternative Models 26th Texas Symposium São Paulo, Brasil, 16/12/2012
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J. A. S. Lima
(IAG/USP)
The Accelerating Universe: Dark Energy and Alternative Models
26th Texas Symposium
São Paulo, Brasil, 16/12/2012
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SUMMARY
1. SNe Ia, Acceleration and Dark Energy
2. Cosmic Concordance Model
3. Λ-Problems/Dark Energy Candidates (GR)
4. Alternative Approaches
5. Perspectives/Conclusion
How do we know there is
dark energy?
We infer its existence only indirectly…
via its influence on the expansion
history of the universe!
Hypothesis: Dark Energy (DE) is a new component
responsible by the present accelerating stage of the
Universe (as indicated by SNe).
Basic Question:
1. Supernovas and the Accelerating Universe
SNe Ia: Best Cosmic Distance Indicator
Measure: (via ) and Ld 2 / 4Ld L F z
Output: constraints on the matter content (m, Λ )
SNe observations provide two basic informations:
1. The current Universe is accelerating (z < zt )
2. The past Universe was decelerating in past (z > zt )
),,(1 zFHd MoL
Model:
There is a transition Redshift: Zt ~ 1
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85 local
SNe 13 distant
SNe 1 very
distant SN
1998 Results: Acceleration! (HZSS) (Riess et al. AJ 116, 1009, 1998)
Allen et al. 2008
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SNe data Transition redshift (zt)
Turner & Huterer (2007)
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Important: Both informations can also be obtained without
reference to a specific dynamic model (Cosmography/Kinematic)
Turner & Riess ApJ 2002; Elgaroy & Multamaki, JCAP 2006
Cunha PRD 2009; Guimarães & Lima CQG 2011
Cunha & Lima, MNRAS 2008
Ω Ω Ω
Ω Ω Ω
Transition Redshift (Flat ΛCDM)
1)(
)()1()(
zH
zHzzq
2)(
a
aatq
ΛCDM - ACCELERATING MODEL
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3/1
m
tz
Transition Redshift:
Lima et al. 2012, arXiv: 1205.4648 [astro-ph.CO]
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CMB (WMAP) SNe Ia
SNe Ia
LSS
BAO
Observational Basis (Flat Universe, k=0)
AGE CMB
LSS + BAO X-RAY/CLUSTERS
SNe Ia
(Cosmic Paradigm – ΛCDM – since 2008!)
Cosmic
Concordance
(ΛCDM)
X-Ray CLUSTERS
Statistical Errors Statistical + Systematic
Ωk = Ωm = Ωm = Ωk =
Amanullah et al. ApJ 2010 - Union2 (557 SNe Ia)
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Riess et al. ApJ 2007 – Gold Sample (182 SNe)
Hicken et al. 2009 (Constitution) (397 SNe Ia)
Kowalski et al. ApJ 2008 - Union1 (307 SNe)
Astier et al. A&A 2006 – Legacy Sample (115 SNe)
Supernovae + Complementary Probes
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“We can be reasonably sure that if a better cosmology is called for
it will describe a Universe that looks like much ΛCDM, because that
is what is observed” (P. J. E. Peebles, arXiv:0910.5142v1)
Paris Conference: The Invisible Universe (2009)
Cosmic Concordance Model
But...there are problems and some answered questions!
Is ΛCDM only an effective model?
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Cosmic Concordance Model (ΛCDM)
0.7
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3. Λ - PROBLEMS:
obs
matter
obs
G e VM cu to ff
1 91 0411010 eVtheory
2. Why Now? (Coincidence Problem - CP)
1. Why so small? (CCP) 41210 eVobs
12010
obs
theory
4. Alternative Models (General Relativity)
)3(3
4
)(3
82
2
XXM
XM
pG
a
a
G
a
k
a
a
0 :onaccelerati ) (3
1 , 0, ap XMXXM
15
21
10 ) 1(
3
1
X
MXXp
FLRW Metric: a(t), k = 0, ± 1
SUPERNOVA OBSERVATIONS
Late-time accelerating expansion of the Universe
What is causing the acceleration of the Universe?
Λ - term, XCDM, Quintessence Chaplygin Gas, Interacting Models, etc.
Extra-dimensions, Branes, Kaluza-Klein, F(R), Inhomogeneities, etc.
