7,076 research outputs found
Non-Minimal Two-Loop Inflation
We investigate the chaotic inflationary model using the two-loop effective
potential of a self-interacting scalar field theory in curved spacetime. We use
the potential which contains a non-minimal scalar curvature coupling and a
quartic scalar self-interaction. We analyze the Lyapunov stability of de Sitter
solution and show the stability bound. Calculating the inflationary parameters,
we systematically explore the spectral index and the tensor-to-scalar
ratio , with varying the four parameters, the scalar-curvature coupling
, the scalar quartic coupling , the renormalization scale
and the e-folding number . It is found that the two-loop correction on
is much larger than the leading-log correction, which has previously been
studied. We show that the model is consistent with the observation by Planck
with WMAP and a recent joint analysis of BICEP2.Comment: 11pages, 7figure
Electric arc discharge damage to ion thruster grids
Arcs representative of those occurring between the grids of a mercury ion thruster were simulated. Parameters affecting an arc and the resulting damage were studied. The parameters investigated were arc energy, arc duration, and grid geometry. Arc attenuation techniques were also investigated. Potentially serious damage occurred at all energy levels representative of actual thruster operating conditions. Of the grids tested, the lowest open-area configuration sustained the least damage for given conditions. At a fixed energy level a long duration discharge caused greater damage than a short discharge. Attenuation of arc current using various impedances proved to be effective in reducing arc damage. Faults were also deliberately caused using chips of sputtered materials formed during the operation of an actual thruster. These faults were cleared with no serious grid damage resulting using the principles and methods developed in this study
Solving the Bethe-Salpeter equation for bound states of scalar theories in Minkowski space
We apply the perturbation theory integral representation (PTIR) to solve for
the bound state Bethe-Salpeter (BS) vertex for an arbitrary scattering kernel,
without the need for any Wick rotation. The results derived are applicable to
any scalar field theory (without derivative coupling). It is shown that solving
directly for the BS vertex, rather than the BS amplitude, has several major
advantages, notably its relative simplicity and superior numerical accuracy. In
order to illustrate the generality of the approach we obtain numerical
solutions using this formalism for a number of scattering kernels, including
cases where the Wick rotation is not possible.Comment: 28 pages of LaTeX, uses psfig.sty with 5 figures. Also available via
WWW at
http://www.physics.adelaide.edu.au/theory/papers/ADP-97-10.T248-abs.html or
via anonymous ftp at
ftp://bragg.physics.adelaide.edu.au/pub/theory/ADP-97-10.T248.ps A number of
(crucial) typographical errors in Appendix C corrected. To be published in
Phys. Rev. D, October 199
Quantum interference effects in particle transport through square lattices
We study the transport of a quantum particle through square lattices of
various sizes by employing the tight-binding Hamiltonian from quantum
percolation. Input and output semi-infinite chains are attached to the lattice
either by diagonal point to point contacts or by a busbar connection. We find
resonant transmission and reflection occuring whenever the incident particle's
energy is near an eigenvalue of the lattice alone (i.e., the lattice without
the chains attached). We also find the transmission to be strongly dependent on
the way the chains are attached to the lattice.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Relativistically Covariant Symmetry in QED
We construct a relativistically covariant symmetry of QED. Previous local and
nonlocal symmetries are special cases. This generalized symmetry need not be
nilpotent, but nilpotency can be arranged with an auxiliary field and a certain
condition. The Noether charge generating the symmetry transformation is
obtained, and it imposes a constraint on the physical states.Comment: Latex file, 9 page
Loewner driving functions for off-critical percolation clusters
We numerically study the Loewner driving function U_t of a site percolation
cluster boundary on the triangular lattice for p<p_c. It is found that U_t
shows a drifted random walk with a finite crossover time. Within this crossover
time, the averaged driving function shows a scaling behavior -(p_c-p)
t^{(\nu +1)/2\nu} with a superdiffusive fluctuation whereas, beyond the
crossover time, the driving function U_t undergoes a normal diffusion with
Hurst exponent 1/2 but with the drift velocity proportional to (p_c-p)^\nu,
where \nu= 4/3 is the critical exponent for two-dimensional percolation
correlation length. The crossover time diverges as (p_c-p)^{-2\nu} as p\to p_c.Comment: 4 pages, 7 figure
Diffusion and spectral dimension on Eden tree
We calculate the eigenspectrum of random walks on the Eden tree in two and
three dimensions. From this, we calculate the spectral dimension and the
walk dimension and test the scaling relation (
for an Eden tree). Finite-size induced crossovers are observed, whereby the
system crosses over from a short-time regime where this relation is violated
(particularly in two dimensions) to a long-time regime where the behavior
appears to be complicated and dependent on dimension even qualitatively.Comment: 11 pages, Plain TeX with J-Phys.sty style, HLRZ 93/9
Fractal Properties of the Distribution of Earthquake Hypocenters
We investigate a recent suggestion that the spatial distribution of
earthquake hypocenters makes a fractal set with a structure and fractal
dimensionality close to those of the backbone of critical percolation clusters,
by analyzing four different sets of data for the hypocenter distributions and
calculating the dynamical properties of the geometrical distribution such as
the spectral dimension . We find that the value of is consistent
with that of the backbone, thus supporting further the identification of the
hypocenter distribution as having the structure of the percolation backbone.Comment: 11 pages, LaTeX, HLRZ 68/9
Markov chain analysis of random walks on disordered medium
We study the dynamical exponents and for a particle diffusing
in a disordered medium (modeled by a percolation cluster), from the regime of
extreme disorder (i.e., when the percolation cluster is a fractal at )
to the Lorentz gas regime when the cluster has weak disorder at and
the leading behavior is standard diffusion. A new technique of relating the
velocity autocorrelation function and the return to the starting point
probability to the asymptotic spectral properties of the hopping transition
probability matrix of the diffusing particle is used, and the latter is
numerically analyzed using the Arnoldi-Saad algorithm. We also present evidence
for a new scaling relation for the second largest eigenvalue in terms of the
size of the cluster, , which provides a
very efficient and accurate method of extracting the spectral dimension
where .Comment: 34 pages, REVTEX 3.
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