The Theory of Local Mass Dimension One Fermions of Spin One Half

About a decade ago the present author in collaboration with Daniel Grumiller presented an 'unexpected theoretical discovery' of spin one-half fermions with mass dimension one (Ahluwalia-Khalilova and Grumiller in Phys Rev D 72: 067701 arXiv: hep-th/0410192, 2005, JCAP 0507: 012, arXiv: hep-th/0412080, 2005). In the decade that followed a significant number of groups explored intriguing mathematical and physical properties of the new construct. However, the formalism suffered from two troubling features, that of non-locality and a subtle violation of Lorentz symmetry. Here, we trace the origin of both of these issues to a hidden freedom in the definition of duals of spinors and the associated field adjoints. In the process, for the first time, we provide a quantum theory of spin one-half fermions that is free from all the mentioned issues. The interactions of the new fermions are restricted to dimension-four quartic self interaction, and also to a dimension-four coupling with the Higgs. A generalised Yukawa coupling of the new fermions with neutrinos provides an hitherto unsuspected source of lepton-number violation. The new fermions thus present a first-principle dark matter partner to Dirac fermions of the standard model of high energy physics with contrasting mass dimensions-that of three halves for the latter versus one of the former without mutating the statistics from fermionic to bosonic.