3,867 research outputs found
Quantum corrections from a path integral over reparametrizations
We study the path integral over reparametrizations that has been proposed as
an ansatz for the Wilson loops in the large- QCD and reproduces the area law
in the classical limit of large loops. We show that a semiclassical expansion
for a rectangular loop captures the L\"uscher term associated with
dimensions and propose a modification of the ansatz which reproduces the
L\"uscher term in other dimensions, which is observed in lattice QCD. We repeat
the calculation for an outstretched ellipse advocating the emergence of an
analog of the L\"uscher term and verify this result by a direct computation of
the determinant of the Laplace operator and the conformal anomaly
Nucleation of quark matter bubbles in neutron stars
The thermal nucleation of quark matter bubbles inside neutron stars is
examined for various temperatures which the star may realistically encounter
during its lifetime. It is found that for a bag constant less than a critical
value, a very large part of the star will be converted into the quark phase
within a fraction of a second. Depending on the equation of state for neutron
star matter and strange quark matter, all or some of the outer parts of the
star may subsequently be converted by a slower burning or a detonation.Comment: 13 pages, REVTeX, Phys.Rev.D (in press), IFA 93-32. 5 figures (not
included) available upon request from [email protected]
On the integrability of Wilson loops in AdS_5 x S^5: Some periodic ansatze
Wilson loops are calculated within the AdS/CFT correspondence by finding a
classical solution to the string equations of motion in AdS_5 x S^5 and
evaluating its action. An important fact is that this sigma-model used to
evaluate the Wilson loops is integrable, a feature that has gained relevance
through the study of spinning strings carrying large quantum numbers and
spin-chains. We apply the same techniques used to solve the equations for
spinning strings to find the minimal surfaces describing a wide class of Wilson
loops. We focus on different cases with periodic boundary conditions on the
AdS_5 and S^5 factors and find a rich array of solutions. We examine the
different phases that appear in the problem and comment on the applicability of
integrability to the general problem.Comment: LaTex, 49 pages, 8 figure
Hadron Correlators and the Structure of the Quark Propagator
The structure of the quark propagator of in a confining background is
not known. We make an Ansatz for it, as hinted by a particular mechanism for
confinement, and analyze its implications in the meson and baryon correlators.
We connect the various terms in the K\"allen-Lehmann representation of the
quark propagator with appropriate combinations of hadron correlators, which may
ultimately be calculated in lattice . Furthermore, using the positivity of
the path integral measure for vector like theories, we reanalyze some mass
inequalities in our formalism. A curiosity of the analysis is that, the exotic
components of the propagator (axial and tensor), produce terms in the hadron
correlators which, if not vanishing in the gauge field integration, lead to
violations of fundamental symmetries. The non observation of these violations
implies restrictions in the space-time structure of the contributing gauge
field configurations. In this way, lattice can help us analyze the
microscopic structure of the mechanisms for confinement.Comment: 12 pp in LaTeX, preprint Univ. of Valencia, FTUV/94-16, IFIC/94-15.
To appear in Z.Phys.
