Origin of Accelerating Universe: Dark-Energy and Particle Cosmology

1. Origin of Accelerating Universe:Dark-Energy and Particle Cosmology Yong-Yeon Keum Institute for Early Universe, Ewha Womans Univ, Korea & CTP-BUE in Egypt Talk at WHEPP XI workshop Jan 03, 2010

2. Motivations: • What is the origin of the accelerating Universe and Dark-Energy ? • The connection between cosmological observations and particle physics is one of the interesting and hot topic in astro-particle physics. • Precision observations of the cosmic microwave background and large scale structure of galaxies can be used to prove neutrino mass with greater precision than current laboratory experiments.

3. Contents Experimental evidence of accelerating universe Candidates of Dark Energy Neutrino Model of Dark Energy (An example of interacting dark matter and dark energy model) Conclusion and discussions on some issues.

4. Breakthrough of 1998: the Winner ASTRONOMY: Cosmic Motion Revealed

5. Breakthrough of 2003: the Winner Illuminating the Dark Universe

6. Measurement of the geometry CMB AT A GIVEN DISTANCE Known physical sizeangledepends on geometry Known luminosityfluxdepends on geometry SN Ia Closed Universe Flat Universe Open Universe

7. Standard Candle-SNIa

8. Hubble diagram: H0DL cz measure of H0 Large z : measure of m, z  0  1+z = a(tobs)/a(tem) At a given z m = - 2.5 log F + cst = 5 log (H0DL) + M - 5 log H0 + 25 Accelerated expansion = smaller rate in the past = more time to reach a given z = larger distance of propagation of the photons = smaller flux fainter Supernova Cosmology Project Magnitude m older Redshift z

9. Galaxies, clusters CMB observable observable Back to thermal history Density perturbations (inflation?) t = 10-35 s Nucleosynthesis t ~ 1 mn t ~ 380000 yrs Recombination: p+e- H+g Matter: Gravitational collapse Photons: Free propagation

10. What Penzias & Wilson saw in 1965

11. Should the CMB sky be perfectly smooth (or isotropic)? • No. Today’s Universe is homogeneous and isotropic on the largest scales, but there is a fair amount of structure on small scales, such as galaxies, clusters of galaxies etc.

12. What are these primordial fluctuations (at the level of 100 micro-Kelvin)?

13. What are the Cℓs? • Qualitatively: ~power in each multipole mode • Quantitatively:

14. 3 regimes of CMB power spectrum Acoustic oscillations Damping tail Large scale plateau

15. In general…. ↓Ωmh2 ←Age of Universe ↑Ωbh2 ←←Ωm+ΩΛ ↓zre

16. Max. scale of anisotropies Limited by causality (remember?)  maximum scale  Max scale relates to total content of Universe Wtot

17. What we know so far • Our universe is flat, accelerating. • The dominance of a dark energy component with negative pressure in the present era is responsible for the universe’s accelerated expansion.

19. Contents of Matter

20. Dark Energy 73% (Cosmological Constant) Neutrinos 0.1-2% Ordinary Matter 4% (of this only about 10% luminous) Dark Matter 23% Title

21. Einstein Equation geometric structure matter distribution Perfect fluid – the zeroth-order approximation : energy density P : pressure : functions of time

22. Einstein’s General Relativity (GR) & Cosmological Principle (CP): (00): (1) (2) (i i): (3)  Supernova Cosmology Projects (1999): or Quintessence (“Dark Energy”) Negative Pressure

25. Puzzles in Accelerating Universe Cosmological Constant Problem: Why is the energy of the vacuum so much small ? Dark Energy Puzzle: What is the nature of the smoothly-distributed energy density which appears to determine the universe. Coincidence Scandal: Why is the dark energy density approximately equal to the matter density in present epoch.

27. Candidates of Dark Energy Cosmological Constant Dynamical Cosmological constant (Time-dependent; Quintessence ) - quintessence: potential term + canonical kinetic term - K-essence: non-canonical kinetic term - phantom - quintom -Tachyon field Modified Gravity (Modified friedman eq.) Cosmological Back Reaction Others ……

28. Cosmological Constant Typical scale： Hence a new energy density is too lower from the particle physics point.

29. Cosmological constant problem • Many different contributions to vacuum energies: (a) QCD ~ (b) EW physics ~ (c) GUT ~ (d) SUSY ~ All these contributions should conspire to cancel down to . Extreme fine tuning !!!

