Miami 2010, Ft. Lauderdale, Dec. 19, 2010 1/20 Niayesh Afshordi, Perimeter Institute/U-Waterloo...

Miami 2010, Ft. Lauderdale, Dec. 19, 2010 1/20Niayesh Afshordi, Perimeter Institute/U-Waterloo

Missing Baryons!!

Gonzalez, Zaritsky, & Zabludoff 2007 NA, Lin, Nagai, & Sanderson 2007

27% § 8% of baryons are neither in stars or gas!Recently confirmed by Atacama Cosmology Telescope & South Pole telescope

X-rays++ Sunyaev-Zel’dovich (WMAP3)


Dark Energy, Black Hole Entropy, and the First Precision Measurement in

Quantum Gravity!

Niayesh Afshordi


Outline

• Motivation: Reviving Gravitational Aether– Horava-Lifshitz (Quantum) Gravity– Cosmological Constant Problem

• Black Hole/Dark Energy connection– Thermodynamic argument– Trans-Planckian Ansatz

• Observations, Puzzles and Problems• Conclusions

NA 2010, arXiv:1004.2901


Reviving Aether I:Horava-Lifshitz Gravity

• Gravity is (power-counting) renormalizable if – frequency / wavelength-3 (! / k3); Horava 09

• Lorentz invariance is broken at high energies• Preferred frame behaves like Aether• Michaelson-Morely experiment++ Aether should

decouple from matter at low energies• At low energies:

General Relativitymean extrinsic curvature of spatial hypersurfaces

local aether expansion (Hubble) rate

Behaves as an incompressible fluid (NA 2009)


Reviving Aether II: Cosmological Constant Problems

• Old Cosmological Constant Problem (Pauli 1920’s)

– |½vac| ¿ 1033 kg/m3 (Standard Model of Particle Physics)

• New Cosmological Constant Problem: Dark Energy

– ½vac = (7.1 § 0.9) £ 10-27 kg/m3

• Coincidence Problem –½vac ' 2.7 ½m,0


Quantum Gravity vs. Aether

Old CC problemNew CC problem

Coincidence problem

(UV-complete ) Quantum Gravity

Incompressible Gravitational Aether

Miaralda-Escude 2010

Horava 2009; NA 2009, …

NA 2008Prescod-Weinstein, NA, & Balogh 2009NA 2010


Outline



• Observations, Puzzles and Problems: • Conclusions


Return of the Cosmological Constant!

(M, DE )(M, DE )(M, DE )

Supernovae Ia (Wood-Vasey et al. 2007)redshift /velocity

Accelerating Universe (post 1998)

Decelerating Universe (pre 1998)Lo

g (

dis

tance

)


How Black Holes lead to cosmic acceleration

• Gravitational Aether:

space

z~ 20, stellar black holes form

z~ 0.5, aether pressure dominates cosmic expansion

acceleration time

Gravitational aether is sourced at black hole horizons

Why should black holes source Aether?

z~ 1000, Aether is uniform


Aether: a thermodynamic theory?

• Black Hole Thermodynamics:– Bardeen, Carter, & Hawking 1973; Bekenstein 1973

• Einstein’s gravity and 2nd law: – TdS = dQ G¹º = T¹º (Jacobson 1995)

– Newtonian gravity as an entropic force (Verlinde 2010)


Back Hole Entropy and Dark Energy

!

Horizon Temperature ¿ Planck Energy = 1

• What if gravitational aether has a thermal pressure?

• Let’s consider QG corrections to BH thermal properties (c.f. entanglement entropy) : – Entropy:– Energy/Mass:– Volume:

• Pressure becomes:

• Could astrophysical Black Holes source Dark Energy?!• Cosmic Acceleration, first precision measurement in Quantum Gravity!

® = (-3.1 § 0.4) £ 10-3 [MBH/10 M¯]-3


Outline



• Observations, Puzzles and Problems• Conclusions


Aether pressure at large distances

Aether/Black Hole spacetime

• Aether (½ = 0) around a spherical Black Hole:

• Limits far from and close to the horizon:

r À 2m

r -2m ¿ 2m

C. Prescod-Weinstein

Prescod-Weinstein, NA, & Balogh 2009


Stellar BH’s and cosmic acceleration

• The same integration constant describes solution close to and far from the BH “horizon”

UV-IR coupling• Maximum redshift: 1/(-32¼p0m2)• Assuming this to be = Planck Energy/Hawking Temp.

p0 = -1/(256 ¼2m3) = - observed ½DE for m = 73 M¯ !!!!

Formation of stellar Black Holes can trigger late-time cosmic acceleration

Cosmic acceleration: first concrete signature of quantum gravity!

