On Schwarzschild's Topology in Brane-Worlds

The topological structure of Schwarzschild's space-time and its maximal analytic extension are investigated in context of brane-worlds. Using the embedding coordinates, these geometries are seen as different states of the evolution of a single brane-world. Comparing the topologies and the embeddings it is shown that this evolution must be followed by a signature change in the bulk.Comment: 6 page

Functional integral over velocities for a spinning particle with and without anomalous magnetic moment in a constant electromagnetic field

The technique of functional integration over velocities is applied to the calculation of the propagator of a spinning particle with and without anomalous magnetic moment. A representation for the spin factor is obtained in this context for the particle in a constant electromagnetic field. As a by-product, we also obtain a Schwinger representation for the first case.Comment: latex, 19 page

K-Rb Fermi-Bose mixtures: vortical states and sag

We study a confined mixture of bosons and fermions in the quantal degeneracy regime with attractive boson-fermion interaction. We discuss the effect that the presence of vortical states and the displacement of the trapping potentials may have on mixtures near collapse, and investigate the phase stability diagram of the K-Rb mixture in the mean field approximation supposing in one case that the trapping potentials felt by bosons and fermions are shifted from each other, as it happens in the presence of a gravitational sag, and in another case, assuming that the Bose condensate sustains a vortex state. In both cases, we have obtained an analytical expression for the fermion effective potential when the Bose condensate is in the Thomas-Fermi regime, that can be used to determine the maxima of the fermionic density. We have numerically checked that the values one obtains for the location of these maxima using the analytical formulas remain valid up to the critical boson and fermion numbers, above which the mixture collapses.Comment: Submitted to Phys. Rev. A (on May 2004), 15 pages with 3 figure

The Infrared Jet In 3C66B

We present images of infrared emission from the radio jet in 3C66B. Data at three wavelengths (4.5, 6.75 and 14.5 microns) were obtained using the Infrared Space Observatory. The 6.75 micron image clearly shows an extension aligned with the radio structure. The jet was also detected in the 14.5 micron image, but not at 4.5 micron. The radio-infrared-optical spectrum of the jet can be interpreted as synchrotron emission from a population of electrons with a high-energy break of 4e11 eV. We place upper limits on the IR flux from the radio counter-jet. A symmetrical, relativistically beamed twin-jet structure is consistent with our results if the jets consist of multiple components.Comment: 7 pages, 4 figure

Composite sandwich lattice structure

A lattice type structural panel is described. The panel utilizes the unidirectional character of filamentary epoxy impregnated composites. The panels are stiff lightweight structures for use in constructing space satellites and the like

Analysis of electric-field-induced spin splitting in wide modulation-doped quantum wells

We analyze the proper inclusion of electric-field-induced spin splittings in the framework of the envelope function approximation. We argue that the Rashba effect should be included in the form of a macroscopic potential as diagonal terms in a multiband approach rather than the commonly used Rashba term dependent on k and electric field. It is pointed out that the expectation value of the electric field in a subband is sometimes not unique because the expectation values can even have opposite signs for the spin-split subband components. Symmetric quantum wells with Dresselhaus terms and the influence of the interfaces on the spin splitting are also discussed. We apply a well established multiband approach to wide modulation-doped InGaSb quantum wells with strong built-in electric fields in the interface regions. We demonstrate an efficient mechanism for switching on and off the Rashba splitting with an electric field being an order of magnitude smaller than the local built-in field that determines the Rashba splitting. The implications of our findings for spintronic devices, in particular the Datta-Das spin transistor and proposed modifications of it, are discussed.Comment: Modified version, now published. 10 pages, 3 figures, 2 table

Method of making a composite sandwich lattice structure

A lattice type structural panel is described, which utilizes the unidirectional character of filamentary epoxy impregnated composites to produce stiff lightweight structural panels for use in constructing large area panels for space satellites and the like

Decoupling of Heavy Kaluza-Klein Modes In Models With Five-Dimensional Scalar Fields

We investigate the decoupling of heavy Kaluza-Klein modes in $\phi^{4}$ theory and scalar QED with space-time topology $\mathbb{R}^{3,1} \times S^{1}$. We calculate the effective action due to integrating out heavy KK modes. We construct generalized RGE's for the couplings with respect to the compactification scale $M$. With the solutions to the RGE's we find the $M$-scale dependence of the effective theory due to higher dimensional quantum effects. We find that the heavy modes decouple in $\phi^{4}$ theory, but do not decouple in scalar QED. This is due to the zero mode of the 5-th component $A_{5}$ of the 5-d gauge field. Because $A_{5}$ is a scalar under 4-d Lorentz transformations, there is no gauge symmetry protecting it from getting mass and $A_{5}^{4}$ interaction terms after loop corrections. In light of these unpleasant features, we explore $S^{1}/\mathbb{Z}_{2}$ compactifications, which eliminate $A_{5}$, allowing for the heavy modes to decouple at low energies. We also explore the possibility of decoupling by including higher dimensional operators. It is found that this is possible, but a high degree of fine tuning is required.Comment: 9 pages, no figures; sign error on equations 20, 36, 37; Added additional reference

Sliding not sloshing in Abell 3744: the influence of radio galaxies NGC 7018 and 7016 on cluster gas

We present new X-ray (Chandra) and radio (JVLA) observations of the nearby cluster Abell 3744. It hosts two prominent radio galaxies with powers in the range critical for radio-mode feedback. The radio emission from these galaxies terminates in buoyant tendrils reaching the cluster's outer edge, and the radio-emitting plasma clearly influences the cluster's X-ray-emitting atmosphere. The cluster's average gas temperature, of kT=3.5 keV, is high for its bolometric luminosity of 3.2 \times 10^{43} ergs s^{-1}, but the 100 kpc-scale cavity carved out by radio-emitting plasma shows evidence of less than 2 per cent of the excess enthalpy. We suggest instead that a high-velocity encounter with a galaxy group is responsible for dispersing and increasing the entropy of the gas in this non-cool-core cluster. We see no evidence for shocks, or established isobaric gas motions (sloshing), but there is much sub-structure associated with a dynamically active central region that encompasses the brightest radio emission. Gas heating is evident in directions perpendicular to the inferred line of encounter between the infalling group and cluster. The radio-emitting tendrils run along boundaries between gas of different temperature, apparently lubricating the gas flows and inhibiting heat transfer. The first stages of the encounter may have helped trigger the radio galaxies into their current phase of activity, where we see X-rays from the nuclei, jets, and hotspots.Comment: Accepted for publication in ApJ (13 pages, 17 figures