16,798 research outputs found
Generalized -conformal change and special Finsler spaces
In this paper, we investigate the change of Finslr metrics which we refer to as a
generalized -conformal change. Under this change, we study some special
Finsler spaces, namely, quasi C-reducible, semi C-reducible, C-reducible,
-like, -like and -like Finsler spaces. We also obtain the
transformation of the T-tensor under this change and study some interesting
special cases. We then impose a certain condition on the generalized
-conformal change, which we call the b-condition, and investigate the
geometric consequences of such condition. Finally, we give the conditions under
which a generalized -conformal change is projective and generalize some
known results in the literature.Comment: References added, some modifications are performed, LateX file, 24
page
Explosive Dark Matter Annihilation
If the Dark Matter (DM) in the Universe has interactions with the
standard-model particle, the pair annihilation may give the imprints in the
cosmic ray. In this paper we study the pair annihilation processes of the DM,
which is neutral, however has the electroweak (EW) gauge non-singlet. In this
estimation the non-relativistic (NR) effective theory in the EW sector is a
suitable technique. We find that if the DM mass is larger than about 1 TeV, the
attractive Yukawa potentials induced by the EW gauge bosons have significant
effects on the DM annihilation processes, and the cross sections may be
enhanced by several orders of magnitude, due to the zero energy resonance under
the potentials. Especially, the annihilation to two 's might have a
comparable cross section to other tree-level processes, while the cross section
under the conventional calculation is suppressed by a loop factor. We also
discuss future sensitivities to the ray from the galactic center by
the GLAST satellite detector and the Air Cerenkov Telescope (ACT) arrays.Comment: 5 pages, 6 Postscript figures, revte
XatA, an AT-1 autotransporter important for the virulence of Xylella fastidiosa Temecula1.
Xylella fastidiosa Temecula1 is the causative agent of Pierce's disease of grapevine, which is spread by xylem-feeding insects. An important feature of the infection cycle is the ability of X. fastidiosa to colonize and interact with two distinct environments, the xylem of susceptible plants and the insect foregut. Here, we describe our characterization of XatA, the X. fastidiosa autotransporter protein encoded by PD0528. XatA, which is classified as an AT-1 (classical) autotransporter, has a C-terminal Ī²-barrel domain and a passenger domain composed of six tandem repeats of approximately 50 amino acids. Localization studies indicate that XatA is present in both the outer membrane and membrane vesicles and its passenger domain can be found in the supernatant. Moreover, XatA is important for X. fastidiosa autoaggregation and biofilm formation based on mutational analysis and the discovery that Escherichia coli expressing XatA acquire these traits. The xatA mutant also shows a significant decrease in Pierce's disease symptoms when inoculated into grapevines. Finally, X. fastidiosa homologs to XatA, which can be divided into three distinct groups based on synteny, form a single, well-supported clade, suggesting that they arose from a common ancestor
Extremely large scale simulation of a Kardar-Parisi-Zhang model using graphics cards
The octahedron model introduced recently has been implemented onto graphics
cards, which permits extremely large scale simulations via binary lattice gases
and bit coded algorithms. We confirm scaling behaviour belonging to the 2d
Kardar-Parisi-Zhang universality class and find a surface growth exponent:
beta=0.2415(15) on 2^17 x 2^17 systems, ruling out beta=1/4 suggested by field
theory. The maximum speed-up with respect to a single CPU is 240. The steady
state has been analysed by finite size scaling and a growth exponent
alpha=0.393(4) is found. Correction to scaling exponents are computed and the
power-spectrum density of the steady state is determined. We calculate the
universal scaling functions, cumulants and show that the limit distribution can
be obtained by the sizes considered. We provide numerical fitting for the small
and large tail behaviour of the steady state scaling function of the interface
width.Comment: 7 pages, 8 figures, slightly modified, accepted version for PR
On Witten multiple zeta-functions associated with semisimple Lie algebras IV
In our previous work, we established the theory of multi-variable Witten
zeta-functions, which are called the zeta-functions of root systems. We have
already considered the cases of types , , , and . In
this paper, we consider the case of -type. We define certain analogues of
Bernoulli polynomials of -type and study the generating functions of them
to determine the coefficients of Witten's volume formulas of -type. Next
we consider the meromorphic continuation of the zeta-function of -type and
determine its possible singularities. Finally, by using our previous method, we
give explicit functional relations for them which include Witten's volume
formulas.Comment: 22 pag
Numerical Renormalization Group Study of Kondo Effect in Unconventional Superconductors
Orbital degrees of freedom of a Cooper pair play an important role in the
unconventional superconductivity. To elucidate the orbital effect in the Kondo
problem, we investigated a single magnetic impurity coupled to Cooper pairs
with a () symmetry using the numerical
renormalization group method. It is found that the ground state is always a
spin doublet. The analytical solution for the strong coupling limit explicitly
shows that the orbital dynamics of the Cooper pair generates the spin 1/2 of
the ground state.Comment: 4 pages, 2 figures, JPSJ.sty, to be published in J. Phys. Soc. Jpn.
