J. Kalinowski

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.

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

Pinning down the Invisible Sneutrino

tilde{chi}_{ D}

N)LO Simulation of Chargino Production and Decay

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.

Color-octet scalars at the LHC

This paper provides a comprehensive discussion of neutralino dark matter within classes of extended supersymmetric models referred to as the USSM containing one additional SM singlet Higgs plus an extra Z, together with their superpartners the singlino and bino. These extra states of the USSM can significantly modify the nature and properties of neutralino dark matter relative to that of the minimal (or even next-to-minimal) supersymmetric standard models. We derive the Feynman rules for the USSM and calculate the dark matter relic abundance and direct detection rates for elastic scattering in the USSM for interesting regions of parameter space where the largest differences are expected.

Dark matter in the U(1) extended SUSY

For points in SUSY parameter space where the sneutrino is lighter than the lightest chargino and next-to-lightest neutralino, its direct mass determination from sneu- trino pair production process at e + e − collider is impossible since it decays invisibly. In such a scenario the sneutrino can be discovered and its mass determined from measurements of two-body decays of charginos produced in pairs at the ILC. Using the event generator WHIZARD we study the prospects of measuring sneutrino properties in a realistic ILC environment. In our analysis we include beamstrahlung, initial state radiation, a complete account of reducible backgrounds from SM and SUSY processes, and a complete matrix- element calculation of the SUSY signal which encompasses all irreducible background and interference contributions. We also simulate photon induced background processes using exact matrix elements. Radiation effects and the cuts to reduce background strongly mod- ify the edges of the lepton energy spectra from which the sneutrino and chargino mass are determined. We discuss possible approaches to measure the sneutrino mass with optimal precision.