arXiv subjects
Publications and source records attributed to F. J. Vanhecke.
In this short communication, we examine the relevance of the signature of the space-time metric in the construction of the product of a pseudo-Riemannian spectral triple with a finite triple describing the internal geometry. We obtain arguments favouring the appearance of SU(2) and U(1) as gauge groups in the standard model.
In earlier work (*) we studied an extension of the canonical symplectic structure in the cotangent bundle of an affine space ${\cal Q}={\bf R}^N$, by additional terms implying the Poisson non-commutativity of both configuration and momentum variables. In this article, we claim that such an extension can be done consistently when ${\cal Q}$ is a Lie group $G$. -- (*) : F.J.Vanhecke, C.Sigaud and A.R.da Silva, arXiv:math-phys/0502003 and Braz.J.Phys.{\bf 36},no IB,194(2006)
Extending earlier work(*), we examine the deformation of the canonical symplectic structure in a cotangent bundle $T^\star(\Q)$ by additional terms implying the Poisson non-commutativity of both configuration and momentum variables. In this short note, we claim this can be done consistently when $\Q$ is a Lie group. -- (*) F.J.Vanhecke, C.Sigaud and A.R.da Silva, arXiv:math-phys/0502003(2005) and Braz.J.Phys.{\bf 36},no IB,194(2006)
In this work we examine noncommutativity of position coordinates in classical symplectic mechanics and its quantisation. In coordinates $\{q^i,p_k\}$ the canonical symplectic two-form is $ω_0=dq^i\wedge dp_i$. It is well known in symplectic mechanics {\bf\cite{Souriau,Abraham,Guillemin}} that the interaction of a charged particle with a magnetic field can be described in a Hamiltonian formalism without a choice of a potential. This is done by means of a modified symplectic two-form $ω=ω_0-e\F$, where $e$ is the charge and the (time-independent) magnetic field $\F$ is closed: $\dif\F=0$. With this symplectic structure, the canonical momentum variables acquire non-vanishing Poisson brackets: $\{p_k,p_l\} = e F_{kl}(q)$. Similarly a closed two-form in $p$-space $\G$ may be introduced. Such a {\it dual magnetic field} $\G$ interacts with the particle's {\it dual charge} $r$. A new modified symplectic two-form $ω=ω_0-e\F+r\G$ is then defined. Now, both $p$- and $q$-variables will cease to Poisson commute and upon quantisation they become noncommuting operators. In the particular case of a linear phase space ${\bf R}^{2N}$, it makes sense to consider constant $\F$ and $\G$ fields. It is then possible to define, by a linear transformation, global Darboux coordinates: $\{ξ^i,π_k\}= {δ^i}_k$. These can then be quantised in the usual way $[\hatξ^i,\hatπ_k]=i\hbar {δ^i}_k$. The case of a quadratic potential is examined with some detail when $N$ equals 2 and 3.
In this short article we review how the classical theory of principal fibre bundles (PFB) transcribes in an algebraic formalism. In this dual formulation, a PFB is given by a right co-module algebra ${\cal P}$ over a Hopf algebra ${\cal H}$ with a mapping $Δ_R:{\cal P}\to{\cal P}\otimes{\cal H}$. In our case ${\cal P}$ is the (commutative) C*-algebra of complex-valued continuous functions on the total space P and ${\cal H}$ is the Hopf algebra of complex-valued functions on the structure group G. These underlying spaces are endowed with a topology only. The subalgebra ${\cal B}$ of $Δ_R$-invariant elements is identified with the algebra of complex-valued functions on the base space B. In order to define horizontal one-forms, a differential calculus is needed. Since no a priori differential structure is assumed, we use the calculus of the universal differential envelope $Ω^\bullet({\cal P})$ which can be defined on any unital algebra. A connection on the PFB is then defined by a splitting of the universal one-forms as a direct sum of horizontal and vertical subspaces : $Ω^1({\cal P})=Γ_{hor}\oplusΓ_{ver}$. In case of a strong connection in a trivial PFB, the general expression and gauge transformation of the connection one-form and the curvature two-form are given. A locally trivial PFB can be constructed through a gluing procedure of a cover of the algebra ${\cal P}$ (see this meeting's poster session P112, where examples are given).
In this work we examine generalized Connes-Lott models on the two-sphere. The Hilbert space of the continuum spectral triple is taken as the space of sections of a twisted spinor bundle, allowing for nontrivial topological structure (magnetic monopoles). The finitely generated projective module over the full algebra is also taken as topologically non-trivial, which is possible over $S^2$. We also construct a real spectral triple enlarging this Hilbert space to include "particle" and "anti-particle" fields.
The product of two real spectral triples {A1,H1,D1,J1,gamma1} and {A2,H2,D2,J2(,gamma2)}, the first of which is necessarily even, was defined by A.Connes as {A,H,D,J(,gamma)} given by A=A1 x A2,H=H1 x H2, D=D1 x I2 + gamma1 x D2, J=J1 x J2 and by, in the even-even case, gamma=gamma1 x gamma2. Generically it is assumed that the real structure J obeys the relations J^2=epsilon Id, JD=epsilon' DJ, Jgamma = epsilon'' gammaJ, where the epsilon-sign table depends on the dimension n, modulo 8, of the spectral triple. If both spectral triples obey Connes' epsilon-sign table, it is seen that their product, defined in the straightforward way above, does not necessarily obey this epsilon-sign table. In this note, we propose an alternative definition of the product real structure such that the epsilon-sign table is also satisfied by the product.
We describe the classical Schwinger model as a study of the projective modules over the algebra of complex-valued functions on the sphere. On these modules, classified by $π_2(S^2)$, we construct hermitian connections with values in the universal differential envelope which leads us to the Schwinger model on the sphere. The Connes-Lott program is then applied using the Hilbert space of complexified inhomogeneous forms with its Atiyah-Kaehler structure. It splits in two minimal left ideals of the Clifford algebra preserved by the Dirac-Kaehler operator D=i(d-delta). The induced representation of the universal differential envelope, in order to recover its differential structure, is divided by the unwanted differential ideal and the obtained quotient is the usual complexified de Rham exterior algebra over the sphere with Clifford action on the "spinors" of the Hilbert space. The subsequent steps of the Connes-Lott program allow to define a matter action, and the field action is obtained using the Dixmier trace which reduces to the integral of the curvature squared.