A. Macpherson

Biased discrete symmetry breaking and Fermi balls

Abstract The spontaneous breading of an approximate discrete symmetry is considered, with the resulting protodomains of true and false vacuum being separated by domain walls. Given a strong, symmetric Yukawa coupling of the real scalar field to a generic fermion, the domain walls accumulate a gas of fermions, which modify the domain wall dynamics. The splitting of the degeneracy of the ground states results in the false vacuum protodomain structures eventually being fragmented into tiny false vacuum bags with a Fermi gas shell (Fermi balls), that may be cosmologically stable due to the Fermi gas pressure and wall curvature forces, acting on the domain walls. As fermions inhabiting the domain walls do not undergo number density freeze out, stable Fermi balls exist only if a fermion anti-fermion asymmetry occurs. Fermi balls formed with a new Dirac fermion that possesses no standard model gauge charges provide a novel cold dark matter candidate.

Toponium tests of top quark Higgs bags

Abstract Recently it has been suggested that top quarks, or very massive fourth generation quarks, might surround themselves with a Higgs “bag” of deformation of the Higgs expectation value from its vacuum magnitude. In this paper we address the question of whether such non-linear Higgs-top interaction effects are subject to experimental test. We first note that if top quarks were necessarily accompanied by Higgs “bags”, then top quark weak decay would involve the sudden disruption of the Higgs “bag”, with copious production of physical Higgs particles accompanying the decay. We then examine the effects that such Higgs “bags” would produce on the spectrum of toponium, where the two bound top (anti) quarks, and their “bags”, overlap. We numerically evaluate the effects that the non-linear feedback in the Higgs-toponium system would have on the energy level splittings of the toponium bound states, and find that for allowed values of the top and Higgs mass the effect is negligible, thus indicating that even in this favourable circumstance Higgs “bag” formation around top quarks does not observably occur. Finally, we consider the case of a second Higgs doublet, allowing the possibility of enhanced couplings for one of the physical Higgs to top. Even in this non-standard scenario the effects are minimal, and we infer the general absence of observable effects at any level that might suggest the utility of considering top quarks to be accompanied by Higgs “bags”.

Nucleon Decay in Non-Minimal Supersymmetric SO(10)

Evaluation of nucleon decay modes and branching ratios in a non-minimal supersymmetric SO(10) grand unified theory is presented. The non-minimal GUT considered is the supersymmetrised version of the ‘realistic’ SO(10) model originally proposed by Harvey, Reiss and Ramond, which is realistic in that it gives acceptable charged fermion and neutrino masses within the context of a phenomenological fit to the low-energy standard model inputs. Despite a complicated Higgs sector, the SO(10) 10 Higgs superfield mass insertion is found to be the sole contribution to the tree-level F-term governing nucleon decay. The resulting dimension-5 operators that mediate nucleon decay give branching ratio predictions parameterised by a single parameter, the ratio of the Yukawa couplings of the 10 to the fermion generations. For parameter values corresponding to a lack of dominance of the third family self-coupling, the dominant nucleon decay modes are p → K+ + νμ and n → K0 + νμ as expected. Further, the charged muon decay modes are enhanced by two orders of magnitude over the standard minimal SUSY SU(5) predictions, thus predicting a distinct spectrum of ‘visible’ modes. These charged muon decay modes, along with p → π+ + νμ and n → π0 + νμ, which are moderately enhanced over the SUSY SU(5) prediction, suggest a distinguishing fingerprint of this particular GUT model, and if nucleon decay is observed at Super-KAMIOKANDE the predicted branching ratio spectrum can be used to determine the validity of this ‘realistic’ SO(10) SUSY GUT model.