scholarly journals Erratum: One loop corrected conformally coupled scalar mode equations during inflation [Phys. Rev. D 96 , 105003 (2017)]

2018 ◽  
Vol 98 (2) ◽  
Author(s):  
Sibel Boran ◽  
Emre Onur Kahya ◽  
Sohyun Park
Keyword(s):  
Scalar Mode

scholarly journals Gravitational waves in modified Gauss–Bonnet gravity

2020 ◽  
Vol 29 (10) ◽  
pp. 2050072
Author(s):  
Tomohiro Inagaki ◽  
Masahiko Taniguchi
Keyword(s):  
General Relativity ◽  
Gravitational Waves ◽  
Wave Equations ◽  
Massive Scalar ◽  
Speed Of Light ◽  
Bonnet Gravity ◽  
Cosmological Background ◽  
Background Curvature ◽  
Scalar Mode ◽  
Metric Perturbation

We study the gravitational waves (GWs) in modified Gauss–Bonnet gravity. Applying the metric perturbation around a cosmological background, we obtain explicit expressions for the wave equations. It is shown that the speed of the traceless mode is equal to the speed of light. An additional massive scalar mode appears in the propagation of the GWs. To find phenomena beyond the general relativity, the scalar mode mass is calculated as a function of the background curvature in some typical models.

scholarly journals Parallel/Vector Integration Methods for Dynamical Astronomy

1999 ◽  
Vol 172 ◽  
pp. 231-241
Author(s):  
Toshio Fukushima
Keyword(s):  
Large Scale ◽  
Acceleration Factor ◽  
Picard Iteration ◽  
Vector Integration ◽  
Vector Mode ◽  
Dynamical Astronomy ◽  
Vector Processors ◽  
Processor Unit ◽  
Symmetric Multistep Methods ◽  
Scalar Mode

AbstractThis paper reviews three recent works on the numerical methods to integrate ordinary differential equations (ODE), which are specially designed for parallel, vector, and/or multi-processor-unit (PU) computers. The first is the Picard-Chebyshev method (Fukushima, 1997a). It obtains a global solution of ODE in the form of Chebyshev polynomial of large (> 1000) degree by applying the Picard iteration repeatedly. The iteration converges for smooth problems and/or perturbed dynamics. The method runs around 100-1000 times faster in the vector mode than in the scalar mode of a certain computer with vector processors (Fukushima, 1997b). The second is a parallelization of a symplectic integrator (Saha et al., 1997). It regards the implicit midpoint rules covering thousands of timesteps as large-scale nonlinear equations and solves them by the fixed-point iteration. The method is applicable to Hamiltonian systems and is expected to lead an acceleration factor of around 50 in parallel computers with more than 1000 PUs. The last is a parallelization of the extrapolation method (Ito and Fukushima, 1997). It performs trial integrations in parallel. Also the trial integrations are further accelerated by balancing computational load among PUs by the technique of folding. The method is all-purpose and achieves an acceleration factor of around 3.5 by using several PUs. Finally, we give a perspective on the parallelization of some implicit integrators which require multiple corrections in solving implicit formulas like the implicit Hermitian integrators (Makino and Aarseth, 1992), (Hut et al., 1995) or the implicit symmetric multistep methods (Fukushima, 1998), (Fukushima, 1999).

scholarly journals Stable, nonsingular bouncing universe with only a scalar mode

2020 ◽  
Vol 102 (2) ◽  
Author(s):  
K. Sravan Kumar ◽  
Shubham Maheshwari ◽  
Anupam Mazumdar ◽  
Jun Peng
Keyword(s):  
Bouncing Universe ◽  
Scalar Mode

scholarly journals Dark energy and modified gravity in degenerate higher-order scalar–tensor (DHOST) theories: A review

2019 ◽  
Vol 28 (05) ◽  
pp. 1942006 ◽  
Author(s):  
David Langlois
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Higher Order ◽  
Second Order ◽  
Compact Objects ◽  
Degree Of Freedom ◽  
Scalar Mode

This paper reviews scalar–tensor theories characterized by a Lagrangian that, despite the presence of second-order derivatives, contains a single scalar degree of freedom. These theories, known as Degenerate Higher-Order Scalar–Tensor (DHOST) theories, include Horndeski and Beyond Horndeski theories. They propagate a single scalar mode as a consequence of the degeneracy of their Lagrangian and, therefore, are not plagued by an Ostrogradsky instability. They have been fully classified up to cubic order in second-order derivatives. The study of their phenomenological consequences restricts the subclass of DHOST theories that are compatible with observations. In cosmology, these theories can be described in the language of the unified effective approach to dark energy and modified gravity. Compact objects in the context of DHOST theories are also discussed.

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