Showing papers on "Electroweak interaction published in 2006"
TL;DR: In this paper, the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP are reported.
1,381 citations
TL;DR: The Inert Doublet Model as discussed by the authors is an extension of the Standard Model to include a second Higgs doublet that has neither a vev nor couplings to quarks and leptons.
Abstract: The quadratic divergences of the Higgs mass may be cancelled either accidentally or by the exchange of some new particles. Alternatively its impact on naturalness may be weakened by raising the Higgs mass, which requires changing the Standard Model below its natural cut-off. We show in detail how this can be achieved, while preserving perturbativity and consistency with the electroweak precision tests, by extending the Standard Model to include a second Higgs doublet that has neither a vev nor couplings to quarks and leptons. This Inert Doublet Model yields a perturbative and completely natural description of electroweak physics at all energies up to 1.5 TeV. The discrete symmetry that yields the Inert Doublet is unbroken, so that Dark Matter may be composed of neutral inert Higgs bosons, which may have escaped detection at LEP2. Predictions are given for multilepton events with missing transverse energy at the Large Hadron Collider, and for the direct detection of dark matter.
888 citations
TL;DR: The twin Higgs model proposed in this paper protects the weak scale from radiative corrections up to scales of order 5-10 TeV by using a pseudo Goldstone Higgs potential.
Abstract: We present ``twin Higgs models,'' simple realizations of the Higgs boson as a pseudo Goldstone boson that protect the weak scale from radiative corrections up to scales of order 5--10 TeV. In the ultraviolet these theories have a discrete symmetry which interchanges each standard model particle with a corresponding particle which transforms under a twin or a mirror standard model gauge group. In addition, the Higgs sector respects an approximate global symmetry. When this global symmetry is broken, the discrete symmetry tightly constrains the form of corrections to the pseudo Goldstone Higgs potential, allowing natural electroweak symmetry breaking. Precision electroweak constraints are satisfied by construction. These models demonstrate that, contrary to the conventional wisdom, stabilizing the weak scale does not require new light particles charged under the standard model gauge groups.
647 citations
TL;DR: In this article, a subgroup of the custodial symmetry O(3) that protects ρ from radiative corrections can also protect the ZbRR coupling, which allows one to build models of electroweak symmetry breaking, such as Higgsless, Little Higgs or 5D composite Higgs models, that are safe from corrections to Z → bb.
613 citations
TL;DR: In this article, the authors describe a QCD correction for W and Z boson production in hadronic collisions, which includes spin correlations, finite width effects, {gamma}-Z interference, and allows for the application of arbitrary cuts on the leptonic decay products of the w and Z. They have implemented this calculation into a numerical program.
Abstract: We describe a calculation of the O({alpha}{sub s}{sup 2}) QCD corrections to the fully differential cross section for W and Z boson production in hadronic collisions. The result is fully realistic in that it includes spin correlations, finite width effects, {gamma}-Z interference and allows for the application of arbitrary cuts on the leptonic decay products of the W and Z. We have implemented this calculation into a numerical program. We demonstrate the use of this code by presenting phenomenological results for several future LHC analyses and recent Tevatron measurements, including the W cross section in the forward rapidity region and the central over forward cross section ratio.
548 citations
Durham University1, University of Helsinki2, University of Wisconsin-Madison3, University of Rochester4, University of Catania5, Weizmann Institute of Science6, University of Warsaw7, University of Southampton8, CERN9, Lawrence Livermore National Laboratory10, Indian Institute of Science11, University of Montpellier12, University of Zurich13, Spanish National Research Council14, ETH Zurich15, Stanford University16, Northwestern University17, University of Pittsburgh18, Carleton University19, University of Hamburg20, Moscow State University21, University of Florida22, Paul Scherrer Institute23, University of Würzburg24, Imperial College London25, Florida State University26, University of Florence27, University of Bonn28, University at Buffalo29, RWTH Aachen University30, University of Sheffield31, University of California, Irvine32, Laboratoire d'Annecy-le-Vieux de physique des particules33, Brookhaven National Laboratory34, Argonne National Laboratory35, University of Bergen36, University of Mainz37, Centers for Medicare and Medicaid Services38, Lancaster University39, University of California, Santa Cruz40, University of Copenhagen41, University of Tokyo42, Austrian Academy of Sciences43, University of Manchester44, University College London45, University of Edinburgh46, University of California, Davis47, University of California, Berkeley48, University of Glasgow49, University of Barcelona50, Max Planck Society51, University of Chicago52, University of Turin53, Royal Holloway, University of London54, Kobe University55, University of Oslo56, Kyoto University57
TL;DR: In this paper, the authors discuss the possible interplay between the Large Hadron Collider (LHC) and the International e(+)e(-) Linear Collider (ILC) in testing the Standard Model and in discovering and determining the origin of new physics.
