Multiple bremsstrahlung in gauge theories at high energies: (III). Finite mass effects in collinear photon bremsstrahlung

We present a method for calculating the various spin amplitudes for QED processes in which an arbitrary number of photons is radiated in directions nearly parallel to the fermion directions. This is accomplished by introducing explicit polarization vectors for the photons and by working in the high energy limit, where finite mass effects are treated in leading order.     

Multiple bremsstrahlung in gauge theories at high energies (I). General formalism for quantum electrodynamics

Multiple bremsstrahlung is studied on the level of tree diagrams for gauge theories. At high energies and in most of the kinematic region, the fermion mass can be neglected. In this case, it is natural to introduce helicity states for both fermions and gauge particles. Our general formalism is given in detail for quantum electrodynamics. In particular, it is expedient to use photon polarization vectors which depend on the fermion helicities. In this way, extensive cancellations between Feynman diagrams are accomplished automatically.     

Constraints from weak hadronic processes on left-right symmetric gauge theories

Using constraints from weak hadronic process we obtain bounds on the right handed gauge boson mass and the flavour changing neutral Higgs masses. The masses of these bosons are in the multi-TeV region. A fit to the quark mixing angle reveals no dramatic changes compared to the standard W-S model. We present some prediction for the \(B^0 \overline {B^0 }\) system.     

Charges in gauge theories

In this article we investigate charged particles in gauge theories. After reviewing the physical and theoretical problems, a method to construct charged particles is presented. Explicit solutions are found in the abelian theory and a physical interpretation is given. These solutions and our interpretation of these variables as the true degrees of freedom for charged particles, are then tested in the perturbative domain and are demonstrated to yield infra-red finite, on-shell Green’s functions at all orders of perturbation theory. The extension to collinear divergences is studied and it is shown that this method applies to the case of massless charged particles. The application of these constructions to the charged sectors of the standard model is reviewed and we conclude with a discussion of the successes achieved so far in this programme and a list of open questions. An erratum to this article is available at .     

ΔS = −ΔQ processes in asymptotically free gauge theories

The possibility of an enhancement of the short-distance contribution to ΔS = ?ΔQ semileptonic processes is investigated in the context of asymptotically free gauge theories of the strong interactions.     

Non-abelian gauge couplings in thermal gauge field theories

Properties of the effective gauge couplings renormalized at finite temperature and density in thermal non-abelian gauge field theories are studied within one-loop approximations. Strong and severe vertex dependence is shown to come out both in the temperature and chemical potential dependences. Difficulties appearing in the perturbative calculation of physical quantities, indicated by the above disaster, are discussed. Also discussed is what insight might be gained from the present analysis into the “magnetic” screening of effective charge.     

Quark fragmentation in gauge theories

A theory of quark fragmentation is based on the phenomenon of spontaneous pair creation in a strong Coulomb field, applied to the color field surrounding the leading quarks.     

Soliton quantization in gauge theories

We study the quantization of the SO₃ gauge theory which possesses the 't Hooft-Polyakov monopole as a classical solution. The one-monopole sector of this model is constructed in lowest-order perturbation theory, with \(\sqrt \hbar \) as expansion parameter. Explicit expressions for the fields are given and their properties discussed. We use a manifestly covariant formalism.     

Space-time symmetries in gauge theories

A general definition of symmetries of gauge fields is proposed and a method developed for constructing symmetric fields for an arbitrary gauge group. Scalar fields occur naturally in the formalism and the pure gauge theory reduces to a Higgs model in lower dimensions.Laboratoire propre du C.N.R.S. associé à l'Ecole Normale Supérieure et à l'Université de Paris Sud     

Phase transition in gauge theories

In this short review we present the consequences of the spontaneously broken gauge theories will lead to when describing matter at high temperature and density. It appears various phase transitions should occur leading to the restoration of symmetry at high temperature of the originally broken one. Symmetry behaviour in external magnetic fields and in the early universe has been briefly mentioned.     

Electric-charge quantization in gauge theories

The electric-charge quantization and fixing conditions of particles are found using a number of gauge theories, and it is shown that the presence of Higgs fields is a necessary condition for the electric-charge quantization in the considered models.     

Physical variables in gauge theories

The symplectic method is applied to obtain the physical variables and the physical Hamiltonian in two examples of gauge theories: the electrodynamics in the Coulomb gauge and the two-dimensional bosonic Schwinger model.     

Vacuum stability in gauge theories

The vacuum behaviour in a quantum SU(2) gauge theory is investigated by calculating the one-loop contributions to the effective action in a covariant constant background field. It is found that the vacuum is stable against decay, for a particular nonzero value of the electric field, indicating a dynamical symmetry breaking.     

Quadratic divergences in gauge theories

Quadratic divergences are analysed using dimensional regularisation in gauge theories in general and the standard model in particular. We give a prediction (under dubious assumptions) thatm _t ≈115 GeV andm _H ≈180 GeV.     

Tumbling in two-dimensional gauge theories

The ideas of tumbling and most attractive channel condensation are confronted in two-dimensional chiral gauge theories. We first demonstrate how to perform a gauge-invariant regularization. We then proceed to find exact results about the spectra in both abelian and non-abelian cases. These conflict with the predictions of tumbling and MAC.     

Magnetic monopoles in gauge theories

Magnetic monopoles in gauge theories are investigated. Let G be the gauge group and H the group of symmetries which are not spontaneously broken. The existence of magnetic monopoles is proved in the case when the group G has a compact covering group but the covering group of H is non-compact.     

Symmetry behavior in gauge theories

A theory of phase transition with symmetry restoration in gauge theories at high temperature is investigated. The phase transition may be of the first or of the second order depending on relations between coupling constants. It is noted that the possible existense of a limiting temperature cannot prevent the high-temperature symmetry restoration. In the theories without neutral currents, symmetry also can be affected by a magnetic field. However in most of the models with neutral currents symmetry restoration takes place not due to a magnetic field but due to massive vector fields, created simultaneously by the magnetic field sources. It is pointed out that in most of the theories with neutral currents an increase of external currents lead to symmetry restoration, while an increase of density results in a further increase of symmetry breaking. In some cases critical values of temperature and external fields and currents appear to be extremely small. At certain relations between coupling constants radiative corrections lead to the absence of symmetry breaking in gauge theories even at zero temperature and in the absence of any other external factors. Strong constraints on masses and coupling constants for the symmetry in the Higgs model to be broken are obtained. It is shown that energy of substance is nonconserved due to energy “pumping” from the non-observable Bose-condensate in the processes under consideration.