Showing papers on "Electroweak interaction published in 2000"
TL;DR: In this paper, the masses of the neutral CP-even Higgs bosons up to two-loop order were calculated using a Fortran code based on the complete diagrammatic on-shell result at the one-loop level.
1,114 citations
TL;DR: In this paper, it is shown that it is not necessary to confine the standard model fields on the brane and analyze the possibility of having the fields actually living in the slice of AdS.
1,079 citations
TL;DR: The Monte Carlo event generator KK version 4.13 as mentioned in this paper was proposed to predict the electroweak standard model for the process e + e − → f f +nγ, f=μ,τ,d,u,s,c,b, that is for LEP, SLC, future Linear Colliders, b,c,τ -factories, etc.
744 citations
TL;DR: In this article, the authors analyze the cosmology of the Randall-Sundrum model and that of compact brane models in general in the presence of a radius stabilization mechanism and find that the expansion of our universe is generically in agreement with the expected effective four dimensional description.
Abstract: We analyze the cosmology of the Randall-Sundrum model and that of compact brane models in general in the presence of a radius stabilization mechanism. We find that the expansion of our Universe is generically in agreement with the expected effective four dimensional description. The constraint (which is responsible for the appearance of nonconventional cosmologies in these models) that must be imposed on the matter densities on the two branes in the theory without a stabilized radius is a consequence of requiring a static solution even in the absence of stabilization. Such constraints disappear in the presence of a stablizing potential, and the ordinary Friedmann-Robertson-Walker (FRW) equations are reproduced, with the expansion driven by the sum of the physical values of the energy densities on the two branes and in the bulk. For the case of the Randall-Sundrum model we examine the kinematics of the radion field, and find that corrections to the standard FRW equations are small for temperatures below the weak scale. We find that the radion field has renormalizable and unsuppressed couplings to standard model particles after electroweak symmetry breaking. These couplings may have important implications for collider searches. We comment on the possibility that matter off the TeV brane could serve as a dark matter candidate.
525 citations
TL;DR: In this article, the authors explore the consequences of placing the Standard Model gauge fields in the bulk of the recently proposed localized gravity model of Randall and Sundrum and find that the Kaluza-Klein excitations of these fields are necessarily strongly coupled and demonstrate that current precision electroweak data constrain the lowest states to lie above ≃23 TeV.
432 citations
TL;DR: In this article, the standard model (SM) is placed on the brane to solve the gauge hierarchy problem in five-dimensional anti-char21{}de Sitter spacetime.
Abstract: We discuss issues in an attempt to put the standard model (SM) in five-dimensional anti\char21{}de Sitter spacetime compactified on ${S}^{1}{/Z}_{2}.$ The recently proposed approach to the gauge hierarchy problem by using this background geometry, with the SM confined on a boundary, is extended to a situation where (some of) the SM particles reside in the five-dimensional bulk. In particular, we find a localization of zero modes of bulk fermions near the boundary with a negative tension. Unlike the compactification with the flat metric, these fermion zero modes couple to Kaluza-Klein (KK) excitations of the SM gauge bosons. Interestingly, only low-lying modes of such KK gauge bosons have non-negligible couplings. Current electroweak precision data give a constraint that the first KK mode be heavier than $9$ TeV. We also argue that at least the Higgs field should be confined on the brane to utilize the Randall-Sundrum background as a solution to the gauge hierarchy.
340 citations
TL;DR: In this paper, a class of non-topological defects in the standard electroweak model and their implications are discussed, and the potential relevance to future particle accelerator experiments and to baryon number violating processes is considered.
327 citations
TL;DR: In this article, the sensitivity of the s-channel W{sup *} mode, the t-channel w-gluon fusion mode, and the tW{sup -} mode to various possible forms of new physics was assessed, indicating that they provide complimentary information about the properties of the top quark.
Abstract: Production of single top quarks at a high energy hadron collider is studied as a means to identify physics beyond the standard model related to the electroweak symmetry breaking. The sensitivity of the s-channel W{sup *} mode, the t-channel W-gluon fusion mode, and the tW{sup -} mode to various possible forms of new physics is assessed, and it is found that the three modes are sensitive to different forms of new physics, indicating that they provide complimentary information about the properties of the top quark. Polarization observables are also considered, and found to provide potentially useful information about the structure of the interactions of top quarks.
