K-dynamics: well-posed 1+1 evolutions in K-essence

Bezares, Miguel; Crisostomi, Marco; Palenzuela, Carlos; Barausse, Enrico

doi:10.48550/arxiv.2008.07546

Cited by 3 publications

(18 citation statements)

References 55 publications

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“…with β ∼ O(1) a dimensionless coupling constant and Λ the EFT strong coupling scale. Note that in the presence of matter, screening is present only in the β < 0 branch [32,33,39]. However, positivity bounds select the branch with β > 0 as the one consistent with embedding in a UV theory [42].…”

Section: Quadratic K-essencementioning

confidence: 98%

“…[66] to perform dynamical evolutions of boson stars, fermionboson stars [63], anisotropic stars [67], and also in Refs. [30,33,39] and in Ref. [68] for neutron stars in kessence and chameleon screening, respectively.…”

Section: Evolution Schemementioning

confidence: 99%

“…Refs. [30,31,33,39]. Alternatively, one may look for a different way to implement the "fixing the equations" approach.…”

Section: Large Couplingmentioning

confidence: 99%

“…[34][35][36][37]) and is both a blessing and a curse. On the one hand it allows k-essence to pass solar-system tests of gravity [30,33], but on the other hand it renders the calculation of GW generation conceptually and practically involved [30,31,33,38,39].…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we take a step back and investigate in depth the relation between first-derivative self interactions of the scalar, well-posedness of the Cauchy problem and UV completions (in both the standard and "fixing the equations" approaches). To this purpose, we consider a k-essence model that potentially suffers from both Tricomi-type and Keldysh-type breakdowns of initialdata evolutions [38,39]. In more detail, the former corresponds to the equations becoming parabolic (and then elliptic) along the evolution, while the latter are caused by diverging (coordinate) characteristic speeds for the scalar mode.…”

Section: Introductionmentioning

confidence: 99%

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UV completions, fixing the equations and nonlinearities in $k$-essence

Lara,

Bezares,

Barausse

2021

Preprint

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Scalar-tensor theories with first-derivative self interactions, known as k-essence, may provide interesting phenomenology on cosmological scales. On smaller scales, however, initial value evolutions (which are crucial for predicting the behavior of astrophysical systems, such as binaries of compact objects) may run into instabilities related to the Cauchy problem becoming potentially ill-posed. Moreover, on local scales the dynamics may enter in the nonlinear regime, which may lie beyond the range of validity of the infrared theory. Completions of k-essence in the ultraviolet, when they are known to exist, mitigate these problems, as they both render Cauchy evolutions well-posed at all times, and allow for checking the relation between nonlinearities and the low energy theory's range of validity. Here, we explore these issues explicitly by considering an ultraviolet completion to k-essence and performing vacuum 1+1 dynamical evolutions within it. The results are compared to those obtained with the low-energy theory, and with the low-energy theory suitably deformed with a phenomenological "fixing the equations" approach. We confirm that the ultraviolet completion does not incur in any breakdown of the Cauchy problem's well-posedness, and we find that evolutions agree with the results of the low-energy theory, when the system is within the regime of validity of the latter. However, we also find that the nonlinear behavior of k-essence lies (for the most part) outside this regime.

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Section: Quadratic K-essencementioning

confidence: 98%

Section: Evolution Schemementioning

confidence: 99%

“…Refs. [30,31,33,39]. Alternatively, one may look for a different way to implement the "fixing the equations" approach.…”

Section: Large Couplingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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UV completions, fixing the equations and nonlinearities in $k$-essence

Lara,

Bezares,

Barausse

2021

Preprint

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Dynamics of Screening in Modified Gravity

et al. 2021

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Gravitational theories differing from general relativity may explain the accelerated expansion of the Universe without a cosmological constant. However, to pass local gravitational tests, a "screening mechanism" is needed to suppress, on small scales, the fifth force driving the cosmological acceleration. We consider the simplest of these theories, i.e., a scalar-tensor theory with first-order derivative selfinteractions, and study isolated (static and spherically symmetric) nonrelativistic and relativistic stars. We produce screened solutions and use them as initial data for nonlinear numerical evolutions in spherical symmetry. We find that these solutions are stable under large initial perturbations, as long as they do not cause gravitational collapse. When gravitational collapse is triggered, the characteristic speeds of the scalar evolution equation diverge, even before apparent black-hole or sound horizons form. This casts doubts on whether the dynamical evolution of screened stars may be predicted in these effective field theories.

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Dynamics of Screening in Modified Gravity

ter Haar,

Bezares,

Crisostomi

et al. 2020

Preprint

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Gravitational theories differing from General Relativity may explain the accelerated expansion of the Universe without a cosmological constant. However, to pass local gravitational tests, a "screening mechanism" is needed to suppress, on small scales, the fifth force driving the cosmological acceleration. We consider the simplest of these theories, i.e. a scalar-tensor theory with first-order derivative self-interactions, and study isolated (static and spherically symmetric) non-relativistic and relativistic stars. We produce screened solutions and use them as initial data for non-linear numerical evolutions in spherical symmetry. We find that these solutions are stable under large initial perturbations, as long as they do not cause gravitational collapse. When gravitational collapse is triggered, the characteristic speeds of the scalar evolution equation diverge, even before apparent black-hole or sound horizons form. This casts doubts on whether the dynamical evolution of screened stars may be predicted in these effective field theories.

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K-dynamics: well-posed 1+1 evolutions in K-essence

Cited by 3 publications

References 55 publications

UV completions, fixing the equations and nonlinearities in $k$-essence

UV completions, fixing the equations and nonlinearities in $k$-essence

Dynamics of Screening in Modified Gravity

Dynamics of Screening in Modified Gravity

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