| 1. |
- Betschart, Gerold, et al.
(författare)
-
Reply to "Comment on 'Primordial magnetic seed field amplification by gravitational waves'"
- 2007
-
Ingår i: Physical review D. - 1550-7998. ; 75:8, s. 7902-4 sidor
-
Tidskriftsartikel (refereegranskat)abstract
- Here we respond to the comment by Tsagas on our earlier paper. We show that the results in that comment are flawed and cannot be used for drawing conclusions about the nature of magnetic field amplification by gravitational waves and give further support that the results of our earlier paper are correct.
|
|
| 2. |
- Bradley, Michael, et al.
(författare)
-
Density growth in Kantowski-Sachs cosmologies with cosmological constant
- 2012
-
Ingår i: Classical and quantum gravity. - Bristol : Institute of Physics (IOP). - 0264-9381 .- 1361-6382. ; 29:9, s. 095023-
-
Tidskriftsartikel (refereegranskat)abstract
- In this work the growth of density perturbations in Kantowski-Sachs cosmologies with a positive cosmological constant is studied, using the 1+3 and 1+1+2 covariant formalisms. For each wave number we obtain a closed system for scalars formed from quantities that are zero on the background and hence are gauge-invariant. The solutions to this system are then analyzed both analytically andnumerically. In particular the effects of anisotropy and the behaviour close to a bounce in the cosmic scale factor are considered.We find that typically the density gradient in the bouncing direction experiences a local maximum at or slightly after the bounce.
|
|
| 3. |
- Bradley, Michael, et al.
(författare)
-
Perturbations of Kantowski-Sachs models
- 2015
-
Ingår i: Proceedings of the thirteenth Marcel Grossman meeting on general relativity. - Singapore : World Scientific. - 9789814612142 - 9789814630009 ; , s. 2547-2549
-
Konferensbidrag (refereegranskat)abstract
- Perturbations of Kantowski-Sachs models with a positive cosmological constant are considered in a harmonic decomposition, in the framework of gauge invariant 1+3 and 1+1+2 covariant splits of spacetime. Scalar, vector and tensor modes are allowed, however they remain vorticity-free and of perfect fluid type. The dynamics is encompassed in six evolution equations for six harmonic coefficients.
|
|
| 4. |
- Forsberg, Mats, et al.
(författare)
-
Density perturbations in Kantowski-Sachs models with a cosmological constant
- 2011
-
Ingår i: Spanish Relativity Meeting (ERE 2010): Gravity as a Crossroad in Physics. - : Institute of Physics (IOP).
-
Konferensbidrag (refereegranskat)abstract
- The growth of density perturbations in Kantowski-Sachs cosmologies with a positive cosmological constant is studied, using the 1+3 and 1+1+2 covariant formalisms. For each wave number a closed system for eight scalars is obtained. These are formed from quantities that are zero on the background and hence are gauge invariant. As an example a numerical solution describing the evolution of density perturbations on a background that experiences a bounce is presented. Typically the density gradient in the bouncing directions experiences a local maxium at or slightly after the bounce.
|
|
| 5. |
- Keresztes, Zoltán, et al.
(författare)
-
Gravitational, shear and matter waves in Kantowski-Sachs cosmologies
- 2015
-
Ingår i: Journal of Cosmology and Astroparticle Physics. - : Institute of Physics (IOP). - 1475-7516. ; :11
-
Tidskriftsartikel (refereegranskat)abstract
- A general treatment of vorticity-free, perfect fluid perturbations of Kantowski-Sachs models with a positive cosmological constant are considered within the framework of the 1+1+2 covariant decomposition of spacetime. The dynamics is encompassed in six evolution equations for six harmonic coefficients, describing gravito-magnetic, kinematic and matter perturbations, while a set of algebraic expressions determine the rest of the variables. The six equations further decouple into a set of four equations sourced by the perfect fluid, representing forced oscillations and two uncoupled damped oscillator equations. The two gravitational degrees of freedom are represented by pairs of gravito-magnetic perturbations. In contrast with the Friedmann case one of them is coupled to the matter density perturbations, becoming decoupled only in the geometrical optics limit. In this approximation, the even and odd tensorial perturbations of the Weyl tensor evolve as gravitational waves on the anisotropic Kantowski-Sachs background, while the modes describing the shear and the matter density gradient are out of phase dephased by pi/2 and share the same speed of sound.
|
|
| 6. |
- Keresztes, Zoltán, et al.
(författare)
-
Perturbations of Kantowski-Sachs Models with a Cosmological Constant
- 2014
-
Ingår i: Progress in Mathematical Relativity, Gravitation and Cosmology. - Heidelberg : Springer Berlin/Heidelberg. - 9783642401565 ; , s. 289-293
-
Konferensbidrag (refereegranskat)abstract
- We investigate perturbations of Kantowski–Sachs models with a positive cosmological constant, using the gauge invariant 1 + 3 and 1 + 1 + 2 covariant splits of spacetime together with a harmonic decomposition. The perturbations are assumed to be vorticity-free and of perfect fluid type, but otherwise include general scalar, vector and tensor modes. In this case the set of equations can be reduced to six evolution equations for six harmonic coefficients.
|
|
