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.     

On the O(αs) infra-red divergences in the axial gauge of QCD

We demonstrate the cancellation of infra-red divergences in the axial gauge of QCD in the first corrections to the deep inelastic quark structure function.     

Algebraic treatment of subsidiary conditions in dual resonance models

The Ward-like identities previously proposed in order to eliminate unphysical states (ghosts) from dual amplitudes and generalized by Virasoro, are investigated within the context of the projective operator language. We are able to generalize further Virasoro's result to the case of amplitudes with different internal trajectories and to release his unphysical condition on the external masses. A purely algebraic treatment of the problem of ghost cancellation is also presented and shown to provide cancellation of ghosts up to the third excited level.     

Space-time supersymmetry of the covariant superstring

We explicitly derive the ghost oscillator contribution to the gauge covariant fermion emission vertex. This vertex is used to construct the space-time supersymmetry transformation laws which are shown to be an invariance of the free gauge covariant action of the superstring. We develop methods to deal with the quadratic exponentials which appear in the fermion emission vertex, in order to study the closure of the supersymmetry algebra. As a by-product, we complete the proof of the equivalence between the “old” and “new” formulations of the superstring.     

Electroweak Corrections with Allowance for Hard Bremsstrahlung in Polarized Bhabha Scattering

Physics of Atomic Nuclei - A total set of one-loop electroweak radiative corrections, including the contribution of the emission of real hard photons (hard-bremsstrahlung contribution), to...     

Radiative return at NLO and the measurement of the hadronic cross-section in electron–positron annihilation

Electron–positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process and the emission of two real hard photons: . A Monte Carlo generator has been constructed, which incorporates these corrections and simulates the production of two charged pions or muons plus one or two photons. Predictions are presented for centre-of-mass energies between 1 and 10 GeV, corresponding to the energies of DANE, CLEO-C and B-meson factories. Received: 14 December 2001 / Published online: 5 April 2002     

Dirac tensor with heavy photon

For the large-angle hard-photon emission by initial leptons in the process of high-energy annihilation of e ⁺ e ^? to hadrons, the Dirac tensor is obtained by taking the lowest-order radiative corrections into account. The case of large-angle emission of two hard photons by initial leptons is considered. In the final result, the kinematic case of collinear emission of hard photons and soft virtual and real photons is included; it can be used for the construction of Monte-Carlo generators.     

Predictions for ${\bar \nu} \nu \gamma$ production at LEP

We study predictions for the reaction . The complete one-loop corrections are taken into account and higher order contributions, in particular those for the observed real photons, are added whenever necessary. The event generator MC, a general-purpose Monte Carlo generator for the process based on the method of exclusive exponentiation, is used as the environment. We extend its applicability to the process ,, where the observation of at least a single is required. The exponentiation is implemented in much the same way as for the s-channel process alone. In particular, all photonic effects present in the case of W exchange, which cannot be included in the s-channel exponentiation scheme, are calculated to a finite order only. The real hard photon matrix element is calculated up to . Leading logarithmic contributions of the two-loop corrections and one-loop photonic corrections accompanying real single-photon emission are included. The electroweak corrections are calculated with the DIZET library of the ZFITTER package. Numerical tests and predictions for typical observables are presented. Received: 30 October 2001 / Revised version: 5 March 2002 / Published online: 22 May 2002     

Verifying the Kugo-Ojima confinement criterion in Landau gauge Yang-Mills theory

Expanding the Landau gauge gluon and ghost two-point functions in a power series we investigate their infrared behavior. The corresponding powers are constrained through the ghost Dyson-Schwinger equation by exploiting multiplicative renormalizability. Without recourse to any specific truncation we demonstrate that the infrared powers of the gluon and ghost propagators are uniquely related to each other. Constraints for these powers are derived, and the resulting infrared enhancement of the ghost propagator signals that the Kugo-Ojima confinement criterion is fulfilled in Landau gauge Yang-Mills theory.     

One-loop leading logarithms in electroweak radiative corrections

We discuss the evaluation of the collinear single-logarithmic contributions to virtual electroweak corrections at high energies. More precisely, we prove the factorization of the mass singularities originating from loop diagrams involving collinear virtual gauge bosons coupled to external legs. We discuss, in particular, processes involving external longitudinal gauge bosons, which are treated using the Goldstone-boson equivalence theorem. The proof of factorization is performed within the 't Hooft–Feynman gauge at one-loop order and applies to arbitrary electroweak processes that are not mass-suppressed at high energies. As basic ingredients we use Ward identities for Green functions with arbitrary external particles involving a gauge boson collinear to one of these. The Ward identities are derived from the BRS invariance of the spontaneously broken electroweak gauge theory. Received: 4 May 2001 / Published online: 6 July 2001     

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.     