30. ( B ) Quintessence • Quintessence = dark energy as a scalar field = dynamical cosmological constant • No evidence for evolving smooth energy, but attractive reasons for dynamical origins ! (a) why small, why not zero, why now ??? (b) suggest the physical cosmological evolution. • Canonical quintessence:

31. Quintessence (2) • If potential energy dominates over the kinetic energy Slow-roll limit: Stiff matter: Accelerating exp.:

32. Quintessence Potentials

33. K-essence Originally kinetic energy driven inflation, called K-inflation [Armendariz-Picon] ; Originates from string theory. • First applied to dark energy by Chiba et al. K-essence is characterized by a scalar field with non-canonical kinetic energy Transformed to the Einstein-frame action:

35. Phantom(ghost field) • Negative sign in the kinetic term; • We obtain for

36. Quintom Feng,Wang and Zhang proposed a hybrid model of quintessence and Phantom (so the name quintom) when while when

37. Big-Rip Singularity in phantom field • Hubble rate diverges as t -> ts, which corresponds to an infinitely large energy density at a finite time in the future. The curvature also glows to infinity. • It should be emphasized that we expect quantum effects to become important when the curvature of universe become large.

38. Tachyon field (A. Sen) An acclerated expansion occurs for

39. Chaplygin gas A special case of a tachyon with a constant potential

40. ( C ) Idea of the Modified Gravity • Newtonian Cosmology: Gravitational Force law determines the evolution Combining the above eqs: Moreover, E = constant and decelleration !!

41. Modified Force For simplicity g=1 (1) Early times t << tc so that matter domination, no acceleration (2) Later time, t > tc when Accelerated expansion !!!

42. Classification of the Modified Gravity • Cardassian : • Different brane world scenarios: a) Dvali, Gabadadze and Porrati (DGP) b) Deffayet, Devali and Gabadadez(DDG) c) Randall and Sundrum d) Shtanov brane Model e) non-linear gravity

43. Candidates of DE (Modified Gravity) • Modification of Gravity 1. Modified Newtonian Dynamics (Milgrom. 83) 2. Brane Models (Binetaury. 98) 3. Cardassian Expansion (Freese. 02)

44. Top-ten accelerating cosmological Models Akaike information: AIC = -2 lnL + 2d: d = # of model param. Bayesian factor: BIC = -2 lnL + d lnN: N = # of data point used in the fit.

46. Observational Constraints on MFE Cosmology Parameters of MFE cosmology • (B,n), (zeq,n) or (m,n) • Hubble Parameter as Function of z,H=H0E(z) • The Critical/Matter Density

47. Observational Constraints on MFE Cosmology From turnaround redshift zq=0 • zq=0 depends on both of m and n. (see eq. below) • For each m, there exists one npeak(m), which leads to a maximum of zq=0. • Higher m is, lower zq=0 is. • For each zq=0, there exists an upper limit for m, e.g., zq=0>0.6, then m<0.328.

48. Observational Constraints on MFE Cosmology From turnaround redshift zq=0 • The thick solid line is zq=0. • The cross-hatched area is the present optimistic m=0.330+-0.035. • The dashed lines are m=0.2 and 0.4 respectively. • The shaded area gives 0.6 < zq=0 <1.7. Zhu & Fujimoto 2004, ApJ, 602, 12

49. Observational Constraints on MFE Cosmology From SNeIa and Fanaroff-Riley type IIb radio galaxies • A 2 minimization method is used to determine (m,n). • The best fit happans at (m,n)=(0.38,-0.20). • The 68.3% and 95.4% confidence level in the (m,n) plane are shown. Zhu, Fujimoto & He 2004, ApJ, 603,365

50. A Brane World Model (BWM): DGP • A self-accelerating 5-dimensional BWM • With a noncompact, infinite volume extra dimension • An ordinary 5-dimensional Einstein-Hilbert action • A 4-dimensional Ricci scalar term induced on the brane Dvali, Gabadadze & Porrati 2000