70 (2001) No. 1
Boltzmann Suppression of Interacting Heavy Particles
Matsumoto and Yoshimura have recently argued that the number density of heavy
particles in a thermal bath is not necessarily Boltzmann-suppressed for T << M,
as power law corrections may emerge at higher orders in perturbation theory.
This fact might have important implications on the determination of WIMP relic
densities. On the other hand, the definition of number densities in a
interacting theory is not a straightforward procedure. It usually requires
renormalization of composite operators and operator mixing, which obscure the
physical interpretation of the computed thermal average. We propose a new
definition for the thermal average of a composite operator, which does not
require any new renormalization counterterm and is thus free from such
ambiguities. Applying this definition to the model of Matsumoto and Yoshimura
we find that it gives number densities which are Boltzmann-suppressed at any
order in perturbation theory. We discuss also heavy particles which are
unstable already at T=0, showing that power law corrections do in general
emerge in this case.Comment: 7 pages, 5 figures. New section added, with the discussion of the
case of an unstable heavy particle. Version to appear on Phys. Rev.
On the Bloch Theorem Concerning Spontaneous Electric Current
We study the Bloch theorem which states absence of the spontaneous current in
interacting electron systems. This theorem is shown to be still applicable to
the system with the magnetic field induced by the electric current. Application
to the spontaneous surface current is also examined in detail. Our result
excludes the possibility of the recently proposed -wave superconductivity
having the surface flow and finite total current.Comment: 12 pages, LaTeX, 3 Postscript figure
Spontaneous flux in a d-wave superconductor with time-reversal-symmetry-broken pairing state at {110} boundaries
The induction of an s-wave component in a d-wave superconductor is
considered. Near the {110}-oriented edges of such a sample, the induced s-wave
order parameter together with d-wave component forms a complex combination
d+e^{i\phi} s, which breaks the time reversal symmetry (BTRS) of the pairing
state. As a result, the spontaneous current is created. We numerically study
the current distribution and the formation of the spontaneous flux induced by
the current. We show that the spontaneous flux formed from a number of defect
lines with {110} orientation has a measurable strength. This result may provide
a unambiguous way to check the existence of BTRS pairing state at
{110}-oriented boundaries.Comment: 4 pages, 2 ps-figures, content changed, references adde
Spin-filter tunnel junction with matched Fermi surfaces
Efficient injection of spin-polarized current into a semiconductor is a basic
prerequisite for building semiconductor-based spintronic devices. Here, we use
inelastic electron tunneling spectroscopy to show that the efficiency of
spin-filter-type spin injectors is limited by spin scattering of the tunneling
electrons. By matching the Fermi-surface shapes of the current injection source
and target electrode material, spin injection efficiency can be significantly
increased in epitaxial ferromagnetic insulator tunnel junctions. Our results
demonstrate that not only structural but also Fermi-surface matching is
important to suppress scattering processes in spintronic devices.Comment: 5 pages, 4 figure
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