Dark Energy a cosmic mystery. Dunkle Energie Ein kosmisches Raetsel

Transcription

1 Dark Energy a cosmic mystery Dunkle Energie Ein kosmisches Raetsel

2 Quintessence C.Wetterich A.Hebecker,M.Doran,M.Lilley,J.Schwindt, C.Müller,G.Sch ller,g.schäfer,e.thommes, R.Caldwell,M.Bartelmann, K.Karwan,G.Robbers

3 What is our universe made of? quintessence! fire, air, water, soil!

4 Dark Energy dominates the Universe Energy - density in the Universe = Matter + Dark Energy 25 % + 75 %

5 ρ c =3 H² H M² critical density critical energy density of the universe ( M : reduced Planck-mass, H : Hubble parameter ) Ω b =ρ b /ρ c fraction in baryons energy density in baryons over critical energy density

6 What is Dark Energy?

7 Matter : Everything that clumps Abell 2255 Cluster ~300 Mpc

8 Dark Matter Ω m = 0.25 total matter Most matter is dark! So far tested only through gravity Every local mass concentration gravitational potential Orbits and velocities of stars and galaxies measurement of gravitational potential and therefore of local matter distribution

9 Ωm= 0.25 gravitational lens, HST

10 Gravitationslinse,HST

11 spatially flat universe Ω = 1 tot theory (inflationary universe ) Ω tot tot = x observation ( WMAP ) Ωtot =1.02 (0.02)

12 picture of the big bang

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14 Ωtot=1

15 WMAP 2006 Polarization

16 Dark Energy Ω + X = 1 m Ω : 25% m Ω : 75% Dark Energy h h : homogenous, often Ω Λ instead of Ω h

17 Space between clumps is not empty : Dark Energy!

18 Dark Energy density is the same at every point of space homogeneous No force in absence of matter In what direction should it draw?

19 Predictions for dark energy cosmologies The expansion of the Universe accelerates today!

20 Power spectrum Baryon - Peak galaxy correlation function Structure formation : One primordial fluctuation- spectrum SDSS

21 consistent cosmological model!

22 Composition of the Universe Ω b = visible clumping Ω dm = 0.2 invisible Ω h = 0.75 invisible clumping homogeneous

23 Dark Energya cosmic mystery Dunkle Energie Ein kosmisches Raetsel

24 What is Dark Energy? Cosmological Constant or Quintessence?

25 Cosmological Constant - Einstein - Constant λ compatible with all symmetries No time variation in contribution to energy density Why so small? λ/m 4 = Why important just today?

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31 λ 0 ( ρ + λ)

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33 asymptotic solution for cosmological constant (k=0)

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35 problems with small λ no symmetry explanation for λ/m 4 = quantum fluctuations contribute

36 Anthropic principle Banks Weinberg Linde

37 Cosmological Constant - Einstein - Constant λ compatible with all symmetries No time variation in contribution to energy density Why so small? λ/m 4 = Why important just today?

38 Cosm. Const. Quintessence static dynamical

39 Cosmological mass scales Energy density ρ ~ ( ev ) - 4 Reduced Planck mass M= GeV Newton s s constant GN=(8πM²) ) Only ratios of mass scales are observable! homogeneous dark energy: ρ h /M 4 = ¹²¹ matter: ρ m /M 4 = ¹²¹

40 Time evolution ρ m /M 4 ~ a ³ a ~ t ² t 3/2 matter dominated universe radiation dominated universe ρ r /M 4 ~ a 4 a ~ t -2 radiation dominated universe Huge age small ratio Same explanation for small dark energy?

41 Quintessence Dynamical dark energy, generated by scalar field (cosmon) C.Wetterich,Nucl.Phys.B302(1988)668, P.J.E.Peebles,B.Ratra,ApJ.Lett.325(1988)L17,

42 Prediction : homogeneous dark energy influences recent cosmology - of same order as dark matter - Original models do not fit the present observations.. modifications

43 Quintessence Cosmon Field φ(x,y,z,t) similar to electric field, but no direction ( scalar field ) x,y,z,t)= )=φ(t) Homogeneous und isotropic Universe : φ(x,y,z,t Potential und kinetic energy of the cosmon -field contribute to a dynamical energy density of the Universe!

44 Cosmon Scalar field changes its value even in the present cosmological epoch Potential und kinetic energy of cosmon contribute to the energy density of the Universe Time - variable dark energy : ρ h (t) ) decreases with time!