422 citations
TL;DR: In this article, the authors discuss radiative corrections to how quark mass thresholds are crossed, as a function of the temperature, in basic thermodynamic observables such as the pressure, the energy and entropy densities, and the heat capacity of high temperature QCD.
Abstract: We discuss radiative corrections to how quark mass thresholds are crossed, as a function of the temperature, in basic thermodynamic observables such as the pressure, the energy and entropy densities, and the heat capacity of high temperature QCD. The indication from leading order that the charm quark plays a visible role at surprisingly low temperatures, is confirmed. We also sketch a way to obtain phenomenological estimates relevant for generic expansion rate computations at temperatures between the QCD and electroweak scales, pointing out where improvements over the current knowledge are particularly welcome.
356 citations
TL;DR: In this paper, the current status of electroweak precision observables in the Minimal Supersymmetric Standard Model (MSSM) is reviewed, and the current theoretical uncertainties from unknown higher-order corrections and from the experimental errors of the input parameters are given.
291 citations
TL;DR: In this paper, the current status of precision measurements in allowed nuclear beta decay, including neutron decay, is reviewed, with emphasis on their potential to look for new physics beyond the standard electroweak model.
Abstract: The current status of precision measurements in allowed nuclear beta decay is reviewed, including neutron decay, with emphasis on their potential to look for new physics beyond the standard electroweak model. Experimental results are interpreted in the framework of phenomenological model-independent descriptions of nuclear beta decay as well as in some specific extensions of the standard model. The values of the standard couplings and the constraints on the exotic couplings of the general beta decay Hamiltonian are updated. The ratio between the axial and vector couplings obtained is ${C}_{A}∕{C}_{V}=\ensuremath{-}1.269\phantom{\rule{0.2em}{0ex}}92(69)$ under standard model assumptions. Particular attention is devoted to the discussion of the sensitivity and complementarity of different precision experiments in direct beta decay. The prospects and impact of recent developments of precision tools and of high intensity low-energy beams are also addressed.
257 citations
TL;DR: In this paper, the custodial and parity symmetries are used to make the tree level contribution to the T parameter and the anomalous couplings of the bottom quark to the Z very small.
242 citations
TL;DR: In this paper, the leading corrections to the properties of W and Z bosons induced at the one-loop level in the SU(5)/SO(5) Littlest Higgs model with T parity were computed and a global fit to precision electroweak data was performed to determine the constraints on the model parameters.
Abstract: We compute the leading corrections to the properties of W and Z bosons induced at the one-loop level in the SU(5)/SO(5) Littlest Higgs model with T parity, and perform a global fit to precision electroweak data to determine the constraints on the model parameters. We find that a large part of the model parameter space is consistent with data. Values of the symmetry breaking scale f as low as 500 GeV are allowed, indicating that no significant fine tuning in the Higgs potential is required. We identify a region within the allowed parameter space in which the lightest T-odd particle, the partner of the hypercharge gauge boson, has the correct relic abundance to play the role of dark matter. In addition, we find that a consistent fit to data can be obtained for large values of the Higgs mass, up to 800 GeV, due to the possibility of a partial cancellation between the contributions to the T parameter from Higgs loops and new physics.
TL;DR: Applying high order perturbative QCD results originally derived for the Bjorken sum rule to the extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element Vud from superallowed nuclear beta decays reduces the theoretical loop uncertainty by about a factor of 2 and gives Vud=0.97377.
