Local Void vs Dark Energy

Local Void vs Dark Energy Tirthabir Biswas IGC, Penn-State University with A Notari and R Mansouri, astro-ph/0606703 with A Notari, astro-ph/0702555 with A Notari, S Alexander & D Vaid, arXiv:0712.0370

Puzzles of Dark Energy • Smallness Problem • Coincidence or Why now Problem These puzzles are not unique to ΛCDM… … we are still very much in the dark Is dark energy real?

Concordant ΛCDM • Type Ia Supernovae • WMAP (CMB) • SDSS (galaxy power spectrum) • LRG (Baryon acoustic peak, BAO) • ISW effect • … Success of ΛCDM, failure of EdS How can we even contemplate not having Λ? What could we have missed?

The Inhomogeneous Universe Is homogeneity a good assumption?Celerier ‘97 • Back-reaction: “average expansion rate changes” • Rees-Schiama effect: What do we really measure Redshift Luminosity Distance Evolution history of universe effects DL(z) , but Inhomogeneities also effect light paths, or DL(z) L ~ 10-20 Mpc/h, RH~ 3000 Mpc/h

LocalEffect: We are sitting inside a large ~ O(100) Mpc/h void! Non-linear evolution  Why we can still be optimistic? • We only need • We regularly observe voids ~ 50 Mpc/h, • & large structures, Great SLOAN wall ~ 400 Mpc/h • huge “hole” spanning 150 Mpc/h, and 25% underdensity! [Frith et al] • How well do we understand nonlinear structure formation? Percolated voids ~ 100 Mpc/h[Shandarin, Sheth and Sahni] Having a large local void may not be as unlikely

Minimal Void Model Distant supernovae has z ~ 0.5-1 ~ O(1000) Mpc/h • Extreamely unlikely • Would effect CMB fluctuations • ruled out by distortion of black-body spectrum [Caldwell & Stebbins] We only need to modify upto z ~ 0.08 ~ O(200) Mpc/h “Currently” acceleration inferred through a mismatch of between Nearby, z < 0.08 & distant , z >0.4 supernovae data

Hout Hin Hout z<0.1, nearby supernova’s inside the patch, experience faster local Hubble expansion z>0.1outside the patch, see average expansion

Fitting WMAP Effect of void • Central Observer+Spherical symmetry  only monopole • Off-center observer  dipole ~ 10-3  within 10% of void-radius [Alnes & Amarzguioui] Higher multipoles are much suppressed • Non-spherical voids: Interresting possibilities, low multipole anomalies in CMB [Silk & Inoue] ? • Many large voids  interesting secondary effects to CMB anisotropies ~ 10-5 , Implications for ISW Assume spherical symmetry, EdS good enough for WMAP

Can EdS fit the WMAP? Yes! Provided we give up near scale-invariance Include running instead of Λ

Best fit WMAP parameters • consistent with BBN • Bayons constitute 9% of matter, may be too low? • zrec ~ 13, broadly consistent • low spectral index & large running • seemingly consistent with BAO [Eisenstein et al] • 0.43< hout <0.47 low Hubble parameter Along with the jump, local h ~ 0.59 possible! HKP: h= .72 .08 supernovae: h= .59 .04 SZ effect: h= .54 .04

Conclusions • SN Ia, WMAP, local h, BBN, BAO can work • SDSS, LRG (BAO), Lyman-, to be done • Several tests: D(z) curve, direct observations of voids, correlated anisotropies in CMB and H measurements Who knows in 5 years we may be talking about the mystery of the void 

Local Void vs Dark Energy