Gauge dependence of gravitational correction to running of gauge couplings

Recently an interesting idea has been put forward by Robinson and Wilczek that the incorporation of quantized gravity in the framework of Abelian and non-Abelian gauge theories results in a correction to the running of gauge coupling and, as a consequence, increase the grand unification scale and asymptotic freedom. In this Letter it is shown by explicit calculations that this correction depends on the choice of gauge.     

Effects of unparticles on running of gauge couplings

Unparticles charged under a gauge group can contribute to the running of the gauge coupling. We show that a scalar unparticle of scaling dimension d contributes to the β function a term that is (2-d) times that from a scalar particle in the same representation. This result has important implications for asymptotic freedom. An unparticle with d>2, in contrast to its matter counterpart, can speed up the approach to asymptotic freedom for a non-Abelian gauge theory and has the tendency to make an Abelian theory also asymptotically free. For not spoiling the excellent agreement of the standard model (SM) with precision tests, the infrared cut-off, m, of such an unparticle would be high but might still be reachable at colliders such as LHC and ILC. Furthermore, if the unparticle scale Λ_U is high enough, unparticles could significantly modify the unification pattern of the SM gauge couplings. For instance, with three scalar unparticles of d∼2.5 in the adjoint representation of the strong gauge group but neutral under the electroweak one, the three gauge couplings would unify at a scale of ∼ 8×10¹² GeV, which is several orders of magnitude below the supersymmetric unification scale. PACS  12.90.+b; 14.80.-j; 11.10.Hi; 12.10.Dm     

Gravitational gauge mediation

It is often the case that the naive introduction of the messenger sector to supersymmetry breaking models causes restoration of supersymmetry. We discuss a possibility of stabilizing the supersymmetry breaking vacuum by gravitational interaction.     

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.     

One-loop generated anomalous gauge couplings

We compute, at one loop, the CP-violating anomalous trilinear gauge-boson form factors which couple theW (or theZ) to the photon and theZ. In order to see which form factors are generated by which types of underlying interactions, we work with as general an underlying model as is possible. After identifying which form factors can arise at one loop in a completely general renormalizable model of spin-half and spin-zero particles, we provide explicit formulae for the induced form factors in a very broad class of such models. Our results include some previous calculations as special cases, and we identify errors in some of these.     

On the interpretation of gravitational corrections to gauge couplings

Several recent papers discuss gravitational corrections to gauge couplings that depend quadratically on the energy. In the framework of the background-field approach, these correspond in general to adding to the effective action terms quadratic in the field strength but with higher-order space–time derivatives. We observe that such terms can be removed by appropriate local field redefinitions, and do not contribute to physical scattering-matrix elements. We illustrate this observation in the context of open string theory, where the effective action includes, among other terms, the well-known Born–Infeld form of non-linear electrodynamics. We conclude that the quadratically energy-dependent gravitational corrections are not physical in the sense of contributing to the running of a physically-measurable gauge coupling, or of unifying couplings as in string theory.     

Gravitational couplings and Z2 orientifolds

The interplay between gravitational couplings on branes and the occurrence of fractional flux in low-dimensional orientifolds is examined. It is argued that gravitational couplings need to be assigned not only to D-branes but also to orientifold planes. The fractional charges of the orientifold d-planes can be understood in terms of flux quantization of the d − 3 form potential and modified Bianchi identities. Detailed results are presented for the case of the type IIB orientifold on T⁶/Z₂, which is dual to F-theory on a complex 4-fold with terminal singularities.     

Hadronic gauge couplings in meson decays

The branching ratiosR(J→ππρ)≡Γ(J→ππρ)/Γ(J→ππ) for naturalJ ^P mesons have been evaluated under the assumption that theT(J→ππρ) amplitudes are generated by the gauge principle for ρ-mesons originally proposed by Sakurai in his approach to VMD. The ratios are predicted to increase withJ and are compatible with the present-day data. This suggests that the hadronic interactions of the photon proceed exclusively through its hadronic (VMD) component.     

Symmetry breaking and time variation of gauge couplings

Astrophysical indications that the fine structure constant has undergone a small time variation during the cosmological evolution are discussed within the framework of the standard model of the electroweak and strong interactions and of grand unification. A variation of the electromagnetic coupling constant could either be generated by a corresponding time variation of the unified coupling constant or by a time variation of the unification scale, of by both. The various possibilities, differing substantially in their implications for the variation of low energy physics parameters like the nuclear mass scale, are discussed. The case in which the variation is caused by a time variation of the unification scale is of special interest. It is supported in addition by recent hints towards a time change of the proton–electron mass ratio. Implications for the analysis of the Oklo remains and for quantum optics tests are discussed.     

Studying trilinear gauge couplings at linear collider energies

We investigate the sensitivity of the semileptonic processes , , on the non-standard trilinear gauge couplings, using the optimal observables method at Linear Collider energies. Our study is based on the four-fermion generator ERATO. Taking into account all possible correlations between the different trilinear gauge coupling parameters, we show that they can be measured with an accuracy of to for typical Linear Collider energies and luminosities. Received: 9 April 1997 / Revised version: 18 June 1997     

Impossibility of adding gauge couplings to spontaneously broken N = 8 supergravity

When the four mass parameters of spontaneously broken N = 8 supergravity are taken to be equal, the theory possesses at global SU(4) symmetry. Since it contains massless vectors in the adjoint representation, it is tempting to add gauge interactions so as to make the SU(4) symmetry local. In this paper we show that it is impossible to do this in a way that is consistent with the spontaneous character of the symmetry breaking.