This is a summary of the projects undertaken by the working group I on high energy and collider physics.

There is a strong and growing interplay between particle physics and cosmology. In this talk, I discuss some aspects of this interplay concerning dark matter candidates put forth by theories beyond the standard model. In explaining the requirements for collider tests of such dark matter candidates, I focus in particular on the case of the lightest neutralino in the MSSM.

This is summary of the activities of the working group on collider physics in the IXth Workshop on High Energy Physics Phenomenology (WHEPP-9) held at the Institute of Physics, Bhubaneswar, India in January 2006. Some of the work subsequently done on these problems by the subgroups formed during the workshop is included in this report.

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson 𝜙 in $\gamma \gamma \rightarrow f\bar{f}$, $f = \tau/t$, from that of the QED continuum. This can help in getting information on the $\gamma \gamma \phi$ coupling in case 𝜙 is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case 𝜙 has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters.