3,342 research outputs found
Hadronic Light-by-Light Contribution to Muon g-2 in Chiral Perturbation Theory
We compute the hadronic light-by-light scattering contributions to the muon
anomalous magnetic moment, \amulbl, in chiral perturbation theory that are
enhanced by large logarithms and a factor of . They depend on a low-energy
constant entering pseudoscalar meson decay into a charged lepton pair. The
uncertainty introduced by this constant is , which is
comparable in magnitude to the present uncertainty entering the leading-order
vacuum polarization contributions to the anomalous moment. It may be reduced to
some extent through an improved measurement of the branching
ratio. However, the dependence of \amulbl on non-logarithmically enhanced
effects cannot be constrained except through the measurement of the anomalous
moment itself. The extraction of information on new physics would require a
future experimental value for the anomalous moment differing significantly from
the 2001 result reported by the E821 collaboration.Comment: 7 pages, 2 figure
Pion pole contribution to hadronic light-by-light scattering and muon anomalous magnetic moment
We derive an analytic result for the pion pole contribution to the
light-by-light scattering correction to the anomalous magnetic moment of the
muon, . Using the vector meson dominance model (VMD) for
the pion transition form factor, we obtain .Comment: 4 pages, revte
Disc loss and renewal in A0535+26
This paper presents observations of the Be/X-ray binary system A0535+26
revealing the first observed loss of its circumstellar disc, demonstrated by
the loss of its JHK infrared excess and optical/IR line emission. However
optical/IR spectroscopy reveals the formation of a new inner disc with
significant density and emission strength at small radii; the disc has proven
to be stable over 5 months in this intermediate state.Comment: 4 pages, 4 figures, accepted by MNRAS, uses mn.st
Thermodynamic Theory of Weakly Excited Granular Materials
We present a thermodynamic theory of weakly excited two-dimensional granular
systems from the view point of elementary excitations of spinless Fermion
systems. We introduce a global temperature T that is associated with the
acceleration amplitude \Gamma in a vibrating bed. We show that the
configurational statistics of weakly excited granular materials in a vibrating
bed obey the Fermi statistics.Comment: 12 pages, 1 figure, To Appear in Phys. Rev. Lett. April, 199
A Nexafs Study of Nitric Oxide Layers Adsorbed from a nitrite Solution onto a Pt(111) Surface
NO molecules adsorbed on a Pt(111) surface from dipping in an acidic nitrite
solution are studied by near edge X-ray absorption fine structure spectroscopy
(NEXAFS), X-ray photoelectron spectroscopy (XPS), low energy electron
diffraction (LEED) and scanning tunnelling microscopy (STM) techniques. LEED
patterns and STM images show that no long range ordered structures are formed
after NO adsorption on a Pt(111) surface. Although the total NO coverage is
very low, spectroscopic features in N K-edge and O K-edge absorption spectra
have been singled out and related to the different species induced by this
preparation method. From these measurements it is concluded that the NO
molecule is adsorbed trough the N atom in an upright conformation. The maximum
saturation coverage is about 0.3 monolayers, and although nitric oxide is the
major component, nitrite and nitrogen species are slightly co-adsorbed on the
surface. The results obtained from this study are compared with those
previously reported in the literature for NO adsorbed on Pt(111) under UHV
conditions
Bob Dole, [Carl T. Curtis, Herman E. Talmadge, James O. Eastland, S.I. Hykawa possibly] to President Jimmy Carter, 31 January 1978
Copy typed letter signed dated 31 January 1978 from Bob Dole, [Curtis, Talmadge, Eastland, Hykawa possibly] to Carter, re: European Community trade negotiations, soybeans.https://egrove.olemiss.edu/joecorr_h/1090/thumbnail.jp
Hadronic light-by-light scattering contribution to the muon g-2
We review recent developments concerning the hadronic light-by-light
scattering contribution to the anomalous magnetic moment of the muon. We first
discuss why fully off-shell hadronic form factors should be used for the
evaluation of this contribution to the g-2. We then reevaluate the numerically
