556 research outputs found
Higgs production in association with bottom quarks
We study the production of a Higgs boson in association with bottom quarks in
hadronic collisions, and present phenomenological predictions relevant to the
13 TeV LHC. Our results are accurate to the next-to-leading order in QCD, and
matched to parton showers through the MC@NLO method; thus, they are fully
differential and based on unweighted events, which we shower by using both
Herwig++ and Pythia8. We perform the computation in both the four-flavour and
the five-flavour schemes, whose results we compare extensively at the level of
exclusive observables. In the case of the Higgs transverse momentum, we also
consider the analytically-resummed cross section up to the NNLO+NNLL accuracy.
In addition, we analyse at the effects of the
interference between the and gluon-fusion production modes.Comment: 33 pages, 17 figure
Higgs pair production at the LHC with NLO and parton-shower effects
We present predictions for the SM-Higgs-pair production channels of relevance
at the LHC: gluon-gluon fusion, VBF, and top-pair, W, Z and single-top
associated production. All these results are at the NLO accuracy in QCD, and
matched to parton showers by means of the MC@NLO method; hence, they are fully
differential. With the exception of the gluon-gluon fusion process, for which a
special treatment is needed in order to improve upon the infinite-top-mass
limit, our predictions are obtained in a fully automatic way within the
publicly available MadGraph5_aMC@NLO framework. We show that for all channels
in general, and for gluon-gluon fusion and top-pair associated production in
particular, NLO corrections reduce the theoretical uncertainties, and are
needed in order to arrive at reliable predictions for total rates as well as
for distributions.Comment: 11 pages, 7 figures, version accepted for publication on PL
The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
We discuss the theoretical bases that underpin the automation of the
computations of tree-level and next-to-leading order cross sections, of their
matching to parton shower simulations, and of the merging of matched samples
that differ by light-parton multiplicities. We present a computer program,
MadGraph5_aMC@NLO, capable of handling all these computations -- parton-level
fixed order, shower-matched, merged -- in a unified framework whose defining
features are flexibility, high level of parallelisation, and human intervention
limited to input physics quantities. We demonstrate the potential of the
program by presenting selected phenomenological applications relevant to the
LHC and to a 1-TeV collider. While next-to-leading order results are
restricted to QCD corrections to SM processes in the first public version, we
show that from the user viewpoint no changes have to be expected in the case of
corrections due to any given renormalisable Lagrangian, and that the
implementation of these are well under way.Comment: 158 pages, 27 figures; a few references have been adde
Single-top t-channel hadroproduction in the four-flavour scheme with POWHEG and aMC@NLO
We present results for the QCD next-to-leading order (NLO) calculation of
single-top t-channel production in the 4-flavour scheme, interfaced to Parton
Shower (PS) Monte Carlo programs according to the POWHEG and MC@NLO methods.
Comparisons between the two methods, as well as with the corresponding process
in the 5-flavour scheme are presented. For the first time results for typical
kinematic distributions of the spectator-b jet are presented in an NLO+PS
approach.Comment: 16+1 pages, 8 figures, matches version accepted for publication in
JHE
NLO Higgs boson production plus one and two jets using the POWHEG BOX, MadGraph4 and MCFM
We present a next-to-leading order calculation of Higgs boson production plus
one and two jets via gluon fusion interfaced to shower Monte Carlo programs,
implemented according to the POWHEG method. For this implementation we have
used a new interface of the POWHEG BOX with MadGraph4, that generates the codes
for generic Born and real processes automatically. The virtual corrections have
been taken from the MCFM code. We carry out a simple phenomenological study of
our generators, comparing them among each other and with fixed next-to-leading
order results.Comment: 27 pages, 21 figure
Scalar and pseudoscalar Higgs production in association with a top-antitop pair
We present the calculation of scalar and pseudoscalar Higgs production in
association with a top-antitop pair to the next-to-leading order (NLO) accuracy
in QCD, interfaced with parton showers according to the MC@NLO formalism. We
apply our results to the cases of light and very light Higgs boson production
at the LHC, giving results for total rates as well as for sample differential
distributions, relevant to the Higgs, to the top quarks, and to their decay
products. This work constitutes the first phenomenological application of
aMC@NLO, a fully automated approach to complete event generation at NLO in QCD.Comment: 15 pages, 8 figures, published version. (2 references added, improved
description of the decay of the top and Higgs bosons
A symmetry-preserving second-order time-accurate PISO-based method
