Trilinear Higgs couplings in the two Higgs doublet model with CP violation

We carry out a detailed analysis of the general two Higgs doublet model with CP violation. We describe two different parametrizations of this model, and then study the Higgs boson masses and the trilinear Higgs couplings for these two parametrizations. Within a rather general model, we find that the trilinear Higgs couplings have a significant dependence on the details of the model, even when the lightest Higgs boson mass is taken to be a fixed parameter. We include radiative corrections in the one-loop effective potential approximation in our analysis of the Higgs boson masses and the Higgs trilinear couplings. The one-loop corrections to the trilinear couplings of the two Higgs doublet model also depend significantly on the details of the model, and can be rather large. We study quantitatively the trilinear Higgs couplings, and show that these couplings are typically several times larger than the corresponding Standard Model trilinear Higgs coupling in some regions of the parameter space. We also briefly discuss the decoupling limit of the two Higgs doublet model.Comment: 23 pages, 15 figures. v2: References added, version to appear in PR

Probing CP-violating Higgs contributions in gamma-gamma -> f anti-f through fermion polarization

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 $\phi$ in $\gamma\gamma\to f \bar f$, $f=\tau/t$, from that of the QED continuum. This can help in getting information on the $\gamma\gamma\phi$ coupling in case $\phi$ is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case $\phi$ 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. In particular, the method suggested can cover the region where a light Higgs boson may have been missed by LEP due to CP violation in the Higgs sector, and may be missed as well at the LHC.Comment: 14 pages, 14 figures, typeset in revtex4. Version which has appeared in Physical Review D; typos in two references correcte

Obstructed D-Branes in Landau-Ginzburg Orbifolds

We study deformations of Landau-Ginzburg D-branes corresponding to obstructed rational curves on Calabi-Yau threefolds. We determine D-brane moduli spaces and D-brane superpotentials by evaluating higher products up to homotopy in the Landau-Ginzburg orbifold category. For concreteness we work out the details for lines on a perturbed Fermat quintic. In this case we show that our results reproduce the local analytic structure of the Hilbert scheme of curves on the threefold.Comment: 44 pages; v3: typos correcte

Constraining the Two-Higgs-Doublet-Model parameter space

We confront the Two-Higgs-Doublet Model with a variety of experimental constraints as well as theoretical consistency conditions. The most constraining data are the \bar B\to X_s\gamma decay rate (at low values of M_{H^\pm}), and \Delta\rho (at both low and high M_{H^\pm}). We also take into account the B\bar B oscillation rate and R_b, or the width \Gamma(Z\to b\bar b) (both of which restrict the model at low values of \tan\beta), and the B^-\to\tau\nu_\tau decay rate, which restricts the model at high \tan\beta and low M_{H^\pm}. Furthermore, the LEP2 non-discovery of a light, neutral Higgs boson is considered, as well as the muon anomalous magnetic moment. Since perturbative unitarity excludes high values of \tan\beta, the model turns out to be very constrained. We outline the remaining allowed regions in the \tan\beta-M_{H^\pm} plane for different values of the masses of the two lightest neutral Higgs bosons, and describe some of their properties.Comment: 17 pages, 17 figure

Resonant CP Violation in Higgs Radiation at e^+e^- Linear Collider

We study resonant CP violation in the Higgsstrahlung process e^+e^- -> H_{1,2,3} (Z -> e^+e^-, \mu^+\mu^-) and subsequent decays H_{1,2,3} -> b \bar{b}, \tau^-\tau^+, in the MSSM with Higgs-sector CP violation induced by radiative corrections. At a high-energy e^+e^- linear collider, the recoil-mass method enables one to determine the invariant mass of a fermion pair produced by Higgs decays with a precision as good as 1 GeV. Assuming an integrated luminosity of 100/fb, we show that the production lineshape of a coupled system of neutral Higgs bosons decaying into b\bar{b} quarks is sensitive to the CP-violating parameters. When the Higgs bosons decay into \tau^-\tau^+, two CP asymmetries can be defined using the longitudinal and transverse polarizations of the tau leptons. Taking into account the constraints from electric dipole moments, we find that these CP asymmetries can be as large as 80 %, in a tri-mixing scenario where all three neutral Higgs states of the MSSM are nearly degenerate and mix significantly.Comment: 22 pages, 8 figures, to appear in Phys. Rev.

On Some Classes of mKdV Periodic Solutions

We obtain exact periodic solutions of the positive and negative modified Kortweg-de Vries (mKdV) equations. We examine the dynamical stability of these solitary wave lattices through direct numerical simulations. While the positive mKdV breather lattice solutions are found to be unstable, the two-soliton lattice solution of the same equation is found to be stable. Similarly, a negative mKdV lattice solution is found to be stable. We also touch upon the implications of these results for the KdV equation.Comment: 8 pages, 3 figures, to appear in J. Phys.

Top quark pair production and decay at hadron colliders

In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair production in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an application we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.Comment: 58 pages, 12 figure

Aspects of CP violation in the HZZ coupling at the LHC

We examine the CP-conserving (CPC) and CP-violating (CPV) effects of a general HZZ coupling through a study of the process H -> ZZ* -> 4 leptons at the LHC. We construct asymmetries that directly probe these couplings. Further, we present complete analytical formulae for the angular distributions of the decay leptons and for some of the asymmetries. Using these we have been able to identify new observables which can provide enhanced sensitivity to the CPV $H ZZ$ coupling. We also explore probing CP violation through shapes of distributions in different kinematic variables, which can be used for Higgs bosons with mH < 2 mZ.Comment: 36 pages, 17 figures, LaTeX, version accepted for publicatio