8,310 research outputs found
Hopf instantons, Chern-Simons vortices, and Heisenberg ferromagnets
The dimensional reduction of the three-dimensional fermion-Chern-Simons model
(related to Hopf maps) of Adam et el. is shown to be equivalent to (i) either
the static, fixed--chirality sector of our non-relativistic spinor-Chern-Simons
model in 2+1 dimensions, (ii) or a particular Heisenberg ferromagnet in the
plane.Comment: 4 pages, Plain Tex, no figure
Numerical Investigation of Monopole Chains
We present numerical results for chains of SU(2) BPS monopoles constructed
from Nahm data. The long chain limit reveals an asymmetric behavior transverse
to the periodic direction, with the asymmetry becoming more pronounced at
shorter separations. This analysis is motivated by a search for semiclassical
finite temperature instantons in the 3D SU(2) Georgi-Glashow model, but it
appears that in the periodic limit the instanton chains either have
logarithmically divergent action or wash themselves out.Comment: 14 pages, 6 figures; v2 minor changes, published versio
Euler-Heisenberg lagrangians and asymptotic analysis in 1+1 QED, part 1: Two-loop
We continue an effort to obtain information on the QED perturbation series at
high loop orders, and particularly on the issue of large cancellations inside
gauge invariant classes of graphs, using the example of the l - loop N - photon
amplitudes in the limit of large photons numbers and low photon energies. As
was previously shown, high-order information on these amplitudes can be
obtained from a nonperturbative formula, due to Affleck et al., for the
imaginary part of the QED effective lagrangian in a constant field. The
procedure uses Borel analysis and leads, under some plausible assumptions, to a
number of nontrivial predictions already at the three-loop level. Their direct
verification would require a calculation of this `Euler-Heisenberg lagrangian'
at three-loops, which seems presently out of reach. Motivated by previous work
by Dunne and Krasnansky on Euler-Heisenberg lagrangians in various dimensions,
in the present work we initiate a new line of attack on this problem by
deriving and proving the analogous predictions in the simpler setting of 1+1
dimensional QED. In the first part of this series, we obtain a generalization
of the formula of Affleck et al. to this case, and show that, for both Scalar
and Spinor QED, it correctly predicts the leading asymptotic behaviour of the
weak field expansion coefficients of the two loop Euler-Heisenberg lagrangians.Comment: 28 pages, 1 figures, final published version (minor modifications,
refs. added
A Search for Jovian Planets around Hot White Dwarfs
Current searches for extrasolar planets have concentrated on observing the
reflex Doppler shift of solar-type stars. Little is known, however, about
planetary systems around non-solar-type stars. We suggest a new method to
extend planetary searches to hot white dwarfs. Near a hot white dwarf, the
atmosphere of a Jovian planet will be photoionized and emit hydrogen
recombination lines, which may be detected by high- dispersion spectroscopic
observations. Multi-epoch monitoring can be used to distinguish between non-LTE
stellar emission and planetary emission, and to establish the orbital
parameters of the detected planets. In the future, high-precision astrometric
measurements of the hot white dwarf will allow the masses of the detected
planets to be determined. Searches for Jovian planets around hot white dwarfs
will provide invaluable new insight on the development of planetary systems
around stars more massive than the Sun and on how stellar evolution affects
these systems. We present high-dispersion spectroscopic observations of the
white dwarf Feige 34 to demonstrate the complexity and feasibility of the
search method.Comment: 10 pages, 2 figures, accepted for publication in the ApJ Letter
The SCUBA Local Universe Galaxy Survey I: First Measurements of the Submillimetre Luminosity and Dust Mass Functions
We have used SCUBA to observe a complete sample of 104 galaxies selected at
60 microns from the IRAS BGS and we present here the 850 micron measurements.
Fitting the 60,100 and 850 micron fluxes with a single temperature dust model
gives the sample mean temperature T=36 K and beta = 1.3. We do not rule out the
possibility of dust which is colder than this, if a 20 K component was present
then our dust masses would increase by factor 1.5-3. We present the first
measurements of the luminosity and dust mass functions, which were well fitted
by Schechter functions (unlike those 60 microns). We have correlated many
global galaxy properties with the submillimetre and find that there is a
tendancy for less optically luminous galaxies to contain warmer dust and have
greater star formation efficiencies (cf. Young 1999). The average gas-to-dust
ratio for the sample is 581 +/- 43 (using both atomic and molecular hydrogen),
significantly higher than the Galactic value of 160. We believe this
discrepancy is due to a cold dust component at T < 20 K. There is a suprisingly
tight correlation between dust mass and the mass of molecular hydrogen as
estimated from CO measurements, with an intrinsic scatter of ~50%.Comment: 24 pages, 15 figures, 8 tables, accepted for publication in MNRA
The I-mode confinement regime at ASDEX Upgrade: global propert ies and characterization of strongly intermittent density fluctuations
Properties of the Imode confinement regime on the ASDEX Upgrade tokamak are
summarized. A weak dependence of the power threshold for the LI transition on the toroidal
magnetic field strength is found. During improved confinement, the edge radial electric field
well deepens. Stability calculations show that the Imode pedestal is peelingballooning stable.
Turbulence investigations reveal strongly intermittent density fluctuations linked to the weakly
coherent mode in the confined plasma, which become stronger as the confinement quality
increases. Across all investigated structure sizes (
≈
⊥
k
5
–
12 cm
−
1
, with
⊥
k
the perpendicular
wavenumber of turbulent density fluctuations), the intermittent turbulence bursts are observed.
Comparison with bolometry data shows that they move poloidally toward the Xpoint and
finally end up in the divertor. This might be indicative that they play a role in inhibiting the
density profile growth, such that no pedestal is formed in the edge density profile.European Union (EUROfusion 633053)European Union (EUROfusion AWP15ENR09/IPP02
Fermion Determinants
The current status of bounds on and limits of fermion determinants in two,
three and four dimensions in QED and QCD is reviewed. A new lower bound on the
two-dimensional QED determinant is derived. An outline of the demonstration of
the continuity of this determinant at zero mass when the background magnetic
field flux is zero is also given.Comment: 10 page
Chern-Simons matrix model: coherent states and relation to Laughlin wavefunctions
Using a coherent state representation we derive many-body probability
distributions and wavefunctions for the Chern-Simons matrix model proposed by
Polychronakos and compare them to the Laughlin ones. We analyze two different
coherent state representations, corresponding to different choices for electron
coordinate bases. In both cases we find that the resulting probability
distributions do not quite agree with the Laughlin ones. There is agreement on
the long distance behavior, but the short distance behavior is different.Comment: 15 pages, LaTeX; one reference added, abstract and section 5
expanded, typos correcte
Analytical solution of the Gross-Neveu model at finite density
Recent numerical calculations have shown that the ground state of the
Gross-Neveu model at finite density is a crystal. Guided by these results, we
can now present the analytical solution to this problem in terms of elliptic
functions. The scalar potential is the superpotential of the non-relativistic
Lame Hamiltonian. This model can also serve as analytically solvable toy model
for a relativistic superconductor in the Larkin-Ovchinnikov-Fulde-Ferrell
phase.Comment: 5 pages, no figures, revtex; vs2: appendix with analytical proof of
self-consistency adde
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