3,951 research outputs found
Sensitivity of Coronal Loop Sausage Mode Frequencies and Decay Rates to Radial and Longitudinal Density Inhomogeneities: A Spectral Approach
Fast sausage modes in solar magnetic coronal loops are only fully contained
in unrealistically short dense loops. Otherwise they are leaky, losing energy
to their surrounds as outgoing waves. This causes any oscillation to decay
exponentially in time. Simultaneous observations of both period and decay rate
therefore reveal the eigenfrequency of the observed mode, and potentially
insight into the tubes' nonuniform internal structure. In this article, a
global spectral description of the oscillations is presented that results in an
implicit matrix eigenvalue equation where the eigenvalues are associated
predominantly with the diagonal terms of the matrix. The off-diagonal terms
vanish identically if the tube is uniform. A linearized perturbation approach,
applied with respect to a uniform reference model, is developed that makes the
eigenvalues explicit. The implicit eigenvalue problem is easily solved
numerically though, and it is shown that knowledge of the real and imaginary
parts of the eigenfrequency is sufficient to determine the width and density
contrast of a boundary layer over which the tubes' enhanced internal densities
drop to ambient values. Linearized density kernels are developed that show
sensitivity only to the extreme outside of the loops for radial fundamental
modes, especially for small density enhancements, with no sensitivity to the
core. Higher radial harmonics do show some internal sensitivity, but these will
be more difficult to observe. Only kink modes are sensitive to the tube
centres. {Variation in internal and external Alfv\'en speed along the loop is
shown to have little effect on the fundamental dimensionless eigenfrequency,
though the associated eigenfunction becomes more compact at the loop apex as
stratification increases, or may even displace from the apex.Comment: Accepted J. Phys. A: Math. Theor. (Oct 31 2017). 20 pages, 12 figure
Holographic thermalization with a chemical potential in Gauss-Bonnet gravity
Holographic thermalization is studied in the framework of
Einstein-Maxwell-Gauss-Bonnet gravity. We use the two-point correlation
function and expectation value of Wilson loop, which are dual to the
renormalized geodesic length and minimal area surface in the bulk, to probe the
thermalization. The numeric result shows that larger the Gauss-Bonnet
coefficient is, shorter the thermalization time is, and larger the charge is,
longer the thermalization time is, which implies that the Gauss-Bonnet
coefficient can accelerate the thermalization while the charge has an opposite
effect. In addition, we obtain the functions with respect to the thermalization
time for both the thermalization probes at a fixed charge and Gauss-Bonnet
coefficient, and on the basis of these functions, we obtain the thermalization
velocity, which shows that the thermalization process is non-monotonic. At the
middle and later periods of the thermalization process, we find that there is a
phase transition point, which divides the thermalization into an acceleration
phase and a deceleration phase. We also study the effect of the charge and
Gauss-Bonnet coefficient on the phase transition point.Comment: 23 pages, many figures,footnote 4 is modified. arXiv admin note:
substantial text overlap with arXiv:1305.484
Symmetry Reduction and Boundary Modes for Fe-Chains on an s-wave Superconductor
We investigate the superconducting phase diagram and boundary modes for a
quasi-1D system formed by three Fe-Chains on an s-wave superconductor,
motivated by the recent Princeton experiment. The onsite
spin-orbit term, inter-chain diagonal hopping couplings, and magnetic disorders
in the Fe-chains are shown to be crucial for the superconducting phases, which
can be topologically trivial or nontrivial in different parameter regimes. For
the topological regime a single Majorana and multiple Andreew bound modes are
obtained in the ends of the chain, while for the trivial phase only low-energy
Andreev bound states survive. Nontrivial symmetry reduction mechanism induced
by the term, diagonal hopping couplings, and magnetic
disorder is uncovered to interpret the present results. Our study also implies
that the zero-bias peak observed in the recent experiment may or may not
reflect the Majorana zero modes in the end of the Fe-chains.Comment: 5 pages, 4 figures; some minor errors are correcte
Holographic thermalization in noncommutative geometry
Gravitational collapse of a shell of dust in noncommutative geometry is
probed by the renormalized geodesic length, which is dual to probe the
thermalization by the two-point correlation function in the dual conformal
field theory. We find that larger the noncommutative parameter is, longer the
thermalization time is, which implies that the large noncommutative parameter
delays the thermalization process. We also investigate how the noncommutative
parameter affects the thermalization velocity and thermalization acceleration.Comment: some materials have been delete
Van der Waals-like phase transition from holographic entanglement entropy in Lorentz breaking massive gravity
In this paper, phase transition of AdS black holes in lorentz breaking
massive gravity has been studied in the framework of holography. We find that
there is a first order phase transition(FPT) and second order phase
transition(SPT) both in Bekenstein-Hawking entropy(BHE)-temperature plane and
holographic entanglement entropy(HEE)-temperature plane. Furthermore, for the
FPT, the equal area law is checked and for the SPT, the critical exponent of
the heat capacity is also computed. Our results confirm that the phase
structure of HEE is similar to that of BHE in lorentz breaking massive gravity,
which implies that HEE and BHE have some potential underlying relationship.Comment: 10 pages, 10 figure
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