1 / 46

THE UNIVERSE AS A BRANE

THE UNIVERSE AS A BRANE. Roy Maartens Portsmouth. QG05 Sardegna. general relativity + particle physics: expanding 4D universe model. confirmed by observations. WMAP satellite and SDSS telescope. the model fits the high-precision data. SDSS. WMAP. 3 independent data sets intersect.

satin
Download Presentation

THE UNIVERSE AS A BRANE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. THE UNIVERSE AS A BRANE Roy Maartens Portsmouth QG05 Sardegna

  2. general relativity + particle physics:expanding 4D universe model confirmed by observations

  3. WMAP satellite and SDSS telescope

  4. the model fits the high-precision data SDSS WMAP

  5. 3 independent data sets intersect

  6. GR + SM particle physics:inflationary LCDM model • successful model • but we know GR breaks down • quantum gravity will explain (pre-) inflation

  7. inflation is not the only puzzle …. • dark energy?? maybe an IR modification to GR? (as well as UV in the early universe) • LCDM is a framework seeking a fundamental theory • more puzzles to come from observations?

  8. is high-precision cosmology probing the limits of GR? • inflation is crucial – what underlies it? • what is dark energy – matter or gravity? • GR must break down in the UV we need quantum gravity in the early universe +… maybe also in the late universe/ IR? • candidate theories (Kiefer 2004) quantum GR (Williams, Markopolou talks) string theory

  9. string theory • removes the infinities of QFT • and includes the graviton • but there is a price … 9 space dimensions!! 6 compact 3

  10. simple observation: we live in a large 3D world

  11. why don’t we see the extradimensions? • conventional Kaluza-Klein idea: extra dimensions too small to be seen • discovery of D-brane • matter fields restricted to lower dimensional brane • external bulk felt only through gravity • extra dimensions can be much larger 4Dspacetime small extra dimension ~ Lp large extra dimension >> Lp gravity matter

  12. (Tanaka)

  13. 1+9 D universe has branes and strings • some of the 6D may be small 5 string theories + supergravity = limits of 1+10 D theory M THEORY (Bousso, Nicolai, Stelle, Zanelli talks)

  14. string theory -the cosmologist’s wish-list*a natural mechanism for 3 dimensions to grow very large/ 6 dimensions to compactify* a natural mechanism for inflation* or … an alternative - eg brane collision * solve the dark energy problem…. then we test the answers COSMOLOGY AS A PROBE OF STRING THEORY

  15. but … string theory is tough! • no convincing stringy inflation yet • no convincing stringy dark energy yet • no convincing progress on perturbations • some progress in string brane inflation *D/ anti-D brane models * higher-Dcosmic strings can be produced * … but still a long way to go

  16. the practical cosmologist’s approach while waiting for progress in string cosmology … develop phenomenology * it’s what we do with inflation * and QG phenomenology(Liberati talk) use string theory ideas in cosmology * in fact this can help string theory … * brings high-precision data into the picture

  17. experimental tests of gravity • Cavendish • neutrons (Bertolami talk) • colliders (Cavaglia) • solar system perihelion bending of light • binary pulsars • gravitational lensing • BHs and GWs • cosmology • BBN, SNe • LSS, CMB

  18. cosmology probes gravity on vast scales (Tegmark)

  19. eg - SDSS test of Newton’s law cccc (Shirata et al)

  20. extra-dimensional gravity brings new features • extra polarizations of the graviton (KK modes) • new fields (dilaton, moduli, radion, form fields) • shadow matter • holography (AdS/CFT) (Bianchi talk) • precision data constrains extra-dimensional gravity • … hopefully rule out some models • signature of extra dimensions • in observations?

  21. graviton KK modes 5D gravitons – effective mass on brane (massive KK modes) polarizations:5 = 2+2+1 5D spin-2 (5) = 4D spin-2 (2) + 4D spin-1 (2) + 4D spin-0 (1)

  22. start with simple models • similar to inflation and dark energy models • simplest models with predictive power • focus on one or two key aspects at a time • KK modes of graviton • scalar fields – dilaton, radion, moduli • …. • motivate by string theory • 2 branes with large separation + small internal space (Horava-Witten) • AdS5 X M models: 1 large dimension, warped • ….

