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 Bouncing universe with Quintom matter

2007 ◽  
Vol 2007 (10) ◽  
pp. 071-071 ◽  
Author(s):  
Yi-Fu Cai ◽  
Taotao Qiu ◽  
Xinmin Zhang ◽  
Yun-Song Piao ◽  
Mingzhe Li
Keyword(s):  
Bouncing Universe

scholarly journals Bouncing universe with non-minimally coupled quintom matter

2008 ◽  
Vol 669 (1) ◽  
pp. 9-13 ◽  
Author(s):  
M.R. Setare ◽  
J. Sadeghi ◽  
A. Banijamali
Keyword(s):  
Bouncing Universe

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 Reconstruction of Mimetic Gravity in a Non-Singular Bouncing Universe from Quantum Gravity

Universe ◽  
2019 ◽  
Vol 5 (5) ◽  
pp. 107 ◽  
Author(s):  
Marco de Cesare
Keyword(s):  
Field Theory ◽  
Quantum Gravity ◽  
Effective Field ◽  
Time Varying ◽  
Reconstruction Procedure ◽  
Cosmological Background ◽  
Bouncing Universe ◽  
Physical Information ◽  
Group Field Theory ◽  
Mimetic Gravity

We illustrate a general reconstruction procedure for mimetic gravity. Focusing on a bouncing cosmological background, we derive general properties that must be satisfied by the function f(□ϕ) implementing the limiting curvature hypothesis. We show how relevant physical information can be extracted from power-law expansions of f in different regimes, corresponding e.g., to the very early universe or to late times. Our results are then applied to two specific models reproducing the cosmological background dynamics obtained in group field theory and in loop quantum cosmology, and we discuss the possibility of using this framework as providing an effective field theory description of quantum gravity. We study the evolution of anisotropies near the bounce, and discuss instabilities of scalar perturbations. Furthermore, we provide two equivalent formulations of mimetic gravity: one in terms of an effective fluid with exotic properties, the other featuring two distinct time-varying gravitational “constants” in the cosmological equations.

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).

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