Inhomogeneous scalar field solutions and inflation

We present new exact cosmological inhomogeneous solutions for gravity coupled to a scalar field in a general framework specified by the parameter $\lambda$. The equations of motion (and consequently the solutions) in this framework correspond either to low-energy string theory or Weyl integrable spacetime according to the sign of $\lambda$. We show that different inflationary behaviours are possible, as suggested by the study of the violation of the strong energy condition. Finally, by the analysis of certain curvature scalars we found that some of the solutions may be nonsingular.Comment: LaTex file, 14 page

On the back reaction of gravitational and particle emission and absorption from straight thick cosmic strings: A toy model

The emission and absorption of gravitational waves and massless particles of an infinitely long straight cosmic string with finite thickness are studied. It is shown in a general term that the back reaction of the emission and absorption {\em always} makes the symmetry axis of the string singular. The singularity is a scalar singularity and cannot be removed.Comment: To appear in Gen. Relativ. Gra

Kaluza-Klein Induced Gravity Inflation

A D-dimensional induced gravity theory is studied carefully in a $4 + (D-4)$ dimensional Friedmann-Robertson-Walker space-time. We try to extract information of the symmetry breaking potential in search of an inflationary solution with non-expanding internal-space. We find that the induced gravity model imposes strong constraints on the form of symmetry breaking potential in order to generate an acceptable inflationary universe. These constraints are analyzed carefully in this paper.Comment: 10 pages, title changed, corrected some typos, two additional comments adde

Inflationary Universe in Higher Derivative Induced Gravity

In an induced-gravity model, the stability condition of an inflationary slow-rollover solution is shown to be $\phi_0 \partial_{\phi_0}V(\phi_0)=4V(\phi_0)$. The presence of higher derivative terms will, however, act against the stability of this expanding solution unless further constraints on the field parameters are imposed. We find that these models will acquire a non-vanishing cosmological constant at the end of inflation. Some models are analyzed for their implication to the early universe.Comment: 6 pages, two typos correcte

Imaging the dephasing of spin wave modes in a square thin film magnetic element

Copyright © 2004 The American Physical SocietyWe have used time-resolved scanning Kerr effect microscopy to study dephasing of spin wave modes in a square Ni81Fe19 element of 10 μm width and 150 nm thickness. When a static magnetic field H was applied parallel to an edge of the square, demagnetized regions appeared at the edges orthogonal to the field. When H was applied along a diagonal, a demagnetized region appeared along the opposite diagonal. Time-resolved images of the out-of-plane magnetization component showed stripes that lie perpendicular to H and indicate the presence of spin wave modes with wave vector parallel to the static magnetization. The transient Kerr rotation was measured at different positions along an axis parallel to H, and the power spectra revealed a number of different modes. Micromagnetic simulations reproduce both the observed images and the mode frequencies. This study allows us to understand an anisotropic damping observed at the center of the square element in terms of dephasing of the resonant mode spectrum