Showing papers in "Physical Review in 2010"

The IR stability of de Sitter QFT: results at all orders

Abstract: We show that the Hartle-Hawking vacuum for theories of interacting massive scalars in de Sitter space is both perturbatively well-defined and stable in the IR. Correlation functions in this state may be computed on the Euclidean section and Wick-rotated to Lorentz-signature. The results are manifestly de Sitter-invariant and contain only the familiar UV singularities. More importantly, the connected parts of all Lorentz-signature correlators decay at large separations of their arguments. Our results apply to all cases in which the free Euclidean vacuum is well defined, including scalars with masses belonging to both the complementary and principal series of $SO(D,1)$. This suggests that interacting QFTs in de Sitter -- including higher spin fields -- are perturbatively IR-stable at least when i) the Euclidean vacuum of the zero-coupling theory exists and ii) corresponding Lorentz-signature zero-coupling correlators decay at large separations. This work has significant overlap with a paper by Stefan Hollands, which is being released simultaneously.

Spin Splitting and Spin Current in Strained Bulk Semiconductors

Abstract: We present a theory for two recent experiments in bulk strained semiconductors and show that a new, previously overlooked, strain spin-orbit coupling term may play a fundamental role. We propose simple experiments that could clarify the origin of strain-induced spin-orbit coupling terms in inversion asymmetric semiconductors. We predict that a uniform magnetization parallel to the electric field will be induced in the samples studied in for specific directions of the applied electric field. We also propose special geometries to detect spin currents in strained semiconductors.

Energy level scheme of InAs/InxGa1?xAs/GaAs quantum-dots-in-a-well infrared photodetector structures

Abstract: A thorough investigation of quantum-dots-in-a-well structures for infrared photodetector applications has been performed employing different experimental techniques. The electronic structure of self-assembled InAs quantum dots embedded in an In0.15Ga0.85As/GaAs quantum well (QW) was deduced from photoluminescence (PL) and PL excitation (PLE) spectroscopy. From polarization-dependent PL it was revealed that the quantum dots hold two electron energy levels and two heavy-hole levels. Tunnel capacitance spectroscopy confirmed an electron energy level separation of about 50 meV, and additionally, that the conduction-band ground state and excited state of the dots are twofold and fourfold degenerates, respectively. Intersubband photocurrent spectroscopy, combined with simultaneous interband pumping of the dots, revealed a dominant transition at 150 meV (8.5 mu m) between the ground state of the quantum dots and the excited state of the QW. Results from detailed full three-dimensional calculations of the electronic structure, including effects of composition intermixing and interdot interactions, confirm the experimentally unravelled energy level scheme of the dots and well.

Longitudinal Weak Gauge Bosons Scattering in Hidden Z' Models

Abstract: Longitudinal weak gauge boson scattering has been well-known as a powerful method to probe the underlying mechanism of the electroweak symmetry breaking sector of the standard model. We point out that longitudinal weak gauge boson scattering is also sensitive to the gauge sector when the non-Abelian trilinear and quartic couplings of the standard model Z boson are modified due to the general mixings with another Z{sup '} boson in the hidden sector and possibly with the photon as well. In particular, these mixings can lead to a partially strong scattering effect in the channels of W{sub L}{sup {+-}W}{sub L}{sup {+-}{yields}W}{sub L}{sup {+-}W}{sub L}{sup {+-}}and W{sub L}{sup {+-}W}{sub L}{sup {+-}{yields}W}{sub L}{sup {+-}W}{sub L}{sup {+-}}which can be probed at the Large Hadron Collider. We study this effect in a simple U(1) extension of the standard model recently suggested in the literature that includes both the symmetry breaking Higgs mechanism as well as the gauge invariant Stueckelberg mass terms for the two Abelian groups. Other types of Z{sup '} models are also briefly discussed.