297 citations
TL;DR: In this article, the one-loop renormalization-group-improved effective potential of the minimal supersymmetric extension of the Standard Model (MSSM), including CP violation induced radiatively by soft trilinear interactions related to squarks of the third generation, was studied.
275 citations
TL;DR: The possibility of additional quarks and leptons beyond the three generations already established is discussed in this paper, with the possibility of exceptionally long lifetimes and decay modes being dependent on the mass spectrum and mixing angles.
251 citations
TL;DR: HELAC as mentioned in this paper is a FORTRAN-based package that is able to compute efficiently helicity amplitudes for arbitrary scattering processes within the standard electroweak theory, exploiting the virtues of the Dyson-Schwinger equations as compared to the traditional Feynman graph approach.
TL;DR: In this article, the complete O(α) electroweak radiative corrections to e + e − → WW→4 f in the double-pole approximation were derived for the W-pair production, angular and W-invariant mass distributions at LEP2.
TL;DR: In this paper, the cosmological relic density of the lightest supersymmetric particle under the assumption of gauge and Yukawa coupling unification is calculated under the universal boundary conditions from gravity-mediated supersymmetry breaking.
Abstract: The cosmological relic density of the lightest supersymmetric particle of the minimal supersymmetric standard model is calculated under the assumption of gauge and Yukawa coupling unification. We employ radiative electroweak breaking with universal boundary conditions from gravity-mediated supersymmetry breaking. Coannihilation of the lightest supersymmetric particle, which turns out to be an almost pure bino, with the next-to-lightest supersymmetric particle (the lightest stau) is crucial for reducing its relic density to an acceptable level. Agreement with the mixed or the pure cold (in the presence of a nonzero cosmological constant) dark matter scenarios for large scale structure formation in the universe requires that the lightest stau mass is about 2-8% larger than the bino mass, which can be as low as 222 GeV. The smallest allowed value of the lightest stau mass turns out to be about 232 GeV.
TL;DR: In this paper, two-loop radiative corrections to the MSSM lightest CP -even Higgs boson mass M h 0 to O (α t 2 ) for arbitrary left-right top-squark mixing and tan β were proposed.
TL;DR: In this article, the authors re-examine the generation of baryon asymmetry in the minimal supersymmetric standard model (MSSM) during the electroweak phase transition and find that the dominant source for baryogenesis arises from the chargino sector.
Abstract: We re-examine the generation of the baryon asymmetry in the minimal supersymmetric standard model (MSSM) during the electroweak phase transition. We find that the dominant source for baryogenesis arises from the chargino sector. The CP-violation comes from the complex phase in the μ parameter, which provides CP-odd contributions to the particle dispersion relations. This leads to different accelerations for particles and antiparticles in the wall region which, combined with diffusion, leads to the separation of higgsinos and their antiparticles in the front of the wall. These asymmetries get transported to produce perturbations in the left-handed chiral quarks, which then drive sphaleron interactions to create the baryon asymmetry. We present a complete derivation of the semiclassical WKB formalism, including the chargino dispersion relations and a self-consistent derivation of the diffusion equations starting from semiclassical Boltzmann equations for WKB-excitations. We stress the advantages of treating the transport equations in terms of the manifestly gauge invariant physical energy and kinetic momentum, rather than in the gauge variant canonical variables used in previous treatments. We show that a large enough baryon asymmetry can be created for the phase of the complex μ-parameter as small as ~ 10−3, which is consistent with bounds from the neutron electric dipole moment.
TL;DR: In this paper, the naturalness of electroweak symmetry breaking and baryogenesis in the next-to-minimal supersymmetric standard model (NMSSM) was studied.
TL;DR: It is pointed out that, since the colliders' initial states carry a definite non-Abelian flavor, electroweak radiative corrections to inclusive hard cross sections at the TeV scale are affected by peculiar Bloch-Nordsieck violating double logs.
Abstract: We point out that, since the colliders' initial states ( e(+)e(-),pp, pp,ellipsis) carry a definite non-Abelian flavor, electroweak radiative corrections to inclusive hard cross sections at the TeV scale are affected by peculiar Bloch-Nordsieck violating double logs. We recall the setup of soft cancellation theorems, and we analyze the magnitude of the noncanceling terms in the example of electron-positron annihilation into hadrons.
TL;DR: In this article, the infrared evolution equation was used to obtain double logarithmic asymptotics of scattering amplitudes and discussed how it can be applied, in the case of broken gauge symmetry, to the standard model of electroweak processes.
