The photon magnetic moment problem revisited

The photon magnetic moment for radiation propagating in magnetized vacuum is defined as a pseudo-tensor quantity, proportional to the external electromagnetic field tensor. After expanding the eigenvalues of the polarization operator in powers of $k^2$, we obtain approximate dispersion equations (cubic in $k^2$), and analytic solutions for the photon magnetic moment, valid for low momentum and/or large magnetic field. The paramagnetic photon experiences a red shift, with opposite sign than the gravitational one, which differs for parallel and perpendicular polarizations. It is due to the drain of photon transverse momentum and energy by the external field. By defining an effective transverse momentum, the constancy of the speed of light orthogonal to the field is guaranteed. We conclude that the propagation of the photon non-parallel to the magnetic behaves as if there is a quantum compression of vacuum or warp of space-time in an amount depending on its angle with regard to the field.Comment: 10 pages, 2 figure

Bipolar spin filter in a quantum dot molecule

We show that the tunable hybridization between two lateral quantum dots connected to non-magnetic current leads in a `hanging-dot' configuration that can be used to implement a bipolar spin filter. The competition between Zeeman, exchange interaction, and interdot tunneling (molecular hybridization) yields a singlet-triplet transition of the double dot {\it ground state} that allows spin filtering in Coulomb blockade experiments. Its generic nature should make it broadly useful as a robust bidirectional spin polarizer.Comment: 5 pages, 3 figures (to appear in Appl. Phys. Lett.

Constraints on the mass and mixing of Z' bosons

We tested several models in which the Standard Model (SM) gauge group is extended by an additional U(1) gauge symmetry, against available electroweak precision data to impose limits on the mass of the neutral Z' boson, M_Z', predicted in all such models, and on the Z-Z' mixing angle, theta_ZZ', at 95% C.L. We found lower limits on M_Z' of order 1 TeV in most cases, while theta_ZZ' was found to be constrained to very small values.Comment: Format fixed, 5 pages, 2 figures, Talk given at the 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY09), Boston, MA, USA, 5-10 June 2009, to be published in the conference proceedings (AIP