12,562 research outputs found
On The {\it Fermi} -Lat Surplus of the Diffuse Galactic Gamma-Ray Emission
Recent observations of the diffuse Galactic \gr emission (DGE) by the {\it
Fermi} Large Area Telescope ({\it Fermi}-LAT) have shown significant
deviations, above a few GeV until about 100 GeV, from DGE models that use the
GALPROP code for the propagation of cosmic ray (CR) particles outside their
sources in the Galaxy and their interaction with the target distributions of
the interstellar gas and radiation fields. The surplus of radiation observed is
most pronounced in the inner Galaxy, where the concentration of CR sources is
strongest. The present study investigates this "{\it Fermi}-LAT Galactic Plane
Surplus" by estimating the \gr emission from the sources themselves, which is
disregarded in the above DGE models. It is shown that indeed the expected hard
spectrum of CRs, still confined in their sources (SCRs), can explain this
surplus. The method is based on earlier studies regarding the so-called EGRET
GeV excess which by now is generally interpreted as an instrumental effect. The
contribution from SCRs is predicted to increasingly exceed the DGE models also
above 100 GeV, up to \gr energies of about ten TeV, where the corresponding
surplus exceeds the hadronic part of the DGE by about one order of magnitude.
Above such energies the emission surplus should decrease again with energy due
to the finite life-time of the assumed supernova remnant sources. Observations
of the DGE in the inner Galaxy at 15 TeV with the Milagro \gr detector and, at
TeV energies, with the ARGO-YBJ detector are interpreted to provide
confirmation of a significant SCR contribution to the DGE.Comment: 6 pages, 1 figure. Accepted for publication in The Astrophysical
Journal, 2013; added referenc
Is a Large Intrinsic k_T Needed to Describe Photon + Jet Photoproduction at HERA?
We study the photoproduction of an isolated photon and a jet based on a code
of partonic event generator type which includes the full set of next-to-leading
order corrections. We compare our results to a recent ZEUS analysis in which an
effective k_T of the incoming partons has been determined. We find that no
additional intrinsic k_T is needed to describe the data.Comment: 23 pages LaTeX, 12 figure
Isolated prompt photon photoproduction at NLO
We present a full next-to-leading order code to calculate the photoproduction
of prompt photons. The code is a general purpose program of partonic event
generator type with large flexibility. We study the possibility to constrain
the photon structure functions and comment on isolation issues. A comparison to
ZEUS data is also shown.Comment: 22 pages LaTeX, 15 figure
A NLO calculation of the hadron-jet cross section in photoproduction reactions
We study the photoproduction of large-p_T charged hadrons in e p collisions,
both for the inclusive case and for the case where a jet in the final state is
also measured. Our results are obtained by a NLO generator of partonic events.
We discuss the sensitivity of the cross section to the renormalisation and
factorisation scales, and to various fragmentation function parametrisations.
The possibility to constrain the parton densities in the proton and in the
photon is assessed. Comparisons are made with H1 data for inclusive charged
hadron production.Comment: 28 pages LaTeX, 14 figure
Tools for NLO automation: extension of the golem95C integral library
We present an extension of the program golem95C for the numerical evaluation
of scalar integrals and tensor form factors entering the calculation of
one-loop amplitudes, which supports tensor ranks exceeding the number of
propagators. This extension allows various applications in Beyond the Standard
Model physics and effective theories, for example higher ranks due to
propagators of spin two particles, or due to effective vertices. Complex masses
are also supported. The program is not restricted to the Feynman diagrammatic
approach, as it also contains routines to interface to unitarity-inspired
numerical reconstruction of the integrand at the tensorial level. Therefore it
can serve as a general integral library in automated programs to calculate
one-loop amplitudes.Comment: 17 pages, 1 figure, the program can be downloaded from
http://golem.hepforge.org/95/. arXiv admin note: substantial text overlap
with arXiv:1101.559
Next-to-leading order multi-leg processes for the Large Hadron Collider
In this talk we discuss recent progress concerning precise predictions for
the LHC. We give a status report of three applications of our method to deal
with multi-leg one-loop amplitudes: The interference term of Higgs production
by gluon- and weak boson fusion to order O(alpha^2 alpha_s^3) and the
next-to-leading order corrections to the two processes pp -> ZZ jet and u ubar
-> d dbar s sbar. The latter is a subprocess of the four jet cross section at
the LHC.Comment: 6 pages, 5 figures. Talk given at the 8th international Symposium on
Radiative Corrections (RADCOR), October 1-5 2007, Florence, Ital
SecDec-3.0: numerical evaluation of multi-scale integrals beyond one loop
SecDec is a program which can be used for the factorization of dimensionally
regulated poles from parametric integrals, in particular multi-loop integrals,
and the subsequent numerical evaluation of the finite coefficients. Here we
present version 3.0 of the program, which has major improvements compared to
version 2: it is faster, contains new decomposition strategies, an improved
user interface and various other new features which extend the range of
applicability.Comment: 46 pages, version to appear in Comput.Phys.Com
Numerical evaluation of two-loop integrals with pySecDec
We describe the program pySecDec, which factorises endpoint singularities
from multi-dimensional parameter integrals and can serve to calculate integrals
occurring in higher order perturbative calculations numerically. We focus on
the new features and on frequently asked questions about the usage of the
program.Comment: 11 pages, to appear in the proceedings of the HiggsTools Final
Meeting, IPPP, University of Durham, UK, September 201
Damping by slow relaxing rare earth impurities in Ni80Fe20
Doping NiFe by heavy rare earth atoms alters the magnetic relaxation
properties of this material drastically. We show that this effect can be well
explained by the slow relaxing impurity mechanism. This process is a
consequence of the anisotropy of the on site exchange interaction between the
4f magnetic moments and the conduction band. As expected from this model the
magnitude of the damping effect scales with the anisotropy of the exchange
interaction and increases by an order of magnitude at low temperatures. In
addition our measurements allow us to determine the relaxation time of the 4f
electrons as a function of temperature
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