1,849 research outputs found
On the spectral distribution of photons between planar interfaces
Using a phenomenological approach to field quantization, an expression for
the Keldysh function of photons between two planar interfaces (Casimir
geometry) is found for any stationary quantum state of the two bodies. The case
of one interface sliding against the other is considered in detail
Reduction of Magnetic Noise in Atom Chips by Material Optimization
We discuss the contribution of the material type in metal wires to the
electromagnetic fluctuations in magnetic microtraps close to the surface of an
atom chip. We show that significant reduction of the magnetic noise can be
achieved by replacing the pure noble metal wires with their dilute alloys. The
alloy composition provides an additional degree of freedom which enables a
controlled reduction of both magnetic noise and resistivity if the atom chip is
cooled. In addition, we provide a careful re-analysis of the magnetically
induced trap loss observed by Yu-Ju Lin et al. [Phys. Rev. Lett. 92, 050404
(2004)] and find good agreement with an improved theory.Comment: 25 pages with 9 figures ep
Finite-Size Scaling and Universality in the Spin 1 Quantum XY Chain
The spin-1 XY chain in a transverse field is studied using finite-size
scaling. The ground state phase diagram displays a paramagnetic, an ordered
ferromagnetic and an ordered oscillatory phase. The paramagnetic-ferromagnetic
transition line belongs to the universality class of the 2D Ising model. Along
this line, universality is confirmed for the finite-size scaling functions of
several correlation lengths and for the conformal operator content.Comment: Latex 8 pages, 2 uucompressed figure
Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
The Standard Model of particle physics assumes that the so-called fundamental
constants are universal and unchanging. Absorption lines arising in molecular
clouds along quasar sightlines offer a precise test for variations in the
proton-to-electron mass ratio, mu, over cosmological time and distance scales.
The inversion transitions of ammonia are particularly sensitive to mu compared
to molecular rotational transitions. Comparing the available ammonia spectra
observed towards the quasar B0218+357 with new, high-quality rotational
spectra, we present the first detailed measurement of mu with this technique,
limiting relative deviations from the laboratory value to |dmu/mu| <
1.8x10^{-6} (95% confidence level) at approximately half the Universe's current
age - the strongest astrophysical constraint to date. Higher-quality ammonia
observations will reduce both the statistical and systematic uncertainties in
these measurements.Comment: Science, 20th June 2008. 22 pages, 5 figures (12 EPS files), 2
tables, including Supporting Online Material; v2: Corrected reference for
laboratory mu-variation bound
The Boundary Conformal Field Theories of the 2D Ising critical points
We present a new method to identify the Boundary Conformal Field Theories
(BCFTs) describing the critical points of the Ising model on the strip. It
consists in measuring the low-lying excitation energies spectra of its quantum
spin chain for different boundary conditions and then to compare them with
those of the different boundary conformal field theories of the
minimal model.Comment: 7 pages, no figures. Talk given at the XXth International Conference
on Integrable Systems and Quantum Symmetries (ISQS-20). Prague, June 201
Decoherence of Bose-Einstein condensates in microtraps
We discuss the impact of thermally excited near fields on the coherent
expansion of a condensate in a miniaturized electromagnetic trap.
Monte Carlo simulations are compared with a kinetic two-component theory and
indicate that atom interactions can slow down decoherence. This is explained by
a simple theory in terms of the condensate dynamic structure factor.Comment: 5 pages, 4 figure
6.7 GHz methanol absorption toward the Seyfert 2 galaxy NGC 3079
The detection of the 6.7 GHz line of methanol (CH3OH) is reported for the
first time toward an object beyond the Magellanic Clouds. Using the Effelsberg
100 m telescope, two absorption features were identified toward the Seyfert 2
galaxy NGC 3079. Both components probably originated on lines-of-sight toward
the central region, presumably absorbing the radio continuum of the nuclear
sources A, B, and E of NGC 3079. One absorption feature, at the systemic
velocity, is narrow and may arise from gas not related to the nuclear
environment of the galaxy. The weaker blue-shifted component is wider and may
trace outflowing gas. Total A-type CH3OH column densities are estimated to be
between a few times 10^13 and a few times 10^15 cm^-2. Because of a highly
frequency-dependent continuum background, the overall similarity of HI, OH, and
CH3OH absorption profiles hints at molecular clouds that cover the entire area
occupied by the nuclear radio continuum sources ~ 4 pc.Comment: 4 pages, 1 figure, accepted for publication in A&A Letter
On the Symmetry of Universal Finite-Size Scaling Functions in Anisotropic Systems
In this work a symmetry of universal finite-size scaling functions under a
certain anisotropic scale transformation is postulated. This transformation
connects the properties of a finite two-dimensional system at criticality with
generalized aspect ratio to a system with . The symmetry
is formulated within a finite-size scaling theory, and expressions for several
universal amplitude ratios are derived. The predictions are confirmed within
the exactly solvable weakly anisotropic two-dimensional Ising model and are
checked within the two-dimensional dipolar in-plane Ising model using Monte
Carlo simulations. This model shows a strongly anisotropic phase transition
with different correlation length exponents parallel
and perpendicular to the spin axis.Comment: RevTeX4, 4 pages, 3 figure
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