364 research outputs found
Supersymmetric Intersecting Branes in Time-dependent Backgrounds
We construct a family of supersymmetric solutions in time-dependent
backgrounds in supergravity theories. One class of the solutions are
intersecting brane solutions and another class are brane solutions in pp-wave
backgrounds, and their intersection rules are also given. The relation to
existing literature is also discussed. An example of D1-D5 with linear null
dilaton together with its possible dual theory is briefly discussed.Comment: 12 pages, corrected typo, added reference, to appear in Phys. Rev.
Parent Actions, Dualities and New Weyl-invariant Actions of Bosonic p-branes
By using the systematic approach of parent action method, we derive one
Weyl-noninvariant and two Weyl-invariant actions of bosonic -branes () starting from the Nambu-Goto action, and establish the duality symmetries
in this set of four actions. Moreover, we discover a new bosonic -brane
action (including the string theory) and deduce two corresponding
Weyl-invariant formulations by proposing a new special parent action. We find
that the same duality symmetries as those mentioned above exist in this new set
of actions. The new -brane actions are also briefly analyzed.Comment: 19 pages, 14 figures. The first section is modified slightly, and
references are adde
The effect of potassium on aluminous phase stability in the lower mantle
The aluminous calcium-ferrite type phase (CF) and new aluminous phase (NAL) are thought to hold the excess alumina produced by the decomposition of garnet in MORB compositions in the lower mantle. The respective stabilities of CF and NAL in the nepheline-spinel binary (NaAlSiO4 –MgAl2O4 ) are well established. However with the addition of further components the phase relations at lower mantle conditions remain unclear. Here we investigate a range of compositions around the nepheline apex of the nepheline-kalsilite-spinel compositional join (NaAlSiO4 –KAlSiO4–MgAl2O4 ) at 28–78 GPa and 2000 K. Our experiments indicate that even small amounts of a kalsilite (KAlSiO4 ) component dramatically impact phase relations. We find NAL to be stable up to at least 71 GPa in potassium-bearing compositions. This demonstrates the stabilizing effect of potassium on NAL, because NAL is not observed at pressures above 48 GPa on the nepheline-spinel binary. We also observe a broadening of the CF stability field to incorporate larger amounts of potassium with increasing pressure. For pressures below 50 GPa only minor amounts (<0.011(1) K/(K+Na+Mg) ) of potassium are soluble in CF, whereas at 68 GPa, we find a solubility in CF of at least 0.088(3) K/(K+Na+Mg). This indicates that CF and NAL are suitable hosts of the alkali content of MORB compositions at lower mantle conditions. For sedimentary compositions at lower mantle pressures, we expect K-Hollandite to be stable in addition to CF and NAL for pressures of 28–48 GPa, based on our simplified compositions
Amorphization and decomposition of scandium molybdate at high pressure
The behavior of negative thermal-expansion material scandium molybdate Sc2(MoO4)3 is investigated at high pressure (HP) and high temperature (HT) using x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The compound exhibits unusually high compressibility (bulk modulus ~6 GPa) and undergoes amorphization at 12 GPa. On the other hand, in situ laser heating of amorphous samples inside the diamond-anvil cell is found to result in crystalline diffraction pattern and Raman spectrum different from those of the original compound. Upon release of the pressure subsequent to laser heating, the Raman spectrum and the diffraction pattern remain unchanged. Matching of several of the diffraction lines and Raman peaks in the laser-heated samples with those of MoO3 suggests a solid-state decomposition of the parent compound under HP-HT conditions into MoO3 and other compounds. Other diffraction lines are found to correspond to Sc2Mo2O9, Sc2O3, and the parent compound. Quantitative analysis of the characteristic x-ray emission from different regions of the sample during scanning electron microscopic observations is used for obtaining the compositions of the daughter compounds. The stoichiometries of two main phases are found to be close to those of MoO3 and Sc2Mo2O9. These results support the model that the pressure-induced amorphization occurred in this system because a pressure-induced decomposition was kinetically constrained
Spacetime Superalgebra in AdS_4 \times S^7 via Supermembrane Probe
The spacetime superalgebra via the supermembrane probe in the background of
AdS_4 \times S^7 is discussed to the lowest order in the spinor coordinate
\t. To obtain the correct spacetime superalgebras, all \t^2 order
corrections for supervielbein and super 3-form gauge potential have to be
included. The central extension of the superalgebra OSp(8|4) of the super
isometries for AdS_4 \times S^7 is found.Comment: 8 pages, Latex, minor corrections, final version to appear in Phys.
