Kristian L. McDonald

Solution to the hierarchy problem from an almost decoupled hidden sector within a classically scale invariant theory

If scale invariance is a classical symmetry then both the Planck scale and the weak scale should emerge as quantum effects. We show that this can be realized in simple scale invariant theories with a hidden sector. The weak/Planck scale hierarchy emerges in the (technically natural) limit in which the hidden sector decouples from the ordinary sector. In this limit, finite corrections to the weak scale are consequently small, while quadratic divergences are absent by virtue of classical scale invariance, so there is no hierarchy problem.

Neutrino mass in radiatively broken scale-invariant models

Scale invariance may be a classical symmetry which is broken radiatively. This provides a simple way to stabilize the scale of electroweak symmetry breaking against radiative corrections. The simplest phenomenologically successful model of this type involves the addition of one real scalar field to the standard model. In this minimal model the electroweak Higgs can be interpreted as the pseudo-Goldstone boson of broken scale invariance. We study the possible origin of neutrino mass in such models, both at tree-level and radiatively.

A Class of Inert N-tuplet Models with Radiative Neutrino Mass and Dark Matter

A bstractWe present a class of models with radiative neutrino mass and stable dark-matter candidates. Neutrino mass is generated by a one-loop diagram with the same topography as Ma’s 2006 proposal (which used an inert scalar-doublet and singlet fermion). We generalize this approach and determine all variants with new fields no larger than the adjoint representation. When the neutrino mass diagram contains a Majorana mass insertion there are two possibilities, both of which are known. If the mass insertion is of the Dirac type there are seven additional models, two of which are excluded by direct-detection experiments. The other five models are also constrained, such that only scalar dark-matter is viable. There are cases with an inert singlet, an inert doublet, and an inert triplet, providing a natural setting for inert N -tuplet models of dark matter, with the additional feature of achieving radiative neutrino mass. We show that some of the models admit a simple explanation for the (requisite) discrete symmetry, and briefly discuss cases with representations larger than the adjoint, which can admit a connection to the astrophysical gamma-ray signal.

Poincaré protection for a natural electroweak scale

We discuss a class of technically-natural UV extensions of the Standard Model in which the electroweak scale is shielded from large radiative corrections from heavy UV physics due to an enhanced Poincare symmetry. Such heavy sectors can be invoked to provide solutions to known shortcomings of the Standard Model, such the strong-CP problem, the absence of dark matter, and the lack of neutrino masses. We discuss the relationship to scale-invariant models.

Three-loop model of neutrino mass with dark matter

Laboratoire de Physique Theorique, ES-SENIA University, DZ-31000 Oran, Algeria(Received 27 April 2014; published 22 July 2014)We propose a model in which the origin of neutrino mass is dependent on the existence of dark matter.Neutrinos acquire mass at the three-loop level and the dark matter is the neutral component of a fermiontriplet. We show that experimental constraints are satisfied and that the dark matter can be tested in futuredirect-detection experiments. Furthermore, the model predicts a charged scalar that can be within reach ofcollider experiments like the LHC.

A Model of Radiative Neutrino Mass: with or without Dark Matter

A bstractWe present a three-loop model of neutrino mass whose most-general Lagrangian possesses a softly-broken accidental Z2 symmetry. In the limit that a single parameter vanishes, λ →0, the Z2 symmetry becomes exact and the model contains a stable dark-matter candidate. However, even for finite λ ≪1, long-lived dark matter is possible, giving a unified solution to the neutrino mass and dark matter problems that does not invoke a new symmetry. Taken purely as a neutrino mass model, the new physics can be at the TeV scale. When dark matter is incorporated, however, only a singlet scalar can remain this light, though the dark matter can be tested in direct-detection experiments.

A class of three-loop models with neutrino mass and dark matter

Abstract We study a class of three-loop models for neutrino mass in which dark matter plays a key role in enabling the mass diagram. The simplest models in this class have Majorana dark matter and include the proposal of Krauss, Nasri and Trodden; we identify the remaining related models, including the viable colored variants. The next-to-simplest models use either more multiplets and/or a slight modification of the loop-diagram, and predict inert N-tuplet scalar dark matter.

A radiative model for the weak scale and neutrino mass via dark matter

A bstractWe present a three-loop model of neutrino mass in which both the weak scale and neutrino mass arise as radiative effects. In this approach, the scales for electroweak symmetry breaking, dark matter, and the exotics responsible for neutrino mass, are related due to an underlying scale-invariance. This motivates the otherwise-independent OTeV

Generalized inverse seesaw mechanisms

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