Abstract: A new method for computing hadronic effects on electroweak radiative corrections to low-energy weak interaction semileptonic processes is described. It employs high order perturbative QCD results originally derived for the Bjorken sum rule along with a large $N$ QCD-motivated interpolating function that matches long- and short-distance loop contributions. Applying this approach to the extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element ${V}_{ud}$ from superallowed nuclear beta decays reduces the theoretical loop uncertainty by about a factor of 2 and gives ${V}_{ud}=0.973\text{ }77(11)(15)(19)$. Implications for CKM unitarity are briefly discussed.
TL;DR: In this article, the relic density of the lightest, neutral, stable technibaryon having imposed weak thermal equilibrium conditions and overall electric neutrality of the universe was determined. But the results were limited to the case of a first order electroweak phase transition and a second order one.
Abstract: We investigate dark matter candidates emerging in recently proposed technicolor theories. We determine the relic density of the lightest, neutral, stable technibaryon having imposed weak thermal equilibrium conditions and overall electric neutrality of the Universe. In addition we consider sphaleron processes that violate baryon, lepton and technibaryon number. Our analysis is performed in the case of a first order electroweak phase transition as well as a second order one. We argue that, in both cases, the new technibaryon contributes to the dark matter in the Universe. Finally we examine the problem of the constraints on these types of dark matter components from earth based experiments.
TL;DR: The exceptional supersymmetric standard model (ESSM) as discussed by the authors is based on the low-energy standard model gauge group together with an extra Z[prime corresponding to an extra U(1)N gauge symmetry under which right-handed neutrinos have zero charge.
Abstract: We make a comprehensive study of the theory and phenomenology of a low-energy supersymmetric standard model originating from a string-inspired E6 grand unified gauge group. The exceptional supersymmetric standard model (ESSM) considered here is based on the low-energy standard model gauge group together with an extra Z[prime] corresponding to an extra U(1)N gauge symmetry under which right-handed neutrinos have zero charge. The low-energy matter content of the ESSM corresponds to three 27 representations of the E6 symmetry group, to ensure anomaly cancellation, plus an additional pair of Higgs-like doublets as required for high-energy gauge coupling unification. The ESSM is therefore a low-energy alternative to the minimal supersymmetric standard model (MSSM) or next-to-minimal supersymmetric standard model (NMSSM). The ESSM involves extra matter beyond the MSSM contained in three 5+5* representations of SU(5), plus three SU(5) singlets which carry U(1)N charges, one of which develops a vacuum expectation value, providing the effective µ term for the Higgs doublets, as well as the necessary exotic fermion masses. We explore the renormalization group flow of the ESSM and examine theoretical restrictions on the values of new Yukawa couplings caused by the validity of perturbation theory up to the grand unification scale. We then discuss electroweak symmetry breaking and Higgs phenomenology and establish an upper limit on the mass of the lightest Higgs particle which can be significantly heavier than in the MSSM and NMSSM, in leading two-loop approximation. We also discuss the phenomenology of the Z[prime] and the extra matter, whose discovery will provide a smoking gun signal of the model.
TL;DR: In this article, a complete analysis of the electroweak precision observables is performed within a recently proposed minimal composite Higgs model, realized as a 5-dimensional warped compactification.
TL;DR: In this article, a method for the analysis of the scalar potential in the general two-Higgs-doublet model is presented, which gives the conditions for the stability of the potential and for electroweak symmetry breaking in this model in a very concise way.
Abstract: A method is presented for the analysis of the scalar potential in the general two-Higgs-doublet model. This allows us to give the conditions for the stability of the potential and for electroweak symmetry breaking in this model in a very concise way. These results are then applied to two different Higgs potentials in the literature, namely the MSSM and the two-Higgs-doublet potential proposed by Gunion et al. The known results for these models follow easily as special cases from the general results. In particular, for the potential of Gunion et al. we can clarify the stability and symmetry-breaking properties of the model with our method.
01 Oct 2006
TL;DR: In this paper, the complex-mass scheme was proposed for perturbative calculations with unstable particles, which fully respects gauge-invariance, is straight-forward to apply, and has been successfully used for the calculation of various tree-level processes and of the electroweak radiative corrections.
Abstract: Perturbative calculations with unstable particles require the inclusion of their finite decay widths. A convenient, universal scheme for this purpose is the complex-mass scheme. It fully respects gauge-invariance, is straight-forward to apply, and has been successfully used for the calculation of various tree-level processes and of the electroweak radiative corrections to e + e − → 4 f and H → 4 f .