Geometry Matter/Energy
Dark Geometry
↑ Dark Matter / Dark Energy
↑
Gμν = 8πGTμν
Modified
Gravity?
Accelerating Models (Inventory)
1. Cosmological Constant (Λ-Problem, Coincidence Problem)
2. Dark energy: p=wϱ, w=const. 3. Variable Dark Energy: w=w(z) 4. Quintessence – [ϕ, V(ϕ) ] - Scalars 5. Coupled Dark Matter-Dark Energy 6. K-essence 7. Chaplygin gas 8. Quartessence 9. Phantoms: p=wϱ, w < -1
1. Backreaction 2. Averaging Models 3. Production of CDM 4. F(R), F(T)... 5. Scalar-tensor models 6. Gauss-Bonnet 7. Brane dark energy 8. Cardassian 9. Degravitation
Dark Energy Models (GR ) : Models Without Dark Energy:
Gen. Rel.
Modified
Gravity
What is the correct solution? Add your solution here! 17
Unifying Dark Sector Models in GR (No Dark Energy!)
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1. XCDM (p=ωϱ , ω constant)
%9515.001.1
%9504.027.0
m
Amanullah et al. ApJ 2010 - Union2 (557 SNe Ia)
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2. Searching for Dark Energy: DETF* Strategy
1. Is the accelerating expansion consistent with Λ: Is w 1 ?
2. Probe the underlying dynamics. Measure the time evolution of DE: w(z) ?
3. Search for possible failures of general relativity (Modified Gravity?).
Goal: Compare the effects of DE on the expansion and in the growth of structures
(galaxies or galaxy clusters) – Difficult do quantify.
* Dark Energy Task Force (2006) – Comissioned by Nasa and NSF
Variable Dark Energy? Λ or not Λ?
pX = (z)X | (z)= o+ az/(1+z)
constant ΛCDM: o = -1 , a = 0
4 Basic Probes: SNe Ia, Galaxy Clusters, BAO and WL
H(z) ! Farooq, Mania & Ratra, et al. 2012, arXiv 1211.4253
DETF Cosmological Approach…
Parameterize dark-energy equation of state parameter :
• Today (z 0) w(1) w0
• In the far past (z>>1 ) w(0) w0 wa w(a) w0 + wa z / 1+z
Komatsu et al. WMAP7 (2011)
OBSERVATIONAL PERSPECTIVE (this decade!)
Measurements of H0 (2 -1%) – now is 3.2% (Riess at al. 2011)
A value of Ho (2% -1% ) would provide insights into fundamental physics!
Modified Gravity?
Accurate distances opportunity to learn about Gravitational Physics of a
locally inhomogeneous Universe
1. The nature of dark energy and its evolution
2. Curvature of the Universe (test for inflation)
3. Total number of relativistic particles
4. Limits on the sum of neutrinos mass (CMB data)
H0 is correlated with many other cosmological quantities!
Freedman & Madore ARAA 2010, Suyu et al. 2012
96% Dark Matter
Possibilities in GR:
REDUCING THE DARK SECTOR?
Modified Gravity: F(R)
Sotiriou & Faraoni, Rev. M. Phys. 2010
Remember: The theoretical status of DM is
greater than Dark Energy!
?
1) Averaging Models / Backreaction – inhomogeneities
Buchert GRG 2001, 2002; Elllis Nat 2008
Kolb et al. PRD 2008; Kolb CQG 2011
Basilakos & Lima PRD 2010; Lima, Basilakos & Costa PRD 2012
2) Grav. Production of CDM Particles - Lima et al. JCAP 2010
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The right framework is still unclear! One important task
is to explore all physically reasonable possibilities.
CONCLUSIONS
• Other DE candidates are not well motivated from FP
• Is the ΛCDM model only an effective cosmology?
More generally: Is dark energy an illusion. New Ether? MG?
Basic Cosmological Problem: What is the nature of DE?
SNe Ia, CMB, GC & BAO are consistent with ΛCDM (68% cl). But…
Any answer will have a fundamental
impact on astroparticle physics/cosmology!
• Vacuum density is plagued with the Λ-Problems
Theory provides either no guidance or far too much, depending on your point of view! Is DE a solution or a new Problem?
Λ or not Λ ?
Play your game and good lucky!
24 THANK YOU!