9,190 research outputs found
Deformation of LeBrun's ALE metrics with negative mass
In this article we investigate deformations of a scalar-flat K\"ahler metric
on the total space of complex line bundles over CP^1 constructed by C. LeBrun.
In particular, we find that the metric is included in a one-dimensional family
of such metrics on the four-manifold, where the complex structure in the
deformation is not the standard one.Comment: 20 pages, no figure. V2: added two references, filled a gap in the
proof of Theorem 1.2. V3: corrected a wrong statement about Kuranishi family
of a Hirzebruch surface stated in the last paragraph in the proof of Theorem
1.2, and fixed a relevant error in the proof. Also added a reference [24]
about Kuranishi family of Hirzebruch surface
Fractal boundary basins in spherically symmetric theory
Results are presented from numerical simulations of the flat-space nonlinear
Klein-Gordon equa- tion with an asymmetric double-well potential in spherical
symmetry. Exit criteria are defined for the simulations that are used to help
understand the boundaries of the basins of attraction for Gaussian "bubble"
initial data. The first exit criteria, based on the immediate collapse or
expan- sion of bubble radius, is used to observe the departure of the scalar
field from a static intermediate attractor solution. The boundary separating
these two behaviors in parameter space is smooth and demonstrates a
time-scaling law with an exponent that depends on the asymmetry of the
potential. The second exit criteria differentiates between the creation of an
expanding true-vacuum bubble and dispersion of the field leaving the false
vacuum; the boundary separating these basins of attraction is shown to
demonstrate fractal behavior. The basins are defined by the number of bounces
that the field undergoes before inducing a phase transition. A third, hybrid
exit criteria is used to determine the location of the boundary to arbitrary
precision and to characterize the threshold behavior. The possible effects this
behavior might have on cosmological phase transitions are briefly discussed.Comment: 10 pages, 13 figures, 1 movie, resubmitted with additional paragraph.
Matches published versio
Extreme Enhancements of r-process Elements in the Cool Metal-Poor Main-Sequence Star SDSS J2357-0052
We report the discovery of a cool metal-poor, main-sequence star exhibiting
large excesses of r-process elements. This star is one of two newly discovered
cool subdwarfs (effective temperatures of 5000 K) with extremely low
metallicity ([Fe/H]<-3) identified from follow-up high-resolution spectroscopy
of metal-poor candidates from the Sloan Digital Sky Survey. SDSS J2357-0052 has
[Fe/H]=-3.4 and [Eu/Fe]=+1.9, and exhibits a scaled solar r-process abundance
pattern of heavy neutron-capture elements. This is the first example of an
extremely metal-poor, main-sequence star showing large excesses of r-process
elements; all previous examples of the large r-process-enhancement phenomena
have been associated with metal-poor giants. The metallicity of this object is
the lowest, and the excess of Eu ([Eu/Fe]) is the highest, among the
r-process-enhanced stars found so far. We consider possible scenarios to
account for the detection of such a star, and discuss techniques to enable
searches for similar stars in the future.Comment: 16 pages, 3 figures, 2 tables, ApJL in pres
Double solid twistor spaces: the case of arbitrary signature
In a recent paper (math.DG/0701278) we constructed a series of new Moishezon
twistor spaces which is a kind of variant of the famous LeBrun twistor spaces.
In this paper we explicitly give projective models of another series of
Moishezon twistor spaces on nCP^2 for arbitrary n>2, which can be regarded as a
generalization of the twistor spaces of a 'double solid type' on 3CP^2 studied
by Kreussler, Kurke, Poon and the author. Similarly to the twistor spaces of
'double solid type' on 3CP^2, projective models of present twistor spaces have
a natural structure of double covering of a CP^2-bundle over CP^1. We
explicitly give a defining polynomial of the branch divisor of the double
covering whose restriction to fibers are degree four. If n>3 these are new
twistor spaces, to the best of the author's knowledge. We also compute the
dimension of the moduli space of these twistor spaces. Differently from
math.DG/0701278, the present investigation is based on analysis of
pluri-(half-)anticanonical systems of the twistor spaces.Comment: 30 pages, 3 figures; v2: title changed (the original title was
"Explicit construction of new Moishezon twistor spaces, II".
