arXiv subjects
Publications and source records attributed to Reinhold Rückl.
We study phenomenological consequences of a noncommutative extension of the standard model in the theta-expanded approach at the ILC. We estimate the sensitivity of the ILC for the noncommutative scale Lambda_NC. Comparing with earlier estimates for the LHC, we demonstrate the complementarity of the experiments at the two colliders.
We derive the most general Seiberg-Witten maps for noncommutative gauge theories in second order of the noncommutative parameter theta. Our results reveal the existence of more ambiguities than previously known. In particular, we demonstrate that some of these ambiguities enter observables like scattering cross sections and enlarge the parameter space of the noncommutative standard model beyond O(theta).
We study collider signals for the noncommutative extension of the standard model using the Seiberg-Witten maps for SU(3)_C x SU(2)_L x U(1)_Y to first order in the noncommutativity parameters theta_munu. In particular, we investigate the ensitivity of Z-gamma-production at the Tevatron and the LHC to the components of theta_munu. We discuss the range of validity of this approximation and estimate exclusion limits from a Monte Carlo simulation.
We discuss the non-commutative extension of the standard model constructed with the Seiberg-Witten maps for SU(3)_C x SU(2)_L x U(1)_Y. Using the first-order approximation in the non-commutative parameters theta, we estimate the sensitivity of Z-gamma-production at the Tevatron and LHC from Monte Carlo simulation.
Five-dimensional field theories compactified on an S^1/Z_2 orbifold naturally include local brane kinetic terms at the orbifold fixed points at the tree as well as the quantum level. We study the quantization of these theories before the Kaluza--Klein reduction and derive the relevant Ward and Slavnov-Taylor identities that result from the underlying gauge and Becchi-Rouet-Stora symmetries of the theory. With the help of these identities, we obtain a generalization of the equivalence theorem, where the known high-energy equivalence relation between the longitudinal Kaluza-Klein gauge modes and their respective would-be Goldstone bosons is extended to consistently include the energetically suppressed terms in the high-energy scatterings. Demanding perturbative unitarity, we compute upper limits on the number of the Kaluza-Klein modes. We find that these limits weakly depend on the size of the brane kinetic terms.
We analyze non-universal 5D standard model extension, where some or all of the gauge and Higgs fields propagate in a flat extra dimension, while all other degrees of freedom are localized on a S^1/Z_2 orbifold brane. From LEP data, model-dependent bounds on the compactification scale M between 4 and 6 TeV are derived. We analyze the correlations between M and the SM Higgs mass m_H. Investigating the prospects at an e^+e^- linear collider such as TESLA, we show that the so-called GigaZ option has the potential to improve the LEP bounds by about a factor 2. At the center of mass energy of 800 GeV and with an integrated luminosity of 10^3 fb^{-1}, linear collider experiments can probe compactification scales up to 20-30 TeV and beyond, depending on the systematic errors.
We derive new improved constraints on the compactification scale of minimal 5-dimensional (5D) extensions of the Standard Model (SM) from electroweak and LEP2 data and estimate the reach of an e^+e^- linear collider such as TESLA. Our analysis is performed within the framework of non-universal 5D models, where some of the gauge and Higgs fields propagate in the extra dimension, while all fermions are localized on a S^1/Z_2 orbifold fixed point. Carrying out simultaneous multi-parameter fits of the compactification scale and the SM parameters to the data, we obtain lower bounds on this scale in the range between 4 and 6 TeV. These fits also yield the correlation of the compactification scale with the SM Higgs mass. Investigating the prospects at TESLA, we show that the so-called GigaZ option has the potential to improve these bounds by about a factor 2 in almost all 5D models. Furthermore, at the center of mass energy of 800 GeV and with an integrated luminosity of 10^3 fb^-1, linear collider experiments can probe compactification scales up to 20-30 TeV, depending on the control of systematic errors.
We study Ward identities for simple processes with external gauge bosons in the time-ordered perturbation theory approach to time-like noncommutative gauge theories. We demonstrate that these Ward identities cannot be satisfied when all orders in the noncommutativity parameters theta_i0 are taken into account. We conclude that in time-ordered perturbation theory one cannot solve the unitarity problem of time-like noncommutative quantum field theories.
We study minimal 5-dimensional extensions of the Standard Model, in which all or only some of the SU(2)$_L$ and U(1)$_Y$ gauge fields and Higgs bosons propagate in the fifth compact dimension. In all the 5-dimensional settings, the fermions are assumed to be localized on a 3-brane. In addition, we present the consistent procedure for quantizing 5-dimensional models in the generalized $R_ξ$ gauge. Bounds on the compactification scale between 4 and 6 TeV, depending on the model, are established by analyzing electroweak precision measurements and LEP2 cross sections.
