We revisit the renormalisation group equations (RGE) for general renormalisable gauge theories at one- and two-loop accuracy. We identify and correct various mistakes in the literature for the ...β-functions of the dimensionful Lagrangian parameters (the fermion mass, the bilinear and trilinear scalar couplings) as well as the dimensionless quartic scalar couplings. There are two sources for these discrepancies. Firstly, the known expressions for the scalar couplings assume a diagonal wave-function renormalisation which is not appropriate for models with mixing in the scalar sector. Secondly, the dimensionful parameters have been derived in the literature using a dummy field method which we critically re-examine, obtaining revised expressions for the β-function of the fermion mass. We perform an independent cross-check using well-tested supersymmetric RGEs which confirms our results. The numerical impact of the changes in the β-function for the fermion mass terms is illustrated using a toy model with a heavy vector-like fermion pair coupled to a scalar gauge singlet. Unsurprisingly, the correction to the running of the fermion mass becomes sizeable for large Yukawa couplings of the order of O(1). Furthermore, we demonstrate the importance of the correction to the β-functions of the scalar quartic couplings using a general type-III Two-Higgs-Doublet-Model. All the corrected expressions have been implemented in updated versions of the Mathematica package SARAH and the Python package PyR@TE.
We present the reweighting of two sets of nuclear parton distribution functions (PDFs), nCTEQ15 and EPPS16, using a selection of experimental data on heavy-flavor meson D0, J/ψ, B → J/ψ and Υ(1S) ...production in proton-lead collisions at the LHC which were not used in the original determination of these nuclear PDFs. The reweighted PDFs exhibit significantly smaller uncertainties thanks to these new heavy-flavor constraints. We present a comparison with another selection of data from the LHC and relativistic heavy ion collider (RHIC) which were not included in our reweighting procedure. The comparison is overall very good and serves as a validation of these reweighted nuclear PDF sets, which we dub nCTEQ 15rwHF and EPPS 16rwHF. This indicates that the LHC and forward RHIC heavy-flavor data can be described within the standard collinear factorization framework with the same (universal) small-x gluon distribution. We discuss how we believe such reweighted PDFs should be used as well as the limitations of our procedure.
Inclusive charmed-meson production at the CERN LHC Kniehl, Bernd A.; Kramer, Gustav; Schienbein, Ingo ...
The European physical journal. C, Particles and fields,
07/2012, Letnik:
72, Številka:
7
Journal Article
Recenzirano
Odprti dostop
We present predictions for the inclusive production of
D
mesons at the CERN LHC in the general-mass variable-flavor-number scheme at next-to-leading order. Detailed numerical results are compared to ...data where available, or presented in a way to ease future comparisons with experimental results. We also point out that measurements at large rapidity have the potential to pin down models of intrinsic charm.
In the framework of quantum chromodynamics (QCD), parton distribution functions (PDFs) quantify how the momentum and spin of a hadron are divided among its quark and gluon constituents. Two main ...approaches exist to determine PDFs. The first approach, based on QCD factorization theorems, realizes a QCD analysis of a suitable set of hard-scattering measurements, often using a variety of hadronic observables. The second approach, based on first-principle operator definitions of PDFs, uses lattice QCD to compute directly some PDF-related quantities, such as their moments. Motivated by recent progress in both approaches, in this document we present an overview of lattice-QCD and global-analysis techniques used to determine unpolarized and polarized proton PDFs and their moments. We provide benchmark numbers to validate present and future lattice-QCD calculations and we illustrate how they could be used to reduce the PDF uncertainties in current unpolarized and polarized global analyses. This document represents a first step towards establishing a common language between the two communities, to foster dialogue and to further improve our knowledge of PDFs.
A
bstract
Based on the Multiple Point Principle, the Higgs boson mass has been predicted to be 135 ± 9 GeV — more than two decades ago. We study the Multiple Point Principle and its prospects with ...respect to the Two-Higgs-Doublet model (THDM). Applying the bilinear formalism we show that concise conditions can be given with a classification of different kinds of realizations of this principle. We recover cases discussed in the literature but identify also different realizations of the Multiple Point Principle.
