Is cosmic speed-up due to new gravitational physics?

Carroll, Sean M.; Duvvuri, Vikram; Trodden, Mark; Turner, Michael S.

doi:10.1103/physrevd.70.043528

Cited by 2,323 publications

(2,213 citation statements)

References 36 publications

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“…Among other approaches, Modified Gravity Models have attracted great interest (see [25][26][27][28][29][30][31][32][33][34][35][36][37]) but also some criticism, partly because they were introduced as purely phenomenological models, but more seriously because it was not clear that they possessed a satisfactory Newtonian limit in the solar system, or that they were free of ghosts (see [38][39][40][41][42][43]). …”

Section: Introductionmentioning

confidence: 99%

Ghosts, instabilities, and superluminal propagation in modified gravity models

Felice

Hindmarsh

Trodden

2006

J. Cosmol. Astropart. Phys.

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165

167

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We consider Modified Gravity models involving inverse powers of fourth-order curvature invariants.Using these models' equivalence to the theory of a scalar field coupled to a linear combination of the invariants, we investigate the properties of the propagating modes. Even in the case for which the fourth derivative terms in the field equations vanish, we find that the second derivative terms can give rise to ghosts, instabilities, and superluminal propagation speeds. We establish the conditions which the theories must satisfy in order to avoid these problems in Friedmann backgrounds, and show that the late-time attractor solutions generically exhibit superluminally propagating tensor or scalar modes. * a. de-felice@sussex.ac.uk

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Section: Introductionmentioning

confidence: 99%

Ghosts, instabilities, and superluminal propagation in modified gravity models

Felice

Hindmarsh

Trodden

2006

J. Cosmol. Astropart. Phys.

Self Cite

165

167

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“…Many of these extensions aim to avoid the usually invoked need of dark components which is required, for instance both in the ΛCDM model, where dark energy is nothing but a cosmological constant, and in phantom/quintessencelike models where a scalar field is needed, among others. Throughout the years, a plethora of modified gravity theories have been shown to be able to preserve the positive results of Einstein theory and obtain the required cosmological evolution with the most relevant cosmological epochs [3][4][5]. Among those attempts, one of the most successful ones is the so-called f (R) theories where the gravitational Lagrangian includes powers of the Ricci scalar R encompassed in an arbitrary function of R (c.f.…”

Section: Introductionmentioning

confidence: 99%

The realistic models of relativistic stars in f ( R ) = R + αR ² gravity

Astashenok

Odintsov

Cruz-Dombriz

2017

Class. Quantum Grav.

164

104

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The realistic models of relativistic stars in f (R) = R + αR 2 gravity In the context of f (R) = R + αR 2 gravity, we study the existence of neutron and quark stars for various α with no intermediate approximation in the system of equations. Analysis shows that for positive α the scalar curvature does not drop to zero at the star surface (as in General Relativity) but exponentially decreases with distance. Also the stellar mass bounded by star surface decreases when the value α increases. Nonetheless distant observers would observe a gravitational mass due to appearance of a so-called gravitational sphere around the star. The non-zero curvature contribution to the gravitational mass eventually is shown to compensate the stellar mass decrease for growing α's. We perform our analysis for several equations of state including purely hadronic configurations as well as hyperons and quark stars. In all cases, we assess that the relation between the parameter α and the gravitational mass weakly depends upon the chosen equation of state. Another interesting feature is the increase of the star radius in comparison with General Relativity for stars with masses close to maximal, whereas for intermediate masses 1.4 − 1.6M⊙ the radius of star depends upon α very weakly. Also the decrease in the mass bounded by star surface may cause the surface redshift to decrease in R 2 -gravity when compared to Einsteinian predictions. This effect is shown to hardly depend upon the observed gravitational mass. Finally, for negative values of α our analysis shows that outside the star the scalar curvature has damped oscillations but the contribution of the gravitational sphere into the gravitational mass increases indefinitely with radial distance putting into question the very existence of such relativistic stars.

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“…The existence of a vector with non-vanishing spatial components turns to be compatible with the isotropy of a Friedmann-Robertson-Walker universe provided the vector is part of a "cosmic triad", i.e. a set of three identical vector 5 Strictly speaking it is not stable either, as the relative perturbations do not decay.…”

Section: Discussionmentioning

confidence: 99%

“…Little is known about the origin of this stage of cosmic acceleration [3]. It might be related to a breakdown of general relativity on large scales [4,5], or it can be the effect of "dark energy" [6], a negative pressure component that causes the universe expansion to accelerate. The simplest possibility is that dark energy merely is a (tiny) cosmological constant.…”

Section: Introductionmentioning

confidence: 99%

Could dark energy be vector-like?

Armendariz-Picon

2004

J. Cosmol. Astropart. Phys.

286

333

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In this paper I explore whether a vector field can be the origin of the present stage of cosmic acceleration. In order to avoid violations of isotropy, the vector has be part of a "cosmic triad", that is, a set of three identical vectors pointing in mutually orthogonal spatial directions. A triad is indeed able to drive a stage of late accelerated expansion in the universe, and there exist tracking attractors that render cosmic evolution insensitive to initial conditions. However, as in most other models, the onset of cosmic acceleration is determined by a parameter that has to be tuned to reproduce current observations. The triad equation of state can be sufficiently close to minus one today, and for tachyonic models it might be even less than that. I briefly analyze linear cosmological perturbation theory in the presence of a triad. It turns out that the existence of non-vanishing spatial vectors invalidates the decomposition theorem, i.e. scalar, vector and tensor perturbations do not decouple from each other. In a simplified case it is possible to analytically study the stability of the triad along the different cosmological attractors. The triad is classically stable during inflation, radiation and matter domination, but it is unstable during (late-time) cosmic acceleration. I argue that this instability is not likely to have a significant impact at present.

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Is cosmic speed-up due to new gravitational physics?

Cited by 2,323 publications

References 36 publications

Ghosts, instabilities, and superluminal propagation in modified gravity models

Ghosts, instabilities, and superluminal propagation in modified gravity models

The realistic models of relativistic stars in f ( R ) = R + αR ² gravity

Could dark energy be vector-like?

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Is cosmic speed-up due to new gravitational physics?

Cited by 2,323 publications

References 36 publications

Ghosts, instabilities, and superluminal propagation in modified gravity models

Ghosts, instabilities, and superluminal propagation in modified gravity models

The realistic models of relativistic stars in f ( R ) = R + αR 2 gravity

Could dark energy be vector-like?

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Product

Resources

About

The realistic models of relativistic stars in f ( R ) = R + αR ² gravity