UV/IR duality in noncommutative quantum field theory

We review the construction of renormalizable noncommutative Euclidean ϕ⁴-theories based on the UV/IR duality covariant modification of the standard field theory, and how the formalism can be extended to scalar field theories defined on noncommutative Minkowski space.     

Induced gauge theory on a noncommutative space

We consider a scalar φ⁴ theory on canonically deformed Euclidean space in 4 dimensions with an additional oscillator potential. This model is known to be renormalisable. An exterior gauge field is coupled in a gauge invariant manner to the scalar field. We extract the dynamics for the gauge field from the divergent terms of the 1-loop effective action, using a matrix basis and propose an action for the noncommutative gauge theory, which is a candidate for a renormalisable model. PACS 11.10.Nx; 11.15.-q     

Solitons on Noncommutative Orbifold T 2/Z N

Following the construction of the projection operators on T ² presented by Gopakumar, Headrick and Spradlin, we construct a set of projection operators on the integral noncommutative orbifold T ²/G(G=Z _N , N=2, 3, 4, 6) which correspond to a set of solitons on T ²/Z _N in noncommutative field theory. In this way, we derive an explicit form of projector on T ²/Z ₆ as an example. We also construct a complete set of projectors on T ²/Z _N by series expansions for integral case.     

Technical remarks and comments on the UV/IR-mixing problem of a noncommutative scalar quantum field theory

The possibility of a resummation procedure in order to cure the UV/IR-mixing problem of noncommutative field theories is discussed. The method is presented for a scalar φ⁴ theory on Euclidean space. Finally, we sketch the idea of resummation forU(1)-gauge theories.     

Noncommutative Manifolds, the Instanton Algebra¶and Isospectral Deformations

We give new examples of noncommutative manifolds that are less standard than the NC-torus or Moyal deformations of ℝ ⁿ . They arise naturally from basic considerations of noncommutative differential topology and have non-trivial global features. The new examples include the instanton algebra and the NC-4-spheres S ⁴ _θ. We construct the noncommutative algebras ?=C ^∞ (S ⁴ _θ) of functions on NC-spheres as solutions to the vanishing, ch _j (e) = 0, j < 2, of the Chern character in the cyclic homology of ? of an idempotent e∈M ₄ (?), e ²=e, e=e ^*. We describe the universal noncommutative space obtained from this equation as a noncommutative Grassmannian as well as the corresponding notion of admissible morphisms. This space Gr contains the suspension of a NC-3-sphere S ³ _θ distinct from quantum group deformations SU _q (2) of SU (2). We then construct the noncommutative geometry of S _θ ⁴ as given by a spectral triple ?, ℋ, D) and check all axioms of noncommutative manifolds. In a previous paper it was shown that for any Riemannian metric g _μν on S ⁴ whose volume form is the same as the one for the round metric, the corresponding Dirac operator gives a solution to the following quartic equation,

Equal-time two-point correlation functions in Coulomb gauge Yang–Mills theory

We apply a functional perturbative approach to the calculation of the equal-time two-point correlation functions and the potential between static color charges to one-loop order in Coulomb gauge Yang–Mills theory. The functional approach proceeds through a solution of the Schrödinger equation for the vacuum wave functional to order g²$g^2$ and derives the equal-time correlation functions from a functional integral representation via new diagrammatic rules. We show that the results coincide with those obtained from the usual Lagrangian functional integral approach, extract the beta function, and determine the anomalous dimensions of the equal-time gluon and ghost two-point functions and the static potential under the assumption of multiplicative renormalizability to all orders.     

High energy improved scalar quantum field theory from noncommutative geometry without UV/IR-mixing

We consider an interacting scalar quantum field theory on noncommutative Euclidean space. We implement a family of noncommutative deformations, which – in contrast to the well known Moyal–Weyl deformation – lead to a theory with modified kinetic term, while all local potentials are unaffected by the deformation. We show that our models, in particular, include propagators with anisotropic scaling z=2$z=2$ in the ultraviolet (UV). For a Φ⁴${\Phi }^4$-theory on our noncommutative space we obtain an improved UV behaviour at the one-loop level and the absence of UV/IR-mixing and of the Landau pole.     

Scalar Field in the Bianchi I: Noncommutative Classical and Quantum Cosmology

Using the ADM formalism in the minisuperspace, we obtain the commutative and noncommutative exact classical solutions and exact wave function to the Wheeler-DeWitt equation with an arbitrary factor ordering, for the anisotropic Bianchi type I cosmological model, coupled to a scalar field, cosmological term and barotropic perfect fluid. We introduce noncommutative scale factors, considering that all minisuperspace variables q ⁱ do not commute, so the symplectic structure was modified. In the classical regime, it is shown that the anisotropic parameter β _±nc and the field φ, for some value in the λ _eff cosmological term and noncommutative θ parameter, present a dynamical isotropization up to a critical cosmic time t _c ; after this time, the effects of isotropization in the noncommutative minisuperspace seems to disappear. In the quantum regimen, the probability density presents a new structure that corresponds to the value of the noncommutativity parameter.     

Hard noncommutative loops resummation

The noncommutative version of the Euclidean g2phi4 theory is considered. By using Wilsonian flow equations the ultraviolet renormalizability can be proved to all orders in perturbation theory. On the other hand, the infrared sector cannot be treated perturbatively and requires a resummation of the leading divergences in the two-point function. This is analogous to what is done in the hard thermal loops resummation of finite temperature field theory. Next-to-leading order corrections to the self-energy are computed, resulting in O(g3) contributions in the massless case, and O(g6logg2) in the massive one.     

