Search results for "loop"
showing 10 items of 608 documents
Magnetohydrodynamic simulations of the ejection of a magnetic flux rope
2013
Context. Coronal mass ejections (CME's) are one of the most violent phenomena found on the Sun. One model to explain their occurrence is the flux rope ejection model. In this model, magnetic flux ropes form slowly over time periods of days to weeks. They then lose equilibrium and are ejected from the solar corona over a few hours. The contrasting time scales of formation and ejection pose a serious problem for numerical simulations. Aims: We simulate the whole life span of a flux rope from slow formation to rapid ejection and investigate whether magnetic flux ropes formed from a continuous magnetic field distribution, during a quasi-static evolution, can erupt to produce a CME. Methods: To …
Homology modeling of an RNP domain from a human RNA-binding protein: Homology-constrained energy optimization provides a criterion for distinguishing…
1998
We have recently described an automated approach for homology modeling using restrained molecular dynamics and simulated annealing procedures (Li et al, Protein Sci., 6:956-970,1997). We have employed this approach for constructing a homology model of the putative RNA-binding domain of the human RNA-binding protein with multiple splice sites (RBP-MS). The regions of RBP-MS which are homologous to the template protein snRNP U1A were constrained by "homology distance constraints," while the conformation of the non-homologous regions were defined only by a potential energy function. A full energy function without explicit solvent was employed to ensure that the calculated structures have good …
Predictive modeling of aryl hydrocarbon receptor (AhR) agonism
2020
Abstract The aryl hydrocarbon receptor (AhR) plays a key role in the regulation of gene expression in metabolic machinery and detoxification systems. In the recent years, this receptor has attracted interest as a therapeutic target for immunological, oncogenic and inflammatory conditions. In the present report, in silico and in vitro approaches were combined to study the activation of the AhR. To this end, a large database of chemical compounds with known AhR agonistic activity was employed to build 5 classifiers based on the Adaboost (AdB), Gradient Boosting (GB), Random Forest (RF), Multilayer Perceptron (MLP) and Support Vector Machine (SVM) algorithms, respectively. The built classifier…
Multiple polylogarithms with algebraic arguments and the two-loop EW-QCD Drell-Yan master integrals
2020
We consider Feynman integrals with algebraic leading singularities and total differentials in $\epsilon\,\mathrm{d}\ln$ form. We show for the first time that it is possible to evaluate integrals with singularities involving unrationalizable roots in terms of conventional multiple polylogarithms, by either parametric integration or matching the symbol. As our main application, we evaluate the two-loop master integrals relevant to the $\alpha \alpha_s$ corrections to Drell-Yan lepton pair production at hadron colliders. We optimize our functional basis to allow for fast and stable numerical evaluations in the physical region of phase space.
A simple formula for the infrared singular part of the integrand of one-loop QCD amplitudes
2010
We show that a well-known simple formula for the explicit infrared poles of one-loop QCD amplitudes has a corresponding simple counterpart in unintegrated form. The unintegrated formula approximates the integrand of one-loop QCD amplitudes in all soft and collinear singular regions. It thus defines a local counter-term for the infrared singularities and can be used as an ingredient for the numerical calculation of one-loop amplitudes.
The importance of being rigid: D6-brane model building on with discrete torsion
2013
Model building with rigid D6-branes on the Type IIA orientifold onT 6 =Z2 Z 0 with discrete torsion is considered. The systematic search for models of particle physics is signicantly reduced by proving new symmetries among dierent lattice orientations. Suitable rigid D6-branes without matter in adjoint and symmetric representations are classied, and SO(2N) and USp(2N) gauge factors on orientifold invariant D6-branes are distinguished in terms of their discrete Wilson line and displacement parameters. Constraints on the nonexistence of exotic matter prohibit global completions of local MSSM and leftright symmetric models, while globally dened supersymmetric Pati-Salam models are found. For t…
Electroweak Higgs Boson Plus Three Jet Production at Next-to-Leading-Order QCD
2013
We calculate next-to-leading order (NLO) QCD corrections to electroweak Higgs boson plus three jet production. Both vector boson fusion (VBF) and Higgs-strahlung type contributions are included along with all interferences. The calculation is implemented within the MATCHBOX NLO framework of the HERWIG++ event generator.
Complete amplitude and cross section structure of one-loop contributions toe + e ??q $$\bar q$$ g
1985
We calculate theO(α 2 ) one-loop contributions to the seven (inn≠4) independent invariant amplitudes describinge + e −→q $$\bar q$$ g in massless QCD. After folding with theO(α 1/2 ) Born term contribution we obtain the nine independentO(α 2 ) structure functions that describe the parity-conserving and parity-violating contributions toe + e −→q $$\bar q$$ g. We use dimensional regularization to control infrared and ultraviolet divergencies.
The real–virtual antenna functions forS→QQ¯Xat NNLO QCD
2014
Abstract We determine, in the antenna subtraction framework for handling infrared divergences in higher order QCD calculations, the real–virtual antenna functions for processes involving the production of a pair of massive quarks by an uncolored initial state at NNLO QCD. The integrated leading and subleading color real–virtual antenna functions are computed analytically in terms of (cyclotomic) harmonic polylogarithms. As a by-product and check we compute R Q = σ ( e + e − → γ ⁎ → Q Q ¯ X ) / σ ( e + e − → γ ⁎ → μ + μ − ) and compare with existing results. Our result for R Q is exact to order α s 2 .
Asymptotic 3-loop heavy flavor corrections to the charged current structure functions FLW+−W−(x,Q2) and F2W+−W−(x,Q2)
2016
We derive the massive Wilson coefficients for the heavy flavor contributions to the nonsinglet charged current deep-inelastic scattering structure functions ${F}_{L}^{{W}^{+}}(x,{Q}^{2})\ensuremath{-}{F}_{L}^{{W}^{\ensuremath{-}}}(x,{Q}^{2})$ and ${F}_{2}^{{W}^{+}}(x,{Q}^{2})\ensuremath{-}{F}_{2}^{{W}^{\ensuremath{-}}}(x,{Q}^{2})$ in the asymptotic region ${Q}^{2}\ensuremath{\gg}{m}^{2}$ to 3-loop order in quantum chromodynamics at general values of the Mellin variable $N$ and the momentum fraction $x$. Besides the heavy quark pair production, also the single heavy flavor excitation $s\ensuremath{\rightarrow}c$ contributes. Numerical results are presented for the charm quark contributions, …