1 / 19

Open issues in Cosmology

Open issues in Cosmology. Michael Rowan-Robinson Imperial College London. the concensus. GR with L. Cosmological Principle FRW models. Standard model of PP. Big Bang + inflation + L CDM. History of the universe. limitations of GR for Cosmology.

tamra
Download Presentation

Open issues in Cosmology

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. Open issues in Cosmology Michael Rowan-Robinson Imperial College London Valencia, June 26th 2006

  2. the concensus GR with L Cosmological Principle FRW models Standard model of PP Big Bang + inflation +LCDM Valencia, June 26th 2006

  3. History of the universe Valencia, June 26th 2006

  4. limitations of GR for Cosmology • GR seems to work excellently for weak and strong gravitational fields, very well tested (solar system tests, gravitational lensing, black holes, gravitational waves) • however GR is a local theory, does not specify large-scale topology of universe, so incomplete - low amplitude of low CMB multipoles has been taken as evidence of unusual topology for universe - anomaly of alignment of low CMB multipoles • GR breaks down at high energy-density, so as we approach Big Bang, need quantum gravity • string theory ? • can’t expect predictions,instead we are supposed to select from the string landscape using observations Valencia, June 26th 2006

  5. limitations of the Cosmological Principle • observed universe is quite isotropic (10-5 at CMB) • quite uniform on large scales (few %) • highly inhomogeneous locally and today • isotropy + homogeneity give FRW models, universal cosmic time (so back to Aristotle) • FRW models are not strictly applicable and are very peculiar Valencia, June 26th 2006

  6. the standard model of Particle Physics • we know this is incomplete because neutrinos have mass, could the required change be major ? • mass differences are small, but we do not know the masses, could be few eV, probably Wn < 0.2 • possibility that dark matter could be sterile neutrino (Biermann and Kusenko 2006, Asaka et al 2006) - hint of support from LSND, will test with Miniboone • LHC had better detect the Higgs boson • best candidate for CDM is neutralino, but supersymmetry by no means an established extension of Standard Model Valencia, June 26th 2006

  7. synthesis of light elements • Big-Bang nucleosynthesis gives deepest reliable probe of the early universe, strong constraints on physics beyond the Standard Model (Fields and Sarkar, 2006, astro-ph/0601514) • constraints on sterile n’s, supersymmetry, new large dimensions, new Z’ guage bosons in superstring models, bounds on MeV mass nt which decays during nucleosynthesis Valencia, June 26th 2006

  8. limitations of Inflation • horizon, monopole and flatness problems are ‘solved’ by inflation • however inflation only reduces inhomogeneity and curvature by a finite factor, still shifts flatness problem back to initial conditions • no unique inflation model • no actual prediction of power-law density fluctuation spectrum, perhaps there should be imprints of various past phase-changes - we have to measure power spectrum and then infer inflaton potential • inflation needs interpretation of L as scalar field, undermined by existence of a residual L (which looks like Einstein’s 2nd gravitational constant) today Valencia, June 26th 2006

  9. power-law assumption • Spergel et al (2006) show that with power-law spectrum, can get wide range of fits just to WMAP3 CMB data • can see that priors on Ho or assumption of flatness force us towards WL=0.72 model • however dropping assumption of power-law opens up possibilities even further (Blanchard et al 2003) Valencia, June 26th 2006

  10. large-scale structure issues • does lack of cuspiness and deficiency of number of satellite galaxies mean CDM has to be a bit warm (Colin et al 2000, Bode et al 2001) or self-interacting/self-annihilating DM (Ostriker and Souradeep 2004) ? - probably not (eg Moore et al, astro-ph/0510370) - positron flux from GC consistent with clumped CDM, provided m << 600 GeV (Cumberbatch and Silk, astro-ph/0602320) • have we really resolved issue of origin of our Galaxy’s motion through the cosmic frame (the dipole) • most galaxy formation problems being resolved by combination of astrophysical feedback and recognition that there are two modes of star-formation - mergers and quiescent • high redshift (z >6) galaxies - are they too old ? - are they too massive ? Valencia, June 26th 2006

  11. convergence of dipole ? • not clear that dipole has converged by z = 0.1, from IRAS PSCz (R-R et al 2000) • Maller et al (2003) use 2MASS K-band flux dipole, K<13.57 (definitely not converged) • Ergogdu et al (2006) use 2MRS, K<11.25 • need AKARI 60 mm all-sky survey to check convergence Valencia, June 26th 2006

  12. WMAP & QSO Results • Year 3 WMAP release has reduced the electron optical depth so the epoch of reionization has been moved from z~17 down to z~10.9 (+2.7, -2.3), equivalent to 360Myr after Big Bang. • Spectra of SDSS z~6 QSOs show hints that Universe was reionized at only somewhat higher z than 6.5. WMAP From Fan et al. Spergel et al. 2006 Valencia, June 26th 2006

  13. Spitzer detection of z ~ 7 galaxy • Spitzer is showing us that galaxies at z~7 formed stars as much as 200-400 million years earlier (z~10) • Epoch of first star formation now seem likely to have been around z~10-15 from combining Spitzer and WMAP results. - light sterile neutrino could help first star formation(Biermann and Kusenko 2006) Egami et al. 2005 Valencia, June 26th 2006

  14. Mobasher et al, 2005, ApJ, z~6.5 galaxy Valencia, June 26th 2006

  15. is this z~6.5 galaxy too massive for LCDM ? Mobasher et al (2006) estimate mass as 6x1011 Mo - problem for hierarchical model ? Valencia, June 26th 2006

  16. the distance scale • HST key program found Ho = 72 +- 7 - used OGLE Cepheid calibration from LMC - need to use only p > 10 day Cepheids (Tammann et al 2003) - difference between P-L relation in Galaxy and LMC (Sandage et al 2005), perhaps Cepheid method does not work ! • WMAP found Ho = 73 +- 3 • new HST-ACS observations of Cepheids in galaxies with well-observed Type Ia supernovae gives Ho = 73 +- 6 (Riess et al 2005) - but LMC distance uncertain to +- 10%, need GAIA - used only 4 out of 8 SN with good data • would like a more geometrical determination of Ho - both Cepheids and supernovae capable of Baade-Wesselink approach Valencia, June 26th 2006

  17. supernova issues • data is clearly excellent • some inconsistencies with earlier results removed if use only modern CCD data (Riess et all 2005) • still some doubts about treatment of luminosity-decline rate relation (new approach by Wang et al 2005, Nobili et al 2005) • still some unresolved inconsistencies in derivation of extinction (Liebundgut 2001, R-R 2002) Valencia, June 26th 2006

  18. galaxy baryon acoustic peak • SDSS (Eistenstein et al 2005) and 2dFGRS (Cole et al 2005) have claimed to detect baryon acoustic peak at 100 h-1 Mpc in galaxy correlation function • Blanchard et al (2006) admit this could be fatal for their L=0 model • perhaps this plus CMB first peak is the ultimate geometrical measurement of Ho Valencia, June 26th 2006

  19. conclusions • we have an excellent cosmological model which works out to large distances but not to or beyond the horizon, and back to nucleosynthesis era, but no evidence it works earlier than this • model is not totally convincing (isotropy, topology, inflation, lambda) and little prospect of improvement • best hope for near future is particle physics (Higgs, neutralino, neutrino sector) - Happy Birthday, Bernard ! Valencia, June 26th 2006

More Related