Observation of a Transient Magnetization Plateau in a Quantum Antiferromagnet on the Kagome Lattice
The magnetization process of an S=1/2 antiferromagnet on the kagome lattice,
[Cu_3(titmb)_2(OCOCH_3)_6]H_2O {titmb= 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6
trimethylbenzene} has been measured at very low temperatures in both pulsed and
steady fields. We have found a new dynamical behavior in the magnetization
process: a plateau at one third of the saturation magnetization appears in the
pulsed field experiments for intermediate sweep rates of the magnetic field and
disappears in the steady field experiments. A theoretical analysis using exact
diagonalization yields J_1=-19K and J_2=6K, for the nearest neighbor and second
nearest neighbor interactions, respectively. This set of exchange parameters
explains the very low saturation field and the absence of the plateau in the
thermodynamic equilibrium as well as the two-peak feature in the magnetic heat
capacity. Supported by numerical results we argue that a dynamical order by
disorder phenomenon could explain the transient appearance of the 1/3 plateau
in pulsed field experiments.Comment: 7 pages, 5 figure
Transitive X-ray spectrum and PeV gamma-ray cutoff in the M87 jet: Electron "Pevatron"
We propose a modified version of the X-ray spectral index and an intrinsic
cutoff frequency of inverse Compton radiation from the brightest knot of the
M87 jet, in conjunction with an application of the new conceptions of injection
and diffusive shock acceleration (DSA) of electrons in magnetized filamentary
plasma to the specified source. The drop of the X-ray flux density in a
transitive frequency region is associated with the interplay of ordinary
synchrotron cooling and weaker magnetic fields concomitant with the smaller
scale filaments that allow the electron injection, while the radio-optical
synchrotron continuum is dominantly established by the major electrons that are
quasi-secularly bound to larger filaments. With reference to, particularly, the
updated external Compton model, we demonstrate that in the Klein-Nishina regime
fading inverse Comptonization, the injected electrons can be stochastically
energized up to a Lorentz factor as high as in the temporal
competition with diffuse synchrotron cooling; this value is larger than that
attainable for a simple DSA scenario based on the resonant scattering diffusion
of the gyrating electrons bound to a supposed magnetic field homogeneously
pervading the entire knot. The upper limits of the photon frequency boosted via
conceivable inverse Compton processes are predicted to be of the common order
of Hz. The variability of the broadband spectrum is also
discussed in comparison to the features of a blazar light curve. The present
scenario of a peta-eV (PeV; eV) electron accelerator, the "Pevatron,"
might provide some guidance for exploring untrod hard X-ray and gamma-ray bands
in forthcoming observations.Comment: 34 pages, 6 figures, matches version published in Ap
Degenerations of LeBrun twistor spaces
We investigate various limits of the twistor spaces associated to the
self-dual metrics on n CP ^2, the connected sum of the complex projective
planes, constructed by C. LeBrun. In particular, we explicitly present the
following 3 kinds of degenerations whose limits of the metrics are: (a) LeBrun
metrics on (n-1) CP ^2$, (b) (Another) LeBrun metrics on the total space of the
line bundle O(-n) over CP ^1 (c) The hyper-Kaehler metrics on the small
resolution of rational double points of type A_{n-1}, constructed by Gibbons
and Hawking.Comment: 21 pages, 7 figures. V2: A new section added at the end of the
article. V3: Reference slightly update
A Modular Toolkit for Distributed Interactions
We discuss the design, architecture, and implementation of a toolkit which
supports some theories for distributed interactions. The main design principles
of our architecture are flexibility and modularity. Our main goal is to provide
an easily extensible workbench to encompass current algorithms and incorporate
future developments of the theories. With the help of some examples, we
illustrate the main features of our toolkit.Comment: In Proceedings PLACES 2010, arXiv:1110.385
Field-induced 3- and 2-dimensional freezing in a quantum spin liquid
Field-induced commensurate transverse magnetic ordering is observed in the
Haldane-gap compound \nd by means of neutron diffraction. Depending on the
direction of applied field, the high-field phase is shown to be either a
3-dimensional ordered N\'{e}el state or a short-range ordered state with
dominant 2-dimensional spin correlations. The structure of the high-field phase
is determined, and properties of the observed quantum phase transition are
discussed.Comment: 4 pages 3 figure
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