dominant pion-exchange contribution in the framework of large-N_C QCD, using an
off-shell pion-photon-photon form factor which fulfills all QCD short-distance
constraints, in particular, a new short-distance constraint on the off-shell
form factor at the external vertex in g-2, which relates the form factor to the
quark condensate magnetic susceptibility in QCD. Combined with available
evaluations of the other contributions to hadronic light-by-light scattering
this leads to the new result a_{\mu}(LbyL; had) = (116 \pm 40) x 10^{-11}, with
a conservative error estimate in view of the many still unsolved problems. Some
potential ways for further improvements are briefly discussed as well. For the
electron we obtain the new estimate a_{e}(LbyL; had) = (3.9 \pm 1.3) x
10^{-14}.Comment: 6 pages, 1 figure, to be published in the proceedings of the PhiPsi09
workshop, Oct. 13-16, 2009, Beijing, Chin
Quenching and Propagation of Combustion Without Ignition Temperature Cutoff
We study a reaction-diffusion equation in the cylinder , with combustion-type reaction term without
ignition temperature cutoff, and in the presence of a periodic flow. We show
that if the reaction function decays as a power of larger than three as
and the initial datum is small, then the flame is extinguished -- the
solution quenches. If, on the other hand, the power of decay is smaller than
three or initial datum is large, then quenching does not happen, and the
burning region spreads linearly in time. This extends results of
Aronson-Weinberger for the no-flow case. We also consider shear flows with
large amplitude and show that if the reaction power-law decay is larger than
three and the flow has only small plateaux (connected domains where it is
constant), then any compactly supported initial datum is quenched when the flow
amplitude is large enough (which is not true if the power is smaller than three
or in the presence of a large plateau). This extends results of
Constantin-Kiselev-Ryzhik for combustion with ignition temperature cutoff. Our
work carries over to the case , when
the critical power is , as well as to certain non-periodic flows
Hamiltonian embedding of the massive noncommutative U(1) theory
We show that the massive noncommutative U(1) can be embedded in a gauge
theory by using the BFFT Hamiltonian formalism. By virtue of the peculiar
non-Abelian algebraic structure of the noncommutative massive U(1) theory,
several specific identities involving Moyal commutators had to be used in order
to make the embedding possible. This leads to an infinite number of steps in
the iterative process of obtaining first-class constraints. We also shown that
the involutive Hamiltonian can be constructed.Comment: 8 pages, Revtex (multicol
Traffic Equations and Granular Convection
We investigate both numerically and analytically the convective instability
of granular materials by two dimensional traffic equations. In the absence of
vibrations the traffic equations assume two distinctive classes of fixed bed
solutions with either a spatially uniform or nonuniform density profile. The
former one exists only when the function V(\rho) that monitors the relaxation
of grains assumes a cut off at the closed packed density, \rho_c, with
V(\rho_c)=0, while the latter one exists for any form of V. Since there is
little difference between the uniform and nonuniform solution deep inside the
bed, the convective instability of the bulk may be studied by focusing on the
stability of the uniform solution. In the presence of vibrations, we find that
the uniform solution bifurcates into a bouncing solution, which then undergoes
a supercritical bifurcation to the convective instability. We determine the
onset of convection as a function of control parameters and confirm this
picture by solving the traffic equations numerically, which reveals bouncing
solutions, two convective rolls, and four convective rolls. Further, convective
patterns change as the aspect ratio changes: in a vertically long container,
the rolls move toward the surface, and in a horizontally long container, the
rolls move toward the walls. We compare these results with those reported
previously with a different continuum model by Hayakawa, Yue and Hong[Phys.
Rev. Lett. 75,2328, 1995]. Finally, we also present a derivation of the traffic
equations from Enskoq equation.Comment: 34 pages, 10 figure
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