1,482 research outputs found
On the peculiarities in the rotational frequency evolution of isolated neutron stars
The measurements of pulsar frequency second derivatives have shown that they
are times larger than expected for standard pulsar spin-down law,
and are even negative for about half of pulsars. We explain these paradoxical
results on the basis of the statistical analysis of the rotational parameters
, and of the subset of 295 pulsars taken mostly
from the ATNF database. We have found a strong correlation between
and for both and , as well as between
and . We interpret these dependencies as evolutionary ones due
to being nearly proportional to the pulsars' age. The derived
statistical relations as well as "anomalous" values of are well
described by assuming the long-time variations of the spin-down rate. The
pulsar frequency evolution, therefore, consists of secular change of
, and according to the power
law with , the irregularities, observed within a timespan as a
timing noise, and the variations on the timescale larger than that timespan --
several tens of years.Comment: 4 pages, 3 figures. Accepted for publication in ApSS, in the
proceedings of the conference "Isolated Neutron Stars: from the Interior to
the Surface", London, April 2006; eds. S. Zane, R. Turolla and D. Pag
Resonance in Asymmetric Warped Geometry
We study the spectrum of an asymmetric warped braneworld model with different
AdS curvatures on either side of the brane. In addition to the RS-like modes we
find a resonance state. Its mass is proportional to the geometric mean of the
two AdS curvature scales, while the difference between them determines the
strength of the resonance peak. There is a complementarity between the RS
zero-mode and the resonance: making the asymmetry stronger weakens the
zero-mode but strengthens the resonance, and vice versa. We calculate
numerically the braneworld gravitational potential and discuss the holographic
correspondence for the asymmetric model.Comment: 17 pages, 9 figures; v2 references with comments added; v3 two
references added, JHEP versio
Robust storage qubits in ultracold polar molecules
Quantum states with long-lived coherence are essential for quantum computation, simulation and metrology. The nuclear spin states of ultracold molecules prepared in the singlet rovibrational ground state are an excellent candidate for encoding and storing quantum information. However, it is important to understand all sources of decoherence for these qubits, and then eliminate them, to reach the longest possible coherence times. Here we fully characterize the dominant mechanisms of decoherence for a storage qubit in an optically trapped ultracold gas of RbCs molecules using high-resolution Ramsey spectroscopy. Guided by a detailed understanding of the hyperfine structure of the molecule, we tune the magnetic field to where a pair of hyperfine states have the same magnetic moment. These states form a qubit, which is insensitive to variations in magnetic field. Our experiments reveal a subtle differential tensor light shift between the states, caused by weak mixing of rotational states. We demonstrate how this light shift can be eliminated by setting the angle between the linearly polarized trap light and the applied magnetic field to a magic angle of arccos(1/3–√)≈55∘. This leads to a coherence time exceeding 5.6 s at the 95% confidence level
Topological censorship for Kaluza-Klein space-times
The standard topological censorship theorems require asymptotic hypotheses
which are too restrictive for several situations of interest. In this paper we
prove a version of topological censorship under significantly weaker
conditions, compatible e.g. with solutions with Kaluza-Klein asymptotic
behavior. In particular we prove simple connectedness of the quotient of the
domain of outer communications by the group of symmetries for models which are
asymptotically flat, or asymptotically anti-de Sitter, in a Kaluza-Klein sense.