A new conservative symmetry-preserving second-order time-accurate PISO-based pressure-velocity coupling for solving the incompressible Navier-Stokes equations on unstructured collocated grids is presented in this paper. This new method for implicit time stepping is an extension of the conservative symmetry-preserving incremental-pressure projection method for explicit time stepping and unstructured collocated meshes of Trias et al. [35]. In order to assess and compare both methods, we have implemented them within one unified solver in the open source code OpenFOAM where we use a Butcher array to prescribe the Runge-Kutta method. Thus, by changing the entries of the Butcher array, explicit and diagonally implicit Runge-Kutta schemes can be combined into one solver. We assess the energy conservation properties of the implemented discretisation methods and the temporal consistency of the selected Runge-Kutta schemes using Taylor-Green vortex and lid-driven cavity flow test cases. Finally, we use a more complex turbulent channel flow test case in order to further assess the performance of the presented new conservative symmetry-preserving incremental-pressure PISO-based method. Although both implemented methods are based on a symmetry-preserving discretisation, we show they still produce a small amount of numerical dissipation when the total pressure is directly solved from a Poisson equation. When an incremental-pressure approach is used, where a pressure correction is solved from a Poisson equation, both methods are effectively fully-conservative. For high-fidelity simulations of incompressible turbulent flows, it is highly desirable to use fully-conservative methods. For such simulations, the presented numerical methods are therefore expected to have large added value, since they pave the way for the execution of truly energy-conservative high-fidelity simulations in complex geometries. Furthermore, both methods are implemented in OpenFOAM, which is widely used within the CFD community, so that a large part of this community can benefit from the developed and implemented numerical methods
Semi-Parametric Drift and Diffusion Estimation for Multiscale Diffusions
We consider the problem of statistical inference for the effective dynamics
of multiscale diffusion processes with (at least) two widely separated
characteristic time scales. More precisely, we seek to determine parameters in
the effective equation describing the dynamics on the longer diffusive time
scale, i.e. in a homogenization framework. We examine the case where both the
drift and the diffusion coefficients in the effective dynamics are
space-dependent and depend on multiple unknown parameters. It is known that
classical estimators, such as Maximum Likelihood and Quadratic Variation of the
Path Estimators, fail to obtain reasonable estimates for parameters in the
effective dynamics when based on observations of the underlying multiscale
diffusion. We propose a novel algorithm for estimating both the drift and
diffusion coefficients in the effective dynamics based on a semi-parametric
framework. We demonstrate by means of extensive numerical simulations of a
number of selected examples that the algorithm performs well when applied to
data from a multiscale diffusion. These examples also illustrate that the
algorithm can be used effectively to obtain accurate and unbiased estimates.Comment: 32 pages, 10 figure
Supramolecular Nucleoside-Based Gel:Molecular Dynamics Simulation and Characterization of Its Nanoarchitecture and Self-Assembly Mechanism
Among the diversity of existing supramolecular hydrogels, nucleic acid-based hydrogels are of particular interest for potential drug delivery and tissue engineering applications because of their inherent biocompatibility. Hydrogel performance is directly related to the nanostructure and the self-assembly mechanism of the material, an aspect that is not well-understood for nucleic acid-based hydrogels in general and has not yet been explored for cytosine-based hydrogels in particular. Herein, we use a broad range of experimental characterization techniques along with molecular dynamics (MD) simulation to demonstrate the complementarity and applicability of both approaches for nucleic acid-based gelators in general and propose the self-assembly mechanism for a novel supramolecular gelator, N4-octanoyl-2′-deoxycytidine. The experimental data and the MD simulation are in complete agreement with each other and demonstrate the formation of a hydrophobic core within the fibrillar structures of these mainly water-containing materials. The characterization of the distinct duality of environments in this cytidine-based gel will form the basis for further encapsulation of both small hydrophobic drugs and biopharmaceuticals (proteins and nucleic acids) for drug delivery and tissue engineering applications
Automation of one-loop QCD corrections
We present the complete automation of the computation of one-loop QCD
corrections, including UV renormalization, to an arbitrary scattering process
in the Standard Model. This is achieved by embedding the OPP integrand
reduction technique, as implemented in CutTools, into the MadGraph framework.
By interfacing the tool so constructed, which we dub MadLoop, with MadFKS, the
fully automatic computation of any infrared-safe observable at the
next-to-leading order in QCD is attained. We demonstrate the flexibility and
the reach of our method by calculating the production rates for a variety of
processes at the 7 TeV LHC.Comment: 64 pages, 12 figures. Corrected the value of m_Z in table 1. In table
2, corrected the values of cross sections in a.4 and a.5 (previously computed
with mu=mtop/2 rather than mu=mtop/4). In table 2, corrected the values of
NLO cross sections in b.3, b.6, c.3, and e.7 (the symmetry factor for a few
virtual channels was incorrect). In sect. A.4.3, the labeling of the
four-momenta was incorrec
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