7,852 research outputs found
Charge and Magnetic Flux Correlations in Chern-Simons Theory with Fermions
Charge and magnetic flux bearing operators are introduced in Chern-Simons
theory both in its pure form and when it is coupled to fermions. The magnetic
flux creation operator turns out to be the Wilson line. The euclidean
correlation functions of these operators are shown to be local and are
evaluated exactly in the pure case and through an expansion in the inverse
fermion mass whenever these are present. Physical states only occur in the
presence of fermions and consist of composite charge-magnetic flux carrying
states which are in general anyonic. The large distance behavior of the
correlation functions indicates the condensation of charge and magnetic flux.Comment: Latex, 17 page
Quantum skyrmions and the destruction of long-range antiferromagnetic order in the high-Tc superconductors La(2-x)Sr(x)CuO(4) and YBa(2)Cu(3)O(6+x)
We study the destruction of the antiferromagnetic order in the high-Tc
superconductors La(2-x)Sr(x)CuO(4) and YBa(2)Cu(3)O(6+x) in the framework of
the CP1-nonlinear sigma model formulation of the 2D quantum Heisenberg
antiferromagnet. The dopants are introduced as independent fermions with
appropriate dispersion relations determined by the shape of the Fermi surface.
The energy of skyrmion topological defects, which are shown to be introduced by
doping, is used as an order parameter for antiferromagnetic order. We obtain
analytic expressions for this as a function of doping which allow us to plot
the curves T_N(x_c)\times x_c and M(x)\times x, for both YBCO and LSCO, in good
quantitative agreement with the experimental data.Comment: 4 pages, revtex, 5 embeeded figure
Charge pairing, superconducting transition and supersymmetry in high-temperature cuprate superconductors
We propose a model for high-T superconductors, valid for
, that includes both the spin fluctuations of the
Cu magnetic ions and of the O doped holes. Spin-charge separation
is taken into account with the charge of the doped holes being associated to
quantum skyrmion excitations (holons) of the Cu spin background. The
holon effective interaction potential is evaluated as a function of doping,
indicating that Cooper pair formation is determined by the competition between
the spin fluctuations of the Cu background and of spins of the O
doped holes (spinons). The superconducting transition occurs when the spinon
fluctuations dominate, thereby reversing the sign of the interaction. At this
point (), the theory is supersymmetric at short distances
and, as a consequence, the leading order results are not modified by radiative
corrections. The critical doping parameter for the onset of superconductivity
at T=0 is obtained and found to be a universal constant determined by the shape
of the Fermi surface. Our theoretical values for are in good
agreement with the experiment for both LSCO and YBCO.Comment: RevTex, 4 pages, no figure
PU(2) monopoles. II: Top-level Seiberg-Witten moduli spaces and Witten's conjecture in low degrees
In this article we complete the proof---for a broad class of
four-manifolds---of Witten's conjecture that the Donaldson and Seiberg-Witten
series coincide, at least through terms of degree less than or equal to c-2,
where c is a linear combination of the Euler characteristic and signature of
the four-manifold. This article is a revision of sections 4--7 of an earlier
version, while a revision of sections 1--3 of that earlier version now appear
in a separate companion article (math.DG/0007190). Here, we use our
computations of Chern classes for the virtual normal bundles for the
Seiberg-Witten strata from the companion article (math.DG/0007190), a
comparison of all the orientations, and the PU(2) monopole cobordism to compute
pairings with the links of level-zero Seiberg-Witten moduli subspaces of the
moduli space of PU(2) monopoles. These calculations then allow us to compute
low-degree Donaldson invariants in terms of Seiberg-Witten invariants and
provide a partial verification of Witten's conjecture.Comment: Journal fur die Reine und Angewandte Mathematik, to appear; 65 pages.
Revision of sections 4-7 of version v1 (December 1997
NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
High-resolution spectroscopic observations were taken of 29 extended main
sequence turn-off (eMSTO) stars in the young (200 Myr) LMC cluster, NGC
1866 using the Michigan/Magellan Fiber System and MSpec spectrograph on the
Magellan-Clay 6.5-m telescope. These spectra reveal the first direct detection
of rapidly rotating stars whose presence has only been inferred from
photometric studies. The eMSTO stars exhibit H-alpha emission (indicative of
Be-star decretion disks), others have shallow broad H-alpha absorption
(consistent with rotation 150 km s), or deep H-alpha core
absorption signaling lower rotation velocities (150 km s ).