Trans-Planckian ansatz quantum gravity near BH horizon



Outline



• Observations, Puzzles and Problems • Conclusions


Multiple BH’s and Effective Dark Energy

• multiple black holes:log m* = hlog mimass weighted

• As super-massive BH’s grow, the effective ½DE / m*

-3 decreases• Using a model for

formation of stars/SMBH’s

mea

n BH

mas

s (m

*)

WMAP5+BAO+SN


2(ln P + Á) = 0

∆


Joint Dark Energy Missions (WFIRST, LSST, EUCLID)

• Probe Dark Energy history with incredible precision over the next decade

confirm/rule out aether predictions


Problems and Puzzles

• Formation of a Black Hole with Aether• Fundamental Theory and/or Action• Cosmological Structure Formation/Evolution• Coupling of Aether to Matter• Predictions for DE need formation history of

Astrophysical Black Hole: • Star Formation history• Initial Mass Function• AGN accretion history


Conclusions

• Revival of Gravitational Aether has lead to novel solutions to the problems of Qunatum Gravity and Cosmological Constant

• Quantum Gravity Corrections to thermodynamics of astrophysical black holes can source Dark Energy– Observable connection between history of astrophysical BH’s and

DE evolution– Only (falsifiable) Dark Energy model without fine-tuning (to my

knowledge)! – First precision measurement in Quantum Gravity ?!

• Many questions remain: BH collapse, cosmological structure formation, Action, coupling to matter …FIN!


Late-time Acceleration scenario

• g00 around the black hole (m ¿ r ¿ H-1) looks like de-Sitter space, so slow-moving particles (i.e. stars/galaxies) accelerate away from the center

• As this happens around every BH, the coarse-grained universe should look like ¤ + matter with ½¤= -p0


“But to claim that dark energy represents a profound mystery, is, in our opinion, nonsense. “Dark energy” is just a catch name for the observed acceleration of the universe, which is a phenomenon well described by currently accepted theories, and predicted by these theories, whose intensity is determined by a fundamental constant, now being measured. The measure of the acceleration only determines the value of a constant that was not previously measured. We have only discovered that a constant that so far (strangely) appeared to be vanishing, in fact is not vanishing. Our universe is full of mystery, but there is no mystery here.”


Thanks to Marcelo Gleiser!


Cosmological Constant and Technical Naturalness

Thanks to Marcelo Gleiser!

• A technically natural effective theory is insensitive to the cut-off• e.g. Newton’s laws, Standard Model (except for Higgs)• A theory that is not technically natural requires fine-tuning• A small (or zero) cosmological constant IS NOT technically natural

momentum


Landscape/Multiverse “solution” to the CC problem

• All the possible choices of CC are realized in the multiverse, and we happen to live in the regions that are habitable

• “Critics claim that many of these theories lack empirical testability, and without hard physical evidence are unfalsifiable; outside the methodology of scientific investigation to confirm or disprove.” wikipedia


Gravitational Aether: (NA 2008)

solves the old cosmological constant problem

• The metric is now blind to vacuum energy:

• In order to satisfy the Bianchi identity:

• Further assume incompressible fluid/aether:

Motivation: Tests of gravity severely constrain new deg’s of freedom+ Horava-Lifshitz gravity

NA 2008


Cosmology with Gravitational Aether

• Friedmann equation (NA 2008):

i.e., effective G depends on the Eq. of state.• Radiation vs. Matter era:• BBN (4He abundance) (Cyburt, Fields, Olive, & Skillman 2005)

(but 7Li prefers lower values)

• Ly-®+WMAP3 (Seljak, Slosar, McDonald 2006):

p/½ for matter


How does aether affect tests of gravity?

• If:– Aether tracks matter– Internal pressure is negligible

Aether is indistinguishable from GR• But:– Cosmological Tests: BBN (He, Li), CMB, Ly-®– Aether is irrotational (?) e.g. gravitomagnetic effect due

to earth rotation can test it (Gravity Probe B, LAGEOS) – Self-gravitating objects with relativistic pressure (e.g.

neutron stars, supernovae) will be sensitive to aetherNA 2008; Aslanbeigi ,et al., in preparation


Example of model predictions:Ly-® forest + WMAP5

GR

Aether

WMAP5

WMAP5+Ly-®

Aether is preferred to GR

G. Robbers

NA, Foster, Kohri, & Robbers, in preparation


The Real BBN Constraints

General Relativity

Gravitational Aether

7Li prefers Aether to GR4He prefers GR to Aether

NA, Foster, Kohri, & Robbers, in preparation

baryon to photon ratio

Miami 2010, Ft. Lauderdale, Dec. 19, 2010 1/20 Niayesh Afshordi, Perimeter Institute/U-Waterloo...

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Transcript of Miami 2010, Ft. Lauderdale, Dec. 19, 2010 1/20 Niayesh Afshordi, Perimeter Institute/U-Waterloo...