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Jens Erler

Publications and source records attributed to Jens Erler.

At least 91 records · Page 5Linked to original sources

Low Energy Tests of the Weak Interaction

The study of low energy weak interactions of light quarks and leptons continues to provide important insights into both the Standard Model as well as the physics that may lie beyond it. We review the status and future prospects for low energy electroweak physics. Recent important experimental and theoretical developments are discussed and open theoretical issues are highlighted. Particular attention is paid to neutrino physics, searches for permanent electric dipole moments, neutral current tests of the running of the weak mixing angle, weak decays, and muon physics. We argue that the broad range of such studies provides an important complement to high energy collider searches for physics beyond the Standard Model. The use of low energy weak interactions to probe novel aspects of hadron structure is also discussed.

hep-ph↗

Precision Determination of Heavy Quark Masses and the Strong Coupling Constant

We present a new QCD sum rule with high sensitivity to the continuum regions of charm and bottom quark pair production. Combining this sum rule with existing ones yields very stable results for the MS-bar quark masses, m_c(m_c) and m_b(m_b). We introduce a phenomenological parametrization of the continuum interpolating smoothly between the pseudoscalar threshold and asymptotic quark regions. Comparison of our approach with recent BES data allows for a robust theoretical error estimate. The parametric uncertainty due to alpha_s is reduced by performing a simultaneous fit to the most precise sum rules and other high precision observables. This includes a new evaluation of the lifetime of the tau lepton, tau_tau, serving as a strong constraint on alpha_s. Our results are m_c(m_c) = 1.289 +0.040 -0.045 GeV, m_b(m_b) = 4.207 +0.030 -0.031 GeV (with a correlation of 29%), and alpha_s(M_Z) [tau_tau] = 0.1221 +0.0026 -0.0023.

hep-ph↗

QCD Sum Rules and the Determination of Fundamental Parameters

We present a new QCD sum rule with high sensitivity to the continuum regions of charm and bottom quark pair production. Combining this sum rule with existing ones yields very stable results for the msbar quark masses, m_c(m_c)$ and m_b (m_b). Comparison of our approach with experimental data allows for a robust theoretical error estimate. We have also provided a new evaluation of the lifetime of the tau lepton, serving as a strong constraint on alpha_s.

hep-ph↗

The Weak Charge of the Proton and New Physics

We address the physics implications of a precision determination of the weak charge of the proton, QWP, from a parity violating elastic electron proton scattering experiment to be performed at the Jefferson Laboratory. We present the Standard Model (SM) expression for QWP including one-loop radiative corrections, and discuss in detail the theoretical uncertainties and missing higher order QCD corrections. Owing to a fortuitous cancellation, the value of QWP is suppressed in the SM, making it a unique place to look for physics beyond the SM. Examples include extra neutral gauge bosons, supersymmetry, and leptoquarks. We argue that a QWP measurement will provide an important complement to both high energy collider experiments and other low energy electroweak measurements. The anticipated experimental precision requires the knowledge of the order alpha_s corrections to the pure electroweak box contributions. We compute these contributions for QWP, as well as for the weak charges of heavy elements as determined from atomic parity violation.

hep-ph↗

Electroweak Standard Model and Precision Tests

I give an introduction and overview of recent developments in high precision tests of the Standard Model. This includes a summary of Z-pole measurements, a brief account of the NuTeV result on neutrino-nucleon scattering, the anomalous magnetic moment of the muon, and implications for the Higgs boson mass.

hep-ph↗

Electroweak Radiative Corrections to Semileptonic Tau Decays

I present an update on the electroweak radiative correction factor to semileptonic tau decays, including a next-to-leading order resummation of large logarithms. My result differs both qualitatively and quantitatively from the one recently obtained by Davier et al. As two consequences, (i) the discrepancy between the predictions for the muon g-2 based on tau decay data and electron-positron annihilation data increases, and (ii) the g-2 prediction based on tau decay data appears to be consistent (within about one standard deviation) with the experimental result from BNL.

hep-ph↗

The Z-Z' Mass Hierarchy in a Supersymmetric Model with a Secluded U(1)'-Breaking Sector

We consider the Z'/Z mass hierarchy in a supersymmetric model in which the U(1)' is broken in a secluded sector coupled to the ordinary sector only by gauge and possibly soft terms. A large mass hierarchy can be achieved while maintaining the normal sparticle spectra if there is a direction in which the tree level potential becomes flat when a particular Yukawa coupling vanishes. We describe the conditions needed for the desired breaking pattern, to avoid unwanted global symmetries, and for an acceptable effective mu parameter. The electroweak breaking is dominated by A terms rather than scalar masses, leading to tan beta ~ 1. The spectrum of the symmetry breaking sector is displayed. There is significant mixing between the MSSM particles and new standard model singlets, for both the Higgs scalars and the neutralinos. A larger Yukawa coupling for the effective mu parameter is allowed than in the NMSSM because of the U(1)' contribution to the running from a high scale. The upper bound on the tree-level mass of the lightest CP even Higgs doublet mass is about c x 174 GeV, where c is of order unity, but the actual mass eigenvalues are generally smaller because of singlet mixing.