Competition between Diffusion and Fragmentation: An Important Evolutionary Process of Nature
We investigate systems of nature where the common physical processes
diffusion and fragmentation compete. We derive a rate equation for the size
distribution of fragments. The equation leads to a third order differential
equation which we solve exactly in terms of Bessel functions. The stationary
state is a universal Bessel distribution described by one parameter, which fits
perfectly experimental data from two very different system of nature, namely,
the distribution of ice crystal sizes from the Greenland ice sheet and the
length distribution of alpha-helices in proteins.Comment: 4 pages, 3 figures, (minor changes
The non-Abelian dual Meissner effect as color-alignment in SU(2) lattice gauge theory
A new gauge (m-gauge) condition is proposed by means of a generalization of
the Maximal Abelian gauge (MAG). The new gauge admits a space time dependent
embedding of the residual U(1) into the SU(2) gauge group. This embedding is
characterized by a color vector . It turns out that this vector
only depends of gauge invariant parts of the link configurations. Our numerical
results show color ferromagnetic correlations of the field in
space-time. The correlation length scales towards the continuum limit. For
comparison with the MAG, we introduce a class of gauges which smoothly
interpolates between the MAG and the m-gauge. For a wide range of the gauge
parameter, the vacuum decomposes into regions of aligned vectors . The
''neutral particle problem'' of MAG is addressed in the context of the new
gauge class.Comment: 15 pages, 6 figures, LaTeX using eps
Correlator of Fundamental and Anti-symmetric Wilson Loops in AdS/CFT Correspondence
We study the two circular Wilson loop correlator in which one is of
anti-symmetric representation, while the other is of fundamental representation
in 4-dimensional super Yang-Mills theory. This correlator has a
good AdS dual, which is a system of a D5-brane and a fundamental string. We
calculated the on-shell action of the string, and clarified the Gross-Ooguri
transition in this correlator. Some limiting cases are also examined.Comment: 22 pages, 5 figures, v2: typos corrected, v3: final version in JHE
Strongly nonlinear dynamics of electrolytes in large ac voltages
We study the response of a model micro-electrochemical cell to a large ac
voltage of frequency comparable to the inverse cell relaxation time. To bring
out the basic physics, we consider the simplest possible model of a symmetric
binary electrolyte confined between parallel-plate blocking electrodes,
ignoring any transverse instability or fluid flow. We analyze the resulting
one-dimensional problem by matched asymptotic expansions in the limit of thin
double layers and extend previous work into the strongly nonlinear regime,
which is characterized by two novel features - significant salt depletion in
the electrolyte near the electrodes and, at very large voltage, the breakdown
of the quasi-equilibrium structure of the double layers. The former leads to
the prediction of "ac capacitive desalination", since there is a time-averaged
transfer of salt from the bulk to the double layers, via oscillating diffusion
layers. The latter is associated with transient diffusion limitation, which
drives the formation and collapse of space-charge layers, even in the absence
of any net Faradaic current through the cell. We also predict that steric
effects of finite ion sizes (going beyond dilute solution theory) act to
suppress the strongly nonlinear regime in the limit of concentrated
electrolytes, ionic liquids and molten salts. Beyond the model problem, our
reduced equations for thin double layers, based on uniformly valid matched
asymptotic expansions, provide a useful mathematical framework to describe
additional nonlinear responses to large ac voltages, such as Faradaic
reactions, electro-osmotic instabilities, and induced-charge electrokinetic
phenomena.Comment: 30 pages, 17 eps-figures, RevTe
Localization and Capacitance Fluctuations in Disordered Au Nano-junctions
Nano-junctions, containing atomic-scale gold contacts between strongly
disordered leads, exhibit different transport properties at room temperature
and at low temperature. At room temperature, the nano-junctions exhibit
conductance quantization effects. At low temperatures, the contacts exhibit
Coulomb-Blockade. We show that the differences between the room-temperature and
low temperature properties arise from the localization of electronic states in
the leads. The charging energy and capacitance of the nano-junctions exhibit
strong fluctuations with applied magnetic field at low temperature, as
predicted theoretically.Comment: 20 pages 8 figure
Non-invasive detection of animal nerve impulses with an atomic magnetometer operating near quantum limited sensitivity
Magnetic fields generated by human and animal organs, such as the heart,
brain and nervous system carry information useful for biological and medical
purposes. These magnetic fields are most commonly detected using
cryogenically-cooled superconducting magnetometers. Here we present the frst
detection of action potentials from an animal nerve using an optical atomic
magnetometer. Using an optimal design we are able to achieve the sensitivity
dominated by the quantum shot noise of light and quantum projection noise of
atomic spins. Such sensitivity allows us to measure the nerve impulse with a
miniature room-temperature sensor which is a critical advantage for biomedical
applications. Positioning the sensor at a distance of a few millimeters from
the nerve, corresponding to the distance between the skin and nerves in
biological studies, we detect the magnetic field generated by an action
potential of a frog sciatic nerve. From the magnetic field measurements we
determine the activity of the nerve and the temporal shape of the nerve
impulse. This work opens new ways towards implementing optical magnetometers as
practical devices for medical diagnostics.Comment: Main text with figures, and methods and supplementary informatio
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