TL;DR: In this article, the authors identify the light degrees of freedom and construct the associated low energy effective theories, which can be used to study signatures and relevant processes in current and future experiments.
Abstract: A fifth force, of technicolor type, responsible for breaking the electroweak theory is an intriguing extension of the standard model. Recently new theories have been shown to feature walking dynamics for a very low number of techniflavors and are not ruled out by electroweak precision measurements. We identify the light degrees of freedom and construct the associated low energy effective theories. These can be used to study signatures and relevant processes in current and future experiments. In our theory the technibaryons are pseudo Goldstone bosons and their masses arise via extended technicolor interactions. There are hypercharge assignments for the techniquarks which renders one of the technibaryons electrically neutral. We investigate the cosmological implications of this scenario and provide a component of dark matter.
TL;DR: In this article, a new class of models that stabilize the weak scale against radiative corrections up to scales of order 5 TeV without large corrections to precision electroweak observables is presented.
Abstract: We present a new class of models that stabilize the weak scale against radiative corrections up to scales of order 5 TeV without large corrections to precision electroweak observables. In these `folded supersymmetric' theories the one loop quadratic divergences of the Standard Model Higgs field are cancelled by opposite spin partners, but the gauge quantum numbers of these new particles are in general different from those of the conventional superpartners. This class of models is built around the correspondence that exists in the large N limit between the correlation functions of supersymmetric theories and those of their non-supersymmetric orbifold daughters. By identifying the mechanism which underlies the cancellation of one loop quadratic divergences in these theories, we are able to construct simple extensions of the Standard Model which are radiatively stable at one loop. Ultraviolet completions of these theories can be obtained by imposing suitable boundary conditions on an appropriate supersymmetric higher dimensional theory compactified down to four dimensions. We construct a specific model based on these ideas which stabilizes the weak scale up to about 20 TeV and where the states which cancel the top loop are scalars not charged under Standard Model color. Its collider signatures are distinct from conventional supersymmetric theories and include characteristic events with hard leptons and missing energy.
TL;DR: In this article, higher-order coefficients required to perform threshold resummation for electroweak annihilation processes, such as Drell-Yan or Higgs production via gluon fusion, can be computed using perturbative results derived in deep inelastic scattering.
CERN1
TL;DR: In this article, various aspects of the Higgs boson phenomenology of the Minimal Supersymmetric Standard Model (MSSM) are reviewed, with emphasis on the effects of higher-order corrections.
Abstract: Various aspects of the Higgs boson phenomenology of the Minimal Supersymmetric Standard Model (MSSM) are reviewed. Emphasis is put on the effects of higher-order corrections. The masses and couplings are discussed in the MSSM with real and complex parameters. Higher-order corrections to Higgs boson production channels at a prospective e+e- linear collider are investigated. Corrections to Higgs boson decays to SM fermions and their phenomenological implications for hadron and lepton colliders are explored.
CERN1
TL;DR: In this article, the authors argue that the level of criticality or fine-tuning that is needed to escape the present collider bounds can be quantitatively accounted for by assuming that the overall scale of the soft terms is an environmental quantity.
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TL;DR: A brief pedagogical overview of the phenomenology of Z' gauge bosons is presented in this paper, where the role of the ILC in determining Z' properties is also discussed.
Abstract: A brief pedagogical overview of the phenomenology of Z' gauge bosons is presented. Such particles can arise in various electroweak extensions of the Standard Model (SM). We provide a quick survey of a number of Z' models, review the current constraints on the possible properties of a Z' and explore in detail how the LHC may discover and help elucidate the nature of these new particles. We provide an overview of the Z' studies that have been performed by both ATLAS and CMS. The role of the ILC in determining Z' properties is also discussed.
TL;DR: This work presents a summary of new features of the ZFITTER program version 6.42 compared to 6.21, including some higher-order QED corrections to fermion pair production, and electroweak one-loop corrections to atomic parity violation.
TL;DR: In this article, the static and dynamical properties of the electroweak phase transition were analyzed for the nMSSM with CP violation in the singlet sector, and it was shown that if the present limits on the mass spectrum are applied, no severe additional tuning is required to obtain a strong first-order phase transition and to generate sufficient baryon asymmetry.
