University of California, Berkeley Lawrence Berkeley National Lab Course on Dark Energy Cosmology at the Beach 2009 Eric Linder University of California, Berkeley Lawrence Berkeley National Lab JDEM constraints

Outline Lecture 1: Dark Energy in Space The panoply of observations Lecture 2: Dark Energy in Theory The garden of models Lecture 3: Dark Energy in your Computer The array of tools – Don’t try this at home!

Describing Our Universe New Stuff Old New Stuff Us STScI 95% of the universe is unknown! Had I been present at the creation of the world, I should have recommended something simpler. - Alfonso X ‘The Wise’, King of Castile and Leon

Mapping History

Acceleration Acceleration has: - Direct (kinematic) effect on spacetime through a(t) - Dynamic effects on objects within spacetime, e.g. growth, ISW What appears in the metric is the cosmic scale factor a(t). The metric can be spatially flat (k=0) but the spacetime is curved if This is exactly the Equivalence Principle: Gravity = Curvature = Acceleration

Windows on Dark Energy Light signals travel on null geodesics (ds=0) and measure dt/a = dz/H. Distances are directly affected by acceleration. Growth, ISW, abundances measure competition between acceleration and gravitational attraction. ISW (decaying potentials) is direct measure of violation of matter domination, not acceleration. Stretching space suppresses growth. Recall Jeans instability gives exponential growth – expanding space reduces this to power law. Friction term ~ (3-q).

Dark Energy – the Easy Way? Direct detection? (Dark energy in solar system = 3 hours of sunlight). Co-dependence? Variations of fundamental constants; lab/accelerator/universe Direct acceleration? Redshift drift (Sandage 1962; McVittie 1962; Linder 1991,1997) dz=10-8 over 100 years Redshifts are changes in scale/position (“velocities”): z=[a(t0)-a(te)]/a(te)  H0 (t0-te) Redshift shifts are changes in changes (“acceleration”): dz/dt0 = [a0-ae]/ae = H0(1+z)-H(z)  -zq0H0 t .

Cosmic Archaeology CMB: direct probe of quantum fluctuations 3D surveys of galaxies and clusters: probes of expansion + growth Pattern of ripples, clumping in space, growing in time. BAO, Lensing, Matter power spectrum. Supernovae: direct probe of cosmic expansion Time: 30-100% of present age of universe CMB: direct probe of quantum fluctuations Time: 0.003% of the present age of the universe.

BREAK CMB

What do we see in the CMB? Planck COBE WMAP “GroundPol” has 2.5x the resolution and 1/5x the noise A view of the universe 99.997% of the way back toward the Big Bang - and much more.

See poster by Roland de Putter and 0901.0916 CMB and Dark Energy CMB provides a lever to break degeneracies CMB provides a key window on microphysics of dark energy - spatial fluctuations  and sound speed cs2 CMB Polarization (B-mode) is dominated at small angles by high redshift lensing - hence high z structure formation. Polarization lensing “focuses” on the universe at z=1-4, giving a window on early dark energy, and neutrinos. See poster by Roland de Putter and 0901.0916

Mapping Our History The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history. STScI

Standard explosion from nuclear physics Type Ia Supernovae Exploding star, briefly as bright as an entire galaxy Characterized by no Hydrogen, but with Silicon Gains mass from companion until undergoes thermonuclear runaway Standard explosion from nuclear physics Insensitive to initial conditions: “Stellar amnesia”

Type Ia Supernovae Brightness tells us distance away (lookback time t) Redshift tells us the expansion factor a Time after explosion

Standardized Candles Supernova Legacy Survey (SNLS) Conley et al 2006

Supernova Properties Astrophysics Understanding Supernovae Supernova Properties Astrophysics Nearby Supernova Factory 400 SN Ia with spectra, z=0.03-0.08 >3000 spectra of SN Ia Cleanly understood astrophysics leads to cosmology (and astrophysics!) G. Aldering (LBL)

