arXiv subjects
Publications and source records attributed to S. A. Abel.
It is shown that in R-parity violating models of supersymmetry, the CP violation observed in the kaon system could arise purely from the R-parity violating scalar interactions (A-terms), with no CP violation in the CKM matrix. The direct CP violating parameter, epsilon', could be as large or larger than that expected in the Standard Model. CP violation in the B system however is expected to be negligible.
The problem of destabilising divergences is discussed for singlet extensions of the MSSM. It is shown that models which possess either gauged-$R$ symmetry or target space duality at the Planck scale are able to circumvent this problem whilst avoiding cosmological domain walls.
We show that all CP violation in the MSSM could originate in the supersymmetry breaking sector rather than the CKM matrix, and discuss the important consequences for $B$-physics.
It is argued that the Next-to-MSSM (NMSSM) is unnatural from the point of view of cosmology and fine tuning. In particular, such singlet extensions to the MSSM do not provide a simple solution to the `$μ$-problem'. Models with singlets can be constructed using gauged-$R$ symmetry or target space duality. However their superpotentials have terms in addition to those of the NMSSM.
We analyse the electric dipole moment of the neutron in the MSSM, induced by the renormalisation of the soft-susy breaking terms. We run the RGEs using two-loop expressions for gauge and Yukawa couplings and retaining family dependence. The $μ$ and $B$ parameters were determined by minimising the full one-loop Higgs potential, and we find that the neutron EDM lies in the range $10^{-33}<|d_n| < 10^{-29} {\; e\;\mbox{cm}} $.
It is argued that singlet extensions of the MSSM at the weak scale are indicative of either gauged-$R$ symmetry or target space duality in a string effective action at the Planck scale. The criteria used are satisfactory primordial nucleosynthesis, absence of fine-tuning, and absence of cosmological problems such as domain walls. Models which have a global discrete symmetry such as the NMSSM may only be accommodated within rather complicated cosmological scenarios which are also discussed.
We discuss the domain wall problem in the Next-to-Minimal Supersymmetric Standard Model, with particular attention to the usual solution of explicit breaking of the discrete symmetry by non-renormalisable operators. This ``solution'' leads to a contradiction between the requirements of cosmology and those of avoiding the destabilisation of the hierarchy.
We study the cosmology of the Supersymmetric Standard Model augmented by a gauge singlet to solve the $μ$-problem and describe the evolution of the domain walls which are created during electroweak symmetry breaking due to the discrete $Z_{3}$ symmetry in this model. The usual assumption, that non-renormalizable terms induced by gravity (which explicitly break this symmetry) may cause the walls to collapse on a cosmologically safe timescale, is reconsidered. Such terms are constrained by considerations of primordial nucleosynthesis, and also by the fact that by not respecting the $Z_{3}$ symmetry they induce divergences which destabilise the hierarchy and reintroduce the $μ$--problem. We find that, even when the Kähler potential is `non-minimal' (i.e. when the hidden sector couples directly to the visible) the model is either ruled out cosmologically or suffers from a naturalness problem.
We consider the production of baryon number from collapsing domain walls, and in particular examine the magnitude of CP violation which is required in such schemes. Taking the conventional solution to the domain wall problem in the Next-to-Minimal Supersymmetric Standard Model as an example, we show that the observed baryon assymmetry of the universe may have been generated, even if the initial {\em explicit} CP violation in the Lagrangian were so small ({\em i.e.} gravitational) that it could never be experimentally detected. This is possible by having the {\em explicit} CP violation affect the way in which the walls collapse, rather than be responsible for the generation of baryon number directly. Net baryon number is created at the domain walls by the spontaneous breaking of CP.
We discuss the cosmology of string models with perturbative supersymmetry breaking at a scale of ${\cal O}$(TeV). Such models exhibit Kaluza-Klein like spectra and contain unstable massive gravitinos/gravitons. We find that considerations of primordial nucleosynthesis constrain the maximum temperature following inflation to be not much larger than the supersymmetry breaking scale. This imposes conflicting requirements on the scalar field driving inflation, making it rather difficult to construct a consistent cosmological history for such models.
We present a classification of (2,2) free field compactifations with one twist in which only 95 distinct models (generations and antigenerations) are found. Models with three generations and no antigenerations are given.
We examine the generation of baryon asymmetry at the weak scale from a primordial lepton asymmetry. If the electroweak phase transition is first order, partial reflection of tau leptons off the bubble walls and the resulting hypercharge transport into the symmetric phase, gives rise to a baryon number consistent with observation.
Replaced with revised (uncorrupted) version We present a general scheme for generating (2,2) symmetric fermionic string models and classify the models in D=8 and D=6 space time dimensions. We discuss the relationship to other compactification schemes.
In this paper we extend the results of previous work on spontaneous baryogenesis to general models involving CP violation in the Higgs sector. We show how to deal with Chern-Simons terms appearing in the effective potential arising from phase changes in the vacuum expectation values of the Higgs fields. In particular, this enables us to apply this mechanism to general supersymmetric models including the minimal supersymmetric standard model, and the extended model with a gauge singlet. A comparison is made between this approach, and that in which one solves the equations of motion for Higgs winding modes. As anticipated in earlier work, the effect of the latter approach is found to be small.
The cosmological significance of the neutralino sector is studied for a class of models in which electroweak symmetry breaking is seeded by a gauge singlet. Extensive use is made of the renormalisation group equations to significantly reduce the parameter space, by deriving analytic expressions for all the supersymmetry-breaking couplings in terms of the universal gaugino mass $m_{1/2}$, the universal scalar mass $m_0$ and the coupling $A$. The composition of the LSP is determined exactly below the W mass, no approximations are made for sfermion masses, and all particle exchanges are considered in calculating the annihilation cross-section; the relic abundance is then obtained by an analytic approximation. We find that in these models, stable neutralinos may make a significant contribution to the dark matter in the universe.