An effective fluid description of scalar-vector-tensor theories under the sub-horizon and quasi-static approximations

Cardona, Wilmar; Orjuela-Quintana, J. Bayron; Valenzuela-Toledo, César A.

doi:10.1088/1475-7516/2022/08/059

Cited by 9 publications

(9 citation statements)

References 154 publications

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“…ref. [60] where a similar divergency was found in the context of Scalar-Vector-Tensor theories [91,92]). As mentioned in previous sections, we do not expect the QSA and the SHA hold for modes JCAP08(2023)019 smaller than k < 0.067 h/Mpc.…”

Section: Linear Power Spectrasupporting

confidence: 65%

“…We would like to stress that a similar divergent behavior was found in ref. [60]. However, note that previous works on Horndeski theories [59], and Scalar-Vector-Tensor theories [60], where these approximations were used, all of them agree, in their corresponding limits, with the standard expressions in f (R).…”

Section: Discussionmentioning

confidence: 55%

“…[60]. However, note that previous works on Horndeski theories [59], and Scalar-Vector-Tensor theories [60], where these approximations were used, all of them agree, in their corresponding limits, with the standard expressions in f (R). In the case of the lowest multipoles of the CMB power spectrum, and in general for the matter power spectrum, the improvement in the accuracy from our expressions do not imply a corresponding improvement in these linear observables.…”

Section: Discussionmentioning

confidence: 55%

“…which are the usual results found in the literature [53,[58][59][60]. We will refer to the steps performed to obtain the last expressions as the "standard QSA-SHA procedure", while the relations for the perturbations, namely eqs.…”

Section: Jcap08(2023)019mentioning

confidence: 89%

“…As shown in refs. [58][59][60], the application of the Quasi-Static Approximation (QSA) and the Sub-Horizon Approximation (SHA) allows to get analytical expressions for the effective DE perturbations in very general MG theories. One of the advantage of this approach is that these expressions can be easily introduced in Boltzmann solvers, such as CLASS [61], facilitating the computation of cosmological observables, e.g., the linear matter power spectrum or the CMB angular power spectrum.…”

Section: Jcap08(2023)019mentioning

confidence: 99%

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Tracking the validity of the quasi-static and sub-horizon approximations in modified gravity

Orjuela-Quintana

Nesseris

2023

J. Cosmol. Astropart. Phys.

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Within the framework of modified gravity, the quasi-static and sub-horizon approximations are widely used in analyses aiming to identify departures from the concordance model at late-times. In general, it is assumed that time derivatives are subdominant with respect to spatial derivatives given that the relevant physical modes are those well inside the Hubble radius. In practice, the perturbation equations under these approximations are reduced to a tractable algebraic system in terms of the gravitational potentials and the perturbations of involved matter fields. Here, in the framework of f(R) theories, we revisit standard results when these approximations are invoked using a new parameterization scheme that allows us to track the relevance of each time-derivative term in the perturbation equations. This new approach unveils correction terms which are neglected in the standard procedure. We assess the relevance of these differences by comparing results from both approaches against full numerical solutions for two well-known toy-models: the designer f(R) model and the Hu-Sawicki model. We find that: i) the sub-horizon approximation can be safely applied to linear perturbation equations for scales 0.06 h/Mpc ≲ k ≲ 0.2 h/Mpc, ii) in this “safety region”, the quasi-static approximation provides a very accurate description of the late-time cosmological dynamics even when dark energy significantly contribute to the cosmic budget, and iii) our new methodology performs better than the standard procedure, even for several orders of magnitude in some cases. Although, the impact of this major improvement on the linear observables is minimal for the studied cases, this does not represent an invalidation for our approach. Instead, our findings indicate that the perturbation expressions derived under these approximations in more general modified gravity theories, such as Horndeski, should be also revisited.

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Section: Linear Power Spectrasupporting

confidence: 65%

Section: Discussionmentioning

confidence: 55%

Section: Discussionmentioning

confidence: 55%

Section: Jcap08(2023)019mentioning

confidence: 89%

Section: Jcap08(2023)019mentioning

confidence: 99%

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Tracking the validity of the quasi-static and sub-horizon approximations in modified gravity

Orjuela-Quintana

Nesseris

2023

J. Cosmol. Astropart. Phys.

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Anisotropic dark energy from string compactifications

Gallego,

Orjuela-Quintana,

Valenzuela-Toledo

2024

J. High Energ. Phys.

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We explore the cosmological dynamics of a minimalistic yet generic string-inspired model for multifield dark energy. Adopting a supergravity four-dimensional viewpoint, we motivate the model’s structure arising from superstring compactifications involving a chiral superfield and a pure U(1) gauge sector. The chiral sector gives rise to a pair of scalar fields, such as the axio-dilaton, which are kinetically coupled. However, the scalar potential depends on only one of them, further entwined with the vector field through the gauge kinetic function. The model has two anisotropic attractor solutions that, despite a steep potential and thanks to multifield dynamics, could explain the current accelerated expansion of the Universe while satisfying observational constraints on the late-times cosmological anisotropy. Nevertheless, justifying the parameter space allowing for slow roll dynamics together with the correct cosmological parameters, would be challenging within the landscape of string theory. Intriguingly, we find that the vector field, particularly at one of the studied fixed points, plays a crucial role in enabling geodesic trajectories in the scalar field space while realizing slow-roll dynamics with a steep potential. This observation opens a new avenue for exploring multifield dark energy models within the superstring landscape.

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