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

2. Puzzles of Dark Energy Is dark energy real? 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?

3. 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?

4. 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 ~ Mpc/h, RH~ 3000 Mpc/h

5. Local Effect: 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

6. “Currently” acceleration inferred through a mismatch of between
Minimal Void Model
Distant supernovae has z ~ ~ 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 < & distant , z >0.4 supernovae data

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

10. 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

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

12. 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

13. 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 