Current Data: World Union SN Set Complete reanalysis, refitting of 13 SN data sets 396 SNe Ia (58+249) - new low z SN Fit Mi between sets and between low-high z Study of set by set deviations (residuals, color) Blind cosmology analysis! Systematic errors ≈ statistical errors Kowalski et al., ApJ 2008 [arXiv:0804.4142]

Tests for Systematics and Evolution No significant deviations from mean of Hubble diagram, or (mostly) in residual slope. Also no evolution seen in redshift or population tests. Kowalski et al. 2008, ApJ 2008 [arXiv:0804.4142]

Current Data: SNLS ~310 confirmed SN Ia, 50-60 to be processed Preliminary ~240 SN Sullivan et al 2008 On track for ~500 total 3y data paper ~ early ’09

Imminent Results SDSS SN: z=0.1-0.4, 99 SN for Y1 release [498] Essence: z=0.2-0.7, Y6 release 156 SN CSP: followup 21 [100+100], I-band Hubble diagram Local SN studies: KAIT, CfA, PTF, SkyMapper Decelerating and Dustfree with HST: 15 SN z>1 (each SNell worth 9x SNext statistically) Preliminary Frieman, Jha, Kessler et al 2008

Gravitational Weak Lensing Gravitational potentials deflect light, creating convergence (magnification) and shear (shape distortion). This depends on the focal length (geometric kernel of dldls/ds) and potential power spectrum (density growth). Acceleration affects both distances and growth. Convergence  is very difficult to measure (no absolute size) and shear  needs to be measured statistically (averaging over intrinsic ellipticities). Need surveys with millions of well-resolved galaxies. Need good source redshift information to un-blur focal lengths.

Weak Lensing Subaru deep field 17 deg2 Miyazaki et al. 2007 CFHT Legacy Survey - Wide + Deep Semboloni et al. 2006, Hoekstra et al. 2006, Benjamin et al. 2007, Fu et al. 2008, Dore et al. 2008 For dark energy not yet precision, “pre-Boomerang” COSMOS (HST) 2 deg2 space WL Full tomographic analysis Kitching, Massey, et al. 2008 Massey et al. 2007

Baryon Acoustic Oscillations In the beginning... (well, 10-350,000 years after) It was hot. Normal matter was p+,e- – charged – interacting fervently with photons. This tightly coupled them, photon mfp << ct, and so they acted like a fluid. Density perturbations in one would cause perturbations in the other, but gravity was offset by pressure, so they couldn’t grow - merely oscillated. On the largest scales, set by the sound horizon, the perturbations were preserved. M. White (CMB) Galaxy cluster size Baryon acoustic oscillations = patterned distribution of galaxies on very large scales (~150 Mpc). “Standard ruler”

Baryon Acoustic Oscillations BAO need millions of galaxy positions spread over >1 Gpc3 volume, ideally spectroscopic z. Issues of nonlinearity, bias, z-space, selection effects. Eisenstein et al. 2005 Martinez et al. 0812.2154 Does any model agree with the data? A peak? Multi-peaks? Sanchez & Cole 2008 Galaxy selection and scale-dependent bias?

Precision Cosmology for Dark Energy? Reality check - what do we really know now: Supernovae see acceleration Weak lensing sees dark matter acc dec 1.5 cl Clusters see dark matter BAO sees baryons Vikhlinin et al. 0812.2720

Distance Complementarity Distances relative to low and high redshift have different degeneracies, hence complementarity

Redshift Range Deep enough that is less than 10% energy density? Not next-to-dominant? Deep enough that have accounted for >2/3 of the acceleration?

END Lecture 1 For more dark energy resources, see Lecture 1: Dark Energy in Space The panoply of observations Lecture 2: Dark Energy in Theory The garden of models Lecture 3: Dark Energy in your Computer The array of tools – Don’t try this at home! For more dark energy resources, see http://supernova.lbl.gov/~evlinder/scires.html Resource Letter on Dark Energy http://arxiv.org/abs/0705.4102 Mapping the Cosmological Expansion http://arxiv.org/abs/0801.2968 and the references cited therein.