LETTER: Gauge Field Corrections to Domain Walls

Gauge field corrections to domain walls are obtained by making use of perturbation method on the usual flat domain wall. The gauge vector field introduces a damping term and an external force on the motion equation for the perturbed domain wall. A thin domain wall approximation solution is found. The vector gauge field also introduces a gauge mass term correction into the perturbed Lagrangean.     

On the radiation of soft gluons

We demonstrate that the cross section for the radiation of soft gluons in quantum chromodynamics does not obey a Poisson distribution (even when the colours of the gluons are summed over.) This implies that any cancellation of infrared divergences between radiative corrections from real and virtual gluons in QCD must be more complicated than in QED. We present an example of such a cancellation.     

The suppression of neutralino annihilation into Zh

The indirect detection of neutralino dark matter is most promising through annihilation channels producing a hard energy spectrum for the detected particles, such as neutralino annihilation into Zh. A cancellation however makes this particular annihilation channel generically subdominant in the huge parameter space of supersymmetric models. This cancellation requires non-trivial relations between neutralino mixings and masses, which we derive from gauge independence and unitarity of the MSSM. To show how the cancellation overshoots leaving only a subdominant result, we use a perturbative expansion in powers of the electroweak/supersymmetry breaking ratio m_Z/m_χ.     

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.     

BRST Cohomology of the Chapline–Manton Model

We completely compute the local BRST cohomology H(s|d) of the combined Yang–Mills 2-form system coupled through the Yang–Mills Chern–Simons term (Chapline–Manton model). We consider the case of a simple gauge group and explicitly include in the analysis the sources for the BRST variations of the fields (antifields). We show that there is an antifield independent representative in each cohomological class of H(s|d) at ghost number 0 or 1. Accordingly, any counterterm may be assumed to preserve the gauge symmetries. Similarly, there is no new candidate anomaly beside those already considered in the literature, even when one takes the antifields into account. We then characterize explicitly all the nontrivial solutions of the Wess–Zumino consistency conditions. In particular, we provide a cohomological interpretation of the Green–Schwarz anomaly cancellation mechanism.     

Accessing directly the properties of fundamental scalars in the confinement and Higgs phase

The properties of elementary particles are encoded in their respective propagators and interaction vertices. For a SU(2) gauge theory coupled to a doublet of fundamental complex scalars these propagators are determined in both the Higgs phase and the confinement phase and compared to the Yang–Mills case, using lattice gauge theory. Since the propagators are gauge dependent, this is done in the Landau limit of the ’t Hooft gauge, permitting to also determine the ghost propagator. It is found that neither the gauge boson nor the scalar differ qualitatively in the different cases. In particular, the gauge boson acquires a screening mass, and the scalar’s screening mass is larger than the renormalized mass. Only the ghost propagator shows a significant change. Furthermore, indications are found that the consequences of the residual non-perturbative gauge freedom due to Gribov copies could be different in the confinement and the Higgs phase.     

Soft and hard photon corrections for μ-pair production and Bhabha scattering in the presence of a resonance

In this paper previous calculations of radiative corrections to μ-pair production and Bhabha scattering are extended to the case where a resonance is present. In contrast to other investigations of radiative corrections to a narrow resonance this paper gives a complete discussion of Bhabha scattering and discusses both for μ-pair production and Bhabha scattering hard photon bremsstrahlung taking into account specific experimental conditions.     

One-loop renormalisation of superfield Yang-Mills theories

We calculate the one-loop ultraviolet and infrared divergences in superfield Yang-Mills theories to fourth order in the gauge field. The ultraviolet divergences require a non-linear field renormalisation, and graphs with external ghost fields show that a non-linear renormalisation of the gauge-fixing function is also needed. These observations are confirmed by calculations incorporating matter fields, which are used to extend the result to all orders for the special case of SU(2). On the other hand the infrared divergences, which occur in general gauges, are apparently impossible to remove in any acceptable way.     

Off-shell gluon production in interaction of a projectile with 2 or 3 targets

Within the effective QCD action for the Regge kinematics, the amplitudes for virtual gluon emission are studied in collision of a projectile with two and three targets. It is demonstrated that all non-Feynman singularities cancel between induced vertices and rescattering contributions. Formulas simplify considerably in a special gauge, which is a straightforward generalization of the light-cone gauge for emission of real gluons.