4,593 research outputs found
Curvature estimates for Weingarten hypersurfaces in Riemannian manifolds
We prove curvature estimates for general curvature functions. As an
application we show the existence of closed, strictly convex hypersurfaces with
prescribed curvature , where the defining cone of is \C_+. is only
assumed to be monotone, symmetric, homogeneous of degree 1, concave and of
class C^{m,\al}, .Comment: 9 pages, v2:final version, to be publishe
Combining gravity with the forces of the standard model on a cosmological scale
We prove the existence of a spectral resolution of the Wheeler-DeWitt
equation when the underlying spacetime is a Friedman universe with flat spatial
slices and where the matter fields are comprised of the strong interaction,
with \SU(3) replaced by a general \SU(n), , and the electro-weak
interaction. The wave functions are maps from to a subspace of the
antisymmetric Fock space, and one noteworthy result is that, whenever the
electro-weak interaction is involved, the image of an eigenfunction is in
general not one dimensional, i.e., in general it makes no sense specifying a
fermion and looking for an eigenfunction the range of which is contained in the
one dimensional vector space spanned by the fermion.Comment: 53 pages, v6: some typos correcte
Critical properties of the one-dimensional spin-1/2 antiferromagnetic Heisenberg model in the presence of a uniform field
In the presence of a uniform field the one-dimensional spin-
antiferromagnetic Heisenberg model develops zero frequency excitations at
field-dependent 'soft mode' momenta. We determine three types of critical
quantities, which we extract from the finite-size dependence of the lowest
excitation energies, the singularities in the static structure factors and the
infrared singularities in the dynamical structure factors at the soft mode
momenta. We also compare our results with the predictions of conformal field
theory.Comment: 12 pages, REVTEX, 7 figures, submitted to Physical Review
Ultrafast circular polarization oscillations in spin-polarized vertical-cavity surface-emitting laser devices
Spin-polarized lasers offer new encouraging possibilities for future devices. We investigate the polarization dynamics of electrically pumped vertical-cavity surface-emitting lasers after additional spin injection at room temperature. We find that the circular polarization degree exhibits faster dynamics than the emitted light. Moreover the experimental results demonstrate a strongly damped ultrafast circular polarization oscillation due to spin injection with an oscillation frequency of approximately 11GHz depending on the birefringence in the VCSEL device. We compare our experimental results with theoretical calculations based on rate-equations. This allows us to predict undamped long persisting ultrafast polarization oscillations, which reveal the potential of spin-VCSELs for ultrafast modulation applications
Birefringence controlled room-temperature picosecond spin dynamics close to the threshold of vertical-cavity surface-emitting laser devices
We analyze the spin-induced circular polarization dynamics at the threshold of vertical-cavity surface-emitting lasers at room-temperature using a hybrid excitation combining electrically pumping without spin preference and spin-polarized optical injection. After a short pulse of spin-polarized excitation, fast oscillations of the circular polarization degree (CPD) are observed within the relaxation oscillations. A theoretical investigation of this behavior on the basis of a rate equation model shows that these fast oscillations of CPD could be suppressed by means of a reduction of the birefringence of the laser cavity
- …