214 research outputs found
BCFW recursion for TMD parton scattering
We investigate the application of the BCFW recursion relation to scattering
amplitudes with one off-shell particle in a Yang-Mills theory with fermions. We
provide a set of conditions of applicability of the BCFW recursion, stressing
some important differences with respect to the pure on-shell case. We show how
the formulas for Maximally-Helicity-Violating (MHV) configurations with any
number of partons, which are well known in the fully on-shell case, are
generalized to this kinematic regime. We also derive analytic expressions for
all the helicity configurations of the 5-point color-stripped tree-level
amplitudes for any of the partons being off the mass shell.Comment: Some typos in text and formulas correcte
Calculation of the Z+jet cross section including transverse momenta of initial partons
We perform calculations of Z+jet cross-section taking into account the
transverse momenta of the initial partons. Transverse Momentum Dependent (TMD)
parton densities obtained with the Parton Branching method are used and higher
order corrections are included via TMD parton showers in the initial state. The
predictions are compared to measurements of forward Z+jet production of the
LHCb collaboration at TeV. We show that the results obtained in
kT-factorization are in good agreement with results obtained from a NLO
calculation matched with traditional parton showers. We also demonstrate that
in the forward rapidity region, kT-factorization and hybrid factorization
predictions agree with each other.Comment: 16 pages, 8 figure
NLO QCD calculations with HELAC-NLO
Achieving a precise description of multi-parton final states is crucial for
many analyses at LHC. In this contribution we review the main features of the
HELAC-NLO system for NLO QCD calculations. As a case study, NLO QCD corrections
for tt + 2 jet production at LHC are illustrated and discussed.Comment: 7 pages, 4 figures. Presented at 10th DESY Workshop on Elementary
Particle Theory: Loops and Legs in Quantum Field Theory, Worlitz, Germany,
April 25-30, 201
Helac-nlo
Based on the OPP technique and the HELAC framework, HELAC-1LOOP is a program
that is capable of numerically evaluating QCD virtual corrections to scattering
amplitudes. A detailed presentation of the algorithm is given, along with
instructions to run the code and benchmark results. The program is part of the
HELAC-NLO framework that allows for a complete evaluation of QCD NLO
corrections.Comment: minor text revisions, version to appear in Comput.Phys.Commu
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Single-jet inclusive rates with exact color at O (αs4)
Next-to-next-to-leading order QCD predictions for single-, double- and even
triple-differential distributions of jet events in proton-proton collisions
have recently been obtained using the NNLOjet framework based on antenna
subtraction. These results are an important input for Parton Distribution
Function fits to hadron-collider data. While these calculations include all of
the partonic channels occurring at this order of the perturbative expansion,
they are based on the leading-color approximation in the case of channels
involving quarks and are only exact in color in the pure-gluon channel. In the
present publication, we verify that the sub-leading color effects in the
single-jet inclusive double-differential cross sections are indeed negligible
as far as phenomenological applications are concerned. This is the first
independent and complete calculation for this observable. We also take the
opportunity to discuss the necessary modifications of the sector-improved
residue subtraction scheme that made this work possible
Golem95C: A library for one-loop integrals with complex masses
We present a program for the numerical evaluation of scalar integrals and
tensor form factors entering the calculation of one-loop amplitudes which
supports the use of complex masses in the loop integrals. The program is built
on an earlier version of the golem95 library, which performs the reduction to a
certain set of basis integrals using a formalism where inverse Gram
determinants can be avoided. It can be used to calculate one-loop amplitudes
with arbitrary masses in an algebraic approach as well as in the context of a
unitarity-inspired numerical reconstruction of the integrand.Comment: 22 pages, 3 figure
Advances in the identification of novel factors required in soybean nodulation, a process critical to sustainable agriculture and food security
Nodulation is a process of organogenesis that results from a symbiotic relationship between legume plants and soil-dwelling, nitrogen-fixing bacteria, called rhizobia. The rhizobia are housed in newly formed structures on the host roots, called nodules. Within nodules, the rhizobia fix atmospheric N2 into useable forms of nitrogen for the plant. This process is highly important to agriculture, as nitrogen is critical for plant growth and development and is typically the main component of fertilizers. Although fertilizers are effective, they are expensive and often pollute, making biological alternatives, such as legume nodulation, attractive for use in agriculture. Nodulation is regulated by the auto regulation of nodulation (AON) pathway, which enables the host plant to balance its needs between nitrogen acquisition and energy expenditure. Current research is elucidating the nodule development and AON signalling networks. Recent technological advances, such as RNA-sequencing, are revolutionizing the discovery of genes that are critical to nodulation. The discovery of such genes not only enhances our knowledge of the nodulation signalling network, but may help to underpin future work to isolate superior legume crops via modern breeding and engineering practices. Here, recent advances using the cutting-edge technique of RNA sequencing to identify new nodulation genes in soybean are discussed
Towards LHC phenomenology at the loop level: A new method for one-loop amplitudes
A precise understanding of LHC phenomenology requires the inclusion of
one-loop corrections for multi-particle final states. In this talk we describe
a semi-numerical method to compute one-loop amplitudes with many external
particles and present first applications.Comment: 5 pages latex, 1 ps fig., 1 eps fig., Conference Proceedings Radcor
200
Dijet azimuthal correlations in p-p and p-Pb collisions at forward LHC calorimeters
We present a state-of-the-art computation for the production of forward
dijets in proton-proton and proton-lead collisions at the LHC, in rapidity
domains covered by the ATLAS calorimeter and the planned FoCal extension of the
ALICE detector. We use the small-x improved TMD (ITMD) formalism, together with
collinearly improved TMD gluon distributions and full b-space Sudakov
resummation, and discuss nonperturbative corrections due to hadronization and
showers using the Pythia event generator. We observe that forward dijets in
proton-nucleus collisions at moderately low pT are excellent probes of
saturation effects, as the Sudakov resummation does not alter the suppression
of the cross section.Comment: 14 page
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