The spectra appear consistent with two populations of stars - one rapidly
rotating, and the other, younger and slowly rotating.Comment: 9 pages, 4 figures, Accepted for publication in ApJ Letter
Superpotentials from flux compactifications of M-theory
In flux compactifications of M-theory a superpotential is generated whose
explicit form depends on the structure group of the 7-dimensional internal
manifold. In this note, we discuss superpotentials for the structure groups:
G_2, SU(3) or SU(2). For the G_2 case all internal fluxes have to vanish. For
SU(3) structures, the non-zero flux components entering the superpotential
describe an effective 1-dimensional model and a Chern-Simons model if there are
SU(2) structures.Comment: 10 page
Oral vinorelbine and cisplatin with concomitant radiotherapy in stage III non-small cell lung cancer (NSCLC): A feasibility study
Background: Concurrent chemoradiotherapy has improved survival in inoperable stage III non-small cell lung cancer (NSCLC). This phase I trial was performed in order to establish a dose recommendation for oral vinorelbine in combination with cisplatin and simultaneous radiotherapy. Patients and Methods: Previously untreated patients with stage IIIB NSCLC received concurrent chemoradiotherapy with 66 Gy and 2 cycles of cisplatin and oral vinorelbine which was administered at 3 different levels (40, 50 and 60 mg/m(2)). This was to be followed by 2 cycles of cisplatin/vinorelbine oral consolidation chemotherapy. The study goal was to determine the maximal recommended dose of oral vinorelbine during concurrent treatment. Results: 11 stage IIIB patients were entered into the study. The median radiotherapy dose was 66 Gy. Grade 3-4 toxicity included neutropenia, esophagitis, gastritis and febrile neutropenia. The dose-limiting toxicity for concurrent chemoradiotherapy was esophagitis. 9 patients received consolidation chemotherapy, with neutropenia and anemia/thrombocytopenia grade 3 being the only toxicities. The overall response was 73%. Conclusion: Oral vinorelbine 50 mg/m(2) (days 1, 8, 15 over 4 weeks) in combination with cisplatin 20 mg/m2 (days 1-4) is the recommended dose in combination with radiotherapy (66 Gy) and will be used for concurrent chemoradiotherapy in a forthcoming phase III trial testing the efficacy of consolidation chemotherapy in patients not progressing after chemoradiotherapy
Superconducting states and depinning transitions of Josephson ladders
We present analytical and numerical studies of pinned superconducting states
of open-ended Josephson ladder arrays, neglecting inductances but taking edge
effects into account. Treating the edge effects perturbatively, we find
analytical approximations for three of these superconducting states -- the
no-vortex, fully-frustrated and single-vortex states -- as functions of the dc
bias current and the frustration . Bifurcation theory is used to derive
formulas for the depinning currents and critical frustrations at which the
superconducting states disappear or lose dynamical stability as and are
varied. These results are combined to yield a zero-temperature stability
diagram of the system with respect to and . To highlight the effects of
the edges, we compare this dynamical stability diagram to the thermodynamic
phase diagram for the infinite system where edges have been neglected. We
briefly indicate how to extend our methods to include self-inductances.Comment: RevTeX, 22 pages, 17 figures included; Errata added, 1 page, 1
corrected figur
Defocusing gravitational microlensing
We introduce the notion of defocusing gravitational lens considering a MACHO
located behind a light source with respect to an observer. The consequence of
defocusing effect is a temporal variability of star luminosity which produces a
gap instead of a peak as tell--tale signature in the light curve. General
theory of (de)focusing rays (geodesics) in a gravitational field is presented.
Furthermore, we give estimations of the mass of the lens and the optical depth
connected to such a phenomenon.Comment: 19 pages, latex, submitted to Physica Script
Some aspects of the cosmological conformal equivalence between ``Jordan Frame'' and ``Einstein Frame''
The conformal equivalence between Jordan frame and Einstein frame can be used
in order to search for exact solutions in general theories of gravity in which
scalar fields are minimally or nonminimally coupled with geometry. In the
cosmological arena a relevant role is played by the time parameter in which
dynamics is described. In this paper we discuss such issues considering also if
cosmological Noether symmetries in the ``point--like'' Lagrangian are
conformally preserved. Through this analysis and through also a careful
analysis of the cosmological parameters \Omega and \Lambda, it is possible to
contribute to the discussion on which is the physical system.Comment: 25 pages, latex, submitted to Class. Quantum Gra
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