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We review constraints on additional Z′ bosons predicted in supersymmetric (SUSY) E6 models from electroweak experiments – Z-pole experiments, mW measurements and the low-energy neutral current (LENC) experiments. Four representative models – χ, ψ, η, ν models – are studied in some detail. We find that the improved data of parity violation in cesium atom,… (More)

- Gi-Chol Cho, AYA OMOTE
- 2004

A generic feature of little Higgs models is presence of extra neutral gauge bosons. In the littlest Higgs model, the neutral extra gauge boson AH is lightest among the extra particles and could be as light as a few hundred GeV, which may be produced directly at an ee linear collider. We study production and decay of AH at the linear collider and compare… (More)

- Gi-Chol Cho
- Physical review letters
- 2002

We address the compatibility of a light sbottom (mass approximately 2-5.5 GeV) and a light gluino (mass approximately 12-16 GeV) with electroweak precision measurements. Such light particles have been suggested to explain the observed excess in the b quark production cross section at the Tevatron. The electroweak observables may be affected by the sbottom… (More)

- Gi-Chol Cho, Minako Honda
- 2005

Supersymmetric contributions to the neutron electric dipole moment (EDM) are studied taking account of the flavor changing interactions. We found that the gluino contribution is sensitive to the flavor changing interaction. Enhancement of neutron EDM via flavor mixing effects is possible when the squark mass difference between the different generations is… (More)

- Mayumi Aoki, Gi-Chol Cho, Makiko Nagashima, Noriyuki Oshimo
- 2001

We calculate the contributions of the vector-like quark model to BsBs mixing, taking into account the constraints from the decay B → Xsγ. In this model the neutral bosons mediate flavor-changing interactions at the tree level. However, BsBs mixing is dominated by contributions from the box diagrams with the top quark and the extra up-type quark. In sizable… (More)

- Gi-Chol Cho, Jun-ichi KAMOSHITA, Mariko Matsunaga, Isamu Watanabe
- 2004

To solve the ‘TeV gamma crisis’, we examine a model whose one spatial direction is discretized at a high energy scale. Assuming the standard extragalactic IR photon distribution, we evaluate the mean free-path of a energetic photon which acquires an effective mass in the model. For a wide range of the value of the lattice energy scale between a few TeV and… (More)

- Gi-Chol Cho, Kaoru Hagiwara, Chung Wen Kao, R . Szalapski
- 1999

We place constraints on the parameter space of the minimal supergravity (SUGRA) inspired supersymmetric (SUSY) extension of the standard model (SM), i.e. the mSUGRA model, by studying the loop-level contributions of SUSY particles to electroweak precision observables. In general the Higgs bosons and the superpartner particles of SUSY models contribute to… (More)

- Gi-Chol Cho
- 2000

We study constraints on the Minimal Supersymmetric Standard Model from electroweak experiments. We find that the light sfermions always make the fit worse than the Standard Model, while the light chargino generally make the fit slightly better through the oblique corrections. The best overall fit to the precision measurements are found when the mass of… (More)

- Gustavo C . Branco, Gi-Chol Cho, Y . Kizukuri, N . Oshimo
- 1994

We show that in the supersymmetric standard model (SSM) box diagrams mediated by charginos and up-type squarks may give large contributions to B − B̄0 and K − K̄0 mixings. This is due to the fact that a heavy top quark mass allows large mass differences among the up-type squarks, which leads to a less efficient cancellation among the different squark… (More)

The string theory predicts the unification of the gauge couplings and gravity. The minimal supersymmetric Standard Model, however, gives the unification scale ∼ 2 × 10 GeV which is significantly smaller than the string scale ∼ 5 × 10 GeV of the weak coupling heterotic string theory. We study the unification scale of the non-supersymmetric minimal Standard… (More)