scholarly journals Timelike vector field dynamics in the early universe

2012 ◽  
Vol 60 (11) ◽  
pp. 1983-1992 ◽  
Author(s):  
Seoktae Koh ◽  
Bin Hu
2011 ◽  
Vol 01 ◽  
pp. 120-125 ◽  
Author(s):  
SEOKTAE KOH

We have investigated if the vector field can give rise to an accelerating phase in the early universe. We consider a timelike vector field with a general quadratic kinetic term in order to preserve an isotropic background spacetime. The vector field potential is required to satisfy the three minimal conditions for successful inflation: i) ρ > 0, ii) ρ + 3P < 0, and iii) the slow-roll conditions. As an example, we consider a massive vector potential and a small-field type potential as in scalar driven inflation.


Author(s):  
Sinya Aoki ◽  
Tetsuya Onogi ◽  
Shuichi Yokoyama

We propose a new class of vector fields to construct a conserved charge in a general field theory whose energy–momentum tensor is covariantly conserved. We show that there always exists such a vector field in a given field theory even without global symmetry. We also argue that the conserved current constructed from the (asymptotically) timelike vector field can be identified with the entropy current of the system. As a piece of evidence we show that the conserved charge defined therefrom satisfies the first law of thermodynamics for an isotropic system with a suitable definition of temperature. We apply our formulation to several gravitational systems such as the expanding universe, Schwarzschild and Banãdos, Teitelboim and Zanelli (BTZ) black holes, and gravitational plane waves. We confirm the conservation of the proposed entropy density under any homogeneous and isotropic expansion of the universe, the precise reproduction of the Bekenstein–Hawking entropy incorporating the first law of thermodynamics, and the existence of gravitational plane wave carrying no charge, respectively. We also comment on the energy conservation during gravitational collapse in simple models.


2002 ◽  
Vol 11 (02) ◽  
pp. 187-205 ◽  
Author(s):  
M. A. CLAYTON ◽  
J. W. MOFFAT

A vector–tensor theory of gravity that was introduced in an earlier publication is analyzed in detail and its consequences for early universe cosmology are examined. The multiple light cone structure of the theory generates different speeds of gravitational and matter wave fronts, and the contraction of these light cones produces acausal, superluminary inflation that can resolve the initial value problems of cosmology.


2012 ◽  
Vol 09 (05) ◽  
pp. 1220006 ◽  
Author(s):  
L. FATIBENE ◽  
M. FRANCAVIGLIA

In view of Ehlers–Pirani–Schild formalism, since 1972 Weyl geometries should be considered to be the most appropriate and complete framework to represent (relativistic) gravitational fields. We shall here show that in any given Lorentzian spacetime (M, g) that admits global timelike vector fields any such vector field u determines an essentially unique Weyl geometry ([g], Γ) such that u is Γ-geodesic (i.e. parallel with respect to Γ).


2017 ◽  
Vol 28 (10) ◽  
pp. 1750071
Author(s):  
Henrique F. de Lima ◽  
Arlandson M. Oliveira ◽  
Márcio S. Santos ◽  
Marco A. L. Velásquez

In this paper, we deal with complete noncompact spacelike hypersurfaces immersed in a weighted conformally stationary spacetime endowed with a closed conformal timelike vector field [Formula: see text]. Under suitable constraints on the weighted mean curvature of such a spacelike hypersurface, we establish sufficient conditions to ensure that it must be an integral leaf of the foliation orthogonal to [Formula: see text].


1989 ◽  
Vol 159 (10) ◽  
pp. 393
Author(s):  
Ya.A. Smorodinskii
Keyword(s):  

Author(s):  
I. I. Kravchenko

The paper considers the mathematical model development technique to build a vector field of the shape deviations when machining flat surfaces of shell parts on multi-operational machines under conditions of anisotropic rigidity in technological system (TS). The technological system has an anisotropic rigidity, as its elastic strains do not obey the accepted concepts, i.e. the rigidity towards the coordinate axes of the machine is the same, and they occur only towards the external force. The record shows that the diagrams of elastic strains of machine units are substantially different from the circumference. The issues to ensure the specified accuracy require that there should be mathematical models describing kinematic models and physical processes of mechanical machining under conditions of the specific TS. There are such models for external and internal surfaces of rotation [2,3], which are successfully implemented in practice. Flat surfaces (FS) of shell parts (SP) are both assembly and processing datum surfaces. Therefore, on them special stipulations are made regarding deviations of shape and mutual arrangement. The axes of the main bearing holes are coordinated with respect to them. The joints that ensure leak tightness and distributed load on the product part are closed on these surfaces. The paper deals with the analytical construction of the vector field F, which describes with appropriate approximation the real surface obtained as a result of modeling the process of machining flat surfaces (MFS) through face milling under conditions of anisotropic properties.


2019 ◽  
Vol 2019 (2) ◽  
pp. 62-67
Author(s):  
R.A. Ilyasova

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