Abstract: At future linear ${e}^{+}{e}^{\ensuremath{-}}$ collider experiments in the TeV range, Sudakov double logarithms originating from massive boson exchange can lead to significant corrections to the cross sections of the observable processes. These effects are important for the high precision objectives of the Next Linear Collider. We use the infrared evolution equation, based on a gauge invariant dispersive method, to obtain double logarithmic asymptotics of scattering amplitudes and discuss how it can be applied, in the case of broken gauge symmetry, to the standard model of electroweak processes. We discuss the double logarithmic effects to both non-radiative processes and to processes accompanied by soft gauge boson emission. In all cases the Sudakov double logarithms are found to exponentiate. We also discuss double logarithmic effects of a non-Sudakov type which appear in Regge-like processes.
TL;DR: In this article, the authors considered the minimal supersymmetric standard model with universal boundary conditions and "asymptotic" Yukawa unification, and calculated the relic abundance of the light-est super-particle (bino) by including its coannihilations with the next-to-lightest superpartner (lightest stau).
Abstract: The minimal supersymmetric standard model with universal boundary conditions and "asymptotic" Yukawa unification is considered. The full one-loop effective potential for radiative electroweak symmetry breaking as well as the one-loop corrections to the charged Higgs boson, b-quark and tau lepton masses are included. The CP-even Higgs boson masses are corrected to two-loops. The relic abundance of the lightest supersymmetric particle (bino) is calculated by including its coannihilations with the next-to-lightest supersymmetric particle (lightest stau) consistently with Yukawa unification. The branching ratio of b --> s gamma is evaluated by incorporating all the applicable next-to-leading order QCD corrections. The bino-stau coannihilations reduce the bino relic abundance below the upper bound from cold dark matter considerations in a sizable fraction of the parameter space allowed by b --> s gamma for mu>0. Thus, the mu>0 case, which also predicts an acceptable b-quark mass, is perfectly compatible with data.
TL;DR: In this paper, the complete O(alpha) electroweak radiative corrections to e+e- --> WW --> 4f in the double-pole approximation were presented. But they are based on the full matrix elements.
Abstract: We calculate the complete O(alpha) electroweak radiative corrections to e+e- --> WW --> 4f in the electroweak Standard Model in the double-pole approximation. We give analytical results for the non-factorizable virtual corrections and express the factorizable virtual corrections in terms of the known corrections to on-shell W-pair production and W decay. The calculation of the bremsstrahlung corrections, i.e. the processes e+e- --> 4f+gamma in lowest order, is based on the full matrix elements. The matching of soft and collinear singularities between virtual and real corrections is done alternatively in two different ways, namely by using a subtraction method and by applying phase-space slicing. The O(alpha) corrections as well as higher-order initial-state photon radiation are implemented in the Monte Carlo generator RACOONWW. Numerical results of this program are presented for the W-pair-production cross section, angular and W-invariant-mass distributions at LEP2. We also discuss the intrinsic theoretical uncertainty of our approach.
TL;DR: In this paper, one-loop corrections to the mass matrix of the neutral Higgs bosons of the Minimal Supersymmetric Standard Model with explicit CP violation are presented. But they do not take into account the running quark masses.
TL;DR: In this article, the authors analyzed the Higgs sector in the next-to-minimal Supersymmetric Standard Model, emphasizing the possibility of a light CP-odd scalar (axion) in the spectrum.
Abstract: We analyze the Higgs sector in the next-to-minimal Supersymmetric Standard Model, emphasizing the possibility of a light CP-odd scalar (axion) in the spectrum. We compute the coupling of the Standard-Model-like Higgs boson to a pair of axions, and show that it can be large enough to modify the Higgs branching fractions, with a significant impact on the Higgs searches. We delineate the range of parameters relevant for this scenario, and also derive analytic expressions for the scalar masses and couplings in two special cases - a decoupling limit where all scalars other than the axion are heavier than the Standard-Model-like Higgs boson, and the large tan β limit.
TL;DR: In this paper, a tree-level Higgs boson couplings to quarks and squarks, in terms of the QCD and SUSY QCD running quark masses, running trilinear couplings $A_q, and on-shell left-right mixing angles of squarks.
