16,167 research outputs found
T-duality of the Green-Schwarz superstring
We study T-duality in the Green-Schwarz formalism to all orders in superspace
coordinates. We find two analogs of Buscher rules for the supervielbein and
clarify their meaning from the superstring point of view. The transformation
rules for the dilaton, spin 1/2 fermions and Ramond-Ramond superfields are also
derived.Comment: 21 pages, late
Single domain YBCO/Ag bulk superconductors fabricated by seeded infiltration and growth
We have applied the seeded infiltration and growth (IG) technique to the processing of samples containing Ag in an attempt to fabricate Ag-doped Y-Ba-Cu-O (YBCO) bulk superconductors with enhanced mechanical properties. The IG technique has been used successfully to grow bulk Ag-doped YBCO superconductors of up to 25 mm in diameter in the form of single grains. The distribution of Ag in the parent Y-123 matrix fabricated by the IG technique is observed to be at least as uniform as that in samples grown by conventional top seeded melt growth (TSMG). Fine Y-211 particles were observed to be embedded within the Y-123 matrix for the IG processed samples, leading to a high critical current density, Jc, of over 70 kA/cm2 at 77.3 K in self-field. The distribution of Y-211 in the IG sample microstructure, however, is inhomogeneous, which leads to a variation in the spatial distribution of Jc throughout the bulk matrix. A maximum-trapped field of around 0.43 T at 1.2 mm above the sample surface (i.e. including 0.7 mm for the sensor mould thickness) is observed at liquid nitrogen temperature, despite the relatively small grain size of the sample (20 mm diameter × 7 mm thickness)
Is there Correlation between Fine Structure and Dark Energy Cosmic Dipoles?
We present a detailed analysis (including redshift tomography) of the cosmic
dipoles in the Keck+VLT quasar absorber and in the Union2 SnIa samples. We show
that the fine structure constant cosmic dipole obtained through the Keck+VLT
quasar absorber sample at level is anomalously aligned with the
corresponding dark energy dipole obtained through the Union2 sample at
level. The angular separation between the two dipole directions is
. We use Monte Carlo simulations to find the
probability of obtaining the observed dipole magnitudes with the observed
alignment, in the context of an isotropic cosmological model with no
correlation between dark energy and fine structure constant . We find
that this probability is less than one part in . We propose a simple
physical model (extended topological quintessence) which naturally predicts a
spherical inhomogeneous distribution for both dark energy density and fine
structure constant values. The model is based on the existence of a recently
formed giant global monopole with Hubble scale core which also couples
non-minimally to electromagnetism. Aligned dipole anisotropies would naturally
emerge for an off-centre observer for both the fine structure constant and for
dark energy density. This model smoothly reduces to \lcdm for proper limits of
its parameters. Two predictions of this model are (a) a correlation between the
existence of strong cosmic electromagnetic fields and the value of and
(b) the existence of a dark flow on Hubble scales due to the repulsive gravity
of the global defect core (`Great Repulser') aligned with the dark energy and
dipoles. The direction of the dark flow is predicted to be towards the
spatial region of lower accelerating expansion. Existing data about the dark
flow are consistent with this prediction.Comment: 14 pages 11 figures (two column revtex). Aceepted in Phys. Rev. D (to
appear). Significant extensions (mostly on section 4 on the theoretical
model), added references, corrected typos. The data, updated mathematica and
C program files used for the numerical analysis may be downloaded from
http://leandros.physics.uoi.gr/defsdipole
Supergravity in Dimensions
Supergravity theory in dimensions is studied. It is invariant
under supertransformations in 2 and 3 dimensions. One-loop divergence is
explicitly computed in the background field method and a nontrivial fixed point
is found. In quantizing the supergravity, a gauge fixing condition is devised
which explicitly isolates conformal and superconformal modes. The
renormalization of the gravitationally dressed operators is studied and their
anomalous dimensions are computed. Problems to use the dimensional reduction
are also examined.Comment: 36 pages, TIT/HEP-238, Imperial/TP/93-94/
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