Open issues in Cosmology

Valencia, June 26th 2006

Open issues in Cosmology

Michael Rowan-RobinsonImperial College London


the concensus

Cosmological PrincipleFRW models

GR with

Standard model of PP

Big Bang + inflation +CDM


History of the universeHistory of the universe


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


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


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 < 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


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 ’s, supersymmetry, new large dimensions, new Z’ guage bosons in superstring models, bounds on MeV mass which decays during nucleosynthesis


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 as scalar field, undermined by existence of a residual (which looks like Einstein’s 2nd gravitational constant) today


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 =0.72 model

• however dropping assumption of power-law opens up possibilities even further (Blanchard et al 2003)


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 ?


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 m all-sky survey to check convergence


WMAP & QSO ResultsWMAP & 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.

Spergel et al. 2006

WMAP

From Fan et al.


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


Mobasher et al, 2005, ApJ, z~6.5 galaxy


is this z~6.5 galaxy too massive for CDM ?

Mobasher et al (2006) estimate mass as 6x1011 Mo

- problem for hierarchical model ?


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


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)


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 =0 model

• perhaps this plus CMB first peak is the ultimate geometrical measurement of Ho


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 !

Open issues in Cosmology

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