arXiv subjects
Publications and source records attributed to Dan-Radu Grigore.
We consider the general framework of perturbative quantum field theory for the general Yang-Mills model including massless and massive vector fields and also scalar and Dirac fields. We describe the chronological products using Wick submonomials and give rigorous proofs of gauge invariance for tree and loop contributions in the second order of the perturbation theory.
We consider the general framework of perturbative quantum field theory for the pure Yang-Mills model developped in [10] and consider the coupling with spin 3/2 particles. We will derive the most general form of the interaction with pure Yang-Mills particles and with the spin $2$ field. The expressions for the interactions are obtained, as in the pure Yang-Mills case, using gauge invariance in the first order of the perturbation theory. Further constrains are obtained using gauge invariance in the second order of the perturbation theory. For the coupling of spin $3/2$ with spin $1$ particles, we obtain some natural restrictions on the coupling. For coupling of spin $3/2$ with spin $2$ particles, we get a negative result: such a coupling is not possible in the causal approach.
We consider the general framework of perturbative quantum field theory for the pure Yang-Mills model developed in [9] and prove that the tree contributions do not give anomalies. We will provide a more general form of this gauge invariance property.
We extend the general framework of perturbative quantum field theory developped for the pure Yang-Mills model to gravity. First we present a variant of the elimination procedure of the anomalies in the second order of perturbation theory. After that we prove that gauge invariance restricts severely the possible finite renormalizations, so at least in the second order of the perturbation theory, the model is renormalizable.
We consider the general framework of perturbative quantum field theory for the pure Yang-Mills model. We give a more precise version of the Wick theorem using Hopf algebra notations for chronological products and not for Feynman graphs. Next we prove that Wick expansion property can be preserved for all cases in order $ n = 2. $ However, gauge invariance is broken for chronological products of Wick submonomials.
We compute the one-loop contributions of the chronological products for massless gravity in the second order of the perturbation theory. We prove that the loop contributions are coboundaries i.e. expressions which give zero when averaged on physical states. We conjecture that such a result should be true in higher orders of the perturbation theory also. This result should make easier the problem of constructive quantum field theory.
The system of multi-gravitons has been considered before in the framework of functional formalism. We consider here the system of multi-gravitons in the causal formalism of quantum field theory. We derive in this formalism the fact that distinct gravitons cannot interact. The proof is based on a careful analysis of the first two orders of the perturbation theory.
We consider perturbative quantum field theory in the causal framework. Gauge invariance is, in this framework, an identity involving chronological products of the interaction Lagrangian; it express the fact that the scattering matrix must leave invariant the sub-space of physical states. We are interested in generalizations of such identity involving Wick sub-monomials of the interaction Lagrangian. The analysis can be performed by direct computation in the lower orders of perturbation theory; guided by these computations we conjecture a generalization for arbitrary orders.
We prove the non-uniqueness theorem for the chronological products of a gauge model. We use a cohomological language where the cochains are chronological products, gauge invariance means a cocycle restriction and coboundaries are expressions producing zero sandwiched between physical states. Suppose that we have gauge invariance up to order n of the perturbation theory and we modify the first-order chronological products by a coboundary (a trivial Lagrangian). Then the chronological products up to order n get modified by a coboundary also.
We consider the standard model up to the second order of the perturbation theory (in the causal approach) and derive the most general form of the interaction Lagrangian for an arbitrary number of Higgs fields.
We consider gauge models in the causal approach and study one-loop contributions to the chronological products and the anomalies they produce. We prove that in order greater than 4 there are no one-loop anomalies. Next we analyze one-loop anomalies in the second and third order of the perturbation theory. We prove that the even parity contributions (with respect to parity) do not produce anomalies; for the odd parity contributions we reobtain the well-known result.
We continue the investigation from a previous paper concerning the super-renormalizablity of gauge models going to the third order of the perturbation theory. Here we consider only the Yang-Mills case and we prove that this property is true iff some supplementary restrictions are imposed on the constants appearing in the interaction Lagrangian. The usual standard model does not verify these restrictions, but there is hope that such models do exist and they are in agreement with the phenomenology. We consider here only the even-parity contributions.
We consider some typical gauge models in the causal approach: Yang-Mills and pure massless gravity up to the second order of the perturbation theory. We prove that the loop contributions are coboundaries, up to super-renormalizable terms in the Yang-Mills case; this means that the ultra-violet behavior is better than expected from power counting considerations. For the pure massless gravity we prove that the loop contributions are coboundaries so the model is essentially classical. We conjecture that such a result should be true in higher orders of the perturbation theory also. This result should make easier the problem of constructive quantum field
In the first sections of this paper we give an elementary but rigorous approach to the construction of the quantum Bosonic and supersymmetric string system continuing the analysis of Dimock. This includes the construction of the DDF operators without using the vertex algebras. Next we give a rigorous proof of the equivalence between the light-cone and the covariant quantization methods. Finally, we provide a new and simple proof of the BRST quantization for these string models.