Noncommutative deformation of instantons

We study instanton solutions on noncommutative Euclidean 4-space which are deformations of instanton solutions on commutative Euclidean 4-space. We show that the instanton numbers of these noncommutative instanton solutions coincide with the commutative solutions and conjecture that the instanton number in R⁴${\mathbb{R}}^4$ is preserved for general noncommutative deformations. We also study noncommutative deformation of instanton solutions on a T⁴$T^4$ with twisted boundary conditions.     

Braided Quantum Field Theory

We develop a general framework for quantum field theory on noncommutative spaces, i.e., spaces with quantum group symmetry. We use the path integral approach to obtain expressions for n-point functions. Perturbation theory leads us to generalised Feynman diagrams which are braided, i.e., they have non-trivial over- and under-crossings. We demonstrate the power of our approach by applying it to φ⁴-theory on the quantum 2-sphere. We find that the basic divergent diagram of the theory is regularised. Received: 3 July 1999 / Accepted: 10 November 2000     

The FKG inequality for the Yukawa2 quantum field theory

We establish the FKG correlation inequality for the Euclidean scalar Yukawa₂ quantum field model and, when the Fermi mass is zero, for pseudoscalar Yukawa₂. To do so we approximate the quantum field model by a lattice spin system and show that the FKG inequality for this system follows from a positivity condition on the fundamental solution of the Euclidean Dirac equation with external field. We prove this positivity condition by applying the Vekua-Bers theory of generalized analytic functions.Research partially supported by the National Research Council of Canada.Alfred P. Sloan Foundation Fellow.     

Renormalisation of <Emphasis Type="Italic">ϕ</Emphasis><Superscript>4</Superscript>-Theory on Noncommutative ℝ<Superscript>4</Superscript> in the Matrix Base

We prove that the real four-dimensional Euclidean noncommutative ⁴-model is renormalisable to all orders in perturbation theory. Compared with the commutative case, the bare action of relevant and marginal couplings contains necessarily an additional term: an harmonic oscillator potential for the free scalar field action. This entails a modified dispersion relation for the free theory, which becomes important at large distances (UV/IR-entanglement). The renormalisation proof relies on flow equations for the expansion coefficients of the effective action with respect to scalar fields written in the matrix base of the noncommutative ⁴. The renormalisation flow depends on the topology of ribbon graphs and on the asymptotic and local behaviour of the propagator governed by orthogonal Meixner polynomials.     

On the perturbation theory of critical phenomena

It is shown how, using the ideas of Brezin, Le Guillou and Zinn-Justin, one may obtain the critical properties of the φ⁴ model from renormalised perturbation theory without the use of the Callan-Symanzik equation and an associated approximation     

Volume dependence of Schwinger functions in the Yukawa2 quantum field theory

We prove upper bounds on the partition function and Schwinger functions for the Euclidean Yukawa₂ quantum field theory which depend on the interaction volume Λ only through a term of the form (const)^|Λ|. We also prove a lower bound of the form (const)^|λ| for the partition function. We work throughout in the Matthews-Salam representation with the fermions integrated out.     

Geometrical relationship between the classical and quantum descriptions of arbitrary force interactions

The paper is a continuation of a series papers by the author in which it is shown that the equations of contemporary quantum theory (the Klein-Gordon equation and the Dirac integral equation) can be interpreted as conditions of harmonicity of linear form in the manifold^sV₄. In this paper, geometrization of classical and quantum interactions of a physical object is performed for the case of an arbitrary external force field in the manifold^kV₄. This manifold is constructed on the same set of surfaces as the manifold^sV₄. The equation representing conditions of harmonicity of linear form in^kV₄ is derived and is analogous to the KleinGordon equation.     

Fermionization,Convergent Perturbation Theory,and Correlations in the Yang–Mills Quantum Field Theory in Four Dimensions

We show that the Yang–Mills quantum field theory with momentum and spacetime cutoffs in four Euclidean dimensions is equivalent, term by term in an appropriately resummed perturbation theory, to a Fermionic theory with nonlocal interaction terms. When a further momentum cutoff is imposed, this Fermionic theory has a convergent perturbation expansion. To zeroth order in this perturbation expansion, the correlation function E(x,y) of generic components of pairs of connections is given by an explicit, finite-dimensional integral formula, which we conjecture will behave as

Descending problem in Green's function approach to quantum field theory

The question how to determine lower many-point functions in terms of higher ones, which we call the descending problem, is discussed for the (ø⁴)₁₊₃ model of quantum field theory. Equations to be considered are non-linear non-compact operator equations in complex Banach spaces.Several sufficient sets of conditions for convergence of successive approximation schemes are presented for small values of the renormalised coupling constant. Local uniqueness of solution is proved under certain conditions.     

Auxiliary “Massless” Spin-2 Field in De Sitter Universe

For the tensor field of rank-2 there are two unitary irreducible representation (UIR) in de Sitter (dS) space denoted by P^±_2,2\Pi^{\pm}_{2,2} and P^±_2,1\Pi^{\pm}_{2,1} (Dixmier in Bull Soc. Math. France 89:9, 1961). In the flat limit only the P^±_2,2\Pi^{\pm}_{2,2} coincides to the UIR of Poincaré group, the second one becomes important in the study of conformal gravity. In the previous work, Dirac’s six-cone formalism has been utilized to obtain conformally invariant (CI) field equation for the “massless” spin-2 field in dS space (Dehghani et al. in Phys. Rev. D 77:064028, 2008). This equation results in a field which transformed according to P^±_2,1\Pi^{\pm}_{2,1}, we name this field the auxiliary field. In this paper this auxiliary field is considered and also related two-point function is calculated as a product of a polarization tensor and “massless” conformally coupled scalar field. This two-point function is de Sitter invariant.