arXiv subjects

S. M. Barr

Publications and source records attributed to S. M. Barr.

80 records · Page 5Linked to original sources

arXiv1995

"An SO(10) Solution to the Puzzle of Quark and Lepton Masses"

It is shown that almost all features of the quark and lepton masses can be satisfactorily and simply explained without family symmetry, including the threefold mass hierarchy among the generations, and the relations $m_τ^0 = m_b^0$, $m_μ^0 = 3 m_s^0$, $m_e^0 = \frac{1}{3} m_d^0$, $m_u^0/m_t^0 << m_d^0/m_b^0$, $\tan θ_c = \sqrt{m_d^0/m_s^0}$, $V_{cb} << \sqrt{m_s^0/m_b^0}$, and $V_{ub} \sim V_{cb}V_{us}$. Various aspects of the group theory of $SO(10)$ play an essential role in explaining these relations. The form of the mass matrices, rather than being imposed arbitrarily, emerges naturally from a simple structure at the unification scale. This structure involves only vector, spinor and adjoint representations. There are distinctive and testable predictions for $\tan β$ and the neutrino mixing angles.

hep-ph↗

arXiv1994

Supersymmetric SO(10) Simplified

In the context of supersymmetric $SO(10)$ grand unified models, it is shown that the gauge symmetry breaking as well as a natural doublet--triplet splitting can be achieved with a minimal Higgs system consisting of a single adjoint and a pair of vector and spinor multiplets. Such a Higgs spectrum has been shown to arise in the free fermionic formulation of superstrings. Since the symmetry breaking mechanism relies on non--renormalizable operators, some of the Higgs particles of the model turn out to have masses somewhat below the GUT scale. As a consequence, the unification scale is raised to about $2 \times 10^{17}~GeV$ and sin$^2θ_W$ is predicted to be slightly larger than the minimal SUSY--$SU(5)$ value. Including threshold uncertainties, which turn out to be surprisingly small in the model, we show that sin$^2θ_W$ prediction is consistent with experiments.

hep-ph↗

arXiv1994

Axion Dissipation Through the Mixing of Goldstone Bosons

By coupling axions strongly to a hidden sector, the energy density in coherent axions may be converted to radiative degrees of freedom, alleviating the ``axion energy crisis''. The strong coupling is achieved by mixing the axion and some other Goldstone boson through their kinetic energy terms, in a manner reminiscent of paraphoton models. Even with the strong coupling it proves difficult to relax the axion energy density through particle absorption, due to the derivative nature of Goldstone boson couplings and the effect of back reactions on the evolution of the axion number density. However, the distribution of other particle species in the hidden sector will be driven from equilibrium by the axion field oscillations. Restoration of thermal equilibrium results in energy being transferred from the axions to massless particles, where it can redshift harmlessly without causing any cosmological problems.

hep-ph↗

arXiv1994

Natural Gauge Hierarchy in SO(10)

It is shown that a natural gauge hierarchy and doublet-triplet splitting can be achieved in SO(10) using the Dimopoulos-Wilczek mechanism. Artificial cancellations (fine-tuning) and arbitrary forms of the superpotential are avoided, the superpotential being the most general compatible with a symmetry. It is shown by example that the Dimopoulos-Wilczek mechanism can be protected against the effects of higher-dimension operators possibly induced by Planck-scale physics. Natural implementation of the mechanism leads to an automatic Peccei-Quinn symmetry. The same local symmetries that would protect the gauge hierarchy against Planck-scale effects tend to protect the axion also. It is shown how realistic quark and lepton masses might arise in this framework. It is also argued that ``weak suppression'' of proton decay can be implemented more economically than can ``strong suppression'', offering some grounds to hope (in the context of SO(10)) that proton decay could be seen at Superkamiokande.

hep-ph↗

arXiv1993

A Solution to the Small Phase Problem of Supersymmetry

It is a well--known problem that in supersymmetric models there are new CP--violating phases which, if unsuppressed, would give a neutron electric dipole moment $10^2$ to $10^3$ times the present experimental limit. Here we propose that these new phases are suppressed by CP invariance, which is broken spontaneously at a high scale and that this breaking shows up at low energies only through a universal phase of the gaugino masses. It is shown that this can well fit both $ε$ and $ε^\prime$ of the neutral Kaon system. The electric dipole moments of the neutron and the electron should be not much below present limits. A model incorporating these ideas in a very economical way is presented.

hep-ph↗

arXiv1993

Spontaneous CP violation in the Supersymmetric Higgs Sector

Spontaneous CP--violation in the minimal supersymmetric standard model with a gauge singlet and a cubic superpotential is examined. Although the tree--level Higgs potential conserves CP, it is shown that with the inclusion of the one--loop top--quark radiative effects, CP may be broken spontaneously. The CP--violating minimum requires two neutral $(h_1,h_2)$ and one charged $(H^\pm)$ Higgs--bosons to be relatively light with $m_{h_1}+m_{h_2} \stackrel{_<}{_\sim} 100~GeV$ and $m_{H^\pm} \stackrel{_<}{_\sim} 110~GeV$. The electric dipole moment of the electron is in the observable range of $({1 \over 3}~{\rm to}~3) \times 10^{-27}$e-cm.

hep-ph↗

arXiv1993

Natural Suppression of Higgsino-Mediated Proton Decay in Supersymmetric SO(10)

In supersymmetric Grand Unified Theories, proton decay mediated by the color--triplet higgsino is generally problematic and requires some fine--tuning of parameters. We present a mechanism which naturally suppresses such dimension 5 operators in the context of SUSY $SO(10)$. The mechanism, which implements natural doublet--triplet splitting using the adjoint higgs, converts these dimension 5 operators effectively into dimension 6. By explicitly computing the higgs spectrum and the resulting threshold uncertainties we show that the successful prediction of $\sin^2θ_W$ is maintained {\it as a prediction} in this scheme. It is argued that only a weak suppression of the higgsino mediated proton decay is achievable within SUSY $SU(5)$ without fine--tuning, in contrast to a strong suppression in SUSY $SO(10)$.

hep-ph↗

arXiv1992

Family Symmetry, Gravity, and the Strong CP Problem

We show how in a class of models Peccei--Quinn symmetry can be realized as an automatic consequence of a gauged $U(1)$ family symmetry. These models provide a solution to the strong CP problem either via a massless $u$--quark or via the DFSZ invisible axion. The local family symmetry protects against potentially large corrections to $\overlineθ $ induced by quantum gravitational effects. In a supersymmetric extension, the `$μ$--problem' is shown to have a natural solution in the context of gravitationally induced operators. We also present a plausible mechanism which can explain the inter--generational mass hierarchy in such a context.

hep-ph↗