428 research outputs found
Extension of HPL to complex arguments
In this paper we describe the extension of the Mathematica package HPL to
treat harmonic polylogarithms of complex arguments. The harmonic polylogarithms
have been introduced by Remiddi and Vermaseren and have many applications in
high energy particle physics.Comment: 42 pages, references added, the package can be downloaded at
http://krone.physik.unizh.ch/~maitreda/HPL
NLO high multiplicity processes
In this presentation some aspects of Next-to-Leading Order (NLO) calculations in QCD are presented. The focus is brought to aspects of such calculations for processes involving a high final-state particle multiplicity
High multiplicity W+jets predictions at NLO
In these proceedings we present results from a recent calculation for the
production of a W boson in conjunction with five jets at next-to-leading order
in perturbative QCD. We also use results at lower multiplicities to extrapolate
the cross section to the same process with six jets.Comment: 5 pages, Proceedings for the DIS2013 conferenc
HypExp, a Mathematica package for expanding hypergeometric functions around integer-valued parameters
We present the Mathematica package HypExp which allows to expand
hypergeometric functions around integer parameters to arbitrary
order. At this, we apply two methods, the first one being based on an integral
representation, the second one on the nested sums approach. The expansion works
for both symbolic argument and unit argument. We also implemented new
classes of integrals that appear in the first method and that are, in part, yet
unknown to Mathematica.Comment: 33 pages, latex, 2 figures, the package can be downloaded from
http://krone.physik.unizh.ch/~maitreda/HypExp/, minor changes, works now
under Window
Master Integrals for Fermionic Contributions to Massless Three-Loop Form Factors
In this letter we continue the calculation of master integrals for massless
three-loop form factors by giving analytical results for those integrals which
are relevant for the fermionic contributions proportional to N_F^2, N_F*N, and
N_F/N. Working in dimensional regularisation, we express one of the integrals
in a closed form which is exact to all orders in epsilon, containing
Gamma-functions and hypergeometric functions of unit argument. In all other
cases we derive multiple Mellin-Barnes representations from which the
coefficients of the Laurent expansion in epsilon are extracted in an analytical
form. To obtain the finite part of the three-loop quark and gluon form factors,
all coefficients through transcendentality six in the Riemann zeta-function
have to be included.Comment: 12 pages, 1 figure. References added and updated. Appendix on
evaluation of Mellin-Barnes integrals added. Version to appear in PL
Electron Entanglement via a Quantum Dot
This Letter presents a method of electron entanglement generation. The system
under consideration is a single-level quantum dot with one input and two output
leads. The leads are arranged such that the dot is empty, single electron
tunneling is suppressed by energy conservation, and two-electron virtual
co-tunneling is allowed. This yields a pure, non-local spin-singlet state at
the output leads. Coulomb interaction is the nonlinearity essential for
entanglement generation, and, in its absence, the singlet state vanishes. This
type of electron entanglement is a four-wave mixing process analogous to the
photon entanglement generated by a Chi-3 parametric amplifier.Comment: 4 page
Application of the Principle of Maximum Conformality to Top-Pair Production
A major contribution to the uncertainty of finite-order perturbative QCD
predictions is the perceived ambiguity in setting the renormalization scale
. For example, by using the conventional way of setting , one obtains the total production cross-section
with the uncertainty \Delta \sigma_{t \bar{t}}/\sigma_{t
\bar{t}}\sim ({}^{+3%}_{-4%}) at the Tevatron and LHC even for the present
NNLO level. The Principle of Maximum Conformality (PMC) eliminates the
renormalization scale ambiguity in precision tests of Abelian QED and
non-Abelian QCD theories. In this paper we apply PMC scale-setting to predict
the cross-section at the Tevatron and LHC
colliders. It is found that remains almost unchanged by
varying within the region of . The convergence
of the expansion series is greatly improved. For the -channel,
which is dominant at the Tevatron, its NLO PMC scale is much smaller than the
top-quark mass in the small -region, and thus its NLO cross-section is
increased by about a factor of two. In the case of the -channel, which is
dominant at the LHC, its NLO PMC scale slightly increases with the subprocess
collision energy , but it is still smaller than for
TeV, and the resulting NLO cross-section is increased by
. As a result, a larger is obtained in comparison
to the conventional scale-setting method, which agrees well with the present
Tevatron and LHC data. More explicitly, by setting GeV, we
predict pb,
pb and pb. [full abstract can be found in the
paper.]Comment: 15 pages, 11 figures, 5 tables. Fig.(9) is correcte
Cyclical Quantum Memory for Photonic Qubits
We have performed a proof-of-principle experiment in which qubits encoded in
the polarization states of single-photons from a parametric down-conversion
source were coherently stored and read-out from a quantum memory device. The
memory device utilized a simple free-space storage loop, providing a cyclical
read-out that could be synchronized with the cycle time of a quantum computer.
The coherence of the photonic qubits was maintained during switching operations
by using a high-speed polarizing Sagnac interferometer switch.Comment: 4 pages, 5 figure
Symmetric qubits from cavity states
Two-mode cavities can be prepared in quantum states which represent symmetric
multi-qubit states. However, the qubits are impossible to address individually
and as such cannot be independently measured or otherwise manipulated. We
propose two related schemes to coherently transfer the qubits which the cavity
state represents onto individual atoms, so that the qubits can then be
processed individually. In particular, our scheme can be combined with the
quantum cloning scheme of Simon and coworkers [C. Simon et al, PRL 84, 2993
(2000)] to allow the optimal clones which their scheme produces to be spatially
separated and individually utilized.Comment: 8 pages, 4 figures, minor typographical errors correcte
Spin Asymmetries in Squark and Gluino Production at Polarized Hadron Colliders
We study the production cross sections for squarks and gluinos in collision
of longitudinally polarized hadrons. The corresponding polarized partonic cross
sections are computed in leading order supersymmetric QCD. The resulting
asymmetries are evaluated for the polarized proton collider RHIC, as well as
for hypothetical polarized options of the Tevatron and the LHC. These
asymmetries turn out to be sizable over a wide range of supersymmetric particle
masses, thus potentially opening a window to detailed sparticle spectroscopy at
future polarized hadron colliders.Comment: 25 pages, LaTeX, typos correcte
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