Various types of electroweak-interacting particles, which have non-trivial charges under the $mathrm{SU}(2)_L times mathrm{U}(1)_Y$ gauge symmetry, appear in various extensions of the Standard Model. These particles are good targets of future lepton
colliders, such as the International Linear Collider (ILC), the Compact LInear Collider (CLIC) and the Future Circular Collider of electrons and positrons (FCC-ee). An advantage of the experiments is that, even if their beam energies are below the threshold of the production of the new particles, quantum effects of the particles can be detected through high precision measurements. We estimate the capability of future lepton colliders to probe electroweak-interacting particles through the quantum effects, with particular focus on the wino, the Higgsino and the so-called minimal dark matters, and found that a particle whose mass is greater than the beam energy by 100-1000 GeV is detectable by measuring di-fermion production cross sections with $O(0.1)$% accuracy. In addition, with the use of the same analysis, we also discuss the sensitivity of the future colliders to model independent higher dimensional operators, and found that the cutoff scales corresponding to the operators can be probed up to a few ten TeV.
We investigate new physics models that can increase the lifetime differences in the $B_q$--$bar{B}_q$ systems ($q = d,s$) above their standard model values. If both $B_q$ as well as $bar{B}_q$ can decay to a final state through flavour dependent new
physics interactions, the so-called Grossman bound may be evaded. As examples, we consider the scalar leptoquark model and $lambda$-type R-parity violating supersymmetry. We find that models with a scalar leptoquark can enhance $DeltaGamma_s/Gamma_s$ all the way up to its experimental upper bound and $DeltaGamma_d/Gamma_d$ to as much as $sim 2.5%$, at the same time allowing the CP violating phase $beta_s$ to vary between $- 45^circ$ and $20^circ$. R-parity violating supersymmetry models cannot enhance the lifetime differences significantly, but can enhance the value of $beta_s$ up to $sim pm 20^circ$. This may bring the values of $DeltaGamma_q/Gamma_q$ as well as $beta_s$ within the measurement capabilities of $B$ factories and LHCb. We also obtain bounds on combinations of these new physics couplings, and predict enhanced branching ratios of $B_{s/d} to tau^+ tau^-$.
