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Dark Energy Cosmology

Dark Energy Cosmology. Robert Caldwell Dartmouth College. INPE Winter School September 12-16, 2005. Cosmic Evolution. Cosmic Acceleration. observations of type 1a supernovae indicate our universe is accelerating. RC, Physics World, May 2005 data: Riess et al, ApJ 607 (2004) 665.

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Dark Energy Cosmology

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  1. Dark Energy Cosmology Robert Caldwell Dartmouth College INPE Winter School September 12-16, 2005

  2. Cosmic Evolution

  3. Cosmic Acceleration observations of type 1a supernovae indicate our universe is accelerating RC, Physics World, May 2005 data: Riess et al, ApJ 607 (2004) 665

  4. Cosmic Acceleration observations of type 1a supernovae indicate our universe is accelerating universe contains m, k,  k=0 (CMB) basic picture spatially-flat RW spacetime acceleration due to : Riess et al, ApJ 607 (2004) 665

  5. Cosmological Constant “The Cosmological Constant and the Theory of Elementary Particles” Zel’dovich, Sov. Phys. Uspekhi 11 (1968) 381 “The genie () has been let out of the bottle….” “A new field of activity arises, namely the determination of ” The quantum vacuum energy of scalar particles resembles a cosmological constant Problem: IR phenomenon has UV divergence

  6. Casimir Effect sketch of basic calculation oscillator energy energy density with boundaries change due to plates pressure difference uniform stress-energy between the plates Milton, 2001

  7. Casimir Effect: Measurements Lamoreaux, PRL 78 (1997) 5 Mohideen & Roy, PRL 81 (1998) 4549 Bressi et al, PRL 88 (2002) 041804

  8. Casimir Effect Vacuum Energy is not Immutable Casimir Effect in a Weak Gravitational Field Energy density carried in vacuum fields distorts in response to a weak gravitational field Caldwell, astro-ph/0209312

  9. Cosmological Constant Are unattached vacuum loops real? Do they gravitate? Casimir Effect: a real manifestation of fluctuations of the QED vacuum Quantum vacuum contributes to inertia Jaekel, Lambricht, Reynaud, New Astron. Rev. 46 (2002) 727 Casimir effect without the vacuum Jaffe, PRD 72 (2005) 021301

  10. Constant Problems Numerous sources of an effective  in physics beyond SM Everywhere you look in QFT (even standard model) Symmetry-breaking vacuum energy (Higgs-like fields) Supergravity 3-form (may be quantized) … Ways to get rid of it Cancellation (unstable to dynamics) Supersymmetry (broken) Euclidean QG (probabilistic) Weinberg, Rev Mod Phys 61 (1989) 1 Any physics content? There must be fluctuations! Ghost Condensation… Arkan-Hamed et al, JHEP 0405 (2004) 074

  11. Action Principle Einstein 1919 Anderson & Finkelstein, Am J. Phys. 39 (1971) 901 van der Bij and van Dam, Physica 116A (1982) 307 Unimodular gravity a theory of (linear quantum) gravitation … subject to symmetries satisfying -det(g)=1 trace: nearly equivalent formulation of Einstein’s GR

  12. Action Principle: Multiplication Linde, PLB 200 (1988) 272 • Two spacetimes, x & y • Identical matter content • Antipodal symmetry: • Result: zero vacuum and trace-free GR quantum effects? observable consequences?

  13. Action Principle: Subtraction Kaplan & Sundrum, hep-th/0505265 • One spacetime • Identical matter content • Energy parity symmetry • Result: zero vacuum but there are ghosts “ghost sector” must be underpopulated classically stable, but QG instability Slow instability with QG cutoff:  ~ 10-3 eV observable consequence: ~30 breakdown of gravitational potential

  14. Cosmological Constant: a bookmark Regard  as a placeholder until observation, experiment, and theory can determine the underlying physical laws behind the dark energy phenomenon. Astrophysical phenomena not sensitive to the dark energy: use  as a simple, economical model Cosmological phenomena sensitive to the dark energy: Question observations / experiments Test theoretical foundation Search for conflicts with baseline  What are the alternatives?

  15. Dark Energy What is it? The cosmological constant? A new particle / field? A new aspect of gravitation? A misinterpretation of observations? Astrophysical confusion?

  16. Lives of the Cosmological Constant 1917 Einstein, deSitter 1968 Zel’dovich History: Kragh, “Cosmology & Controversy” 1980s  + dark matter or baryonic models Numerous authors investigated the cosmological consequences of an additional smooth, time-varying component of the cosmic fluid. Kinematic Tests of Exotic, Flat Cosmological Models Charlton & Turner, ApJ 313 (1987) 495 Cosmology with a Time-Variable Cosmological “Constant” Peebles & Ratra, ApJ 325 (1988) L17

  17. Dark Energy close the system of equations evaluate classical tests of cosmology to constrain “w”

  18. Dark Energy w: equation-of-state controls the slope of the dark energy curve past: in the simplest model, the dark energy does not play a significant role in cosmic evolution before z~2 present: the time-evolution of w determines the time-evolution of the dark energy future: unknown without a reliable model of the dark energy

  19. Dark Energy The dark energy phenomena could be due to a new, very-light scalar field. (-+++) Why a scalar field? This is arguably the simplest method of introducing new physics within the well-tested framework of quantum physics. Due to the similarity of the dark energy phenomena with inflation, it seems plausible that a similar mechanism is responsible. Scalar fields, while not necessarily fundamental, are ubiquitous in theories beyond the standard model of particle physics.

  20. Dark Energy The scalar field is a pioneer, sent out to explore new worlds of physics! • Waves, Optics • Electrodynamics • Quantum Mechanics • Scalar QED • Field Theory • Symmetry Breaking • Dilatons, Moduli • … • Nordstrom’s Scalar Gravity • Kaluza-Klein Unification • Dirac and Jordan’s Cosmology • Scalar-Tensor Gravity • Inflaton • Quintessence • …  Gravity and the Tenacious Scalar Field Carl Brans, gr-qc/9705069

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