989 research outputs found
Ghostbusters in supergravity
supergravity is known to contain a ghost mode associated with
higher-derivative terms if it contains with greater than two.We
remove the ghost in supergravity by introducing auxiliary gauge field to
absorb the ghost. We dub this method as the ghostbuster
mechanism~\cite{Fujimori:2016udq}. We show that the mechanism removes the ghost
supermultiplet but also terms including with , after integrating
out auxiliary degrees of freedom. For pure supergravity case, there appears an
instability in the resultant scalar potential. We then show that the
instability of the scalar potential can be cured by introducing matter
couplings in such a way that the system has a stable potential.Comment: 24 pages, v2: comments, references, new section added, version
published in JHE
Switching magnetic vortex core by a single nanosecond current pulse
In a ferromagnetic nanodisk, the magnetization tends to swirl around in the
plane of the disk and can point either up or down at the center of this
magnetic vortex. This binary state can be useful for information storage. It is
demonstrated that a single nanosecond current pulse can switch the core
polarity. This method also provides the precise control of the core direction,
which constitutes fundamental technology for realizing a vortex core memory.Comment: 13 pages, 4 figure
Equivalent mechanical and electrical models of vibration control system using piezoelectric elements
Three-Dimensional Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae
We have studied non-axisymmetric standing accretion shock instability, or
SASI, by 3D hydrodynamical simulations. This is an extention of our previous
study on axisymmetric SASI. We have prepared a spherically symmetric and steady
accretion flow through a standing shock wave onto a proto-neutron star, taking
into account a realistic equation of state and neutrino heating and cooling.
This unperturbed model is supposed to represent approximately the typical
post-bounce phase of core-collapse supernovae. We then have added a small
perturbation (~1%) to the radial velocity and computed the ensuing evolutions.
Not only axisymmetric but non-axisymmetric perturbations have been also
imposed. We have applied mode analysis to the non-spherical deformation of the
shock surface, using the spherical harmonics. We have found that (1) the growth
rates of SASI are degenerate with respect to the azimuthal index m of the
spherical harmonics Y_l^m, just as expected for a spherically symmetric
background, (2) nonlinear mode couplings produce only m=0 modes for the
axisymmetric perturbations, whereas m=!0 modes are also generated in the
non-axisymmetric cases according to the selection rule for the quadratic
couplings, (3) the nonlinear saturation level of each mode is lower in general
for 3D than for 2D because a larger number of modes are contributing to
turbulence in 3D, (4) low l modes are dominant in the nonlinear phase, (5) the
equi-partition is nearly established among different m modes in the nonlinear
phase, (6) the spectra with respect to l obey power laws with a slope slightly
steeper for 3D, and (7) although these features are common to the models with
and without a shock revival at the end of simulation, the dominance of low l
modes is more remarkable in the models with a shock revival.Comment: 37 pages, 16 figures, and 1 table, submitted to Ap
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