Cosmological background solutions and cosmological backreactions V. - PowerPoint PPT Presentation

Department of Physics, University of Jyväskylä GGI, Firenze, January 27, 2009 Helsinki Institute of Physics, University of Helsinki SIGRAV School in Cosmology Valerio Marra in collaboration with Rocky Kolb and Sabino Matarrese Cosmological background solutions and cosmological backreactions V. Marra, E. W. Kolb, S. Matarrese, A. Riotto E. W. Kolb, V. Marra, S. Matarrese On cosmological observables in a swiss-cheese universe. Description of our cosmological spacetime as a perturbed Phys. Rev. D 76, 123004 (2007) conformal Newtonian metric and implications for the backreaction proposal for the accelerating universe. Phys. Rev. D 78, 103002 (2008) V. Marra, E. W. Kolb, S. Matarrese V. Marra Light-cone averages in a swiss-cheese universe. A back-reaction approach to dark energy. Phys. Rev. D 77, 023003 (2008) Padua@research ID588; arXiv:0803.3152

The cosmic concordance model 2.0 No Big Bang Ω M 0 . 25 ≃ Ω DE 0 . 75 ≃ 1.5 − 1 ≃ w DE 1.0 SNe successful, but.. 0.5 • coincidence problem CMB • origin problem Flat BAO 0.0 0.0 0.5 1.0 Kowalski et al. 08

A point of view The “safe” consequence of the success of the concordance model is that the isotropic and homogeneous LCDM model is a good observational fit to the real inhomogeneous universe.

Cosmological backgrounds ρ GBS = � ρ � H • Global Background Solution (GBS) + local equation of state 3 R GBS = � 3 R � H ρ ABS � = � ρ � H • Average Background Solution (ABS) a H ( t ) ∝ V H ( t ) 1 / 3 3 R ABS � = � 3 R � H [Buchert’s background] “averaged” equation of state: no local energy conditions ρ P BS � = � ρ � H • Phenomenological Background d L ( z ) 3 R P BS � = � 3 R � H Solution (PBS)

Backreactions Description of the spacetime: GBS, ABS, none? [perturbatively] Description of the observer: on what does the PBS depend? are all the PBSs the same?

Description of the spacetime Cosmological Principle FLRW Assumption: No-go theorem by GBS=ABS=PBS Ishibashi and Wald, 2006 FLRW models even with : δ ≫ 1 ds 2 a 2 ( τ ) − (1 + 2 ψ ) d τ 2 � = GBS describes the spacetime (1 − 2 ψ ) γ ij dx i dx j � + with ψ ≪ 1

Description of the spacetime No-go theorems are made by assumptions reconsider the assumption “with velocity much smaller than light relative to the Hubble flow” Ishibashi and Wald, 2006

Description of the spacetime observations do not see • Phenomenological small big departures from the Peculiar Velocities observed Hubble flow otherwise we assume that • Global Peculiar to be relaxed - as a starting point - the Velocities GBS describes the spacetime small GPV are a restriction on the dynamics of the inhomogeneities If inhomogeneities alone explain the concordance model, then there will be big GPV wrt EdS-GBS

Big Global Peculiar Velocities The GBS does not describe the spacetime: hint for Strong Backreaction E. W. Kolb, V. Marra, S. Matarrese Phys. Rev. D 78, 103002 (2008)

Description of the observer observer comoving with the • Global Observer GBS/ABS Hubble flow • Phenomenological observer comoving with the Observer PBS Hubble flow

Description of the observer Copernican every phenomenological Principle observer is the same observed isotropy FLRW Cosmological every observer assumption Principle sees the GBS The success of concordance model verifies this reasoning a posteriori

Bare principles the ABS (not necessarily the GBS!) • Bare Cosmological homogeneity and isotropy describes the universe: insensitive Principle on a large enough scale to the scale of averaging the PBS (not necessarily the GBS/ABS!) • Bare Copernican observed isotropy, describes observations for every observer, Principle success of LCDM even though not necessarily the same

Swiss cheese a 2 ( r, t ) a 2 ( r, t ) = 8 π G ˙ k ( r ) ρ ( r, t ) − ˆ EdS cheese with LTB holes: 3 a 2 ( r, t ) CHEESE VOID matching at r h CRUST CHEESE VOID wrong model to by construction: ABS = EdS study GBS vs ABS

PBS ≠ GBS Λ CDM with Ω M = 0 . 3, Ω DE = 0 . 7 concordance model: q 0 = Ω M / 2 − Ω DE = − 0 . 55 Λ CDM with Ω M = 0 . 6, Ω DE = 0 . 4 reference model: q 0 = Ω M / 2 − Ω DE = − 0 . 1 V. Marra, E. W. Kolb, S. Matarrese, A. Riotto Λ CDM with Ω M = 1, Ω DE = 0 EdS model: Phys. Rev. D 76, 123004 (2007) q 0 = Ω M / 2 − Ω DE = 0 . 5 V. Marra, E. W. Kolb, S. Matarrese Phys. Rev. D 77, 023003 (2008)

“Hubble bubble” scenario Far from the center, cosmological principle holds. Variance in H r too big: global observer ≠ phenomenological observer " CDM EdS o Empty ( # =0) b s e r 0.5 v e r i n a n u n d e r 1.4 d e n s i t y 1.2 0 ! (m-M) 1 o b s e r v e r i n a n E d S - l i k e r e g i o n -0.5 0.8 o b s e r v e r i n a n o v e r d e n s i t 0.6 y -1 0 83 166 249 332 415 501 0 0.2 0.4 0.6 0.8 1 Mpc z The GBS describes the spacetime but not the PBSs of the phenomenological observers: Weak Backreaction

Observable backreaction The PBS is the only one that matters from an observational point of view. The distinction between strong and weak backreaction is indeed good to lay a framework, but it might be illusory and unphysical. Only the “end result” matters Observable Backreaction: the evolution of inhomogeneities leads the PBS to have an energy content and curvature different from the corresponding local quantities

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