On the quantum structure of spacetime and its relation to the quantum theory of fields: $κ$-Poincaré invariant field theories and other examples

Abstract

The dissertation deals with noncommutative field theories, namely field theories compatible with the existence of a minimal (quantum gravity) length scale. Two families of quantum spacetime are considered. One is characterized by semisimple Lie algebras of coordinates. The other is characterized by solvable Lie algebras. The explicit construction of corresponding Weyl-like star products is given. We then focus on two specific examples of quantum space and study the quantum properties of various models of scalar field theory with quartic interactions built on them. The corresponding 2-point and 4-point functions are computed at one-loop and the UV/IR mixing is discussed. The first quantum spacetime considered is known as $\mathbb{R}^3_θ$ which is a deformation of $\mathbb{R}^3$ with $\mathfrak{su}(2)$ noncommutativity. In this case, the one-loop 2-point function is found to be finite with the deformation parameter playing the role of a cutoff. The second quantum space is known as $κ$-Minkowski. In this case, the action functional is required $κ$-Poincaré invariant and various kinetic operators are considered. In one case, we find that the one-loop 2-point function has milder UV divergence than in the commutative case and that the one-loop 4-point function is finite. The renormalization properties are discussed. Besides, the loss of cyclicity of the Lebesgue integral (which results from the $κ$-Poincaré invariance of the action functional) is interpreted as reflecting the occurrence of KMS condition at the level of the algebra of fields modelling $κ$-Minkowski. This interpretation sheds new light on $κ$-deformation-based quantum gravity models, and solved a 25 years old problem in the study of $κ$-Poincaré invariant quantum field theories. Possible extensions of this work are finally discussed.