hep-ph↗

Determinations of alpha(M_Z): Comparison and Prospects

I review and compare various techniques to obtain the value of the QED coupling, alpha, at the Z pole. GigaZ precisions would require a much more accurate determination than available today. A combination of the virtues of current methods may help to achieve this goal.

hep-ph↗

On Type II Superstrings in Less Than Four Dimensions

We study gauge theories which are associated with classical vacua of perturbative Type II string theory that allows for a conformal field theory description. We show that even if we compactify seven spatial dimensions (allowing for one macroscopic dimension to arise non-perturbatively) the Standard Model cannot be obtained from the perturbative sector of Type II superstrings. Therefore, the construction of the Standard Model (or extensions thereof) from M theory must involve fields that are non-perturbative from the Type II perspective. We also address the case of eight compact dimensions.

hep-th↗

Hadronic Loop Corrections to the Muon Anomalous Magnetic Moment

The dominant theoretical uncertainties in both, the anomalous magnetic moment of the muon and the value of the electromagnetic coupling at the Z scale arise from their hadronic contributions. Since these will ultimately dominate the experimental errors, we study the correlation between them, as well as with other fundamental parameters. To this end we present analytical formulas for the QCD contribution from higher energies and from heavy quarks. Including these correlations affects the Higgs boson mass extracted from precision data.

hep-ph↗

Fundamental Parameters from Precision Tests

I review how electroweak precision observables can be used to constrain the Higgs boson mass and the strong coupling constant. Implications for physics beyond the Standard Model are also addressed.

hep-ph↗

GigaZ: High Precision Tests of the SM and the MSSM

The high-energy lepton collider TESLA can be operated in the GigaZ mode on the Z resonance, producing a billion Z bosons per year. This will allow the measurement of the effective electroweak mixing angle to an accuracy much better than one part in 10,000. Similarly, the W boson mass is expected to be measurable with an error of 6 MeV near threshold. We discuss the impact of these observables on the accuracy with which the Higgs boson mass can be determined from loop corrections within the Standard Model. We also study indirect constraints on new mass scales within the Minimal Supersymmetric Standard Model.

hep-ph↗

The Probability Density of the Higgs Boson Mass

The LEP Collaborations have reported a small excess of events in their combined Higgs boson analysis at center of mass energies up to about 208 GeV. In this communication, I present the result of a calculation of the probability distribution function of the Higgs boson mass which can be rigorously obtained if the validity of the Standard Model is assumed. It arises from the combination of the most recent set of precision electroweak data and the current results of the Higgs searches at LEP 2.

hep-ph↗

Chiral Models of Weak Scale Supersymmetry

I discuss supersymmetric extensions of the Standard Model containing an extra U(1)' gauge symmetry which provide a solution to the mu-problem and at the same time protect the proton from decaying via dimension 4 operators. Moreover, all fields are protected by chirality and supersymmetry from acquiring high scale masses. The additional requirements of anomaly cancellation and gauge coupling unification imply the existence of extra matter multiplets and that several fields participate in U(1)' symmetry breaking simultaneously. While there are several studies addressing subsets of these requirements, this work uncovers simultaneous solutions to all of them. It is surprising and encouraging that extending the Minimal Supersymmetric Standard Model by a simple U(1) factor solves its major drawbacks with respect to the non-supersymmetric Standard Model, especially as current precision data seem to offer a hint to the existence of its corresponding Z' boson. It is also remarkable that there are many solutions where the U(1)' charges of the known quarks and leptons are predicted to be identical to those E_6 motivated Z' bosons which give the best fit to the data. I discuss the solutions to these constraints including some phenomenological implications.

hep-ph↗

Global Fits to Electroweak Data Using GAPP

At Run II of the Tevatron it will be possible to measure the W boson mass with a relative precision of about 2 times 10^-4, which will eventually represent the best measured observable beyond the input parameters of the SM. Proper interpretation of such an ultrahigh precision measurement, either within the SM or beyond, requires the meticulous implementation and control of higher order radiative corrections. The FORTRAN package GAPP, described here, is specifically designed to meet this need and to ensure the highest possible degrees of accuracy, reliability, adaptability, and efficiency.

hep-ph↗

Indications for an Extra Neutral Gauge Boson in Electroweak Precision Data

A new analysis of the hadronic peak cross section at LEP 1 implies a small amount of missing invisible width in Z decays, while the effective weak charge in atomic parity violation has been determined recently to 0.6% accuracy, indicating a significantly negative S parameter. As a consequence of these two deviations, the data are described well if the presence of an additional Z' boson, such as predicted in Grand Unified Theories, is assumed. Moreover, the data are now rich enough to study an arbitrary extra Z' boson and to determine its couplings in a model independent way. An excellent best fit to the data is obtained in this case, suggesting the possibility of a family non-universal Z' with properties similar to ones predicted in a class of superstring theories.

hep-ph↗