Why Photon Colliders are necessary in a future collider program

Subjects of discussion Different scenarios Higgs window to a New Physics Anomalies in the interactions of gauge and Higgs bosons Some problems with t-quarks and MSSM. Some problems in QCD and hadron physics. By-product: Production of axions, etc. from region of conversion e --> gamma.Comment: LaTeX 2e, 9 pages with 6 figure

Physics at \ggam and \egam colliders

I discuss, what really new could give Photon Colliders ($\gamma\gamma$ and $e\gamma$) after LHC and \epe Linear Collider operations.Comment: 7pages,LaTEX, To be published in proceedings "PHOTON99". The forgotten title, author and abstract are added in the tex

Two-Higgs-Doublet Models with CP violation

We consider the Two-Higgs-Doublet Model and determine the range of parameters for which CP violation and Flavor Changing Neutral Current effects are naturally small. It corresponds to small values of the mass parameter m_{12}^2, describing soft (\phi_1,\phi_2) mixing in the potential. We discuss how, in this approach, some Higgs bosons can be heavy, with mass of the order of 1 TeV. The possibility that at the Tevatron, LHC and an e^+e^- Linear Collider, only one Higgs boson will be found, with properties indistinguishable from those in the Standard Model (SM), we define as the SM-like scenario. While this scenario can be obtained with large \mu^2 \sim \Re m_{12}^2 parameter, in which case there is decoupling, we here discuss the opposite case of small \mu^2, without decoupling.Comment: 5 pages, LaTeX, including figures. Presented at SUSY02, DESY, June 2002 and LCWS02, Jeju, Korea, August 2002. To appear in the proceedings. Version 2: minor changes, additional reference

Distinguishing Higgs models at photon colliders

We consider the two effective couplings hZ\gamma and h\gamma\gamma involving a neutral scalar Higgs boson with a mass around 100 GeV in the Standard Model, in the Two Higgs Doublet Model, and in the Minimal Supersymmetric Standard Model. The couplings can be tested at Photon Colliders, and used to distinguish these models.Comment: 5 pages, LaTeX, using sprocl.sty, including 2 figures. Contribution to the Proceedings of the International Workshop on Linear Colliders, April 28-May 5, 1999, Sitges (Spain). Version 2: minor clarification

Resolving SM-like scenarios via Higgs boson production at a Photon Collider: I. 2HDM versus SM

We consider the possibility that after operations at the LHC and e^+e^- Linear Colliders a Higgs boson will be discovered, but no signal of New Physics will be found (Standard-Model-like scenario). This can occur in the Standard Model (SM) as well as in other models, including the Two-Higgs-Doublet Model (2HDM), the MSSM, etc. Experiments at a Photon Collider can resolve these cases. In this paper we compare the SM and the 2HDM~(II). In the analysis we use as independent quantities the ratios, to the SM values, of couplings of the observed Higgs boson to gauge bosons, and to up and down-type quarks (basic couplings). We derive a relation between these ratios within the 2HDM~(II), a pattern relation. With the aid of this relation, different possible realizations of an SM-like scenario are found. For these realizations, we calculate the loop couplings of the Higgs boson with \gamma\gamma and Z \gamma, and also with gluons, taking into account the expected accuracy in the measurements of the basic couplings. The obtained deviation of the two-photon width from its SM value is generally higher than the expected inaccuracy in the measurement of \Gamma_{\gamma \gamma} at a Photon Collider. The result is sensitive to the parameters of the Higgs self interaction.Comment: 29 pages, LaTeX, including figure

Standard-Model-like scenarios in the 2HDM and Photon Collider potential

After operations at the LHC and e^+e^- Linear Colliders it may be found that a Standard-Model-like scenario is realized. In this scenario no new particle will be discovered, except a single Higgs boson having partial widths or coupling constants with fundamental particles, whose squares are close, within anticipated experimental uncertainty, to those of the SM. Experiments at a Photon Collider can resolve whether the SM or e.g. the Two-Higgs-Doublet Model is realized in Nature. For the SM-like realizations of the 2HDM (II) we study the loop couplings of the Higgs boson with \gamma\gamma and Z \gamma, and also with gluons. The deviation of the two-photon width from its SM value is generally higher than the expected inaccuracy in the measurement of \Gamma_{\gamma \gamma} at a Photon Collider. The deviation is sensitive to the parameters of the Higgs self interaction.Comment: 8 pages, aipproc, including figures. Presented at 5th International Linear Collider Workshop (LCWS 2000), Fermilab, Batavia, Illinois, 24-28 Oct 2000, to appear in proceeding