Mass dimension one fermions

In theoretical physics and cosmology the mass dimension one fermions of spin one half are a dark matter candidate. These fermions are fundamentally different from the hitherto known matter particles, like electrons or neutrinos. Despite being endowed with spin one half they are not described by the celebrated Dirac formalism but, instead, by a spinorial Klein-Gordon formalism.
In 2004 Dharam Vir Ahluwalia (IIT Guwahati) in collaboration with Daniel Grumiller presented an unexpected theoretical discovery of spin one-half fermions with mass dimension one. In the decade that followed a significant number of groups explored intriguing mathematical and physical properties of the new construct while Ahluwalia and his students developed the formalism further.
However, the formalism suffered from two troubling features, that of non-locality and a subtle violation of Lorentz symmetry. The origin of both of these issues has now been traced to a hidden freedom in the definition of duals of spinors and the associated field adjoints. As a result there now exists an entirely new quantum field 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 with contrasting mass dimensions — that of three halves for the latter versus one of the former without mutating the statistics from fermionic to bosonic.
Mass dimension one fermionic field of spin one half uses ELKO as its expansion coefficients. ELKO is an acronym of the original German term "Eigenspinoren des Ladungskonjugationsoperators", designating spinors that are eigenspinors of the charge conjugation operator.
Since the new fermions have a mass dimensionality mismatch with standard model matter fields they were suggested as a dark matter candidate. As a result of their scalar-like mass dimension they differ significantly from the mass dimension 3/2 Dirac fermions.
Mass dimension one fermions have unexpected implications for cosmology by providing first principle dark matter and dark energy fields. Immediately after the publication of the Ahluwalia-Grumiller papers in 2005, Christian Boehmer pioneered application of Elko to cosmology and argued that Elko "are not only prime dark matter candidates but also prime candidates for inflation."
Einstein-Cartan-Elko system was first introduced in cosmology by Boehmer.
Saulo Pereira and colleagues have shown that Elko can also induce a time varying cosmological constant.
Abhishek Basak and colleagues have argued that the fast-roll inflation attractor point is unique for Elko and it is independent of the form of the potential.
Roldao da Rocha has argued that Elko can also be used as a tool for probing exotic topological features of spacetime.
Elko localization on the branes has been investigated in, and.
The following references serve as a guide to the lively activity on Elko, and mass dimension one fermions:
Earlier history of Elko is summarized in references: and.
How Weinberg no go theorem is evaded is explained by Ahluwalia in 2017. Also in 2017, it was shown that mass-dimension-one fermions, even in the absence of a cosmological constant, can induce a 'cosmological constant' term by quantum effects. These effects, leading to the non-vanishing Λ could be responsible for the inflationary phase at early universe stages. Furthermore, for the late time evolution, corresponding to a model with a time varying cosmological term, such quantum effects are in agreement with a previous recent work.
Detailed discussion on mass dimension one fermions can be found in a recent Cambridge Monograph on Mathematical Physics.
A further incompleteness in the Dirac formalism has been discovered after the cited monograph was published in mid 2019. This leads to (a) a new class of mass dimension one fermions
, and to (b) unexpected existence of mass dimension three-half bosons of spin one-half
.

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