We present a new version of PyR@TE, a Python tool for the computation of renormalization group equations for general, non-supersymmetric gauge theories. Its new core relies on a recent paper by Poole ...& Thomsen (2019) to compute the β-functions. In this framework, gauge kinetic mixing is naturally implemented, and the Weyl consistency relations between gauge, quartic and Yukawa couplings are automatically satisfied. One of the main new features is the possibility for the user to compute the gauge coupling β-functions up to the three-loop order. Large parts of the PyR@TE code have been rewritten and improved, including the group theory module PyLie. As a result, the overall performance in terms of computation speed was drastically improved and the model file is more flexible and user-friendly.
Program Title: PyR@TE 3
CPC Library link to program files:https://doi.org/10.17632/8h454kdd5n.2
Licensing provisions: Apache 2.0
Programming language: Python 3
Journal reference of previous version: PyR@TE 1, PyR@TE 2 2
Does the new version supersede the previous version?: Yes.
Reasons for new version: The software was essentially rewritten and new functionalities were added. The performance in terms of computation speed was improved by a factor of 100 to 10000 compared to the previous version. The code now relies on Python 3 instead of the deprecated Python 2.
Summary of revisions: The core of the software was rewritten, based on a new formalism. One of the major new features is the possibility of computing the 3-loop RGEs for gauge couplings. The structure and the syntax of the model file were enhanced. The output of the software was improved.
Nature of problem : Computing the renormalization group equations for any renormalizable, 4-dimensional, non-supersymmetric quantum field theory.
Solution method: Group theory, tensor algebra.
References:
1 F. Lyonnet, I. Schienbein, F. Staub, A. Wingerter, PyR@TE: Renormalization group equations for general gauge theories 185 (3) 1130–1152. http://dx.doi.org/10.1016/j.cpc.2013.12.002.
2 F. Lyonnet, I. Schienbein, PyR@TE 2: A Python tool for computing RGEs at two-loop 213 181–196. http://dx.doi.org/10.1016/j.cpc.2016.12.003.
The sensitivity of particle-level fiducial cross section measurements
from ATLAS, CMS and LHCb to a leptophobic top-colour model is studied.
The model has previously been the subject of resonance ...searches. Here we
compare it directly to state-of-the-art predictions for Standard Model
top quark production and also take into account next-to-leading order
predictions for the new physics signal. We make use of the Contur
framework to evaluate the sensitivity of the current measurements, first
under the default Contur assumption that the measurement and the SM
exactly coincide, and then using the full SM theory calculation for t ¯t
at next-to-leading and next-to-next-to-leading order as the background
model. We derive exclusion limits, discuss the differences between these
approaches, and compare to the limits from resonance searches by ATLAS
and CMS.
We study the relevance of experimental data on heavy-flavor D^{0}, J/ψ, B→J/ψ and ϒ(1S) mesons production in proton-lead collisions at the LHC to improve our knowledge of the gluon-momentum ...distribution inside heavy nuclei. We observe that the nuclear effects encoded in both most recent global fits of nuclear parton densities at next-to-leading order (nCTEQ15 and EPPS16) provide a good overall description of the LHC data. We interpret this as a hint that these are the dominant ones. In turn, we perform a Bayesian-reweighting analysis for each particle data sample which shows that each of the existing heavy-quark(onium) data set clearly points-with a minimal statistical significance of 7σ-to a shadowed gluon distribution at small x in the lead. Moreover, our analysis corroborates the existence of gluon antishadowing. Overall, the inclusion of such heavy-flavor data in a global fit would significantly reduce the uncertainty on the gluon density down to x≃7×10^{-6}-where no other data exist-while keeping an agreement with the other data of the global fits. Our study accounts for the factorization-scale uncertainties which dominate for the charm(onium) sector.
Frontiers of QCD with Precision nPDFs Kusina, Aleksander; Lyonnet, Florian; Olness, Fredrick I. ...
EPJ Web of Conferences,
01/2016, Letnik:
112
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Searches for new physics will increasingly depend on identifying deviations from precision Standard Model (SM) predictions. Quantum Chromodynamics (QCD) will necessarily play a central role in this ...endeavor as it provides the framework for the parton model. However, as we move to higher orders and into extreme kinematic regions, we begin to see the full complexities of the QCD theory. Recent theoretical developments improve our ability to analyze both proton and nuclear PDFs across the full kinematic range. These developments are incorporated into the new nCTEQ15 PDFs, and we review these developments with respect to future measurements, and identify areas where additional effort is required.
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