High energy factorization in electroweak processes

We propose to use high energy, k-dependent, factorization (HEF) in electroweak fusion processes in order to systematically improve the effective W approximation (EWA) at collider energies. Starting from the example of top production, we show that HEF provides correctly all quasi constant terms in the production cross section, i.e. not only the ones O(1/M_w²) which are typical of the EWA and are due to longitudinal polarizations of exchanged bosons, but also the ones O(1/M_w²) which are partly due to transverse polarizations. It turns out that latter contributions cannot be accounted for by collinear factorization only, but also come from longitudinal off-shell effects, typical of broken gauge theories, which are explicitly evaluated here.     

Towards collinear evolution equations in electroweak theory

We investigate collinear factorization in electroweak radiative corrections to hard inclusive processes at the TeV scale. Because of the uncanceled double logs found previously, we find a factorization pattern which is qualitatively different from the analogous one in QCD. New types of splitting functions emerge which are needed to describe the initial beam charges and are dependent on an infrared cutoff provided by the symmetry breaking scale. We derive such splitting functions at the one-loop level for broken SU(2) gauge theory, and we also discuss the structure functions' evolution equations, under the assumption that isospin breaking terms are sufficiently subleading at higher orders.     

On the 1-Loop Renormalization of the Electroweak Standard Model and its Application to Leptonic Processes

A renormalization scheme for the electroweak standard model is presented in which the electric charge and the masses of the gauge bosons, Higgs particle and fermions are used as physical parameters. The photon is treated such that quantum electrodynamics is contained as a simple substructure. Field renormalization respecting the gauge symmetry gives finite propagators and vertex functions. The Ward identities between the Green functions of the unphysical sector allow a renormalization that maintains the simple pole structure of the propagators in the t'Hooft-Feynman gauge. We give a complete list of self energies and all renormalization constants also in the unphysical Higgs and ghost sector. Explicit results are given for the renormalized self energies, vertex functions and boxes that enter the evaluation of 1-loop radiative corrections to fermionic processes. We calculate the 1-loop radiative corrections to purely leptonic reactions like μ decay, vμ_μe scattering and μ pair production in e⁺e⁻annihilation. A test of the standard model is performed by comparing these low energy data with the results of the PP collider experiments for the W and Z boson masses.     

Sequential W and Z bosons

We present and discuss a class of electroweak gauge models where the low-energy phenomenology is naturally identical to that of the standard model, but which allows for the existence of an arbitrary number of weak gauge bosons which have nontrivial couplings to the known fermions. The lightest W and Z in these models must be lighter than the W and Z of the standard model.     

对规范粒子极化矢量的一些讨论

对规范粒子的极化矢量做了较为系统的论述. 讨论内容包括极化矢量的具体形式和性质、求和规则和规范传播子之间的关系以及由其张成的投影算子的性质. 通过若干精选的例子, 进一步演示了计算牵涉规范粒子的过程时采用的基本方法和应当注意事项.     

Signals of the degenerate BESS model at the LHC

We discuss the possible signals of the degenerate BESS model at the LHC. This model describes a strongly interacting scenario responsible of the spontaneous breaking of the electroweak symmetry. It predicts two triplets of extra gauge bosons which are almost degenerate in mass. Due to this feature, the model has the property of decoupling and therefore, at low energies (below or of the order of 100 GeV) it is nearly indistinguishable from the Standard Model. However the new resonances, both neutral and charged, should give quite spectacular signals at the LHC, where the c.o.m. energy will allow to produce these gauge bosons directly. Received: 11 July 2000 / Published online: 13 November 2000     

One-loop leading logarithms in electroweak radiative corrections

We present results for the complete one-loop electroweak logarithmic corrections for general processes at high energies and fixed angles. Our results are applicable to arbitrary matrix elements that are not mass suppressed. We give explicit results for 4-fermion processes and gauge-boson pair production in annihilation. Received: 20 October 2000 / Published online: 23 January 2001     

Predictions for all processes ee → fermions + γ

The complete matrix elements for e⁺e⁻ → 4 and e⁺e⁻ → 4fγy are calculated in the Electroweak Standard Model for polarized massless fermions. The matrix elements for all final states are reduced to a few compact generic functions. Monte Carlo generators for e⁺e⁻ → 4f and e⁺e⁻ → 4fγ are constructed. We compare different treatments of the finite widths of the electroweak gauge bosons; in particular, we include a scheme with a complex gauge-boson mass that obeys all Ward identities. The detailed discussion of numerical results comprises integrated cross sections as well as photon-energy distributions for all different final states.     

Electroweak radiative corrections to e+e− → Z0Z0

The cross section for e⁺e⁻ → Z⁰Z⁰ with arbitrary polarizations of the leptons and bosons is calculated in the standard electroweak model including the complete one-loop virtual and soft-photon bremsstrahlung corrections. All necessary analytical formulas are presented; numerical results are discussed for the unpolarized case and for the polarization asymmetry. At LEP 200 energies the weak corrections are dominated by the self-energy of the external Z⁰-bosons which contributes about +15%. With increasing energy, the weak corrections decrease up to -18% at 1 TeV due to other contributions.     