I review the basic ideas behind lattice QCD calculations that involve charm and bottom quarks. I report on the progress in getting the correct hyperfine splitting in charmonium from lattice QCD. Some of the basic technology behind numerical lattice QCD calculations is explained by studying some specific examples: computation of the charm quark mass, and the calculation of fB.
We derive electroweak constraints on the compactification scale of minimal 5-dimensional extensions of the Standard Model, in which all or only some of the SU(2)$_L$ and U(1)$_Y$ gauge fields and Higgs bosons feel the presence of the fifth dimension. In our analysis, we assume that the fermions are always localized on a 3-brane. In this context, we also present the consistent quantization procedure of the higher-dimensional models in the generalized $R_ξ$ gauge. We find that the usually derived lower bound of $\sim 4$ TeV on the compactification scale may be significantly lowered to $\sim 3$ TeV if the SU(2)$_L$ gauge boson is the only particle that propagates in all 5 dimensions.
We consider minimal 5-dimensional extensions of the Standard Model compactified on an $S^1/Z_2$ orbifold, in which the SU(2)$_L$ and U(1)$_Y$ gauge fields and Higgs bosons may or may not all propagate in the fifth dimension while the observable matter is always assumed to be confined to a 4-dimensional subspace. We pay particular attention to consistently quantize the higher-dimensional models in the generalized $R_ξ$ gauge and derive analytic expressions for the mass spectrum of the resulting Kaluza-Klein states and their couplings to matter. Based on recent data from electroweak precision tests, we improve previous limits obtained in the 5-dimensional Standard Model with a common compactification radius and extend our analysis to other possible 5-dimensional Standard-Model constructions. We find that the usually derived lower bound of $\sim 4$ TeV on an universal compactification scale may be considerably relaxed to $\sim 3$ TeV in a minimal scenario, in which the SU(2)$_L$ gauge boson is the only field that feels the presence of the fifth dimension.
We investigate hadroproduction of $B_c$ mesons from initial gluons using QCD perturbation theory and nonrelativistic bound state approximations. Our results obtained by two completely independent calculations are confronted with existing results which contradict each other. Moreover, we examine the approximation based on heavy quark fragmentation and determine the range of validity of it. Predictions for cross sections and differential distributions at Tevatron and LHC energies are presented.
We discuss the calculation of the $B \rightarrow π$ and $D \rightarrow π$ form factors based on an expansion in terms of pion wave functions on the light-cone with increasing twist and QCD sum rule methods. The results are compared with predictions of conventional QCD sum rules and other approaches.
Linear collider designs are optimized for \ep\ collisions. However, from the physics point of view, \lc s may also be advantageously operated in an \ee, \eg\ or \pp\ mode. These options, which have not been available up to now, will provide unique tests of the \sm\ and of physics beyond it. As an example, we review the prospects for discovering and studying \susy\ at linear colliders in \ee, \eg\ and \pp\ collisions. In particular, we argue that \ee\ scattering is much better suited than \ep\ annihilation for discovering \sel s or \co s.
We consider the production and decay of selectrons and charginos in $e^-e^-$ collisions. The advantage over usual $e^+e^-$ collisions is the very low level of standard model backgrounds which should make the discovery of selectrons or charginos relatively straightforward. The use of polarized beams provides an additional powerful tool to determine the supersymmetry parameters.
We study the occurrence of final states with only an electron-positron pair and missing transverse momentum as a signal of \susy\ in photon-photon collisions. Suitable high energy photon beams may be provided at linear colliders by back-scattering laser beams on electron beams. The final states considered represent a typical signature for the production and decay of selctron and chargino pairs within the \mssm. We show that, away from the kinematical threshold, selctrons produce this signal far more abundantly than charginos. The standard model background is dominated by W-pair production. We propose a series of kinematical cuts which reduce this background to an acceptable level. With a 1 TeV collider operated in the $γγ$-mode, we find that interesting and complementary tests of \susic\ models can be performed for selctron masses up to 350 GeV.
Associated selectron-neutralino production in the process $e^-γ\to\tilde e^-\tildeχ^0$ provides a striking supersymmetric signal: events with a single high $p_\perp$ electron and otherwise only invisible particles. For $e^-γ$ collisions obtained at high energy linear colliders through back-scattering of a laser beam, this reaction is shown to be complementary to selectron pair production in the processes $e^+e^-\to\tilde e^+\tilde e^-$ and $e^-e^-\to\tilde e^-\tilde e^-$, and to be a probe of heavy selectrons beyond the kinematical limit of pair production. The standard model background from $e^-γ\to e^-Z^0$ and $W^-ν$ is studied and substantially reduced by rapidity and transverse momentum cuts. The minimum required integrated luminosities for observing this \susic\ signal are given as functions of several model parameters and collider energies.