arXiv subjects

Wolfgang Kilian

Publications and source records attributed to Wolfgang Kilian.

49 records · Page 3Linked to original sources

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.

hep-ph↗

arXiv2013

Constraints on Spin-Dependent Short-Range Interaction between Nucleons

We report on the search for a new spin-dependent P- and T-violating interaction between nucleons mediated by light, pseudoscalar bosons such as the axion which was invented to solve the strong CP problem. Our experimental approach is to use an ultra-sensitive low-field magnetometer based on the detection of free precession of co-located 3He and 129Xe nuclear spins using SQUIDs as low-noise magnetic flux detectors. In the presence of an unpolarized mass the precession frequency shif

hep-ex↗

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.

hep-ph↗

arXiv2011

WHIZARD: Simulating Multi-Particle Processes at LHC and ILC

We describe the universal Monte-Carlo event generator WHIZARD. The program automatically computes complete tree-level matrix elements, integrates them over phase space, evaluates distributions of observables, and generates unweighted event samples that can be used directly in detector simulation. There is no principal limit on the process complexity; using current hardware, the program has successfully been applied to hard scattering processes with up to eight particles in the final state. Matrix elements are computed as helicity amplitudes, so spin and color correlations are retained. The Standard Model, the MSSM, and many alternative models such as Little Higgs, anomalous couplings, or effects of extra dimensions or noncommutative SM extensions have been implemented. Using standard interfaces to PDF, beamstrahlung, parton shower and hadronization programs, WHIZARD generates complete physical events and covers physics at hadron, lepton, and photon colliders.

hep-ph↗

arXiv2010

Using Feynman's Tree Theorem to Evaluate Loop Integrals Numerically

We report on a new method for the numerical evaluation of loop integrals, based on the Feynman Tree Theorem. The loop integrals are replaced by phase-space integration over fictitious extra on-shell particles. This integration can be performed alongside with the Monte-Carlo integration of ordinary phase-space, directly leading to NLO event generation.

hep-ph↗

arXiv2009

Numerical Evaluation of Feynman Loop Integrals by Reduction to Tree Graphs

We present a new method for the numerical evaluation of loop integrals which is based on the Feynman Tree Theorem. The loop integrals are replaced by phase-space integration over fictitious extra on-shell particles. This integration can be performed alongside with the Monte-Carlo integration of ordinary phase space, avoiding the time-consuming nesting of loop evaluation inside the integrand, and directly leading to NLO event generation. We systematically construct subtractions, necessary to cancel both ultraviolet divergences and the extra threshold singularities in phase-space which arise in the numerical evaluation. Infrared singularities can be dealt with by standard methods. As a proof of concept, we apply the method to NLO Bhabha scattering in QED and construct the corresponding NLO Monte Carlo event generator.

hep-ph↗

arXiv2008

Resonances and Unitarity in Weak Boson Scattering at the LHC

A crucial test of the Standard Model is the measurement of electroweak gauge-boson scattering. In this paper, we describe a generic parameterization aimed at a realistic simulation of weak-boson scattering at the LHC. The parameterization implements resonances of all possible spin and isospin combinations, properly matched to the low-energy effective (chiral) Lagrangian, includes leading higher-order effects and contains a minimal unitarization scheme. We implement the parameterization in the Monte-Carlo event generator WHIZARD and present results for complete partonic cross-section integration and event generation. We provide a comparison with the effective W approximation that previously has been used for most WW scattering studies at hadron colliders.

hep-ph↗

arXiv2005

Pseudo-Axions in Little Higgs Models

In Little Higgs models, the Higgs mass is stabilized at the one-loop level by the mechanism of collective symmetry breaking. Typically, the basic ingredient of these models is a large(r) global symmetry group spontaneously broken at a scale of several TeV. The (light) Higgs appears as a Goldstone boson corresponding to a non-diagonal broken generator of this global symmetry. There could also be physical pseudoscalar particles present which belong to diagonal generators, having the properties of axions with masses in the range from several GeV up to the electroweak scale. We investigate the interesting phenomenology of these pseudo-axions at the linear collider as well as the photon collider.

hep-ph↗

arXiv1995

Higgs-strahlung and $WW$ fusion in $e^+e^-$ collisions

Higgs-strahlung $e^+e^-\to ZH$ and $WW$ fusion $e^+e^-\to\barν_eν_e H$ are the most important mechanisms for the production of Higgs bosons in $e^+e^-$ collisions at LEP2 and future $e^+e^-$ linear colliders. We have calculated the cross sections and energy/angular distributions of the Higgs boson for these production mechanisms. When the $Z$ boson decays into (electron-)neutrinos, the two production amplitudes interfere. In the cross-over region between the two mechanisms the interference term is positive and of the same size as the individual cross sections, thus enhancing the production rate.

hep-ph↗

arXiv1995

Renormalized Soft-Higgs Theorems

The Higgs couplings to matter fields are proportional to their masses. Thus Higgs amplitudes can be obtained by differentiating amplitudes without Higgs with respect to masses. We show how this well-known statement can be extended to higher order when renormalization effects are taken into account. We establish the connection with the Callan-Symanzik and renormalization group equations and consider also pseudoscalar Higgs couplings to fermions. Furthermore, we address the case where the Higgs couples to a heavy particle that is integrated out from the low-energy effective Lagrangian. We derive effective interactions where mass logarithms are resummed by renormalization-group methods, and give expansions of the results up to next-to-leading order.

hep-ph↗

arXiv1994

Renormalization of Heavy Quark Effective Field Theory: Quantum Action Principles and Equations of Motion

We discuss the quantum action principles and equations of motion for Heavy Quark Effective Field Theory. We prove the so-called equivalence theorem for HQEFT which states that the physical predictions of HQEFT are independent from the choice of interpolating fields. En passant we point out that HQEFT is in fact more subtle than the quantum mechanical Foldy-Wouthuysen transformation.

hep-ph↗

arXiv1993

Unimagined Imaginary Parts in Heavy Quark Effective Field Theory

We argue that the imaginary parts of the anomalous dimensions in the multiparticle sectors of heavy quark effective field theory may be removed by a suitable redefinition of the multiparticle states. The connection between the imaginary parts of the anomalous dimensions and the interquark potential is pointed out

hep-ph↗

arXiv1992

QCD Corrected $1/m_b$ Contributions to $B\bbar$--Mixixng

We calculate the QCD corrected effective Hamiltonian for $B\bbar$--Mixing in heavy quark effective theory including corrections of the order $Λ_{QCD} / m_b$. The matrix elements of the subleading operators are estimated using the vacuum insertion assumption. We show that the major part of the subleading corrections may be absorbed into the heavy meson decay constant $f_B$; the remaining corrections are only due to QCD effects and give an enhancement of $ΔM$ of 5\%.

hep-ph↗