45 Cosmon Tiny mass m c ~ H New long - range interaction

46 Fundamental Interactions Strong, electromagnetic, weak interactions On astronomical length scales: graviton + gravitation cosmodynamics cosmon

47 Evolution of cosmon field Field equations Potential V(φ) ) determines details of the model e.g. V(φ) ) =M 4 exp( - φ/m ) for increasing φ the potential decreases towards zero!

48 Cosmological equations

49 Cosmic Attractors Solutions independent of initial conditions typically V~t -2 φ ~ ln ( t ) Ω h ~ const. details depend on V(φ) or kinetic term early cosmology

50 Cosmological equations matter/radiation ^ ^

51 asymptotic solution for large time M ^M

52 exponential potential constant fraction in dark energy

53 realistic quintessence fraction in dark energy has to increase in recent time!

54 Quintessence becomes important today

55 Equation of state p=t-v V pressure kinetic energy ρ=t+v energy density Equation of state Depends on specific evolution of the scalar field

56 Negative pressure w < 0 Ω h increases (with decreasing z ) late universe with small radiation component : w < -1/3 expansion of the Universe is accelerating w = -11 cosmological constant

57 Quintessence becomes important today No reason why w should be constant in time!

58 How can quintessence be distinguished from a cosmological constant?

59 Time dependence of dark energy cosmological constant : Ω h ~ t² ~ (1+z) -3 M.Doran,

60 small early and large present dark energy fraction in dark energy has substantially increased since end of structure formation expansion of universe accelerates in present epoch

61 Early Dark Energy A few percent in the early Universe Not possible for a cosmological constant 1σ and 2σ limits Doran,Karwan,..

62 Little Early Dark Energy can make large effect! More clusters at high redshift Cluster number relative to ΛCDM Two models with 4% Dark Energy during structure formation Fixed σ 8 ( normalization dependence! ) Early Quintessence slows downs the growth of structure Dark Energy during structure formation

63 How to distinguish Q from Λ? A) Measurement Ω h (z) H(z) i) Ω h (z) ) at the time of structure formation, CMB - emission or nucleosynthesis ii) equation of state w h (today)) > -1 B) Time variation of fundamental constants C) Apparent violation of equivalence principle D) Possible coupling between Dark Energy and Dark Mater

64 Cosmodynamics Cosmon mediates new long-range interaction Range : size of the Universe horizon Strength : weaker than gravity photon electrodynamics graviton gravity cosmon cosmodynamics Small correction to Newton s s law

65 Fifth Force Mediated by scalar field Coupling strength: weaker than gravity ( nonrenormalizable interactions ~ M -2 ) Composition dependence violation of equivalence principle Quintessence: connected to time variation of fundamental couplings R.Peccei,J.Sola,C.Wetterich,Phys.Lett.B195,183(1987) C.Wetterich, Nucl.Phys.B302,645(1988)

66 Violation of equivalence principle Different couplings of cosmon to proton and neutron p,n Differential acceleration earth cosmon Violation of equivalence principle only apparent : new fifth force! p,n

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69 Differential acceleration Two bodies with equal mass experience a different acceleration! η = ( a 1 a 2 ) / ( a 1 + a 2 ) bound : η <

70 Cosmon coupling to atoms Tiny!!! Substantially weaker than gravity. Non-universal couplings bounded by tests of equivalence principle. Universal coupling bounded by tests of Brans- Dicke parameter ω in solar system. Only very small influence on cosmology.

71 Cosmon coupling to Dark Matter Only bounded by cosmology Substantial coupling possible Can modify scaling solution and late cosmology Role in clustering of extended objects? L. Amendola

72 Quintessence and time variation of fundamental constants Generic prediction Strong, electromagnetic, weak interactions Strength unknown C.Wetterich, Nucl.Phys.B302,645(1988) gravitation cosmodynamics

73 Time varying constants It is not difficult to obtain quintessence potentials from higher dimensional or string theories Exponential form rather generic ( after Weyl scaling) But most models show too strong time dependence of constants!

74 Are fundamental constants time dependent? Fine structure constant α (electric charge) Ratio electron mass to proton mass Ratio nucleon mass to Planck mass

75 Quintessence and Time dependence of fundamental constants Fine structure constant depends on value of cosmon field : α(φ) (similar in standard model: couplings depend on value of Higgs scalar field) Time evolution of φ Time evolution of α Jordan,

76 Standard Model of electroweak interactions : Higgs - mechanism The masses of all fermions and gauge bosons are proportional to the ( vacuum expectation ) value of a scalar field φ H ( Higgs scalar ) For electron, quarks, W-W and Z-Z bosons : melectron = h φ electron * H etc.

