Late-time acceleration by a residual cosmological constant from sequestering vacuum energy in ultimate collapsed structures

Lombriser, Lucas

doi:10.1088/1475-7516/2019/09/065

Cited by 8 publications

(10 citation statements)

References 49 publications

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“…While generally expected to be attributed to a cosmological constant arising from vacuum fluctuations, it has proven extraordinarily difficult to motivate the observed acceleration from quantum theoretical predictions [7,8] (however, see, e.g., Refs. [9][10][11][12][13][14]). Given the broad possibilities for modifying gravity, the cosmic large-scale structure was shown to be insufficient to exhaustively probe the vast available model space, being fundamentally limited by a dark degeneracy that is however broken by measurements of the cosmological propagation of gravitational waves [15,16].…”

Section: Introductionmentioning

confidence: 99%

Limitations on Standard Sirens tests of gravity from screening

Dalang

Lombriser

2019

J. Cosmol. Astropart. Phys.

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Modified gravity theories with an effective Newton constant that varies over cosmological timescales generally predict a different gravitational wave luminosity distance than General Relativity. While this holds for a uniform variation, we show that if locally screened at the source and at the observer as required to pass stringent astrophysical tests of gravity, the General Relativistic distance is restored. In the absence of such a screening, the same effect must modify electromagnetic luminosity distances inferred from supernovae Type Ia, to the extent that the effects can cancel in the comparison. Hence, either the modifications considered employ screening, which leaves no signature in Standard Sirens of a cosmological modification of gravity, or screening does not operate, in which case there can be a signal that is however well below the forseeable sensitivity of the probe when astrophysical bounds are employed. We recover these results both in the Jordan and Einstein frames, paying acute attention to pecularities of each frame such as the notion of redshift or geodesic motions. We emphasise that despite these limitations, Standard Sirens provide valuable independent tests of gravity that differ fundamentally from other probes, a circumstance that is generally important for the wider scope of gravitational modifications and related scenarios. Finally, we use our results to show that the gravitational wave propagation is not affected by dark sector interactions, which restores a dark degeneracy between conformal and disformal couplings that enables observationally viable cosmic self-acceleration to emenate from those.

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Section: Introductionmentioning

confidence: 99%

Limitations on Standard Sirens tests of gravity from screening

Dalang

Lombriser

2019

J. Cosmol. Astropart. Phys.

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“…There are also very promising approaches to the cosmological constant problem that are outside of classical well-tempering and trivial scalar self-tuning (see Refs. [62][63][64][65]).…”

Section: Discussionmentioning

confidence: 99%

Self-tuning kinetic gravity braiding: Cosmological dynamics, shift symmetry, and the tadpole

Bernardo

2021

Preprint

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We study the self-tuning subclass of kinetic gravity braiding and obtain robust predictions on self-tuning and dynamics in the tadpole-free shift symmetric sector of the theory. In particular, we show inevitability of cosmic acceleration, prove the dynamical stability of this late-time asymptotic state, and derive ghost and gradient stability constraints on the self-tuning vacuum. We discuss the results concretely in the context of generalized cubic covariant Galileon theory and an exponential kinetic gravity braiding.

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“…Either the Universe turns out to be consistent with ΛCDM, which will motivate a more directed effort in tackling the cosmological constant problem (see, e.g., Refs. [70][71][72][73][74][75][76][77][78][79][80][81][82][83]). On the other hand, if recent observational tensions [3,84,85] persist then that will be strong evidence that the theory describing the Universe on cosmological scales requires revision and potentially will go beyond a cosmological constant.…”

Section: Discussionmentioning

confidence: 99%

Screening and degenerate kinetic self-acceleration from the nonlinear freedom of reconstructed Horndeski theories

2019

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We have previously presented a reconstruction of Horndeski scalar-tensor theories from linear cosmological observables. It includes free nonlinear terms which can be added onto the reconstructed covariant theory without affecting the background and linear dynamics. After discussing the uniqueness of these correction terms, we apply this nonlinear freedom to a range of different applications. First we demonstrate how the correction terms can be configured to endow the reconstructed models with screening mechanisms such as the chameleon, k-mouflage and Vainshtein effects. A further implication is the existence of classes of Horndeski models that are degenerate with standard cosmology to an arbitrary level in the cosmological perturbations. Particularly interesting examples are kinetically self-accelerating models that mimic the dynamics of the cosmological constant to an arbitrary degree in perturbations. Finally, we develop the reconstruction method further to the level of higher-order effective field theory, which under the restriction to a luminal propagation speed of gravitational waves introduces two new free functions per order. These functions determine the corresponding correction terms in the linearly reconstructed action at the same order. Our results enable the connection of linear cosmological constraints on generalised modifications of gravity and dark energy with the nonlinear regime and astrophysical probes for a more global interpretation of the wealth of forthcoming cosmological survey data.

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Late-time acceleration by a residual cosmological constant from sequestering vacuum energy in ultimate collapsed structures

Cited by 8 publications

References 49 publications

Limitations on Standard Sirens tests of gravity from screening

Limitations on Standard Sirens tests of gravity from screening

Self-tuning kinetic gravity braiding: Cosmological dynamics, shift symmetry, and the tadpole

Screening and degenerate kinetic self-acceleration from the nonlinear freedom of reconstructed Horndeski theories

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