The Minimal Scale Invariant extension of the Standard Model (MSISM) is a model of lowenergy particle physics which is identical to the Standard Model except for the inclusion of an additional complex singlet scalar and treelevel scale invariance. Scale invariance is a classical symmetry which is explicitly broken by quantum corrections whose interplay with the quartic couplings can be used to trigger electroweak symmetry breaking. The scale invariant Standard Model suﬀers from a number of problems, however the inclusion of a complex singlet scalar results in a perturbative and phenomenologically viable theory. We present a thorough and systematic investigation of the MSISM for a number of representative scenarios along two of its three classified types of ﬂat direction. In these scenarios we determine the permitted quartic coupling parameter space, using both theoretical and experimental constraints, and apply these limits to make predictions of the scalar mass spectrum and the energy scale at which scale invariance is broken. We calculate the oneloop eﬀective potential and the oneloop beta functions of the pertinent couplings of the MSISM specifically for this purpose. We also discuss the phenomenological implications of these scenarios, in particular, whether they realise explicit or spontaneous CP violation, contain neutrino masses or provide dark matter candidates. Of particular importance is the discovery of a new minimal scale invariant model which provides maximal spontaneous CP violation, can naturally incorporate neutrino masses, produces a massive stable scalar dark matter candidate and can remain perturbative up to the Planck scale. It can be argued that the last property, along with the classical scale invariance, can potentially solve the gauge hierarchy problem for this model.
Date of Award  31 Dec 2010 

Original language  English 

Awarding Institution   The University of Manchester


Supervisor  Apostolos Pilaftsis (Supervisor) 

 Beyond the Standard Model
 Extended Higgs Sector
 NonStandard Model Neutrino model
The Minimal Scale Invariant Extension of the Standard Model
AlexanderNunneley, L. (Author). 31 Dec 2010
Student thesis: Phd