arXiv subjects
Publications and source records attributed to K. -I. Izawa.
We consider dilaton stabilization with R invariance, which insures a vanishing cosmological constant at the scale of stabilization. We construct a few models which accommodate weak gauge couplings with large or small gauge groups. Matter condensation plays a central role in the dilaton stabilization.
We propose a topological inflation model in the framework of supergravity with $R$ invariance. This topological inflation model is not only free from the initial value problem of the inflaton field but also gives low reheating temperature which is favored in supergravity since the overproduction of gravitinos is avoided. Furthermore, the predicted spectrum of the density fluctuations is generally tilted, which will be tested by future observations on CMB anisotropies and large scale structure of the universe.
We derive cosmological constraints on the masses of generic scalar fields which decay only through gravitationally suppressed interactions into unstable gravitinos and ordinary particles in the supersymmetric standard model. For the gravitino mass 100GeV-1TeV, the scalar masses should be larger than 100TeV to keep the success of big-bang nucleosynthesis if no late-time entropy production dilutes the gravitino density.
We consider gauge-mediated models of supersymmetry (SUSY) breaking with strongly coupled nonabelian messenger gauge theory. After integrating out the SUSY-breaking and messenger sectors, we directly see that the effective Kahler potential transmits the SUSY breaking to the standard model sector.
In supersymmetric theories, the Peccei-Quinn symmetry has a complex extension as a symmetry of the superpotential, so that the scalar potential always has an almost flat direction, the dilaton. We discuss how coherent oscillation of the dilaton affects axion cosmology. We stress that the dilaton decay, if its dominant mode is not into axions, releases large entropy at a late epoch of the Universe's evolution to dilute axion energy density and the upperbound of the decay constant is raised up to about $10^{15}$ GeV. The case of the M-theory axion is also discussed.
We consider an inflationary universe scenario with multiple stages of inflation. The primary inflation, which may start at the Planck epoch, is followed by secondary inflations, which include the cosmological inflation that causes the primordial density fluctuations of our universe. We point out that an initial condition for a secondary inflation is naturally realized if the e-fold number of the primary inflation is sufficiently large.
We consider dynamical models of supersymmetry breaking which naturally incorporate cosmological inflation. The inflaton plays an inevitable role in dynamical SUSY breaking and the hierarchical scales of inflation and SUSY breaking are simultaneously realized through a single dynamics.
We point out that for a class of `new inflation' models in supergravity the required initial value of the inflaton field is dynamically set if there is another inflation (`pre-inflation') before the `new inflation'. We study the dynamics of both inflatons by taking a hybrid inflation model for the `pre-inflation' as an example. We find out that our `new inflation' model provides reheating temperatures T_R \simeq 10 MeV - 10^4 GeV low enough to avoid the gravitino problem even in gauge-mediated supersymmetry-breaking models. We also construct a model where the scale for the `new inflation' is generated by nonperturbative dynamics of a supersymmetric gauge theory.
We systematically construct gauge-mediated supersymmetry(SUSY)-breaking models with direct transmission of SUSY-breaking effects to the standard-model sector. We obtain a natural model with the gravitino mass $m_{3/2}$ smaller than 1 keV as required from the standard cosmology. If all Yukawa coupling constants are of order one,the SUSY-breaking scale $m_{SUSY}$ transmitted into the standard-model sector is given by $m_{SUSY} \simeq 0.1 α_i/(4π) Λ$ where $Λ$ is the original dynamical SUSY-breaking scale. Imposing $m_{SUSY} \simeq (10^2-10^3)$ GeV, we get $Λ\simeq (10^5-10^6)$ GeV, which yields the gravitino mass $m_{3/2}\simeq (10^{-2}-1)$ keV.
We construct R-invariant unification models where a pair of massless Higgs doublets is naturally obtained. The masslessness of the Higgs doublets is guaranteed by the unbroken R symmetry. Mass generation for the Higgs doublets is considered from various viewpoints.
We consider a natural new inflationary model in broken supergravity based on an R symmetry. The model predicts a concrete relation between the amplitude of primordial density fluctuations and the scale of supersymmetry breaking. The observed value of the density fluctuations is obtained for the gravitino mass of order the weak scale along with a power-law spectral index considerably less than one, which may be tested in future observations.
We investigate low-energy models of supersymmetry (SUSY) breaking by means of vector-like gauge theories for dynamical SUSY breaking. It is not necessary to introduce messenger gauge interactions utilized so far to mediate the SUSY breaking to the standard-model sector, which reduces complication in the model building. We also consider various other ways of SUSY-breaking transmission.
We provide vector-like gauge theories which break supersymmetry dynamically.
We consider strongly interacting supersymmetric gauge theories which break dynamically the GUT symmetry and produce the light Higgs doublets naturally. Two models we proposed in the previous articles are reanalyzed as two phases of one theory and are shown to have desired features. Furthermore, employing nonabelian duality proposed recently by Seiberg, we study the dual theory of the above one and show that the low-energy physics of the original and dual models are the same as expected. We note that the Higgs multiplets in the original model are regarded as composite states of the elementary hyperquarks in its dual theory. Theories with other hypercolors and similar matter contents are also analyzed in the same way.
We propose a supersymmetric hypercolor SU(3)_H gauge theory interacting strongly at the grand unification scale, in which the hyperquark condensation breaks SU(5)_GUT down to SU(3)_C x SU(2)_L without unbroken U(1)_Y at the classical level. However, we show that the broken U(1)_Y symmetry is restored by quantum mechanical effects and hence there remains the standard-model gauge symmetry at the electroweak scale. The dynamics of the strong interactions also produces naturally a pair of massless Higgs doublets. In addition to these Higgs doublets, we have a pair of massless singlets which contributes to the renormalization-group equations of gauge coupling constants and hence affects the GUT unification. We discuss a simple solution to this problem.
We consider a supersymmetric hypercolor gauge theory with six flavors of quarks interacting strongly at the grand unification scale. This model solves the most serious problem -- doublet-triplet splitting in the grand unified theories. We also show that the dangerous dimension-five operators for nucleon decays are suppressed simultaneously, which makes our model yet more attractive.
QCD-like hidden sector models of supersymmetry breaking are considered which do not suffer from a cosmological problem due to the Polonyi field. Avoidance of a light gluino leads to introduction of quasi-symmetry -- symmetry broken explicitly only through gravitational effects.
The cosmological term prevents perturbation based on derivative expansion in Einstein gravity. We consider quantum theory of gravitation invariant under volume-preserving diffeomorphism and Weyl transformation, which is suitable for derivative expansion.