Dark energy and the accelerating universe Grigoris Panotopoulos - PowerPoint PPT Presentation

Dark energy and the accelerating universe Grigoris Panotopoulos University of Valencia & IFIC Astroparticle seminar, 4 November 2010, MPI, Munich

Outline Outline Introduction/Motivation  Introduction/Motivation Dynamical dark energy Dynamical dark energy  Geometrical dark energy  Geometrical dark energy Statefinder diagnostics  Statefinder diagnostics Conclusions Conclusions  G Panotopoulos MPI seminar, Munich 2010 2

Evolution of the universe Evolution of the universe G Panotopoulos MPI seminar, Munich 2010 3

1998: The accelerating universe 1998: The accelerating universe breakthrough of the year breakthrough of the year G Panotopoulos MPI seminar, Munich 2010 4

Slow-roll inflation: A paradigm for the early universe Slow-roll inflation: A paradigm for the early universe V G Panotopoulos MPI seminar, Munich 2010 5

Μagnitude versus red-shift Μagnitude versus red-shift Several theoretical  Several theoretical curves curves Observational data  Observational data Best fit when dark Best fit when dark  energy ~3/4 energy ~3/4 G Panotopoulos MPI seminar, Munich 2010 6

Age of the Universe and Hubble constant Age of the Universe and Hubble constant G Panotopoulos MPI seminar, Munich 2010 7

Primordial Nucleosynthesis Primordial Nucleosynthesis G Panotopoulos MPI seminar, Munich 2010 8

Today's picture of the universe Today's picture of the universe 3 independent 3 independent data sets coincide data sets coincide Concordance cosmological model! Concordance cosmological model! G Panotopoulos MPI seminar, Munich 2010 9

Dark energy dominates in the (flat) universe Dark energy dominates in the (flat) universe Εnergy in the universe Εnergy in the universe = = Matter 27% Matter 27% (baryons 4% & cold dark matter 23%) (baryons 4% & cold dark matter 23%) + + Dark energy 73% Dark energy 73% G Panotopoulos MPI seminar, Munich 2010 10

Dark energy equation of state w Dark energy equation of state w Theory : w < - 1/3  Theory : w < - 1/3 Observations : -1.2 < w < -0.8 Observations : -1.2 < w < -0.8  G Panotopoulos MPI seminar, Munich 2010 11

What is dark energy? What is dark energy? Cosmological constant: the simplest case Cosmological constant: the simplest case  Introduced by Einstein for a Introduced by Einstein for a static universe static universe  Allowed by all symmetries Allowed by all symmetries  ΛCDM agrees with data ΛCDM agrees with data  The cosmological and The cosmological and coincidence problems coincidence problems G Panotopoulos MPI seminar, Munich 2010 12

Cosmological constant Cosmological constant  Fluid with w=-1  Fluid with w=-1 Very different evolution Very different evolution  Value much lower than expected Value much lower than expected  G Panotopoulos MPI seminar, Munich 2010 13

Field equations for gravity Field equations for gravity Observation: accelerated expansion  Observation: accelerated expansion → decelerated expansion Theory: with matter or radiation → decelerated expansion  Theory: with matter or radiation Disagreement between theory and observation between theory and observation  Disagreement G Panotopoulos MPI seminar, Munich 2010 14

Two choices Two choices  Geometrical Geometrical dark energy dark energy  Modify Modify left left hand side hand side → → new gravitational theory new gravitational theory  Dynamical Dynamical dark energy dark energy  Modify → new dynamical component → Modify right right hand side hand side new dynamical component G Panotopoulos MPI seminar, Munich 2010 15

A very active field A very active field S. Nojiri, S. D. Odintsov and M. Sami, arXiv:hep-th/0605039; V. Sahni S. Nojiri, S. D. Odintsov and M. Sami, arXiv:hep-th/0605039; V. Sahni and Y. Shtanov, arXiv:astro-ph/0202346; R. A. Brown, R. Maartens, E. and Y. Shtanov, arXiv:astro-ph/0202346; R. A. Brown, R. Maartens, E. Papantonopoulos and V. Zamarias, arXiv:gr-qc/0508116; P. S. Papantonopoulos and V. Zamarias, arXiv:gr-qc/0508116; P. S. Apostolopoulos and N. Tetradis, arXiv:hep-th/0604014; arXiv:astro- Apostolopoulos and N. Tetradis, arXiv:hep-th/0604014; arXiv:astro- ph/0605450; C. Wetterich, L. P. Chimento, R. Lazkoz, R. Maartens and ph/0605450; C. Wetterich, L. P. Chimento, R. Lazkoz, R. Maartens and I. Quiros, Nucl.\ Phys.\ B 302 (1988) 668; B.Ratra and P.J.E.Peebles, I. Quiros, Nucl.\ Phys.\ B 302 (1988) 668; B.Ratra and P.J.E.Peebles, Phys.\ Rev.\ D 37 (1988) 3406; Phys.\ Rev.\ D 37 (1988) 3406; R. R. Caldwell, R. Dave and P. J. Steinhardt, arXiv:astro-ph/9708069]; R. R. Caldwell, R. Dave and P. J. Steinhardt, arXiv:astro-ph/9708069]; G Panotopoulos MPI seminar, Munich 2010 16

