Seong Youl Choi

The next-generation high-energy facilities, the CERN Large Hadron Collider (LHC) and the prospective $e^+e^-$ International Linear Collider (ILC), are expected to unravel new structures of matter and forces from the electroweak scale to the TeV scale. In this report we review the complementary role of LHC and ILC in drawing a comprehensive and high-precision picture of the mechanism breaking the electroweak symmetries and generating mass, and the unification of forces in the frame of supersymmetry.

Two next-generation high-energy experiments, the Large Hadron Collider (LHC) and the $e^+e^-$ International Linear Collider (ILC), are highly expected to unravel the new structure of matter and forces from the electroweak scale to the TeV scale. In this talk we give a compelling but rather descriptive review of the complementary role of LHC and ILC in drawing a comprehensive and high precision picture of the mechanism breaking the electroweak symmetries and generating mass, the unification of forces and the structure of spacetime. Supersymmetry is exploited in this description as a prototype scenario of the physics beyond the Standard Model.

The lightest neutralino is a compelling candidate to account for cold dark matter in the universe in supersymmetric theories with $R$--parity. In the CP-invariant theory, the neutralino relic density can be found in accord with recent WMAP data if neutralino annihilation in the early universe occurs via the s-channel $A$ funnel. In contrast, in the CP-noninvariant theory two heavy neutral Higgs bosons can contribute to the Higgs funnel mechanism significantly due to a CP-violating {\it complex} mixing between two heavy states, in particular, when they are almost degenerate. With a simple analytic and numerical analysis, we demonstrate that the CP-violating Higgs mixing can modify the profile of the neutralino relic density {\it considerably} in the heavy Higgs funnel with the neutralino mass close to half of the heavy Higgs masses.

If supersymmetry (SUSY) is realized at the electroweak scale, its underlying structure and breaking mechanism may be explored with great precision by a future linear $e^+ e^-$ collider (LC) with a clean environment, tunable collision energy, high luminosity polarized beams, and additional $e^-e^-$, $e\gamma$ and $\gamma\gamma$ modes. In this report we summarize four papers submitted to the ICHEP04 conference about the precise measurements of the top squark parameters and $\tan\beta$, the impacts of the CP phases on the search for top/bottom squarks, the Majorana nature and CP violation in the neutralino system, the implications of the SUSY dark matter scenario for the LC experiments, and the characteristics of the neutralino sector of the next--to--minimal supersymmetric standard model at the LC

If supersymmetry (SUSY) is realized at the electroweak scale, its underlying structure and breaking mechanism may be explored with great precision by a future linear $e^+ e^-$ collider (LC) with a clean environment, tunable collision energy, high luminosity polarized beams, and additional $e^-e^-$, $e\gamma$ and $\gamma\gamma$ modes. We review a few recent developments for determining fundamental SUSY and Higgs parameters, measuring CP violating $H/A$ mixing in the decoupling regime and probing the next--to--minimal supersymmetric standard model at the LC.