— The theme is the influence of the spin structure on the Dirac spectrum of a spin manifold. We survey examples and results related to this question. Résumé (Dépendance du Spectre de l’Opérateur de Dirac de la Structure Spinorielle) Sur une variété spinorielle, nous étudions la dépendance du spectre de l’opérateur de Dirac par rapport à la structure spinorielle. Nous donnons un résumé des exemp...

— The theme is the influence of the spin structure on the Dirac spectrum of a spin manifold. We survey examples and results related to this question. Résumé (Dépendance du spectre de l’opérateur de Dirac par rapport à la structure spinorielle) Sur une variété spinorielle, nous étudions la dépendance du spectre de l’opérateur de Dirac par rapport à la structure spinorielle. Nous donnons ensuite ...

This paper offers a geometric framework for modeling port-Hamiltonian systems on discrete manifolds. The simplicial Dirac structure, capturing the topological laws of the system, is defined in terms of primal and dual cochains related by the coboundary operators. This finitedimensional Dirac structure, as discrete analogue of the canonical Stokes-Dirac structure, allows for the formulation of f...

We study multiplicative Dirac structures on Lie groups. We show that the characteristic foliation of a multiplicative Dirac structure is given by the cosets of a normal Lie subgroup and, whenever this subgroup is closed, the leaf space inherits the structure of a Poisson-Lie group. We also describe multiplicative Dirac structures on Lie groups infinitesimally. Résumé Nous étudions les structure...

The Lie derivation of multivector fields along multivector fields has been introduced by Schouten (see cite{Sc, S}), and studdied for example in cite{M} and cite{I}. In the present paper we define the Lie derivation of differential forms along multivector fields, and we extend this concept to covariant derivation on tangent bundles and vector bundles, and find natural relations between them and...

The honeycomb lattice possesses a novel energy band structure, which is characterized by two distinct Dirac points in the Brillouin zone, dominating most of the physical properties of the honeycomb structure materials. However, up till now, the origin of the Dirac points is unclear yet. Here, we discover a hidden symmetry on the honeycomb lattice and prove that the existence of Dirac points is ...

We study the implications of neutrino oscillations with maximal mixing for the neutrino Dirac and Majorana matrices in the see-saw mechanism for three non degenerate neutrino masses. We find the form of the Dirac matrix for a structure-less Majorana matrix and, conversely, the structure of the Majorana matrix if the Dirac matrix is according to our naive intuition. We give some examples of Majo...

A zero-gap state with a Dirac cone type energy dispersion was discovered in an organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. In contrast to the case of graphene, the Dirac cone in this system is highly anisotropic. The present system, therefore, provides a new type o...

Coupling Dirac structures are Dirac structures defined on the total space of a fibration, generalizing hamiltonian fibrations from symplectic geometry, where one replaces the symplectic structure on the fibers by a Poisson structure. We study the associated Poisson gauge theory, in order to describe the presymplectic groupoid integrating coupling Dirac structures. We find the obstructions to in...

The existence of Dirac cones in the band structure of two-dimensional materials accompanied by unprecedented electronic properties is considered to be a unique feature of graphene related to its hexagonal symmetry. Here, we present other two-dimensional carbon materials, graphynes, that also possess Dirac cones according to first-principles electronic structure calculations. One of these materi...