On holomorphic factorization of WZW and coset models

It is shown how coupling to gauge fields can be used to explain the basic facts concerning holomorphic factorization of the WZW model of two dimensional conformal field theory, which previously have been understood primarily by using conformal field theory Ward identities. We also consider in a similar vein the holomorphic factorization ofG/H coset models. We discuss theG/G model as a topological field theory and comment on a conjecture by Spiegelglas.Research supported in part by NSF Grant PHY86-20266     

The SM as the quantum low-energy effective theory of the MSSM

In the framework of the minimal supersymmetric standard model we compute the one-loop effective action for the electroweak bosons obtained after integrating out the different sleptons, squarks, neutralinos and charginos, and present the result in terms of the physical sparticle masses. In addition we study the asymptotic behavior of the two-, three- and four-point Green's functions with external electroweak bosons in the limit where the physical sparticle masses are very large in comparison with the electroweak scale. We find that in this limit all the effects produced by the supersymmetric particles can either be absorbed in the standard model parameters and gauge bosons wave functions, or else they are suppressed by inverse powers of the supersymmetric particle masses. This work, therefore, completes the proof of decoupling of the heavy supersymmetric particles from the standard ones in the electroweak bosons effective action and in the sense of the Appelquist–Carazzone theorem; we started this proof in a previous work. From the point of view of effective field theories this work can be seen as a (partial) proof that the SM can indeed be obtained from the MSSM as the quantum low-energy effective theory of the latter when the SUSY spectra are much heavier than the electroweak scale. Received: 27 March 1999 / Revised version: 7 September 1999 / Published online: 27 January 2000     

Electroweak Sudakov logarithms and real gauge-boson radiation in the TeV region

Electroweak radiative corrections give rise to large negative, double-logarithmically enhanced corrections in the TeV region. These are partly compensated by real radiation and, moreover, affected by selecting isospin-non-invariant external states. We investigate the impact of real gauge boson radiation more quantitatively by considering different restricted final state configurations. We consider successively a massive abelian gauge theory, a spontaneously broken SU(2) theory and the electroweak Standard Model. We find that details of the choice of the phase space cuts, in particular whether a fraction of collinear and soft radiation is included, have a strong impact on the relative amount of real and virtual corrections.     

Electroweak effects in a superconductor

We show that mixing of the electroweak gauge bosons may occur in a superconductor, resulting in an enhanced neutral current with long-range electromagnetic parity-violating interactions or electric charge non-conserving processes.     

Double-real corrections at $${{\mathcal {O}}(\alpha \alpha _s)}\,$$to single gauge boson production

We consider the \({{\mathcal {O}}(\alpha \alpha _s)}\,\)corrections to single on-shell gauge boson production at hadron colliders. We concentrate on the contribution of all the subprocesses where the gauge boson is accompanied by the emission of two additional real partons and we evaluate the corresponding total cross sections. The latter are divergent quantities, because of soft and collinear emissions, and are expressed as Laurent series in the dimensional regularization parameter. The total cross sections are evaluated by means of reverse unitarity, i.e. expressing the phase-space integrals in terms of two-loop forward box integrals with cuts on the final-state particles. The results are reduced to a combination of master integrals, which eventually are evaluated in terms of generalized polylogarithms. The presence of internal massive lines in the Feynman diagrams, due to the exchange of electroweak gauge bosons, causes the appearance of 14 master integrals which were not previously known in the literature and have been evaluated via differential equations.     

Quantum weakdynamics as an SU(3)_I gauge theory: Grand unification of strong and electroweak interactions

Quantum weakdynamics (QWD) as an gauge theory with the vacuum term is considered to be the unification of the electroweak interaction as an gauge theory. The grand unification of beyond the standard model is established by the group . The grand unified interactions break down to weak and strong interactions at a new grand unification scale, GeV, through dynamical spontaneous symmetry breaking (DSSB); the weak and strong coupling constants are the same, , at this scale. DSSB is realized by the condensation of scalar fields, postulated to be spatially longitudinal components of gauge bosons, instead of Higgs particles. Quark and lepton family generation, the Weinberg angle , and the Cabbibo angle are predicted. The electroweak coupling constants are , , , and ; there are symmetric isospin interactions. Received: 21 January 2001 / Published online: 21 November 2001     

Higher level string resonances in four dimensions

We study higher level Regge resonances of open superstrings, focusing on the universal part of the Neveu-Schwarz sector common to all D-brane realizations of the standard model. For Regge states with masses far above the fundamental string scale, we discuss the spin-dependence of their decay rates into massless gauge bosons. Extending our previous work on lowest level string excitations, we study the second mass level at which spins range from 0 to 3. We construct the respective vertex operators and compute the amplitudes involving one massive particle and two or three gauge bosons. To illustrate the use of Britto-Cachazo-Feng-Witten (BCFW) recursion relations in superstring theory, we build the four-gluon amplitude from on-shell amplitudes involving string resonances and gauge bosons.     

On the lowest order electroweak corrections to spin-12 fermion scattering: (I). The one-loop diagrammar

Based on a gauge model of the electroweak interaction the total set of all one-loop diagrams for scattering of $\text{spin}\text{-}\text{1}\text{2}$ fermions is calculated. Throughout the calculations, the type of fermions (?, ν, …) and of heavy vector bosons (W^±Z⁰, …) is not specified. Derivation of finite parts of each diagram is carried out under the restriction that all invariants of the amplitude are much larger than all fermion masses squared. This allows us to use the expression obtained at arbitrary high energies where weak and electromagnetic interaction strengths are comparable.     

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.     

Infrared divergence cancellation in pure Yang-Mills theory

Virtual and real corrections to massless external lines in pure Yang-Mills theory are considered in order to look for general features of the infrared divergence cancellation. Use of the Ward identities and sums over transverse polarization states give rise to terms formally corresponding to real ghost emission, cancelling ghost loop singularities, and to a factorisation of the hard narrow single gauge boson emission. Other virtual corrections are examined in the soft region and a graph cancellation is also found. An illustrative explicit calculation of scattering of a gauge particle in an external scalar potential, including hard narrow angle emission is presented.