20,299 research outputs found
Markov quantum fields on a manifold
We study scalar quantum field theory on a compact manifold. The free theory
is defined in terms of functional integrals. For positive mass it is shown to
have the Markov property in the sense of Nelson. This property is used to
establish a reflection positivity result when the manifold has a reflection
symmetry. In dimension d=2 we use the Markov property to establish a sewing
operation for manifolds with boundary circles. Also in d=2 the Markov property
is proved for interacting fields.Comment: 14 pages, 1 figure, Late
Statistical Analysis of Small Ellerman Bomb Events
The properties of Ellerman bombs (EBs), small-scale brightenings in the
H-alpha line wings, have proved difficult to establish due to their size being
close to the spatial resolution of even the most advanced telescopes. Here, we
aim to infer the size and lifetime of EBs using high-resolution data of an
emerging active region collected using the Interferometric BIdimensional
Spectrometer (IBIS) and Rapid Oscillations of the Solar Atmosphere (ROSA)
instruments as well as the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO). We develop an algorithm to track EBs through
their evolution, finding that EBs can often be much smaller (around 0.3") and
shorter lived (less than 1 minute) than previous estimates. A correlation
between G-band magnetic bright points and EBs is also found. Combining SDO/HMI
and G-band data gives a good proxy of the polarity for the vertical magnetic
field. It is found that EBs often occur both over regions of opposite polarity
flux and strong unipolar fields, possibly hinting at magnetic reconnection as a
driver of these events.The energetics of EB events is found to follow a
power-law distribution in the range of "nano-flare" (10^{22-25} ergs).Comment: 19 pages. 7 Figure
Concise theory of chiral lipid membranes
A theory of chiral lipid membranes is proposed on the basis of a concise free
energy density which includes the contributions of the bending and the surface
tension of membranes, as well as the chirality and orientational variation of
tilting molecules. This theory is consistent with the previous experiments
[J.M. Schnur \textit{et al.}, Science \textbf{264}, 945 (1994); M.S. Spector
\textit{et al.}, Langmuir \textbf{14}, 3493 (1998); Y. Zhao, \textit{et al.},
Proc. Natl. Acad. Sci. USA \textbf{102}, 7438 (2005)] on self-assembled chiral
lipid membranes of DCPC. A torus with the ratio between its two
generated radii larger than is predicted from the Euler-Lagrange
equations. It is found that tubules with helically modulated tilting state are
not admitted by the Euler-Lagrange equations, and that they are less
energetically favorable than helical ripples in tubules. The pitch angles of
helical ripples are theoretically estimated to be about 0 and
35, which are close to the most frequent values 5 and
28 observed in the experiment [N. Mahajan \textit{et al.}, Langmuir
\textbf{22}, 1973 (2006)]. Additionally, the present theory can explain twisted
ribbons of achiral cationic amphiphiles interacting with chiral tartrate
counterions. The ratio between the width and pitch of twisted ribbons is
predicted to be proportional to the relative concentration difference of left-
and right-handed enantiomers in the low relative concentration difference
region, which is in good agreement with the experiment [R. Oda \textit{et al.},
Nature (London) \textbf{399}, 566 (1999)].Comment: 14 pages, 7 figure
Density-functional theory of freezing of vortex-liquid in quasi two-dimensional superconductors
We present a theory of vortex liquid-to-solid transition in homogeneous quasi
2D superconductors. The free energy is written as a functional l of density of
zeroes of the fluctuating order parameter. The transition is weakly first-order
and well below the Hc2(T) line. Transition temperature, discontinuities of the
average Abrikosov ratio and of the average superfluid density, the Debay-Waller
factor and the latent heat are in good agreement with Monte Carlo simulations.
The density is only weakly modulated in the "vortex-solid" phase, consistent
with the density-wave behavior.Comment: 12 pages and 1 figure available upon request, LaTex Version 2.09,
submitted to Phys. Rev. Let
Transition amplitudes and sewing properties for bosons on the Riemann sphere
We consider scalar quantum fields on the sphere, both massive and massless.
In the massive case we show that the correlation functions define amplitudes
which are trace class operators between tensor products of a fixed Hilbert
space. We also establish certain sewing properties between these operators. In
the massless case we consider exponential fields and have a conformal field
theory. In this case the amplitudes are only bilinear forms but still we
establish sewing properties. Our results are obtained in a functional integral
framework.Comment: 33 page
ACCRETION OUTBURSTS IN SELF-GRAVITATING PROTOPLANETARY DISKS
We improve on our previous treatments of long-term evolution of protostellar
disks by explicitly solving disk self-gravity in two dimensions. The current
model is an extension of the one-dimensional layered accretion disk model of
Bae et al. We find that gravitational instability (GI)-induced spiral density
waves heat disks via compressional heating (i.e. work), and can
trigger accretion outbursts by activating the magnetorotational instability
(MRI) in the magnetically inert disk dead-zone. The GI-induced spiral waves
propagate well inside of gravitationally unstable region before they trigger
outbursts at AU where GI cannot be sustained. This long-range
propagation of waves cannot be reproduced with the previously used local
treatments for GI. In our standard model where zero dead-zone residual
viscosity () is assumed, the GI-induced stress measured at the
onset of outbursts is locally as large as in terms of the generic
parameter. However, as suggested in our previous one-dimensional
calculations, we confirm that the presence of a small but finite triggers thermally-driven bursts of accretion instead of the GI +
MRI-driven outbursts that are observed when . The inclusion
of non-zero residual viscosity in the dead-zone decreases the importance of GI
soon after mass feeding from the envelope cloud ceases. During the infall phase
while the central protostar is still embedded, our models stay in a quiescent
accretion phase with
over of the time and spend less than of the infall phase in
accretion outbursts.Comment: 16 pages, 17 figures, 1 table, Accepted for publication in Ap
Glassy behavior induced by geometrical frustration in a hard-core lattice gas model
We introduce a hard-core lattice-gas model on generalized Bethe lattices and
investigate analytically and numerically its compaction behavior. If
compactified slowly, the system undergoes a first-order crystallization
transition. If compactified much faster, the system stays in a meta-stable
liquid state and undergoes a glass transition under further compaction. We show
that this behavior is induced by geometrical frustration which appears due to
the existence of short loops in the generalized Bethe lattices. We also compare
our results to numerical simulations of a three-dimensional analog of the
model.Comment: 7 pages, 4 figures, revised versio
Theory of Double-Sided Flux Decorations
A novel two-sided Bitter decoration technique was recently employed by Yao et
al. to study the structure of the magnetic vortex array in high-temperature
superconductors. Here we discuss the analysis of such experiments. We show that
two-sided decorations can be used to infer {\it quantitative} information about
the bulk properties of flux arrays, and discuss how a least squares analysis of
the local density differences can be used to bring the two sides into registry.
Information about the tilt, compressional and shear moduli of bulk vortex
configurations can be extracted from these measurements.Comment: 17 pages, 3 figures not included (to request send email to
[email protected]
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