5,774 research outputs found
Sealed containers in Z
Physical means of securing information, such as sealed envelopes and scratch cards, can be used to achieve cryptographic objectives. Reasoning about this has so far been informal.
We give a model of distinguishable sealed envelopes in Z, exploring design decisions and further analysis and development of such models
Ultrasoft NLL Running of the Nonrelativistic O(v) QCD Quark Potential
Using the nonrelativistic effective field theory vNRQCD, we determine the
contribution to the next-to-leading logarithmic (NLL) running of the effective
quark-antiquark potential at order v (1/mk) from diagrams with one potential
and two ultrasoft loops, v being the velocity of the quarks in the c.m. frame.
The results are numerically important and complete the description of ultrasoft
next-to-next-to-leading logarithmic (NNLL) order effects in heavy quark pair
production and annihilation close to threshold.Comment: 25 pages, 7 figures, 3 tables; minor modifications, typos corrected,
references added, footnote adde
Automation of NLO processes and decays and POWHEG matching in WHIZARD
We give a status report on the automation of next-to-leading order processes
within the Monte Carlo event generator WHIZARD, using GoSam and OpenLoops as
provider for one-loop matrix elements. To deal with divergences, WHIZARD uses
automated FKS subtraction, and the phase space for singular regions is
generated automatically. NLO examples for both scattering and decay processes
with a focus on e+e- processes are shown. Also, first NLO-studies of
observables for collisions of polarized leptons beams, e.g. at the ILC, will be
presented. Furthermore, the automatic matching of the fixed-order NLO
amplitudes with emissions from the parton shower within the POWHEG formalism
inside WHIZARD will be discussed. We also present results for top pairs at
threshold in lepton collisions, including matching between a resummed threshold
calculation and fixed-order NLO. This allows the investigation of more
exclusive differential observables.Comment: 5 pages, 3 figures, Talk presented at ACAT 2016 at UTFSM,
Valpara\'iso, Chil
Top Physics in WHIZARD
In this talk we summarize the top physics setup in the event generator
WHIZARD with a main focus on lepton colliders. This includes full six-, eight-
and ten-fermion processes, factorized processes and spin correlations. For
lepton colliders, QCD NLO processes for top quark physics are available and
will be discussed. A special focus is on the top-quark pair threshold, where a
special implementation combines a non-relativistic effective field theory
calculation augmented by a next-to-leading threshold logarithm resummation with
a continuum relativistic fixed-order QCD NLO simulation.Comment: 6 pages, 2 figures, Talk presented at the International Workshop on
Future Linear Colliders (LCWS15), Whistler, Canada, 2-6 November 201
1S and MSbar Bottom Quark Masses from Upsilon Sum Rules
The bottom quark 1S mass, , is determined using sum rules which
relate the masses and the electronic decay widths of the mesons to
moments of the vacuum polarization function. The 1S mass is defined as half the
perturbative mass of a fictitious bottom-antibottom quark bound
state, and is free of the ambiguity of order which plagues the
pole mass definition. Compared to an earlier analysis by the same author, which
had been carried out in the pole mass scheme, the 1S mass scheme leads to a
much better behaved perturbative series of the moments, smaller uncertainties
in the mass extraction and to a reduced correlation of the mass and the strong
coupling. We arrive at GeV taking
as an input. From that we determine the
mass as GeV. The error in can be reduced if the three-loop corrections to the relation of
pole and mass are known and if the error in the strong coupling is
decreased.Comment: 20 pages, latex; numbers in Tabs. 2,3,4 corrected, a reference and a
comment on the fitting procedure added, typos in Eqs. 2 and 23 eliminate
Top Quark Pair Production close to Threshold: Top Mass, Width and Momentum Distribution
The complete NNLO QCD corrections to the total cross section in the kinematic region close to the top-antitop
threshold are calculated by solving the corresponding Schroedinger equations
exactly in momentum space in a consistent momentum cutoff regularization
scheme. The corrections coming from the same NNLO QCD effects to the top quark
three-momentum distribution are determined. We discuss
the origin of the large NNLO corrections to the peak position and the
normalization of the total cross section observed in previous works and propose
a new top mass definition, the 1S mass M_1S, which stabilizes the peak in the
total cross section. If the influence of beamstrahlung and initial state
radiation on the mass determination is small, a theoretical uncertainty on the
1S top mass measurement of 200 MeV from the total cross section at the linear
collider seems possible. We discuss how well the 1S mass can be related to the
mass. We propose a consistent way to implement the top quark width
at NNLO by including electroweak effects into the NRQCD matching coefficients,
which then can become complex.Comment: 53 pages, latex; minor changes, a number of typos correcte
Running of the heavy quark production current and 1/k potential in QCD
The 1/k contribution to the heavy quark potential is first generated at one
loop order in QCD. We compute the two loop anomalous dimension for this
potential, and find that the renormalization group running is significant. The
next-to-leading-log coefficient for the heavy quark production current near
threshold is determined. The velocity renormalization group result includes the
alpha_s^3 ln^2(alpha_s) ``non-renormalization group logarithms'' of Kniehl and
Penin.Comment: 30 pages, journal versio
On the form of growing strings
Patterns and forms adopted by Nature, such as the shape of living cells, the
geometry of shells and the branched structure of plants, are often the result
of simple dynamical paradigms. Here we show that a growing self-interacting
string attached to a tracking origin, modeled to resemble nascent polypeptides
in vivo, develops helical structures which are more pronounced at the growing
end. We also show that the dynamic growth ensemble shares several features of
an equilibrium ensemble in which the growing end of the polymer is under an
effective stretching force. A statistical analysis of native states of proteins
shows that the signature of this non-equilibrium phenomenon has been fixed by
evolution at the C-terminus, the growing end of a nascent protein. These
findings suggest that a generic non-equilibrium growth process might have
provided an additional evolutionary advantage for nascent proteins by favoring
the preferential selection of helical structures.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. Let
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