S.Y. Choi

Loop corrections to the neutral Higgs boson sector of the MSSM with explicit CP violation

Abstract We compute one-loop corrections to the mass matrix of the neutral Higgs bosons of the Minimal Supersymmetric Standard Model with explicit CP violation. We use the effective potential method, allowing for arbitrary splitting between squark masses. We include terms O (g 2 h 2 ) , where g and h stand for electroweak gauge and Yukawa couplings, respectively. Leading two-loop corrections are taken into account by means of appropriately defined running quark masses.

Color-Octet Scalars of N=2 Supersymmetry at the LHC

Abstract The color gauge hyper-multiplet in N = 2 supersymmetry consists of the usual N = 1 gauge vector/gaugino super-multiplet, joined with a novel gaugino/scalar super-multiplet. Large cross sections are predicted for the production of pairs of the color-octet scalars σ [sgluons] at the LHC: gg, q q ¯ → σ σ * . Single σ production is possible at one-loop level, but the g g → σ amplitude vanishes in the limit of degenerate L and R squarks. When kinematically allowed, σ decays predominantly into two gluinos, whose cascade decays give rise to a burst of eight or more jets together with four LSPs as signature for σ pair events at the LHC. σ can also decay into a squark–antisquark pair at tree level. At one-loop level σ decays into gluons or a t t ¯ pair are predicted, generating exciting resonance signatures in the final states. The corresponding partial widths are very roughly comparable to that for three body final states mediated by one virtual squark at tree level.

Testing the Majorana nature of gluinos and neutralinos

Gluinos and neutralinos, supersymmetric partners of gluons and neutral electroweak gauge and Higgs bosons, are Majorana particles in the minimal supersymmetric standard model (MSSM). Decays of such self-conjugate particles generate charge symmetric ensembles of final states. Moreover, production channels of supersymmetric particles at colliders are characteristically affected by the Majorana nature of particles exchanged in the production processes. The sensitivity to the Majorana character of the particles can be quantified by comparing the predictions with Dirac exchange mechanisms. A consistent framework for introducing gluino and neutralino Dirac fields can be designed by extending the N=1 supersymmetry of the MSSM to N=2 in the gauge sector. We examine to which extent like-sign dilepton production in the processes qq{yields}q-tildeq-tilde and e{sup -}e{sup -}{yields}e-tilde{sup -}e-tilde{sup -} is affected by the exchange of either Majorana or Dirac gluinos and neutralinos, respectively, at the Large Hadron Collider (LHC) and in the prospective e{sup -}e{sup -} mode of a lepton linear collider.

H/A Higgs mixing in CP-noninvariant supersymmetric theories

Abstract.For large masses, the two heavy neutral Higgs bosons are nearly degenerate in many 2-Higgs doublet models, and particularly in supersymmetric models. In such a scenario the mixing between the states can be very large if the theory is CP-noninvariant. We analyze the formalism describing this configuration, and we point to some interesting experimental consequences.

The neutralino sector in the U(1)-extended supersymmetric Standard Model

Abstract Motivated by grand unified theories and string theories we analyze the general structure of the neutralino sector in the USSM, an extension of the minimal supersymmetric Standard Model that involves a broken extra U(1) gauge symmetry. This supersymmetric U(1)-extended model includes an Abelian gauge superfield and a Higgs singlet superfield in addition to the standard gauge and Higgs superfields of the MSSM. The interactions between the MSSM fields and the new fields are in general weak and the mixing is small, so that the coupling of the two subsystems can be treated perturbatively. As a result, the mass spectrum and mixing matrix in the neutralino sector can be analyzed analytically and the structure of this 6-state system is under good theoretical control. We describe the decay modes of the new states and the impact of this extension on decays of the original MSSM neutralinos, including radiative transitions in cross-over zones. Production channels in cascade decays at the LHC and pair production at e + e − colliders are also discussed.

Dirac Neutralinos and Electroweak Scalar Bosons of N=1/N=2 Hybrid Supersymmetry at Colliders

In the N = 1 supersymmetric extension of the Standard Model, neutralinos associated in supermultiplets with the neutral electroweak gauge and Higgs bosons are, as well as gluinos, Majorana fermions. They can be paired with the Majorana fermions of novel gaugino/scalar supermultiplets, as suggested by extended N = 2 supersymmetry, to Dirac particles. Matter fields are not extended beyond the standard N = 1 supermultiplets in N = 1/N = 2 hybrid supersymmetry to preserve the chiral character of the theory. Complementing earlier analyses in the color sector, central elements of such an electroweak scenario are analyzed in the present study. The decay properties of the Dirac fermions

Theoretical Basis of Higgs-Spin Analysis in

\tilde{\chi}_{ D}

and

and of the scalar bosons σ are worked out, and the single and pair production-channels of the new particles are described for proton collisions at the LHC, and electron/positron and γγ collisions at linear colliders. Special attention is paid to modifications of the Higgs sector, identified with an N = 2 hypermultiplet, by the mixing with the novel electroweak scalar sector.