Dynamics of bigravity and general...
Transcript of Dynamics of bigravity and general...
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Dynamics of bigravity
and
general relativity
Waseda University
Kei-ichi Maeda
with K. Aoki (in preparation) & M. Volkov PRD87 (2013) 104009
Bianchi universe
FLRW universe
Homothetic solution
Observational consequence ?
Introduction
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Dark Energy
Modified gravity
cosmological constant L
General Relativity graviton: massless spin 2
massive gravity
Fierz-Pauli ghost-free linear theory
de Rham-Gabadadze-Tolley Non-linear extension
Hassan-Rosen Extension to bigravity
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Question:
Stability of FLRW universe
de Sitter : attractor ? cosmic no hair conjecture
An accelerating universe is naturally found ?
GR+ a cosmological constant: attractor ?
In GR with a cosmological constant
cosmic no hair theorem (Wald 83) for Bianchi spacetime
Any anisotropic homogeneous spacetime except for type IX is
always isotropized and de Sitter solution is realized.
(Type IX : initially → de Sitter )
large black holes are not formed (Shiromizu et al 93)
in asymptotically de Sitter spacetime
Inhomogeneous case → Schwarzschild-de Sitter solution
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Bianchi universe (homogeneous but anisotropic spacetime) KM, Volkov (’13)
homothetic solution is an attractor
the shear density drops as (In GR )
chaotic behaviour in Type IX
Homothetic solution gives (GR+ a cosmological constant)
stability against perturbations
FLRW universe (homogeneous and isotropic spacetime)
Aoki, KM (in prep.) existence condition of de Sitter solution
matter effect on dynamics
Equation of state of DE ?
cosmological constant with dark matter ?
Observational consequence ?
content
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Bigravity theory
Interaction term
two metrics
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a flat space is a solution
Basic equations two free coupling constants
energy-momentum conservation
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homothetic metrics:
K: constant
GR with a cosmological constant
: quartic equation for K
homothetic solution de Sitter
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perturbations around a homothetic solution
de Sitter background
massless mode
massive mode
stable
general vacuum homothetic background
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FLRW universe
g-spacetime FLRW spacetime
f-spacetime spherically symmetric spacetime
two cases:
bidiagonal
non-bidiagonal g- and f- spacetimes are decoupled
special solution
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Matter : radiation + dust
flat FLRW
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[1] vacuum
quartic equation
Minkowski
cosmological constant
1 dS
2 AdS
(stable)
(stable)
(unstable) No dS
dS dS
dS
homothetic solution
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matter : dust
Minkowski dS
stable spacetimes
dS
M dS
M
dS
: the ratio of initial matter densities
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dS
M
dS
M (zero L)
Matter dominant universe
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dS (homothetic sol)
singularity
matter effect
the ratio of initial matter densities
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For the coupling constants with de Sitter homothetic solution,
there always exist a finite range of initial values,
in which de Sitter spacetime is realized asymptotically.
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Bianchi Spacetimes
Class A
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Bianchi I
perfect fluid
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homothetic
Hamiltonian constraints + EOM
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homothetic solution=vacuum Bianchi I with a cosmological constant L in GR
analytic solution
Homothetic solution is an attractor in Bianchi I
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More General Bianchi Types
Numerical Results
Type IX
Approach to homothetic metrics
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homothetic solution GR with a cosmological constant
Shear drops fast as
However, it does not drop so fast:
This is the same as matter fluid
Any Observational Effect ?
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de Sitter spacetime is not always an attractor
Closed FLRW universe
bounce -> de Sitter
collapse -> singularity
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Initial Stage (near singularity)
Bianchi I Bianchi IX
Three spatial components of metrics
vacuum Bianchi IX
bounce -> de Sitter
initial singularity chaotic behaviour near singularity
small anisotropy
large anisotropy
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homothetic solution is an attractor
the shear density drops as (In GR )
chaotic behaviour near singularity in Type IX
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Observational constraints
: dark energy
Planck (‘13)
[1]
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[2]
dark energy = a cosmological constant
exotic matter
“dust fluid”
Dark Matter ?
baryon
“Dark Matter”
Dark Energy
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Summary
A homothetic solution corresponds to
that in GR with a cosmological constant
We discuss dynamics of bigravity
The homothetic solution with a positive (or zero) cosmological constant
is an attractor in FLRW and Bianchi class A spacetimes
cosmic no hair
There may be observational constraints
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Homothetic solution (GR+L) is also an attractor
for inhomogeneous spacetimes ?
More generic spacetimes
Cosmic no hair conjecture ?
Black hole uniqueness ?
Further Questions:
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