362 research outputs found
Automatic Integral Reduction for Higher Order Perturbative Calculations
We present a program for the reduction of large systems of integrals to
master integrals. The algorithm was first proposed by Laporta; in this paper,
we implement it in MAPLE. We also develop two new features which keep the size
of intermediate expressions relatively small throughout the calculation. The
program requires modest input information from the user and can be used for
generic calculations in perturbation theory.Comment: 23 page
Discovery of extended radio emission in the young cluster Wd1
We present 10 micron, ISO-SWS and Australia Telescope Compact Array
observations of the region in the cluster Wd1 in Ara centred on the B[e] star
Ara C. An ISO-SWS spectrum reveals emission from highly ionised species in the
vicinity of the star, suggesting a secondary source of excitation in the
region. We find strong radio emission at both 3.5cm and 6.3cm, with a total
spatial extent of over 20 arcsec. The emission is found to be concentrated in
two discrete structures, separated by 14''. The westerly source is resolved,
with a spectral index indicative of thermal emission. The easterly source is
clearly extended and nonthermal (synchrotron) in nature. Positionally, the B[e]
star is found to coincide with the more compact radio source, while the
southerly lobe of the extended source is coincident with Ara A, an M2 I star.
Observation of the region at 10micron reveals strong emission with an almost
identical spatial distribution to the radio emission. Ara C is found to have an
extreme radio luminosity in comparison to prior radio observations of hot stars
such as O and B supergiants and Wolf-Rayet stars, given the estimated distance
to the cluster. An origin in a detatched shell of material around the central
star is therefore suggested; however given the spatial extent of the emission,
such a shell must be relatively young (10^3 yrs). The extended non thermal
emission associated with the M star Ara A is unexpected; to the best of our
knowledge this is a unique phenomenon. SAX (2-10keV) observations show no
evidence of X-ray emission, which might be expected if a compact companion were
present.Comment: 5 pages including encapsulated figures, figure 3 separate. Accepted
for MNRAS pink page
The electromagnetic dipole operator effect on B -> Xs gamma at O(alpha_s^2)
The flavor-changing electromagnetic dipole operator O_7 gives the dominant
contribution to the B -> Xs gamma decay rate. We calculate two-loop QCD
corrections to its matrix element together with the corresponding
bremsstrahlung contributions. The optical theorem is applied, and the relevant
imaginary parts of three-loop diagrams are computed following the lines of our
recent t -> Xb W calculation. The complete result allows us to test the
validity of the naive non-abelianization (NNA) approximation that has been
previously applied to estimate the NNLO QCD correction to Gamma(B -> Xs
gamma)/Gamma(B -> Xu e nu). When both decay widths are normalized to m^5_{b,R}
in the same renormalization scheme R, the calculated O(alpha_s^2) correction is
sizeable (~ 6%), and the NNA estimate is about 1/3 too large. On the other
hand, when the ratio of the decay widths is written as
S*(m_b(m_b)/m_{b,pole})^2, the calculated O(alpha_s^2) correction to S is at
the level of 1% for both the complete and the NNA results.Comment: Corrected pi^2 terms in the description of intermediate steps in
Section II. Final results unchange
Non-locality and Medium Effects in the Exclusive Photoproduction of Eta Mesons on Nuclei
A relativistic model for the quasifree exclusive photoproduction of
mesons on nuclei is extended to include both non-local and medium effects. The
reaction is assumed to proceed via the dominant contribution of the
S(1535) resonance. The complicated integrals resulting from the
non-locality are simplified using a modified version of a method given by
Cooper and Maxwell. The non-locality effects are found to affect the magnitude
of the cross section. Some possibilities reflecting the effects of the medium
on the propagation and properties of the intermediate S resonance are
studied. The effects of allowing the S to interact with the medium via
mean field scalar and vector potentials are considered. Both broadening of
width and reduction in mass of the resonance lead to a suppression of the
calculated cross sections.Comment: 19 pages, 7 figure
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
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