This allows one, e.g., to define the twist potentials needed for the reduction
of the field equations in uniqueness theorems. Finally, the methods used to
prove the above are used to show that weakly trapped compact surfaces cannot be
seen from Scri.Comment: minor correction
Classical and Thermodynamic Stability of Black Branes
It is argued that many non-extremal black branes exhibit a classical
Gregory-Laflamme instability if, and only if, they are locally
thermodynamically unstable. For some black branes, the Gregory-Laflamme
instability must therefore disappear near extremality. For the black -branes
of the type II supergravity theories, the Gregory-Laflamme instability
disappears near extremality for but persists all the way down to
extremality for (the black D3-brane is not covered by the analysis of
this paper). This implies that the instability also vanishes for the
near-extremal black M2 and M5-brane solutions.Comment: 21 pages, LaTeX. v2: Various points clarified, typos corrected and
reference adde
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A tillering inhibition gene influences root-shoot carbon partitioning and pattern of water use to improve wheat productivity in rainfed environments
Genetic modification of shoot and root morphology has potential to improve water and nutrient
19 uptake of wheat crops in rainfed environments. Near-isogenic lines (NILs) varying for a tillering
20 inhibition (tin) gene and representing multiple genetic backgrounds were investigated in contrasting
21 controlled environments for shoot and root growth. Leaf area, shoot and root biomass were similar
22 until tillering whereupon reduced tillering in tin-containing NILs produced reductions of up to 60% in
23 total leaf area and biomass, and increases in total root length of up to 120% and root biomass to
24 145%. Together, root-to-shoot ratio increased two-fold with the tin gene. The influence of tin on shoot
25 and root growth was greatest in the cv. Banks genetic background, particularly in the biculm-selected
26 NIL, and was typically strongest in cooler environments. A separate de-tillering study confirmed
27 greater root-to-shoot ratios with regular tiller removal in non-tin containing genotypes. In validating
28 these observations in a rainfed field study, the tin allele had a negligible effect on seedling growth but
29 was associated with significantly (P<0.05) reduced tiller number (-37%), leaf area index (-26%) and
30 spike number (-35%) to reduce plant biomass (-19%) at anthesis. Root biomass, root-to-shoot ratio at
31 early stem elongation and root depth at maturity were increased in tin-containing NILs. Soil water use
32 was slowed in tin-containing NILs resulting in greater water availability, greater stomatal
33 conductance, cooler canopy temperatures and maintenance of green leaf area during grain-filling.
34 Together these effects contributed to increases in harvest index and grain yield. In both the controlled
35 and field environments, the tin gene was commonly associated with increased root length and biomass
36 but the significant influence of genetic background and environment suggests careful assessment of
37 tin-containing progeny in selection for genotypic increases in root growth
Localized Tachyons and the Quantum McKay Correspondence
The condensation of closed string tachyons localized at the fixed point of a
C^d/\Gamma orbifold can be studied in the framework of renormalization group
flow in a gauged linear sigma model. The evolution of the Higgs branch along
the flow describes a resolution of singularities via the process of tachyon
condensation. The study of the fate of D-branes in this process has lead to a
notion of a ``quantum McKay correspondence.'' This is a hypothetical
correspondence between fractional branes in an orbifold singularity in the
ultraviolet with the Coulomb and Higgs branch branes in the infrared. In this
paper we present some nontrivial evidence for this correspondence in the case
C^2/Z_n by relating the intersection form of fractional branes to that of
``Higgs branch branes,'' the latter being branes which wrap nontrivial cycles
in the resolved space.Comment: 25 pages; harvma
Core Structure of Global Vortices in Brane World Models
We study analytically and numerically the core structure of global vortices
forming on topologically deformed brane-worlds with a single toroidally compact
extra dimension. It is shown that for an extra dimension size larger than the
scale of symmetry breaking the magnitude of the complex scalar field at the
vortex center can dynamically remain non-zero. Singlevaluedness and regularity
are not violated. Instead, the winding escapes to the extra dimension at the
vortex center. As the extra dimension size decreases the field magnitude at the
core dynamically decreases also and in the limit of zero extra dimension size
we reobtain the familiar global vortex solution. Extensions to other types of
defects and gauged symmetries are also discussed.Comment: 6 two column pages, 3 figure
Cosmology of codimension-two braneworlds
We present a comprehensive study of the cosmological solutions of 6D
braneworld models with azimuthal symmetry in the extra dimensions, moduli
stabilization by flux or a bulk scalar field, and which contain at least one
3-brane that could be identified with our world. We emphasize an unusual
property of these models: their expansion rate depends on the 3-brane tension
either not at all, or in a nonstandard way, at odds with the naive expected
dimensional reduction of these systems to 4D general relativity at low
energies. Unlike other braneworld attempts to find a self-tuning solution to
the cosmological constant problem, the apparent failure of decoupling in these
models is not associated with the presence of unstabilized moduli; rather it is
due to automatic cancellation of the brane tension by the curvature induced by
the brane. This provides some corroboration for the hope that these models
provide a distinctive step toward understanding the smallness of the observed
cosmological constant. However, we point out some challenges for obtaining
realistic cosmology within this framework.Comment: 30 pages, 4 figures; generalized result for nonconventional Friedmann
equation, added referenc
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