First-order Theory of Fields with Arbitrary Spin

By exploiting the previously exposed results in 2-spinor geometry, a general description of fields of arbitrary spin is exposed and shown to admit a first-order Lagrangian which extends the theory of Dirac spinors. The needed bundle is the fibered direct product of a symmetric ‘main sector’—carrying an irreducible representation of the angular-momentum algebra—and an induced sequence of ‘ghost sectors’. Several special cases are considered; in particular, one recovers the Bargmann-Wigner and Joos-Weinberg equations.

Spinors and Minkowski Space

A partly original approach to spinor geometry, showing how a 2-dimensional vector space, without any further assumpions, generates by natural constructions the fundamental algebraic structures needed to deal with spacetime geometry and particles with spin. Several related notions are expressed in a concise, intrinsic form.

Spinor Bundles and Spacetime Geometry

Spinor bundles and other related bundles are constructed by exploiting the algebraic notions introduced in the previous chapter. The linear connections of these bundles and their mutual relations are studied. The notion of 2-spinor soldering form, or ‘tetrad’, yields the fundamental link between spinor algebra and spacetime geometry. The Fermi transport of spinors is studied in view of the definition of free states of particles with spin. The notion of Lorentzian distance is examined in relation to 2-spinor geometry, obtaining simplifications in regard to certain issues which are discussed, in the literature, in relation to the ‘algebraic approach’ to spacetime geometry.

Two-spinor geometry and gauge freedom

Gauge freedom in quantum particle physics is shown to arise in a natural way from the geometry of two-spinors (Weyl spinors). Various related mathematical notions are reviewed, and a special ansatz of the kind "the system defines the geometry" is discussed in connection with the stated results.

SPINOR GEOMETRY

It has been proposed that quantum mechanics and string theory share a common inner syntax, the relational logic of C. S. Peirce. Along this line of thought we consider the relations represented by spinors. Spinor composition leads to the emergence of Minkowski space–time. Inversely, the Minkowski space–time is istantiated by the Weyl spinors, while the merger of two Weyl spinors gives rise to a Dirac spinor. Our analysis is applied also to the string geometry. The string constraints are represented by real spinors, which create a parametrization of the string worldsheet identical to the Enneper–Weierstass representation of minimal surfaces. Further, a spinorial study of the AdS3 space–time reveals a Hopf fibration AdS3 → AdS2. The conformal symmetry inherent in AdS3 is pointed out. Our work indicates the hidden ties between logic-quantum mechanics-string theory-geometry and vindicates the Wheeler's proposal of pregeometry as a large network of logical propositions.

FERMI TRANSPORT OF SPINORS AND FREE QED STATES IN CURVED SPACETIME

Fermi transport of spinors can be precisely understood in terms of two-spinor geometry. By using a partly original, previously developed treatment of two-spinors and classical fields, we describe the family of all transports, along a given one-dimensional timelike submanifold of spacetime, which yield the standard Fermi transport of vectors. Moreover, we show that this family has a distinguished member, whose relation to the Fermi transport of vectors is similar to the relation between the spinor connection and spacetime connection. Various properties of the Fermi transport of spinors are discussed, and applied to the construction of free electron states for a detector-dependent QED formalism introduced in a previous paper.

SPACE–TIME STRUCTURE AND SPINOR GEOMETRY

The structure of space–time is examined by extending the standard Lorentz connection group to its complex covering group, operating on a 16-dimensional “spinor” frame. A Hamiltonian variation principle is used to derive the field equations for the spinor connection. The result is a complete set of field equations which allow the sources of the gravitational and electromagnetic fields, and the intrinsic spin of a particle, to appear as a manifestation of the space–time structure. A cosmological solution and a simple particle solution are examined. Further extensions to the connection group are proposed.