4,640 research outputs found
Modelling the measured local time evolution of strongly nonlinear heat pulses in the Large Helical Device
In some magnetically confined plasmas, an applied pulse of rapid edge cooling can trigger either a positive or negative excursion in the core electron temperature from its steady state value. We present a new model which captures the time evolution of the transient, non-diffusive local dynamics in the core plasma. We show quantitative agreement between this model and recent spatially localized measurements (Inagaki et al 2010 Plasma Phys. Control. Fusion 52 075002) of the local time-evolving temperature pulse in cold pulse propagation experiments in the Large Helical Device
High density quark matter in the NJL model with dimensional vs. cut-off regularization
We investigate color superconducting phase at high density in the extended
Nambu--Jona-Lasinio model for the two flavor quarks. Because of the
non-renormalizability of the model, physical observables may depend on the
regularization procedure, that is why we apply two types of regularization, the
cut-off and the dimensional one to evaluate the phase structure, the equation
of state and the relationship between the mass and the radius of a dense star.
To obtain the phase structure we evaluate the minimum of the effective
potential at finite temperature and chemical potential. The stress tensor is
calculated to derive the equation of state. Solving the
Tolman-Oppenheimer-Volkoff equation, we show the relationship between the mass
and the radius of a dense star. The dependence on the regularization is found
not to be small for these phenomena in the color superconducting phase.Comment: 10 pages, 11 figures; a few points corrected and references adde
Phase Structure of a Four- and Eight-Fermion Interaction Model at Finite Temperature and Chemical Potential in Arbitrary Dimensions
The phase structure of a four- and eight-fermion interaction model is
investigated at finite temperature and chemical potential in arbitrary
space-time dimensions, . The effective potential and the gap
equation are calculated in the leading order of the 1/N expansion. If the first
order phase transition takes place, the phase boundary dividing the symmetric
and the broken phase is modified by the eight-fermion interaction.Comment: 20 pages, 26 figures; revised argument and added reference for
section
Schwinger-Dyson Analysis of Dynamical Symmetry Breaking on a Brane with Bulk Yang-Mills Theory
The dynamically generated fermion mass is investigated in the flat brane
world with (4+delta)-dimensional bulk space-time, and in the Randall-Sundrum
(RS) brane world. We consider the bulk Yang-Mills theory interacting with the
fermion confined on a four-dimensional brane. Based on the effective theory
below the reduced cutoff scale on the brane, we formulate the Schwinger-Dyson
equation of the brane fermion propagator. By using the improved ladder
approximation we numerically solve the Schwinger-Dyson equation and find that
the dynamical fermion mass is near the reduced cutoff scale on the brane for
the flat brane world with delta >= 3 and for the RS brane world. In RS brane
world KK excited modes of the bulk gauge field localized around the y = pi R
brane and it enhances the dynamical symmetry breaking on the brane. The decay
constant of the fermion and the anti-fermion composite operator can be taken to
be the order of the electroweak scale much smaller than the Planck scale.
Therefore electroweak mass scale can be realized from only the Planck scale in
the RS brane world due to the fermion and the anti-fermion pair condensation.
That is a dynamical realization of Randall-Sundrum model which solves the
weak-Planck hierarchy problem.Comment: 21 pages, 12 figures; typos corrected, references added and updated,
footnotes adde
Space-time evolution induced by spinor fields with canonical and non-canonical kinetic terms
We study spinor field theories as an origin to induce space-time evolution.
