Yashar Akrami Modern Cosmology: Early Universe, CMB and LSS/ Benasque/ August 17, 2012 Postdoctoral Fellow Institute of Theoretical Astrophysics University of Oslo, Norway (Hans Kristian Eriksen, David Mota) with: Tomi S. Koivisto & Marit Sandstad [arXiv:1208.xxxx] Cosmic Acceleration from Ghost-free, Massive BiGravity: A Statistical Analysis with Improved Generality
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Yashar Akrami Modern Cosmology: Early Universe, CMB and LSS/ Benasque/ August 17, 2012 Postdoctoral Fellow Institute of Theoretical Astrophysics University.
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Yashar Akrami
Modern Cosmology: Early Universe, CMB and LSS/ Benasque/ August 17, 2012
Postdoctoral FellowInstitute of Theoretical AstrophysicsUniversity of Oslo, Norway(Hans Kristian Eriksen, David Mota)
with:Tomi S. Koivisto & Marit Sandstad
[arXiv:1208.xxxx]
Cosmic Accelerationfrom
Ghost-free, Massive BiGravity:
A Statistical Analysis with Improved Generality
Yashar Akrami / Modern Cosmology: Early Universe, CMB and LSS/ Benasque / August 17, 2012 2
Late-time Acceleration
Motivation
2011 Nobel Prize in Physics
“…for the discovery of the accelerating expansion of the Universe through observations of distant supernovae”
Saul Perlmutter Brian P. Schmidt Adam G. Riess
+1
too big:CC problem
=0- Symmetry- Degravitation,- …
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Motivation+1
Dark Energyor
Modified GravityExample:
Scalar Fields:
[Luca’s talk]
The most general 4D scalar field theory with second order equation of motion:
Horndeski LagrangianAnyAlternatives?
Fierz & Pauli (1939):
Demand for Massive Gravity+1
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The only ghost-free mass term:
(linearized metric fluctuations around flat space-time)
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{-281.73 for (B1, Ωm) & -278.50 for ΛCDM}
{0.8355 for (B1, Ωm) & 0.8709 for ΛCDM}
complexity of the model increases considerably when we increase the number of model parameters
Some Results: (B1, B2, Ωm0)
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+1
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Enlargedprior ranges:
Some Results: (B1, B2, Ωm0)
+1
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Enlargedprior ranges:
Some Results: (B1, B2, Ωm0)
+1
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Enlargedprior ranges:
Some Results: (B1, B2, Ωm0)
+1
Yashar Akrami / Modern Cosmology: Early Universe, CMB and LSS/ Benasque / August 17, 201221
Enlargedprior ranges:
Some Results: (B1, B2, Ωm0)
+1
Yashar Akrami / Modern Cosmology: Early Universe, CMB and LSS/ Benasque / August 17, 201222
① A comprehensive statistical analysis of Hassan-Rosen ghost-free, massive, bimetric gravity (for cosmology at background level) + several analytical explanations of results,
② Massive gravity can give “Accelerated Expansion” with no explicit Cosmological Constant,
③ Very good fit even in the 1-parameter case,
④ Parameters are correlated for the full model,
⑤ Background data are not enough to constrain the full model (not robust and prior-independent),
⑥ Analysis of perturbations and other astrophysical probes needed to break degeneracy and constrain the model,
⑦ Further theoretical generalizations, e.g. curvature, coupling of “f” to matter, other background metrics, etc.
Summary & Conclusions+1
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