LARGE DISTANCE MODIFICATION OF GRAVITY Gia Dvali New York University
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LARGE DISTANCE MODIFICATION OF GRAVITY
Gia Dvali
New York University
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Modified gravity versus dark energy
Dvali, Gabadadze, Porrati;Dvali, Gabadadze;
Deffayet, Dvali, Gabadadze;
Dvali, Gruzinov and Zaldarriaga;Dvali, Turner;
Modified Gravity and Cosmological Constant
Dvali, Gabadadze, Shifman;
Adams, McGreevy, Silverstein;
Arkani-Hamed, Dimopoulos, Dvali, Gabadadze
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Universe’s acceleration:
Friedmann equation (flat universe)
Dark energy or Modified Gravity?
Hubble parameter:
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Gravitational shortcut
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FRW Equation is modified
H2-H/rc = GN8 3
Early cosmology in normal H>>rc-1
Late cosmology HH=rc-1
At late times Universe is self-accelerating!
NO NEED IN DARK ENERGY.
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LUNAR RANGING TEST OF MODIFIED GRAVITY
Predicted anomalous perihelion precession of the lunar orbit
=1.4 x 10 -12
Todays accuracy:
=2.4 x 10 -11
10-fold improvement is expected
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Why: modified gravity universes acceleration?
Universe’s acceleration at a constant rate implies:
CONSTANT CURVATURE = GRAVITON “CONDENSATE”
BUT, MASSLESS BOSONS DO NOT CONDENSE WITHOUT A SOURCE
This is why in Einstein’s gravity the Universe’s acceleration requires a dark energy source!
R = 12 H2 = constant
Because of acceleration our Universe is filled with a minuscule nearly-constant graviton condensate ~ 10-29g/cm3
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But, in modified gravity gravitons are no longer massless, and can condense without any dark energy source!
Resulting into the self-accelerated Universe
H2 - H/rc = 0
Friedmann equation for flat and empty universe:
H2 = 0
Modified Friedmann equation for flat and empty Universe:
No expansion
Acceleration at a constant rate: H=1/rc
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STRING THEORY PICTURE
open strings
closed strings
ordinary particles
gravity
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Discontinuity
Crossover distance rc
Lim New Gravity Einstein rc ∞
New gravity is no longer mediated by a massless
spin-2 graviton!
hNew = h
Einstein + ?
~ 1028cm
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