Rev.
Dynamic Spin Fluctuations in the Frustrated A-site Spinel CuAl2O4
We performed nuclear magnetic resonance (NMR) and muon spin relaxation
({\mu}SR) experiments to identify the magnetic ground state of the frustrated
quantum A-site spinel, CuAl2O4. Our results verify that the ground state does
not exhibit a long-range magnetic ordering, but a glass-like transition
manifests at T*=2.3 K. However, the Gaussian shape and the weak longitudinal
field dependence of {\mu}SR spectra below T* show that the ground state has
dynamic spin fluctuations, distinct from those of conventional spin-glasses.Comment: 22 pages, 7 figure
Meta-analysis of genetic variants associated with human exceptional longevity
Despite evidence from family studies that there is a strong genetic influence upon exceptional longevity, relatively few genetic variants have been associated with this trait. One reason could be that many genes individually have such weak effects that they cannot meet standard thresholds of genome wide significance, but as a group in specific combinations of genetic variations, they can have a strong influence. Previously we reported that such genetic signatures of 281 genetic markers associated with about 130 genes can do a relatively good job of differentiating centenarians from non-centenarians particularly if the centenarians are 106 years and older. This would support our hypothesis that the genetic influence upon exceptional longevity increases with older and older (and rarer) ages. We investigated this list of markers using similar genetic data from 5 studies of centenarians from the USA, Europe and Japan. The results from the meta-analysis show that many of these variants are associated with survival to these extreme ages in other studies. Since many centenarians compress morbidity and disability towards the end of their lives, these results could point to biological pathways and therefore new therapeutics to increase years of healthy lives in the general population
A Complete Classification of Higher Derivative Gravity in 3D and Criticality in 4D
We study the condition that the theory is unitary and stable in
three-dimensional gravity with most general quadratic curvature,
Lorentz-Chern-Simons and cosmological terms. We provide the complete
classification of the unitary theories around flat Minkowski and (anti-)de
Sitter spacetimes. The analysis is performed by examining the quadratic
fluctuations around these classical vacua. We also discuss how to understand
critical condition for four-dimensional theories at the Lagrangian level.Comment: 20 pages, v2: minor corrections, refs. added, v3: logic modified, v4:
typos correcte
Intersecting black branes in strong gravitational waves
We consider intersecting black branes with strong gravitational waves
propagating along their worldvolume in the context of supergravity theories.
Both near-horizon and space-filling gravitational wave modes are included in
our ansatz. The equations of motion (originally, partial differential
equations) are shown to reduce to ordinary differential equations, which
include a Toda-like system. For special arrangements of intersecting black
branes, the Toda-like system becomes integrable, permitting a more thorough
analysis of the gravitational equations of motion.Comment: 17 pages; v2: cosmetic improvements, published versio
Uniqueness of M-theory PP-Wave Background with Extra Supersymmetries
We examine Killing spinor equations of the general eleven-dimensional pp-wave
backgrounds, which contain a scalar H(x^m,x^-) in the metric and a three-form
\xi(x^m,x^-) in the flux. Considering non-harmonic extra Killing spinors, we
show that if the backgrounds admit at least one extra Killing spinor in
addition to the standard 16 Killing spinors, they can be reduced to the form
with H=A_{mn}(x^-)x^mx^n and \xi(x^-) modulo coordinate transformations. We
further examine the cases in which the extra Killing spinor is characterized by
a set of Cartan matrices. The super-isometry algebras of the resulting
backgrounds are also derived.Comment: 25 pages, LaTeX2e, comments added, version to appear in PR
- …