66,887 research outputs found
Rigorous theory of nuclear fusion rates in a plasma
Real-time thermal field theory is used to reveal the structure of plasma
corrections to nuclear reactions. Previous results are recovered in a fashion
that clarifies their nature, and new extensions are made. Brown and Yaffe have
introduced the methods of effective quantum field theory into plasma physics.
They are used here to treat the interesting limiting case of dilute but very
highly charged particles reacting in a dilute, one-component plasma. The highly
charged particles are very strongly coupled to this background plasma. The
effective field theory proves that this mean field solution plus the one-loop
term dominate; higher loop corrections are negligible even though the problem
involves strong coupling. Such analytic results for very strong coupling are
rarely available, and they can serve as benchmarks for testing computer models.Comment: 4 pages and 2 figures, presented at SCCS 2005, June 20-25, Moscow,
Russi
Putting an Edge to the Poisson Bracket
We consider a general formalism for treating a Hamiltonian (canonical) field
theory with a spatial boundary. In this formalism essentially all functionals
are differentiable from the very beginning and hence no improvement terms are
needed. We introduce a new Poisson bracket which differs from the usual
``bulk'' Poisson bracket with a boundary term and show that the Jacobi identity
is satisfied. The result is geometrized on an abstract world volume manifold.
The method is suitable for studying systems with a spatial edge like the ones
often considered in Chern-Simons theory and General Relativity. Finally, we
discuss how the boundary terms may be related to the time ordering when
quantizing.Comment: 36 pages, LaTeX. v2: A manifest formulation of the Poisson bracket
and some examples are added, corrected a claim in Appendix C, added an
Appendix F and a reference. v3: Some comments and references adde
Low-loss flake-graphene saturable absorber mirror for laser mode-locking at sub-200-fs pulse duration
Saturable absorbers are a key component for mode-locking femtosecond lasers.
Polymer films containing graphene flakes have recently been used in
transmission as laser mode-lockers, but suffer from high nonsaturable loss,
limiting their application in low-gain lasers. Here we present a saturable
absorber mirror based on a film of pure graphene flakes. The device is used to
mode lock an erbium-doped fiber laser, generating pulses with state-of-the-art,
sub-200-fs duration. The laser characteristic indicate that the film exhibits
low nonsaturable loss (13% per pass) and large absorption modulation depth (45%
of low-power absorption)
Boundary States and Black Hole Entropy
Black hole entropy is derived from a sum over boundary states. The boundary
states are labeled by energy and momentum surface densities, and parametrized
by the boundary metric. The sum over state labels is expressed as a functional
integral with measure determined by the density of states. The sum over metrics
is expressed as a functional integral with measure determined by the universal
expression for the inverse temperature gradient at the horizon. The analysis
applies to any stationary, nonextreme black hole in any theory of gravitational
and matter fields.Comment: 4 pages, Revte
Gravitational Constraint Combinations Generate a Lie Algebra
We find a first--order partial differential equation whose solutions are all
ultralocal scalar combinations of gravitational constraints with Abelian
Poisson brackets between themselves. This is a generalisation of the Kucha\v{r}
idea of finding alternative constraints for canonical gravity. The new scalars
may be used in place of the hamiltonian constraint of general relativity and,
together with the usual momentum constraints, replace the Dirac algebra for
pure gravity with a true Lie algebra: the semidirect product of the Abelian
algebra of the new constraint combinations with the algebra of spatial
diffeomorphisms.Comment: 10 pages, latex, submitted to Classical and Quantum Gravity. Section
3 is expanded and an additional solution provided, minor errors correcte
Entropy of Constant Curvature Black Holes in General Relativity
We consider the thermodynamic properties of the constant curvature black hole
solution recently found by Banados. We show that it is possible to compute the
entropy and the quasilocal thermodynamics of the spacetime using the
Einstein-Hilbert action of General Relativity. The constant curvature black
hole has some unusual properties which have not been seen in other black hole
spacetimes. The entropy of the black hole is not associated with the event
horizon; rather it is associated with the region between the event horizon and
the observer. Further, surfaces of constant internal energy are not isotherms
so the first law of thermodynamics exists only in an integral form. These
properties arise from the unusual topology of the Euclidean black hole
instanton.Comment: 4 pages LaTeX2e (RevTeX), 2 PostScript figures. Small corrections in
the text and the reference
Free Boundary Poisson Bracket Algebra in Ashtekar's Formalism
We consider the algebra of spatial diffeomorphisms and gauge transformations
in the canonical formalism of General Relativity in the Ashtekar and ADM
variables. Modifying the Poisson bracket by including surface terms in
accordance with our previous proposal allows us to consider all local
functionals as differentiable. We show that closure of the algebra under
consideration can be achieved by choosing surface terms in the expressions for
the generators prior to imposing any boundary conditions. An essential point is
that the Poisson structure in the Ashtekar formalism differs from the canonical
one by boundary terms.Comment: 19 pages, Latex, amsfonts.sty, amssymb.st
Relativistic Magnetic Monopole Flux Constraints from RICE
We report an upper limit on the flux of relativistic monopoles based on the
non-observation of in-ice showers by the Radio Ice Cherenkov Experiment (RICE)
at the South Pole. We obtain a 95% C.L. limit of order 10^{-18}/(cm^2-s-sr) for
intermediate mass monopoles of 10^7<gamma<10^{12} at the anticipated energy
E=10^{16} GeV. This bound is over an order of magnitude stronger than all
previously published experimental limits for this range of boost parameters
gamma, and exceeds two orders of magnitude improvement over most of the range.
We review the physics of radio detection, describe a Monte Carlo simulation
including continuous and stochastic energy losses, and compare to previous
experimental limits.Comment: 16 pages, 6 figures. Accepted for publication in Phys. Rev. D. Minor
revisions, including expanded discussion of monopole energy uncertaint
Phonon anomaly at the charge ordering transition in 1T-TaS2
The infrared reflectance of the transition metal chalcogenide 1T-TaS2 has
been measured at temperatures from 30K to 360K over 30-45,000cm^-1
(4meV-5.5eV). The optical conductivity was obtained by Kramers-Kronig analysis.
At 360K only modest traces of the phonon lines are noticeable. The phonon modes
are followed by a pseudogap-like increase of the optical conductivity, with
direct optical transitions observed at frequencies above 1eV. As the
temperature decreases, the low frequency conductivity also decreases, phonon
modes become more pronounced and pseudogap develops into a gap at 800cm^-1
(100meV). We observe an anomalous frequency dependence of the 208cm^-1
infrared-active phonon mode. This mode demonstrates softening as the
temperature decreases below the 180K metal-to-insulator transition. The same
mode demonstrates strong hysteresis of the frequency and linewidth changes,
similar in its temperature behavior to the hysteresis in the dc-resistivity. We
discuss a possible relation of the observed softening of the mode to the
structural changes associated with the metal-to-insulator transition.Comment: 7 pages, 4 figures, 1 table; corrected typo
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