Zeeman and Orbital Effects of an in-Plane Magnetic Field in Cuprate Superconductors

We discuss the effects of a magnetic field applied parallel to the Cu-O ($ab$) plane of the high $T_c$ cuprate superconductors. After briefly reviewing the Zeeman effect of the field, we study the orbital effects, using the Lawrence-Doniach model for layered superconductors as a guide to the physics. We argue that the orbital effect is qualitatively different for in-plane and inter-layer mechanisms for superconductivity. In the case of in-plane mechanisms, interlayer couplings may be modeled as a weak interlayer Josephson coupling, whose effects disappear as $H\to\infty$; in this case Zeeman dominates the effect of the field. In contrast, in the inter-layer mechanism the Josephson coupling {\em is} the driving force of superconductivity, and we argue that the in-plane field suppresses superconductivity and provides an upper bound for $H_{c2}$ which we estimate very crudely.Comment: 4 pages with 1 embedded ps figure. Manuscript submitted to the MMM'99 conferenc

Bose-Einstein Condensate Dark Matter Halos confronted with galactic rotation curves

We present a comparative confrontation of both the Bose-Einstein Condensate (BEC) and the Navarro-Frenk-White (NFW) dark halo models with galactic rotation curves. We employ 6 High Surface Brightness (HSB), 6 Low Surface Brightness (LSB), and 7 dwarf galaxies with rotation curves falling into two classes. In the first class rotational velocities increase with radius over the observed range.The BEC and NFW models give comparable fits for HSB and LSB galaxies of this type, while for dwarf galaxies the fit is significantly better with the BEC model. In the second class the rotational velocity of HSB and LSB galaxies exhibits long flat plateaus, resulting in better fit with the NFW model for HSB galaxies and comparable fits for LSB galaxies. We conclude that due to its central density cusp avoidance the BEC model fits better dwarf galaxy dark matter distribution. Nevertheless it suffers from sharp cutoff in larger galaxies, where the NFW model performs better. The investigated galaxy sample obeys the Tully-Fisher relation, including the particular characteristics exhibited by dwarf galaxies. In both models the fitting enforces a relation between dark matter parameters: the characteristic density and the corresponding characteristic distance scale with an inverse power.Comment: published versio

Constraining the parameters of the putative supermassive binary black hole in PG 1302-102 from its radio structure

We investigate the pc-scale kinematics and kpc-scale radio morphology of the quasar PG 1302-102, which may harbour a sub-pc separation supermassive binary black hole system at its centre as inferred from optical variability. High-resolution radio interferometric measurements obtained with the Very Long Baseline Array (VLBA) in the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) programme at 15 GHz at 20 epochs spanning 17 years were analysed to investigate the pc-scale radio structure. Archival observations with the Very Large Array (VLA) at 1.4 GHz and 5 GHz were obtained to study the kpc-scale morphology. We find that the pc-scale jet is inclined within ~2.2 deg to the line of sight and has a half-opening angle of about 0.2 deg. The parameters derived from the pc-scale radio jet are qualitatively consistent with those obtained from the analysis of the optical light curve of PG 1302-102. We obtain at least 0.08 for the mass ratio of the two black holes in the system. We find some indication for a helical jet structure on kpc-scale, but the directions of the inner and the extended radio jets are significantly different, obstructing a straightforward connection of the pc- and kpc-scale jets within the binary scenario.Comment: 9 pages, 4 figures, 1 table, accepted to MNRA

Macroscopic quantum superpositions in highly-excited strongly-interacting many-body systems

We demonstrate a break-down in the macroscopic (classical-like) dynamics of wave-packets in complex microscopic and mesoscopic collisions. This break-down manifests itself in coherent superpositions of the rotating clockwise and anticlockwise wave-packets in the regime of strongly overlapping many-body resonances of the highly-excited intermediate complex. These superpositions involve $\sim 10^4$ many-body configurations so that their internal interactive complexity dramatically exceeds all of those previously discussed and experimentally realized. The interference fringes persist over a time-interval much longer than the energy relaxation-redistribution time due to the anomalously slow phase randomization (dephasing). Experimental verification of the effect is proposed.Comment: Title changed, few changes in the abstract and in the main body of the paper, and changes in the font size in the figure. Uses revTex4, 4 pages, 1 ps figur

Infinite-Randomness Fixed Points for Chains of Non-Abelian Quasiparticles

One-dimensional chains of non-Abelian quasiparticles described by $SU(2)_k$ Chern-Simons-Witten theory can enter random singlet phases analogous to that of a random chain of ordinary spin-1/2 particles (corresponding to $k \to \infty$). For $k=2$ this phase provides a random singlet description of the infinite randomness fixed point of the critical transverse field Ising model. The entanglement entropy of a region of size $L$ in these phases scales as $S_L \simeq \frac{\ln d}{3} \log_2 L$ for large $L$, where $d$ is the quantum dimension of the particles.Comment: 4 pages, 4 figure

A single radio-emitting nucleus in the dual AGN candidate NGC 5515

The Seyfert galaxy NGC 5515 has double-peaked narrow-line emission in its optical spectrum, and it has been suggested that this could indicate that it has two active nuclei. We observed the source with high resolution Very Long Baseline Interferometry (VLBI) at two radio frequencies, reduced archival Very Large Array data, and re-analysed its optical spectrum. We detected a single, compact radio source at the position of NGC 5515, with no additional radio emission in its vicinity. The optical spectrum of the source shows that the blue and red components of the double-peaked lines have very similar characteristics. While we cannot rule out unambiguously that NGC 5515 harbours a dual AGN, the assumption of a single AGN provides a more plausible explanation for the radio observations and the optical spectrum.Comment: 6 pages, 1 figure, accepted for publication in MNRA