1,571 research outputs found
Covariant Matrix Model of Superparticle in the Pure Spinor Formalism
On the basis of the Berkovits pure spinor formalism of covariant quantization
of supermembrane, we attempt to construct a M(atrix) theory which is covariant
under Lorentz group. We first construct a bosonic M(atrix) theory by
starting with the first-order formalism of bosonic membrane, which precisely
gives us a bosonic sector of M(atrix) theory by BFSS. Next we generalize this
method to the construction of M(atrix) theory of supermembranes. However, it
seems to be difficult to obtain a covariant and supersymmetric M(atrix) theory
from the Berkovits pure spinor formalism of supermembrane because of the matrix
character of the BRST symmetry. Instead, in this paper, we construct a
supersymmetric and covariant matrix model of 11D superparticle, which
corresponds to a particle limit of covariant M(atrix) theory. By an explicit
calculation, we show that the one-loop effective potential is trivial, thereby
implying that this matrix model is a free theory at least at the one-loop
level.Comment: 13 pages, no figures, two references adde
Outflows driven by Giant Protoplanets
We investigate outflows driven by a giant protoplanet using three-dimensional
MHD nested grid simulations. We consider a local region around the protoplanet
in the protoplanetary disk, and calculate three models: (a) unmagnetized disk
model, (b) magnetized disk model having magnetic field azimuthally parallel to
the disk, and (c) magnetic field perpendicular to the disk. Outflows with
velocities, at least, 10 km/s are driven by the protoplanets in both magnetized
disk models, while outflow does not appear in unmagnetized disk model.
Tube-like outflows along the azimuthal direction of the protoplanetary disk
appear in model with magnetic field being parallel to the disk. In this model,
the magnetically dominated regions (i.e., density gap) are clearly contrasted
from other regions and spiral waves appear near the protoplanet. On the other
hand, in model with magnetic field being perpendicular to the disk, outflows
are driven by a protoplanet with cone-like structure just as seen in the
outflow driven by a protostar. Magnetic field lines are strongly twisted near
the protoplanet and the outflows have well-collimated structures in this
model.These outflows can be landmarks for searching exo-protoplanets in their
formation stages. Our results indicate that the accretion rate onto the
protoplanet tend to have a larger value than that expected from previous
hydrodynamical calculations, since a fraction of the angular momentum of
circum-planetary disk is removed by outflows, enhanced non-axisymmetric
patterns caused by magnetic field, and magnetic braking. Possible implications
for observation are also briefly discussed.Comment: 11 pages, 3 figures, Submitted to ApJL, For high resolution figures
see http://www2.scphys.kyoto-u.ac.jp/~machidam/jupiter/doc/resubmit_0703.pd
Dynamical properties of S=1 bond-alternating Heisenberg chains in transverse magnetic fields
We calculate dynamical structure factors of the S=1 bond-alternating
Heisenberg chain with a single-ion anisotropy in transverse magnetic fields,
using a continued fraction method based on the Lanczos algorithm. In the
Haldane-gap phase and the dimer phase, dynamical structure factors show
characteristic field dependence. Possible interpretations are discussed. The
numerical results are in qualitative agreement with recent results for
inelastic neutron-scattering experiments on the S=1 bond-alternating
Heisenberg-chain compound and the
S=1 Haldane-gap compound in
transverse magnetic fields.Comment: 7 pages, 6 figure
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