Measurement of the Higgs coupling to W-bosons is an important test of our understanding of the electroweak symmetry breaking mechanism. We study the sensitivity of the International Linear Collider (ILC) to the presence of anomalous HW+W- couplings u
sing ZH -> nu nu WW* -> nu nu 4j events. Using an effective Lagrangian approach, we calculate the differential decay rates of the Higgs boson including the effects of new dimension-5 operators. We present a Monte Carlo simulation of events at the ILC, using a full detector simulation based on geant4 and a real event reconstruction chain. Expected constraints on the anomalous couplings are given.
We present a new geometric approach to the flavour decomposition of an arbitrary soft supersymmetry-breaking sector in the MSSM. Our approach is based on the geometry that results from the quark and lepton Yukawa couplings, and enables us to derive t
he necessary and sufficient conditions for a linearly-independent basis of matrices related to the completeness of the internal [SU(3) x U(1)]^5 flavour space. In a second step, we calculate the effective Yukawa couplings that are enhanced at large values of tan(beta) for general soft supersymmetry-breaking mass parameters. We highlight the contributions due to non-universal terms in the flavour decompositions of the sfermion mass matrices. We present numerical examples illustrating how such terms are induced by renormalization-group evolution starting from universal input boundary conditions, and demonstrate their importance for the flavour-violating effective Yukawa couplings of quarks.
Inclusive Higgs boson pair production through the mechanism of gauge boson fusion e^{+} e^{-} -> V* V* -> h h + X (V=W,Z) in the general Two-Higgs-Doublet Model (2HDM), with h=h^0,H^0,A^0,H^{pm}, is analyzed at order alpha^4_{ew} in the linear collid
ers ILC and CLIC. This kind of processes is highly sensitive to the trilinear Higgs (3H) boson self-interactions and hence can be a true keystone in the reconstruction of the Higgs potential. For example, in the ILC at 1 TeV, the most favorable scenarios yield cross-sections up to roughly 1 pb, thus entailing 10^5 events per 100 fb^{-1} of integrated luminosity, whilst remaining fully consistent with the perturbativity and unitarity bounds on the 3H couplings, the electroweak precision data and the constraints from BR(b->sgamma). Comparing with other competing mechanisms, we conclude that the Higgs boson-pair events could be the dominant signature for Higgs-boson production in the TeV-class linear colliders for a wide region of the 2HDM parameter space, with no counterpart in the Minimal Supersymmetric Standard Model. Owing to the extremely clean environment of these colliders, inclusive 2H events should allow a comfortable tagging and might therefore open privileged new vistas into the structure of the Higgs potential.
Higgs singlet superfields, usually present in extensions of the Minimal Supersymmetric Standard Model (MSSM) which address the $mu$-problem, such as the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and the Minimal Nonminimal Supersymmetric S
tandard Model (mnSSM), can have significant contributions to $B$-meson flavour-changing neutral current observables for large values of $tanbeta gsim 50$. Illustrative results are presented including effects on the $B_s$ and on the rare decay $B_stomu^+mu^-$. In particular, we find that in the NMSSM, the branching ratio for $B_stomu^+mu^-$ can be enhanced or even suppressed with respect to the Standard Model prediction by more than one order of magnitude.
Higgs singlet superfields are usually present in most extensions of the Minimal Supersymmetric Standard Model (MSSM) that address the mu-problem, such as the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and the Minimal Nonminimal Supersymmet
ric Standard Model (MNSSM). Employing a gauge- and flavour-covariant effective Lagrangian formalism, we show how the singlet Higgs bosons of such theories can have significant contributions to B-meson flavour-changing neutral current (FCNC) observables for large values of $tanbeta stackrel{>}{{}_sim} 50$ at the 1-loop level. Illustrative results are presented including effects on the B_s and B_d mass differences and on the rare decay $B_stomu^+mu^-$. In particular, we find that depending on the actual value of the lightest singlet pseudoscalar mass in the NMSSM, the branching ratio for $B_stomu^+mu^-$ can be enhanced or even suppressed with respect to the Standard Model prediction by more than one order of magnitude.
We investigate the effects of the radiatively-generated tan beta-enhanced Higgs-singlet Yukawa couplings on the decay $Upsilonto gamma A_1$ in the NMSSM, where $A_1$ is the lightest CP-odd scalar. This radiative coupling is found to dominate in the c
ase of a highly singlet Higgs pseudoscalar. The branching ratio for the production of such a particle is shown to be within a few orders of magnitude of current experimental constraints across a significant region of parameter space. This represents a potentially observable signal for experiments at present B-factories.
Extensions of the MSSM generically feature gauge singlet Higgs bosons. These singlet Higgs bosons have tan(beta)-enhanced Yukawa couplings to down-type quarks and leptons at the one-loop level. We present an effective Lagrangian incorporating these Y
ukawa couplings and use it to study their effect on singlet Higgs boson phenomenology within both the mnSSM and NMSSM. It is found that the loop-induced couplings represent an appreciable effect for the singlet pseudoscalar in particular, and may dominate its decay modes in some regions of parameter space.
Singlet Higgs bosons present in extensions of the MSSM can have sizable Yukawa couplings to the b quark and the tau lepton for large values of tan(beta) at the 1-loop level. We present an effective Lagrangian which incorporates these tan(beta)-enhanc
ed Yukawa couplings and which enables us to study their effect on singlet Higgs-boson phenomenology within the context of both the mnSSM and the NMSSM. In particular, we find that the loop-induced coupling can be a significant effect for the singlet pseudoscalar, and may dominate its decay modes. Further implications of the tan(beta)-enhanced Yukawa couplings for the phenomenology of the singlet Higgs bosons are briefly discussed.