  23. small extra dimensions (moduli stabilised) exp(-y/L) visible brane shadow brane brane anti de Sitter 5D (infinite extra dimension) L large extra dimension

  24. all extra dimensions large (Antoniadis, Arkani-Hamed, Dimopoulos, Dvali 1998) brane n-torus identify (…. Antoniadis talk)

  25. testing gravity in the laboratory • extra dimension changes Newton’s law torsion pendulum L

  26. (Randall & Sundrum 1999) 5D solution of Einstein equations warped geometry • extra dimension shrinks toward infinity • finite volume bulk • curvature scale 4D GR is recovered on large scales y

  27. KK modes of the graviton (Garriga, Tanaka) Discrete spectrum • m=0: zero mode for tensors • no zero-mode for scalars/ vectors Continuous spectrum • m>0: massive KK modes of the graviton • same massive modes for scalar/ vector/ tensor U(z) d • ～ z –2 (de Risi talk) z

  28. time cosmic expansion = movement of brane 3D space

  29. deviation from 4D GR in the early universe • modified Friedmann equation • gravity leakage: gravity becomes 5D gravity leakage (Binetruy, Deffayet, Langlois) (Shiromizu, Maeda, Sasaki)

  30. RS inflation 5D metric perturbation • modified Friedmann • boosts 4D perturbations • but also creates 5D GW * back-reaction of 5D metric perturbations * loss of power • large scales boosted • but small scales? * Vinf lowered * AS and AT boosted * but AT/ AS suppressed (RM et al) (Langlois, RM, Wands) (Koyama,Mizuno,Wands)

  31. modified background boosts 4D GW • but 5D GW emission damps 4D GW • competing effects – cancel! recover GR result (Hiramatsu,Koyama,Taruya)

  32. BH time bulk brane CMB anisotropies • 5D BH induces “dark radiation” on the brane perturbation isocurvature perturbation • 5D anisotropy induces anisotropic stress BH

  33. Spectralindex simple model constraint on small BH mass in 5D bulk spacetime BH mass probability 00 (Koyama)

  34. is dark energy a gravitational effect? general relativity observations (nearly) flat, accelerating universe, with sub-critical matter field equations imply dark energy example from history Mercury perihelion – Newton + missing matter? no: modified gravity

  35. modify Einstein’s equations? try GR + light scalar field – same as DE field try ghosts try massive graviton (Pauli-Fierz) unstable theory try infinite extra degrees of freedom?

  36. braneworld models with late-time acceleration Randall-Sundrum modifies GR in UV (early universe) - via gravity leakage off the brane at early times recover GR in IR DGP model is an alternative (Dvali, Gabadadze, Porrati 2000) - gravity leakage off the brane at late times recover GR in UV L = crossover scale

  37. L = crossover scale: • 5D gravity dominates at late times • no graviton zero-mode: 4D gravity recovered at high energy via lightest KK modes ‘metastable graviton’ brane 5D Minkowski bulk: infinite volume extra dimension gravity leakage

  38. DGP cosmology Friedmann (Deffayet) • early universe – recover GR dynamics • late universe – acceleration without dark energy * from leakage of gravity * but fine-tuned

  39. need to test this against SNe redshifts

  40. comparison with SNe observations (Deffayet et al) (Sahni et al) (Song) (Bento talk)

  41. structure formation • degeneracy between DGP and GR+DE: both can fit SNe observations but this is broken by structure formation

  42. how to distinguish DGP from GR+DE? • structure formation is suppressed: * in GR – because DE dominates over matter * in DGP – because gravity weakens need to compute LSS and compare with SDSS L~1/H0

  43. CMB – the ISW effect difference in LSS formation will leave an imprint (Nichol)

  44. DE curve: scalar field model with the same background evolution as DGP DGP(4D) curve: neglects 5D term ISW effect gravity leakage must be taken into account …. SNe+SDSS+CMB may rule out DGP LCDM Dark Energy DGP (4D) (Takahashi)

  45. brane cosmology brings new ideas * new effects in inflation, CMB, dark energy - even in the simplest models * RS + DGP models – extra-D gravity is central (unlike string brane inflation models) * probe stringy ideas via gravity – and test against observations exciting challenges for theorists!

  46. string theory demands extra dimensions conclusion - the universe as a brane • this may explain the beginning of the universe • this may explain what inflation is • this may explain what the dark energy is • ….. but not yet - brane models can help

More Related