Self-interacting spinor fields with canonical and non-canonical kinetic terms
are considered in a Friedman-Robertson-Walker universe. The deceleration
parameter is calculated by solving the equation of motion and the Friedman
equation, simultaneously. It is shown that the spinor fields can accelerate and
decelerate the universe expansion. To construct realistic models we discuss the
contributions from the dynamical symmetry breaking.Comment: 16 pages, 19 figure
Synchronously-pumped OPO coherent Ising machine: benchmarking and prospects
The coherent Ising machine (CIM) is a network of optical parametric oscillators (OPOs) that solves for the ground state of Ising problems through OPO bifurcation dynamics. Here, we present experimental results comparing the performance of the CIM to quantum annealers (QAs) on two classes of NP-hard optimization problems: ground state calculation of the Sherrington-Kirkpatrick (SK) model and MAX-CUT. While the two machines perform comparably on sparsely-connected problems such as cubic MAX-CUT, on problems with dense connectivity, the QA shows an exponential performance penalty relative to CIMs. We attribute this to the embedding overhead required to map dense problems onto the sparse hardware architecture of the QA, a problem that can be overcome in photonic architectures such as the CIM
Leading Log Solution for Inflationary Yukawa
We generalize Starobinskii's stochastic technique to the theory of a
massless, minimally coupled scalar interacting with a massless fermion in a
locally de Sitter geometry. The scalar is an ``active'' field that can engender
infrared logarithms. The fermion is a ``passive'' field that cannot cause
infrared logarithms but which can carry them, and which can also induce new
interactions between the active fields. The procedure for dealing with passive
fields is to integrate them out, then stochastically simplify the resulting
effective action following Starobinski\u{\i}. Because Yukawa theory is
quadratic in the fermion this can be done explicitly using the classic solution
of Candelas and Raine. We check the resulting stochastic formulation against an
explicit two loop computation. We also derive a nonperturbative, leading log
result for the stress tensor. Because the scalar effective potential induced by
fermions is unbounded below, back-reaction from this model might dynamically
cancel an arbitrarily large cosmological constant.Comment: 35 pages, LaTeX 2epsilon, 4 figures (using axodraw), version 2 has an
updated reference lis
Dynamical Symmetry Breaking in Spaces with Constant Negative Curvature
By using the Nambu-Jona-Lasinio model, we study dynamical symmetry breaking
in spaces with constant negative curvature. We show that the physical reason
for zero value of critical coupling value in these spaces is
connected with the effective reduction of dimension of spacetime in the infrared region, which takes place for any dimension . Since
the Laplace-Beltrami operator has a gap in spaces with constant negative
curvature, such an effective reduction for scalar fields is absent and there
are not problems with radiative corrections due to scalar fields. Therefore,
dynamical symmetry breaking with the effective reduction of the dimension of
spacetime for fermions in the infrared region is consistent with the
Mermin-Wagner-Coleman theorem, which forbids spontaneous symmetry breaking in
(1 + 1)-dimensional spacetime.Comment: minor text changes, added new reference
Galaxy Cluster Shapes and Systematic Errors in H0 Measured by the Sunyaev-Zel'dovich Effect
Imaging of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters combined
with cluster plasma x-ray diagnostics can measure the cosmic distance scale to
high redshift. Projecting the inverse-Compton scattering and x-ray emission
along the cluster line-of-sight introduces systematic errors in the Hubble
constant, H0, because the true shape of the cluster is not known. I present a
study of the systematic errors in the value of H0, as determined by the x-ray
and SZ properties of theoretical samples of triaxial isothermal ``beta'' model
clusters, caused by projection effects and observer orientation. I calculate
estimates for H0 for each cluster based on their large and small apparent
angular core radii and their arithmetic mean. I demonstrate that the estimates
for H0 for a sample of 25 clusters have 99.7% confidence intervals for the mean
estimated H0 analyzing the clusters using either their large or mean angular
core radius are within 14% of the ``true'' (assumed) value of H0 (and enclose
it), for a triaxial beta model cluster sample possessing a distribution of
apparent x-ray cluster ellipticities consistent with that of observed x-ray
clusters. This limit on the systematic error in H0 caused by cluster shape
assumes that each sample beta model cluster has fixed shape; deviations from
constant shape within the clusters may introduce additional uncertainty or bias
into this result.Comment: Accepted for publication in the Astrophysical Journal, 24 March 1998;
4 pages, 2 figure
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