15,805 research outputs found
QED Radiative Corrections to the Non-annihilation Processes Using the Structure Function and the Parton Shower
Inclusion of the QED higher order radiative corrections in the two-photon
process, e+e- -> e+e- mu+mu-, is examined by means of the structure function
and the parton shower. Results are compared with the exact
calculations and give a good agreement. These two methods should be universally
applicable to any other non-annihilation processes like the single-W
productions in the e+e- collisions. In this case, however, the energy scale for
the evolution by the renormalization-group equation should be chosen properly
depending on the dominant diagrams for the given process. A method to find the
most suitable energy scale is proposed.Comment: 17 pages, LaTeX, 5 figure
A Relativistic Description of Gentry's New Redshift Interpretation
We obtain a new expression of the Friedmann-Robertson-Walker metric, which is
an analogue of a static chart of the de Sitter space-time. The reduced metric
contains two functions, and , which are interpreted as,
respectively, the mass function and the gravitational potential. We find that,
near the coordinate origin, the reduced metric can be approximated in a static
form and that the approximated metric function, , satisfies the
Poisson equation. Moreover, when the model parameters of the
Friedmann-Robertson-Walker metric are suitably chosen, the approximated metric
coincides with exact solutions of the Einstein equation with the perfect fluid
matter. We then solve the radial geodesics on the approximated space-time to
obtain the distance-redshift relation of geodesic sources observed by the
comoving observer at the origin. We find that the redshift is expressed in
terms of a peculiar velocity of the source and the metric function, ,
evaluated at the source position, and one may think that this is a new
interpretation of {\it Gentry's new redshift interpretation}.Comment: 11 pages. Submitted to Modern Physics Letters
The small-scale structure of photospheric convection retrieved by a deconvolution technique applied to Hinode/SP data
Solar granules are bright patterns surrounded by dark channels called
intergranular lanes in the solar photosphere and are a manifestation of
overshooting convection. Observational studies generally find stronger upflows
in granules and weaker downflows in intergranular lanes. This trend is,
however, inconsistent with the results of numerical simulations in which
downflows are stronger than upflows through the joint action of gravitational
acceleration/deceleration and pressure gradients. One cause of this discrepancy
is the image degradation caused by optical distortion and light diffraction and
scattering that takes place in an imaging instrument. We apply a deconvolution
technique to Hinode/SP data in an attempt to recover the original solar scene.
Our results show a significant enhancement in both, the convective upflows and
downflows, but particularly for the latter. After deconvolution, the up- and
downflows reach maximum amplitudes of -3.0 km/s and +3.0 km/s at an average
geometrical height of roughly 50 km, respectively. We found that the velocity
distributions after deconvolution match those derived from numerical
simulations. After deconvolution the net LOS velocity averaged over the whole
FOV lies close to zero as expected in a rough sense from mass balance.Comment: 32 pages, 13 figures, accepted for publication in Ap
GRACE at ONE-LOOP: Automatic calculation of 1-loop diagrams in the electroweak theory with gauge parameter independence checks
We describe the main building blocks of a generic automated package for the
calculation of Feynman diagrams. These blocks include the generation and
creation of a model file, the graph generation, the symbolic calculation at an
intermediate level of the Dirac and tensor algebra, implementation of the loop
integrals, the generation of the matrix elements or helicity amplitudes,
methods for the phase space integrations and eventually the event generation.
The report focuses on the fully automated systems for the calculation of
physical processes based on the experience in developing GRACE-loop. As such, a
detailed description of the renormalisation procedure in the Standard Model is
given emphasizing the central role played by the non-linear gauge fixing
conditions for the construction of such automated codes. The need for such
gauges is better appreciated when it comes to devising efficient and powerful
algorithms for the reduction of the tensorial structures of the loop integrals.
A new technique for these reduction algorithms is described. Explicit formulae
for all two-point functions in a generalised non-linear gauge are given,
together with the complete set of counterterms. We also show how infrared
divergences are dealt with in the system. We give a comprehensive presentation
of some systematic test-runs which have been performed at the one-loop level
for a wide variety of two-to-two processes to show the validity of the gauge
check. These cover fermion-fermion scattering, gauge boson scattering into
fermions, gauge bosons and Higgs bosons scattering processes. Comparisons with
existing results on some one-loop computation in the Standard Model show
excellent agreement. We also briefly recount some recent development concerning
the calculation of mutli-leg one-loop corrections.Comment: 131 pages. Manuscript expanded quite substantially with the inclusion
of an overview of automatic systems for the calculation of Feynman diagrams
both at tree-level and one-loop. Other additions include issues of
regularisation, width effects and renormalisation with unstable particles and
reduction of 5- and 6-point functions. This is a preprint version, final
version to appear as a Phys. Re
Magnetic Flux Loss and Flux Transport in a Decaying Active Region
We estimate the temporal change of magnetic flux perpendicular to the solar
surface in a decaying active region by using a time series of the spatial
distribution of vector magnetic fields in the photosphere. The vector magnetic
fields are derived from full spectropolarimetric measurements with the Solar
Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux
transport rate in a decaying sunspot and its surrounding moat region. The
amount of magnetic flux that decreases in the sunspot and moat region is very
similar to magnetic flux transported to the outer boundary of the moat region.
The flux loss rates [] of magnetic elements with positive and
negative polarities are balanced each other around the outer boundary of the
moat region. These results suggest that most of the magnetic flux in the
sunspot is transported to the outer boundary of the moat region as moving
magnetic features, and then removed from the photosphere by flux cancellation
around the outer boundary of the moat region.Comment: 16 pages, 7 figures, Accepted for publication in Ap
Quadrupole Collective Dynamics from Energy Density Functionals: Collective Hamiltonian and the Interacting Boson Model
Microscopic energy density functionals (EDF) have become a standard tool for
nuclear structure calculations, providing an accurate global description of
nuclear ground states and collective excitations. For spectroscopic
applications this framework has to be extended to account for collective
correlations related to restoration of symmetries broken by the static mean
field, and for fluctuations of collective variables. In this work we compare
two approaches to five-dimensional quadrupole dynamics: the collective
Hamiltonian for quadrupole vibrations and rotations, and the Interacting Boson
Model. The two models are compared in a study of the evolution of non-axial
shapes in Pt isotopes. Starting from the binding energy surfaces of
Pt, calculated with a microscopic energy density functional, we
analyze the resulting low-energy collective spectra obtained from the
collective Hamiltonian, and the corresponding IBM-2 Hamiltonian. The calculated
excitation spectra and transition probabilities for the ground-state bands and
the -vibration bands are compared to the corresponding sequences of
experimental states.Comment: 10 pages, 4 figures; to be published in Phys. Rev.
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