Cosmology in new gravitational scalar-tensor theories

Saridakis, Emmanuel N.; Tsoukalas, Minas

doi:10.1103/physrevd.93.124032

Cited by 53 publications

(59 citation statements)

References 43 publications

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“…It would be interesting to examine whether there are any issues related to the fifth force, as it has been done previously on the original Horndeski theory [78,79]. Finally, it could be interesting to apply extended nonminimal derivative couplings to bi-scalar theories, such as those proposed recently in [80][81][82][83]. These investigations lie beyond the scope of the present work, and are left for future projects.…”

Section: Discussionmentioning

confidence: 93%

Cosmological models in modified gravity theories with extended nonminimal derivative couplings

2017

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We construct gravitational modifications that go beyond Horndeski, namely theories with extended nonminimal derivative couplings, in which the coefficient functions depend not only on the scalar field but also on its kinetic energy. Such theories prove to be ghost-free in a cosmological background. We investigate the early-time cosmology and show that a de Sitter inflationary phase can be realized as a pure result of the novel gravitational couplings. Additionally, we study the latetime evolution, where we obtain an effective dark energy sector which arises from the scalar field and its extended couplings to gravity. We extract various cosmological observables and analyse their behavior at small redshifts for three choices of potentials, namely, for the exponential, the powerlaw, and the Higgs potential. We show that the Universe passes from deceleration to acceleration in the recent cosmological past, while the effective dark-energy equation-of-state parameter tends to the cosmological-constant value at present. Finally, the effective dark energy can be phantom-like, although the scalar field is canonical, which is an advantage of the model.PACS numbers: 04.50. Kd, 95.36.+x

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Section: Discussionmentioning

confidence: 93%

Cosmological models in modified gravity theories with extended nonminimal derivative couplings

2017

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“…Refs. [217][218][219][220][221]). 2 In the cCDM model, the quintessence field (whose effective EoS w φ we allow to be phantom, again from a purely effective perspective) is treated as an additional contribution to the total energy density along with the (possibly negative) cosmological constant and the usual components of matter and radiation.…”

Section: Introductionmentioning

confidence: 99%

Revisiting a Negative Cosmological Constant from Low-Redshift Data

2019

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Persisting tensions between high-redshift and low-redshift cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the ΛCDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (i.e. maximally symmetric spacetimes with a negative cosmological constant) ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, with a dark energy component with equation of state w φ on top. We test the consistency of the model against low-redshift Baryon Acoustic Oscillation and Type Ia Supernovae distance measurements, assessing two alternative choices of distance anchors: the sound horizon at baryon drag determined by the Planck collaboration, and the Hubble constant determined by the SH0ES program. We find no evidence for a negative cosmological constant, and mild indications for an effective phantom dark energy component on top. A model comparison analysis reveals the ΛCDM model is favoured over our negative cosmological constant model. While our results are inconclusive, should low-redshift tensions persist with future data, it would be worth reconsidering and further refining our toy negative cosmological constant model by considering realistic string constructions.tions between dark matter particles, or between dark matter and baryons, could alleviate these issues (see e.g. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] for an incomplete list of proposed models).

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“…Thus, one can obtain f (R) gravity [5], Gauss-Bonnet a e-mail: nunes@ecm.ub.edu b e-mail: abonillar@udistrital.edu.com c e-mail: span@iiserkol.ac.in d e-mail: Emmanuel_Saridakis@baylor.edu and f (G) gravity [6,7], gravity with higher-order curvature invariants [8,9], massive gravity [10] etc. Nevertheless, one could start from the equivalent, torsional formulation of gravity, namely from the Teleparallel Equivalent of General Relativity (TEGR) [11][12][13], in which the gravitational Lagrangian is the torsion scalar T , and construct various modifications, such as f (T ) gravity [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] (see [30] for a review), teleparallel Gauss-Bonnet gravity [31,32], gravity with higher-order torsion invariants [33], etc.…”

Section: Introductionmentioning

confidence: 99%

Observational constraints on f(T) gravity from varying fundamental constants

et al. 2017

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We use observations related to the variation of fundamental constants, in order to impose constraints on the viable and most used f (T ) gravity models. In particular, for the fine-structure constant we use direct measurements obtained by different spectrographic methods, while for the effective Newton constant we use a model-dependent reconstruction, using direct observational Hubble parameter data, in order to investigate its temporal evolution. We consider two f (T ) models and we quantify their deviation from CDM cosmology through a sole parameter. Our analysis reveals that this parameter can be slightly different from its CDM value, however, the best-fit value is very close to the CDM one. Hence, f (T ) gravity is consistent with observations, nevertheless, as every modified gravity, it may exhibit only small deviations from CDM cosmology, a feature that must be taken into account in any f (T ) model-building.

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Cosmology in new gravitational scalar-tensor theories

Cited by 53 publications

References 43 publications

Cosmological models in modified gravity theories with extended nonminimal derivative couplings

Cosmological models in modified gravity theories with extended nonminimal derivative couplings

Revisiting a Negative Cosmological Constant from Low-Redshift Data

Observational constraints on f(T) gravity from varying fundamental constants

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