3,436 research outputs found
Comments on AdS2 solutions of D=11 Supergravity
We study the supersymmetric solutions of 11-dimensional supergravity with a
factor of made of M2-branes. Such solutions can provide gravity duals
of superconformal quantum mechanics, or through double Wick rotation, the
generic bubbling geometry of M-theory which are 1/16-BPS. We show that, when
the internal manifold is compact, it should take the form of a warped
U(1)-fibration over an 8-dimensional Kahler space.Comment: 11 pages, no figure, JHEP3.cl
Superalgebra for M-theory on a pp-wave
We study the superalgebra of the M-theory on a fully supersymmetric pp-wave.
We identify the algebra as the special unitary Lie superalgebra, su(2|4;2,0) or
su(2|4;2,4), and analyze its root structure. We discuss the typical and
atypical representations deriving the typicality condition explicitly in terms
of the energy and other four quantum numbers. We classify the BPS multiplets
preserving 4,8,12,16 real supercharges and obtain the corresponding spectrum.
We show that in the BPS multiplet either the lowest energy floor is an su(2)
singlet or the highest energy floor is an su(4) singlet.Comment: 22 pages, 1 figure; Section on examples revised, Refs added; Typ
Gravin orchestrates protein kinase A and 2-adrenergic receptor signaling critical for synaptic plasticity and memory
A kinase-anchoring proteins (AKAPs) organize compartmentalized pools of protein kinase A (PKA) to enable localized signaling events within neurons. However, it is unclear which of the many expressed AKAPs in neurons target PKA to signaling complexes important for long-lasting forms of synaptic plasticity and memory storage. In the forebrain, the anchoring protein gravin recruits a signaling complex containing PKA, PKC, calmodulin, and PDE4D (phosphodiesterase 4D) to the β2-adrenergic receptor. Here, we show that mice lacking the α-isoform of gravin have deficits in PKA-dependent long-lasting forms of hippocampal synaptic plasticity including β2-adrenergic receptor-mediated plasticity, and selective impairments of long-term memory storage. Furthermore, both hippocampal β2-adrenergic receptor phosphorylation by PKA, and learning-induced activation of ERK in the CA1 region of the hippocampus are attenuated in mice lacking gravin-α. We conclude that gravin compartmentalizes a significant pool of PKA that regulates learning-induced β2-adrenergic receptor signaling and ERK activation in the hippocampus in vivo, thereby organizing molecular interactions between glutamatergic and noradrenergic signaling pathways for long-lasting synaptic plasticity, and memory storage
Two-Dimensional Diffusion in the Presence of Topological Disorder
How topological defects affect the dynamics of particles hopping between
lattice sites of a distorted, two-dimensional crystal is addressed.
Perturbation theory and numerical simulations show that weak, short-ranged
topological disorder leads to a finite reduction of the diffusion coefficient.
Renormalization group theory and numerical simulations suggest that
longer-ranged disorder, such as that from randomly placed dislocations or
random disclinations with no net disclinicity, leads to subdiffusion at long
times.Comment: 10 pages, 6 figure
Fuzzy BIon
We construct a solution of the BFSS matrix theory, which is a counterpart of
the BIon solution representing a fundamental string ending on a bound state of
a D2-brane and D0-branes. We call this solution the `fuzzy BIon' and show that
this configuration preserves 1/4 supersymmetry of type IIA superstring theory.
We also construct an effective action for the fuzzy BIon by analyzing the
nonabelian Born-Infeld action for D0-branes. When we take the continuous limit,
with some conditions, this action coincides with the effective action for the
BIon configuration.Comment: 11 pages, 1 figure, reference and note adde
Measurements of the Composite Fermion masses from the spin polarization of 2-D electrons in the region
Measurements of the reflectivity of a 2-D electron gas are used to deduce the
polarization of the Composite Fermion hole system formed for Landau level
occupancies in the regime 1<\nu<2. The measurements are consistent with the
formation of a mixed spin CF system and allow the density of states or
`polarization' effective mass of the CF holes to be determined. The mass values
at \nu=3/2 are found to be ~1.9m_{e} for electron densities of 4.4 x 10^{11}
cm^{-2}, which is significantly larger than those found from measurements of
the energy gaps at finite values of effective magnetic field.Comment: 4 pages, 3 fig
Toric AdS4/CFT3 duals and M-theory Crystals
We study the recently proposed crystal model for three dimensional
superconformal field theories arising from M2-branes probing toric Calabi-Yau
four-fold singularities. We explain the algorithms mapping a toric Calabi-Yau
to a crystal and vice versa, and show how the spectrum of BPS meson states fits
into the crystal model.Comment: 24 pages, 24 figure
On the deflection of asteroids with mirrors
This paper presents an analysis of an asteroid deflection method based on multiple solar concentrators. A model of the deflection through the sublimation of the surface material of an asteroid is presented, with simulation results showing the achievable orbital deflection with, and without, accounting for the effects of mirror contamination due to the ejected debris plume. A second model with simulation results is presented analyzing an enhancement of the Yarkovsky effect, which provides a significant deflection even when the surface temperature is not high enough to sublimate. Finally the dynamical model of solar concentrators in the proximity of an irregular celestial body are discussed, together with a Lyapunov-based controller to maintain the spacecraft concentrators at a required distance from the asteroid
Three-algebra for supermembrane and two-algebra for superstring
While string or Yang-Mills theories are based on Lie algebra or two-algebra
structure, recent studies indicate that M-theory may require a one higher,
three-algebra structure. Here we construct a covariant action for a
supermembrane in eleven dimensions, which is invariant under global
supersymmetry, local fermionic symmetry and worldvolume diffeomorphism. Our
action is classically on-shell equivalent to the celebrated
Bergshoeff-Sezgin-Townsend action. However, the novelty is that we spell the
action genuinely in terms of Nambu three-brackets: All the derivatives appear
through Nambu brackets and hence it manifests the three-algebra structure.
Further the double dimensional reduction of our action gives straightforwardly
to a type IIA string action featuring two-algebra. Applying the same method, we
also construct a covariant action for type IIB superstring, leading directly to
the IKKT matrix model.Comment: 1+15 pages, no figure; Refs added, Accepted for publication in JHE
Is manganese-doped diamond a ferromagnetic semiconductor?
We use density-functional theoretical methods to examine the recent
prediction, based on a mean-field solution of the Zener model, that diamond
doped by Mn (with spin S=5/2) would be a dilute magnetic semiconductor that
remains ferromagnetic well above room temperature. Our findings suggest this to
be unlikely, for four reasons: (1) substitutional Mn in diamond has a low-spin
S=1/2 ground state; (2) the substitutional site is energetically unfavorable
relative to the much larger "divacancy" site; 3) Mn in the divacancy site is an
acceptor, but with only hyperdeep levels, and hence the holes are likely to
remain localized; (4) the calculated Heisenberg couplings between Mn in nearby
divacancy sites are two orders of magnitude smaller than for substitutional Mn
in germanium.Comment: 5 pages, 5 figure
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