77 Restoration of symmetry at high temperature in the early Universe Low T SSB <φ H >=φ 0 0 High T SYM <φ H >=0 high T : less order more symmetry example: magnets

78 In the hot plasma of the early Universe : No difference in mass for electron and muon!

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80 Quintessence : Couplings are still varying now! Strong bounds on the variation of couplings - interesting perspectives for observation!

81 baryons : the matter of stars and humans Ω b = 0.045

82 Abundancies of primordial light elements from nucleosynthesis A.Coc

83 Allowed values for variation of fine structure constant : α/α ( z=10 10 ) = GUT 1 α/α ( z=10 10 ) = GUT 2 C.Mueller,G.Schaefer,

84 variation of Li- abundance Coc,Nunes,Olive, Uzan,Vangioni 10/06

85 Variation of fine structure constant as function of redshift Three independent data sets from Keck/HIRES α/α = (12) 10-5 Murphy,Webb,Flammbaum, june 2003 VLT α/α = (6) 10-5 Srianand,Chand,Petitjean,Aracil, feb.2004 z 2

86 Atomic clocks and OKLO assumes that both effects are dominated by change of fine structure constant

87 Time variation of coupling constants must be tiny would be of very high significance! Possible signal for Quintessence

88 Παντα ρει Everything is flowing

89 Apparent violation of equivalence principle and time variation of fundamental couplings measure both the cosmon coupling to ordinary matter

90 Differential acceleration η For unified theories ( GUT ) : η= a/2a Q : time dependence of other parameters

91 Link between time variation of α and violation of equivalence principle typically : η = if time variation of α near Oklo upper bound to be tested ( MICROSCOPE, )

92 small change of couplings in space Fine structure constant depends on location in space Experiments with satellites? for r = 2 R E δ α em / α em = / k 2

93 Summary o Ω h = 0.7 o Q/Λ : dynamical und static dark energy will be distinguishable o Q : time varying fundamental coupling constants violation of equivalence principle

94 ???????????????????????? Why becomes Quintessence dominant in the present cosmological epoch? Are dark energy and dark matter related? Can Quintessence be explained in a fundamental unified theory?

95 Quintessence and solution of cosmological constant problem should be related!

96 End

97 A few references C.Wetterich, Nucl.Phys.B302,668(1988), received P.J.E.Peebles,B.Ratra, Astrophys.J.Lett.325,L17(1988), received B.Ratra,P.J.E.Peebles, Phys.Rev.D37,3406(1988), received J.Frieman,C.T.Hill,A.Stebbins,I.Waga, Phys.Rev.Lett.75,2077(1995) P.Ferreira, M.Joyce, Phys.Rev.Lett.79,4740(1997) C.Wetterich, Astron.Astrophys.301,321(1995) P.Viana, A.Liddle, Phys.Rev.D57,674(1998) E.Copeland,A.Liddle,D.Wands, Phys.Rev.D57,4686(1998) R.Caldwell,R.Dave,P.Steinhardt, Phys.Rev.Lett.80,1582(1998) P.Steinhardt,L.Wang,I.Zlatev, Phys.Rev.Lett.82,896(1999)

98 Dynamics of quintessence Cosmon ϕ : scalar singlet field Lagrange density L = V + ½ k(φ) ϕ ϕ (units: reduced Planck mass M=1) Potential : V=exp[-ϕ] Natural initial value in Planck era ϕ=0 today: ϕ=276

99 cosmon mass changes with time! for standard kinetic term m 2 c = V V for standard exponential potential, k = const. m 2 c = V / V / k 2 = V/( k 2 M 2 ) = 3 Ω h (1 - w h ) H 2 /( 2 k 2 )

100 Quintessence models Kinetic function k(φ) : parameterizes the details of the model - kinetial k(φ) ) = k=const. Exponential Q. k(φ ) = exp ((φ φ 1 )/α) ) Inverse power law Q. k²(φ )= 1/(2E( 1/(2E(φ c φ)) )) Crossover Q. possible naturalness criterion: k(φ=0)/ k(φ today ) : not tiny or huge! - else: explanation needed -

101 More models Phantom energy ( Caldwell ) negative kinetic term ( w < -11 ) consistent quantum theory? essence ( Amendariz Picon, Mukhanov,, Steinhardt ) K essence Amendariz-Picon higher derivative kinetic terms why derivative expansion not valid? Coupling cosmon / (dark ) matter ( C.W., Amendola ) why substantial coupling to dark matter and not to ordinary matter? Non-minimal coupling to curvature scalar f(φ) ) R - can be brought to standard form by Weyl scaling!

102 kinetial Small almost constant k : Small almost constant Ω h Large k : Cosmon dominated universe ( like inflation )