Abstract: We improve the calculation of the supersymmetric $O(\alpha_s)$ QCD corrections to the decays of Higgs bosons into quarks and squarks in the Minimal Supersymmetric Standard Model. In the on-shell renormalization scheme these corrections can be very large, which makes the perturbative expansion unreliable. This is especially serious for decays into bottom quarks and squarks for large $\tan\beta$. Their corrected widths can even become negative. We show that this problem can be solved by a careful choice of the tree-level Higgs boson couplings to quarks and squarks, in terms of the QCD and SUSY QCD running quark masses, running trilinear couplings $A_q$, and on-shell left-right mixing angles of squarks. We also present numerical results for the corrected partial decay widths for the large $\tan\beta$ case.
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TL;DR: In this article, the naturalness problem of the Fermi scale after a decade of electroweak precision measurements, mostly done at LEP, has been discussed, and the LEP paradox has been pointed out.
Abstract: Is there a Higgs? Where is it? Is supersymmetry there? Where is it? By discussing these questions, we call attention to the `LEP paradox', which is how we see the naturalness problem of the Fermi scale after a decade of electroweak precision measurements, mostly done at LEP.
TL;DR: In this article, it is shown that it is not necessary to confine the standard model fields on the brane and analyze the possibility of having the fields actually living in the slice of AdS.
Abstract: Five-dimensional models where the bulk is a slice of AdS have the virtue of solving the hierarchy problem. The electroweak scale is generated by a ``warp'' factor of the induced metric on the brane where the standard model fields live. However, it is not necessary to confine the standard model fields on the brane and we analyze the possibility of having the fields actually living in the slice of AdS. Specifically, we study the behaviour of fermions, gauge bosons and scalars in this geometry and their implications on electroweak physics. These scenarios can provide an explanation of the fermion mass hierarchy by warp factors. We also consider the case of supersymmetry in the bulk, and analyze the conditions on the mass spectrum. Finally, a model is proposed where the warp factor generates a small (TeV) supersymmetry-breaking scale, with the gauge interactions mediating the breaking to the scalar sector.
TL;DR: In this paper, the determination of the Fermi coupling constant, G F, is examined in the light of recently calculated two-loop QED corrections and planned experiments to measure the muon lifetime to a level below 1.
TL;DR: In this article, the authors considered the minimal supersymmetric standard model with universal boundary conditions and "asymptotic" Yukawa unification and calculated the relic abundance of the lightest supersymmymmetric particle (bino) by including its coannihilations with the next-to-lightest super-stau particle (lightest stau).
TL;DR: In this article, the complete fermionic two-loop contributions to the prediction for the W-boson mass from muon decay in the electroweak Standard Model are evaluated exactly, i.e., no expansion in the top-quark and the Higgs boson mass is made.
TL;DR: In this article, the implications of extra dimensions of size R ~ 1/TeV on electroweak and flavor physics due to the presence of Kaluza-Klein excitations of the SM gauge-bosons were studied.
Abstract: We study the implications of extra dimensions of size R ~ 1/TeV on electroweak and flavor physics due to the presence of Kaluza-Klein excitations of the SM gauge-bosons. We consider several scenarios with the SM fermions either living in the bulk or being localized at different points of an extra dimension. Global fits to electroweak observables provide lower bounds on 1/R, which are generically in the 2-5 TeV range. We find, however, certain models where the fit to electroweak observables is better than in the SM, because of an improvement in the prediction to the weak charge QW. We also consider the case of softly-broken supersymmetric theories and we find new non-decoupling effects that put new constraints on 1/R. If quarks of different families live in different points of the extra dimension, we find that the Kaluza-Klein modes of the SM gluons generate (at tree level) dangerous flavor and CP-violating interactions. The lower bounds on 1/R can increase in this case up to 5000 TeV, disfavoring these scenarios in the context of TeV-strings.
TL;DR: In this article, the authors apply the strategy of regions within dimensional regularization to find functions involved in evolution equations which govern the asymptotic dynamics of the Abelian form factor and four-fermion amplitude in the SU(N) gauge theory in the Sudakov limit up to the next-to-leading logarithmic approximation.
Abstract: We apply the strategy of regions within dimensional regularization to find functions involved in evolution equations which govern the asymptotic dynamics of the Abelian form factor and four-fermion amplitude in the SU(N) gauge theory in the Sudakov limit up to the next-to-leading logarithmic approximation. The results are used for the analysis of the dominant electroweak corrections to the fermion-antifermion pair production in the $e^+e^-$
annihilation at high energy.