TL;DR: In this article, the authors consider the effect of lepton flavor-violation constraints on the spectrum of loop-induced dipole decays in the Randall-Sundrum model of flavor.
Abstract: The anarchic Randall-Sundrum model of flavor is a low energy solution to both the electroweak hierarchy and flavor problems Such models have a warped, compact extra dimension with the standard model fermions and gauge bosons living in the bulk, and the Higgs living on or near the TeV brane In this paper we consider bounds on these models set by lepton flavor-violation constraints We find that loop-induced decays of the form l{yields}l{sup '}{gamma} are ultraviolet sensitive and incalculable when the Higgs field is localized on a four-dimensional brane; this drawback does not occur when the Higgs field propagates in the full five-dimensional space-time We find constraints at the few TeV level throughout the natural range of parameters, arising from {mu}-e conversion in the presence of nuclei, rare {mu} decays, and rare {tau} decays A tension exists between loop-induced dipole decays such as {mu}{yields}e{gamma} and tree-level processes such as {mu}-e conversion; they have opposite dependences on the five-dimensional Yukawa couplings, making it difficult to decouple flavor-violating effects We emphasize the importance of the future experiments MEG and PRIME These experiments will definitively test the Randall-Sundrum geometric origin of hierarchies in the lepton sector at the TeV scale
TL;DR: In this paper, the chargino-mediated baryogenesis in the Minimal Supersymmetric Standard Model (MSMS) was investigated. But the authors only considered the chargin-mediated Baryogenesis with respect to the top sector of the SSMs.
TL;DR: In this article, exact results for the complete electroweak two-loop contributions to the effective weak mixing angle were published, in particular the methods for evaluating the loop diagrams and the proper definition of Z-pole observables at next-to-next-toleading order.
Abstract: Recently exact results for the complete electroweak two-loop contributions to the effective weak mixing angle were published. This paper illustrates the techniques used for this computation, in particular the methods for evaluating the loop diagrams and the proper definition of Z-pole observables at next-to-next-to-leading order. Numerical results are presented in terms of simple parametrization formulae and compared in detail with a previous result of an expansion up to next-to-leading order in the top-quark mass. Finally, an estimate of the remaining theoretical uncertainties from unknown higher-order corrections is given.
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TL;DR: In this article, the authors summarized the activities of the "SM and Higgs" working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005.
Abstract: This Report summarises the activities of the "SM and Higgs" working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. On the one hand, we performed a variety of experimental and theoretical studies on standard candles (such as W, Z, and ttbar production), treating them either as proper signals of known physics, or as backgrounds to unknown physics; we also addressed issues relevant to those non-perturbative or semi-perturbative ingredients, such as Parton Density Functions and Underlying Events, whose understanding will be crucial for a proper simulation of the actual events taking place in the detectors. On the other hand, several channels for the production of the Higgs, or involving the Higgs, have been considered in some detail. The report is structured into four main parts. The first one deals with Standard Model physics, except the Higgs. A variety of arguments are treated here, from full simulation of processes constituting a background to Higgs production, to studies of uncertainties due to PDFs and to extrapolations of models for underlying events, from small-$x$ issues to electroweak corrections which may play a role in vector boson physics. The second part of the report treats Higgs physics from the point of view of the signal. In the third part, reviews are presented on the current status of multi-leg, next-to-leading order and of next-to-next-to-leading order QCD computations. Finally, the fourth part deals with the use of Monte Carlos for simulation of LHC physics.
TL;DR: In this paper, it was shown that the cascade decays of (1,1) particles generate a series of closely-spaced narrow resonances in the tt invariant mass distribution.
Abstract: Standard model gauge bosons propagating in two universal extra dimensions give rise to heavy spin-1 and spin-0 particles. The lightest of these, carrying Kaluza-Klein numbers (1,0), may be produced only in pairs at colliders, whereas the (1,1) modes, which are heavier by a factor of {radical}(2), may be singly produced. We show that the cascade decays of (1,1) particles generate a series of closely-spaced narrow resonances in the tt invariant mass distribution. At the Tevatron, s-channel production of (1,1) gluons and electroweak bosons will be sensitive to tt resonances up to masses in the 0.5-0.7 TeV range. Searches at the LHC for resonances originating from several higher-level modes will further test the existence of two universal extra dimensions.