arXiv subjects

Celine Degrande

Publications and source records attributed to Celine Degrande.

29 records · Page 2Linked to original sources

arXiv2014

Top quarks as a probe for heavy new physics

The heaviest fermion is expected to couple strongly to new physics and appears therefore as a natural probe in many BSM scenarios. Moreover, top physics has now entered in a precision era thanks to the huge amount of top quarks produced at hadron colliders, advanced experimental methods and accurate theoretical predictions. In this talk, we will used effective field theory to search for heavy new physics in a model independent way. This method can also be used to quantify the room left for new physics if no deviation from the SM is found.

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arXiv2014

Automatic evaluation of UV and R2 terms for beyond the Standard Model Lagrangians: a proof-of-principle

The computation of renormalized one-loop amplitudes in quantum field theory requires not only the knowledge of the Lagrangian density and the corresponding Feynman rules, but also that of the ultraviolet counterterms. More in general, and depending also on the methods used in the actual computation of the one-loop amplitudes, additional interactions might be needed. One example is that of the R2 rational terms in the OPP method. In this paper, we argue that the determination of all elements necessary for loop computations in arbitrary models can be automated starting only from information on the Lagrangian at the tree-level. In particular, we show how the R2 rational and ultraviolet counterterms for any renormalizable model can be computed with the help of a new package, which we name NLOCT and builds upon FeynRules and FeynArts. To show the potential of our approach, we calculate all additional rules that are needed to promote a Two Higgs Doublet Model Lagrangian to one-loop computations in QCD and electroweak couplings.

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arXiv2014

FeynRules 2.0 - A complete toolbox for tree-level phenomenology

FeynRules is a Mathematica-based package which addresses the implementation of particle physics models, which are given in the form of a list of fields, parameters and a Lagrangian, into high-energy physics tools. It calculates the underlying Feynman rules and outputs them to a form appropriate for various programs such as CalcHEP, FeynArts, MadGraph, Sherpa and Whizard. Since the original version, many new features have been added: support for two-component fermions, spin-3/2 and spin-2 fields, superspace notation and calculations, automatic mass diagonalization, completely general FeynArts output, a new universal FeynRules output interface, a new Whizard interface, automatic 1 to 2 decay width calculation, improved speed and efficiency, new guidelines for validation and a new web-based validation package. With this feature set, FeynRules enables models to go from theory to simulation and comparison with experiment quickly, efficiently and accurately.

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arXiv2013

Monte Carlo tools for studies of non-standard electroweak gauge boson interactions in multi-boson processes: A Snowmass White Paper

In this Snowmass 2013 white paper, we review the effective field theory approach for studies of non-standard electroweak interactions in electroweak vector boson pair and triple production and vector boson scattering. We present an overview of the implementation of dimension six and eight operators in MadGraph5, VBFNLO, and WHIZARD, and provide relations between the coefficients of these higher dimensions operators used in these programs and in the anomalous couplings approach. We perform a tuned comparison of predictions for multi-boson processes including non-standard electroweak interactions with MadGraph5, VBFNLO, and WHIZARD. We discuss the role of higher-order corrections in these predictions using VBFNLO and a POWHEG BOX implementation of higher-order QCD corrections to WWjj production. The purpose of this white paper is to collect useful tools for the study of non-standard EW physics at the LHC, compare them, and study the main physics issues in the relevant processes.

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arXiv2013

New developments in FeynRules

The program FeynRules is a Mathematica package developed to facilitate the implementation of new physics theories into high-energy physics tools. Starting from a minimal set of information such as the model gauge symmetries, its particle content, parameters and Lagrangian, FeynRules provides all necessary routines to extract automatically from the Lagrangian (that can also be computed semi-automatically for supersymmetric theories) the associated Feynman rules. These can be further exported to several Monte Carlo event generators through dedicated interfaces, as well as translated into a Python library, under the so-called UFO model format, agnostic of the model complexity, especially in terms of Lorentz and/or color structures appearing in the vertices or of number of external legs. In this work, we briefly report on the most recent new features that have been added to FeynRules, including full support for spin-3/2 fermions, a new module allowing for the automated diagonalization of the particle spectrum and a new set of routines dedicated to decay width calculations.

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arXiv2013

BSM constraints from EW measurements

We investigate the impact of heavy new physics on W bosons productions at hadron colliders using an effective field theory. After listing all the relevant dimension-six operators, their effects are computed taking into account LEP constraints. Additionally, the effective approach is compared to anomalous couplings regarding several issues like unitarity.

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arXiv2013

New physics in top decay

After a short introduction to effective field theories, most of their features are illustrated using the top decay. The effects of heavy new physics on the top decay are computed and the constraints on the coefficients of the dimension-six operators are derived from the available measurements.

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arXiv2012

New physics signal in top physics

Effective field theories provide a model independent parametrization of the physics beyond the SM if the new degrees of freedom are heavy and complement thus the searches for resonances. In this talk, I will apply this method to the top sector which is expected to play a special role in many BSM scenarios. I will then show the effects of those dimension-six operators on cross-sections and distributions at hadron colliders. Those results together with the present data from the LHC and the Tevatron already constrain the parameter space

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arXiv2012

Effective Field Theory: A Modern Approach to Anomalous Couplings

We advocate an effective field theory approach to anomalous couplings. The effective field theory approach is the natural way to extend the standard model such that the gauge symmetries are respected. It is general enough to capture any physics beyond the standard model, yet also provides guidance as to the most likely place to see the effects of new physics. The effective field theory approach also clarifies that one need not be concerned with the violation of unitarity in scattering processes at high energy. We apply these ideas to pair production of electroweak vector bosons.

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arXiv2011

An effective approach to same sign top pair production at the LHC and the forward-backward asymmetry at the Tevatron

We study the phenomenology of same sign top pair production at the LHC in a model-independent way. The complete set of dimension six operators involving two top (or anti-top) quarks is introduced and the connection with all possible t- or s-channel particle exchanges is established. Only in the former case, same and opposite sign top pair production can be related. We find that while current Tevatron data disfavor t-channel models, other production mechanisms are viable and can be tested at the LHC.

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arXiv2009

A comprehensive approach to new physics simulations

We describe a framework to develop, implement and validate any perturbative Lagrangian-based particle physics model for further theoretical, phenomenological and experimental studies. The starting point is FeynRules, a Mathematica package that allows to generate Feynman rules for any Lagrangian and then, through dedicated interfaces, automatically pass the corresponding relevant information to any supported Monte Carlo event generator. We prove the power, robustness and flexibility of this approach by presenting a few examples of new physics models (the Hidden Abelian Higgs Model, the general Two-Higgs-Doublet Model, the most general Minimal Supersymmetric Standard Model, the Minimal Higgsless Model, Universal and Large Extra Dimensions, and QCD-inspired effective Lagrangians) and their implementation/validation in FeynArts/FormCalc, CalcHep, MadGraph/MadEvent, and Sherpa.

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