Q: Why Ωs of matter and dark energy are so similar in Q: Why Ωs of matter and dark energy are so similar in magnitude ? magnitude ? First answer  First answer  Special initial conditions Special initial conditions: current universe : current universe finite point in phase-space finite point in phase-space Second answer Second answer   Because of Because of values of parameters values of parameters: current universe close to a : current universe close to a fixed fixed point point G Panotopoulos MPI seminar, Munich 2010 17

Not so simple to realize ! Not so simple to realize ! Cosmology of type  Cosmology of type  Without Without energy exchange energy exchange  With With energy exchange energy exchange G Panotopoulos MPI seminar, Munich 2010 18

Superstring theory: basic idea Superstring theory: basic idea Really fundamental objects are one-  Really fundamental objects are one- dimensional (strings) dimensional (strings) In low energies string looks like a In low energies string looks like a  point-like particle point-like particle All known particles are different All known particles are different  oscillatory modes of the string oscillatory modes of the string G Panotopoulos MPI seminar, Munich 2010 19

Εxtended objects: Βranes Εxtended objects: Βranes String theory does not contain strings only  String theory does not contain strings only Normally, open strings satisfy Neumann  Normally, open strings satisfy Neumann boundary conditions boundary conditions End points move at speed of light  End points move at speed of light Dirichlet boundary conditions also make sense  Dirichlet boundary conditions also make sense  End points are stuck on a hypersurface. End points are stuck on a hypersurface.  This hyperurface is interpreted as a heavy solitonic This hyperurface is interpreted as a heavy solitonic object, a D-brane. object, a D-brane.  Brane-world idea : We are confined on such an object. Brane-world idea : We are confined on such an object. G Panotopoulos MPI seminar, Munich 2010 20

A simple brane model A simple brane model (Dvali, Gabadadze, Porrati, 2000) (Dvali, Gabadadze, Porrati, 2000) Action Action  One extra dimension One extra dimension  Gravity in 5D, our world in 4D Gravity in 5D, our world in 4D  Reduced to known gravity and cosmology in the early universe Reduced to known gravity and cosmology in the early universe  New gravity and cosmology in the recent times New gravity and cosmology in the recent times G Panotopoulos MPI seminar, Munich 2010 21

Cosmology for DGP Cosmology for DGP (Deffayet, 2001) (Deffayet, 2001) Friedmann eqn  Friedmann eqn Early times Early times  4D Friedmann 4D Friedmann Recent times  Recent times Same number of parameters as LCDM  Same number of parameters as LCDM G Panotopoulos MPI seminar, Munich 2010 22

A more realistic model A more realistic model (G.Kofinas, G.P., T.N.Tomaras, 2005) (G.Kofinas, G.P., T.N.Tomaras, 2005) Matter  Matter  in 5 dimensions (undetermined) in 5 dimensions (undetermined)  Fluid on the brane Fluid on the brane G Panotopoulos MPI seminar, Munich 2010 23

Cosmological solution Cosmological solution G Panotopoulos MPI seminar, Munich 2010 24

Cosmological equations Cosmological equations With new variables With new variables G Panotopoulos MPI seminar, Munich 2010 25

Final form Final form New quantities for dynamical study New quantities for dynamical study G Panotopoulos MPI seminar, Munich 2010 26

Critical points and their stability Critical points and their stability G Panotopoulos MPI seminar, Munich 2010 27

Numerical results for brane model Numerical results for brane model Evolution in the ω ω m - Z plane plane Evolution in the m - Z for for k=0, w=0, A<0 k=0, w=0, A<0 G Panotopoulos MPI seminar, Munich 2010 28