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Keywords
(18)
Brane World
Cosmic Microwave Background
Cosmological Constant
Dark Energy
Degree of Freedom
Early Universe
Equation of State
Exponential Model
Field Theory
Large Scale
Modified Gravity
Quantum Field Theory
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(3)
Does the Planck ...
Viable Palatini...
Cosmological perturbations in the Palatini formulation of modified gravity
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Cuscuton cosmology: Dark energy meets modified gravity
Cuscuton cosmology: Dark energy meets modified gravity,10.1103/PhysRevD.75.123509,Physical Review D,Niayesh Afshordi,Daniel J. H. Chung,Michael Doran,
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Cuscuton cosmology: Dark energy meets modified gravity
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Citations: 5
)
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Niayesh Afshordi
,
Daniel J. H. Chung
,
Michael Doran
,
Ghazal Geshnizjani
In a companion paper, we have introduced a model of
scalar field
dark energy, Cuscuton, which can be realized as the incompressible (or infinite speed of sound) limit of a kessence fluid. In this paper, we study how Cuscuton modifies the constraint sector of Einstein gravity. In particular, we study Cuscuton cosmology and show that even though Cuscuton can have an arbitrary equation of state, or time dependence, and is thus inhomogeneous, its perturbations do not introduce any additional dynamical
degree of freedom
and only satisfy a constraint equation, amounting to an effective modification of gravity on large scales. Therefore, Cuscuton can be considered to be a minimal theory of evolving dark energy, or a minimal modification of a cosmological constant, as it has no internal dynamics. Moreover, this is the only modification of Einstein gravity to our knowledge, that does not introduce any additional degrees of freedom (and is not conformally equivalent to the Einstein gravity). We then study two simple Cuscuton models, with quadratic and exponential potentials. The quadratic model has the exact same expansion history as LambdaCDM, and yet contains an early
dark energy
component with constant energy fraction, which is constrained to OmegaQ≲2%, mainly from WMAP
Cosmic Microwave Background
and
Sloan Digital Sky Survey
Lymanalpha forest observations. The
exponential model
has the same expansion history as the DvaliGabadadzePoratti selfaccelerating braneworld model, but generates a much smaller Integrated SachsWolfe effect, and is thus consistent with the
Cosmic Microwave Background
observations. Finally, we show that the evolution is local on superhorizon scales, implying that there is no gross violation of causality, despite Cuscuton's infinite speed of sound.
Journal:
Physical Review D  PHYS REV D
, vol. 75, no. 12, 2007
DOI:
10.1103/PhysRevD.75.123509
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Citation Context
(2)
...rium energy density, this term vanishes as a consequence of the equations of motion (see section 7). 2 Interestingly, this action has also been investigated in the context of dark energy, see [17,
18
]...
Geoffrey Compère
,
et al.
The holographic fluid dual to vacuum Einstein gravity
...Such constrained models could be applied to construct effectively nondynamical cosmological fields like in the so called Cuscuton models or in modified gravity within the Palatini approach [
43
, 44, 45, 46]...
Tomi S. Koivisto
,
et al.
Inflation from Nforms and its stability
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Citations
(5)
The holographic fluid dual to vacuum Einstein gravity
(
Citations: 1
)
Geoffrey Compère
,
Paul McFadden
,
Kostas Skenderis
,
Marika Taylor
Journal:
Journal of High Energy Physics  J HIGH ENERGY PHYS
, vol. 2011, no. 7, pp. 130, 2011
Approaches to understanding cosmic acceleration
(
Citations: 13
)
Alessandra Silvestri
,
Mark Trodden
Journal:
Reports on Progress in Physics  REP PROGR PHYS
, vol. 72, no. 9, 2009
Inflation from Nforms and its stability
(
Citations: 5
)
Tomi S. Koivisto
,
David F. Mota
,
Cyril Pitrou
Journal:
Journal of High Energy Physics  J HIGH ENERGY PHYS
, vol. 2009, no. 09, pp. 092092, 2009
The extreme limit of the generalized Chaplygin gas
(
Citations: 1
)
Oliver F. Piattella
,
Dennis Sciama
Journal:
Journal of Cosmology and Astroparticle Physics  JCAP
, vol. 2010, no. 03, pp. 012012, 2009
Constraining modified gravity with large nonGaussianities
Samuel E. Vazquez
,
Samuel E
Journal:
Physical Review D  PHYS REV D
, vol. 79, no. 4, pp. 043520043520, 2009