Dissecting Dark Energy

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Dissecting Dark Energy
Eric Linder Lawrence Berkeley National Laboratory
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Our Tools
Expansion rate of the universe a(t) ds2
?dt2a2(t)dr2/(1-kr2)r2d?2 Einstein
equation (å/a)2 H2 (8?/3) ?m ?H2(z)
(8?/3) ?m C exp?dlna 1w(z) Growth
rate of density fluctuations g(z) (??m/?m)/a
Poisson equation ?2?(a)4?Ga2 ??m 4?G?m(0) g(a)
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Tying HEP to Cosmology
Linder Phys.Rev.Lett. 2003 following Corasaniti
Copeland 2003
w(a) w0wa(1-a)
Accurate to 3 in EOS back to z1.7 (vs. 27 for
w1). Accurate to 0.2 in distance back to
zlss1100!
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All w, All the time
Time variation w is a critical clue to
fundamental physics. Alterations to Friedmann
framework ? w(z)
Suppose we admit our ignorance H2 (8?/3) ?m
?H2(z) Effective equation of state w(z) -1
(1/3) d ln(?H2) / d ln(1z) Modifications of the
expansion history are equivalent to time
variation w(z). Period.
gravitational extensions or high energy physics
Linder 2003
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The world is w(z)
Dont care if its braneworld, cardassian, vacuum
metamorphosis, chaplygin, etc.
Simple, robust parametrization
w(a)w0wa(1-a) Braneworld DDG vs.
(w0,wa)(-0.78,0.32) Vacuum metamorph vs.
(w0,wa)(-1,-3) Also agree on m(z) to 0.01 mag
out to z2
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Revealing Physics
Some details of the underlying physics are not in
w(z). Need an underlying theory - ??? beyond
Einstein gravity? Growth history and
expansion history work together.
w0-0.78 wa0.32
Linder 2004 cf. Lue, Scoccimarro, Starkman Phys.
Rev. D69 (2004) 124015 for braneworld
perturbations
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Questions
How does a(t) teach us something fundamental
(beyond w(z))? Benchmarks à la energy scale for
inflation models rule out theories tying DE to
inflation scalar tensor ??2 slow roll
parameters of V(?) like linear potential Predictiv
e power Albrecht-Skordis-Burgess w(z)
naturalness constraints flatness and w(z)
wlt-1 Crossing w-1 with hybrid
quintessence Other tools astronomy (strong
gravity, solar system), accelerator, tabletop
experiments
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Lambda, Quintessence, or Not?
Many models asymptote to w-1, making distinction
from ? difficult. Can models cross w-1? (Yes,
if wlt-1 exists.)
All models match CMB power spectrum for ?CDM
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Naturalness and w
Consider the analogy with inflation. Tilt n1
(Harrison-Zeldovich) is roughly predicted
profound if n1 exactly (deSitter, limited
dynamics). Same w-1 exactly is profound, but
w-1 maybe not too surprising. Small deviation
w?-1 important so precision sought. However,
while n0.97, constant without running, is
possible, w-0.97 constant is almost ridiculous.
Thus, searching for w is critical even if find
w very near -1.
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Predictions Benchmarks
Linear potential Linde 1986 V(?)V0?? leads to
collapsing universe, can constrain tc
curves of ?
Would like predictions of w(z) - or at least w.
In progress for Albrecht-Skordis-Burgess model
V(?) (1 ?/b ?/b2) exp(-?)
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Predictions Benchmarks
Extensions to gravitation E.g. scalar-tensor
theories f/2?-?(?)????-V Take linear coupling
to Ricci scalar R f/? F R Allow nonminimal
coupling F1/(8?G) ??2 R-boost (note R?0 in
radiation dominated epoch) gives large basin of
attraction solves fine tuning yet w -1.
Matarrese,Baccigalupi,Perrotta 2004 But growth
of mass fluctuations altered S?0 since G ? 1/F.
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Questions
How does a(t) teach us something fundamental
(beyond w(z))? Benchmarks à la energy scale for
inflation models rule out theories tying DE to
inflation scalar tensor ??2 slow roll
parameters of V(?) like linear potential Predictiv
e power Albrecht-Skordis-Burgess w(z)
naturalness constraints flatness and w(z)
wlt-1 Crossing w-1 with hybrid
quintessence Other tools astronomy (strong
gravity, solar system), accelerator, tabletop
experiments