Results 1 - 10 of 58
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[en] Diquarks are part of various models of Physics Beyond the Standard Model, for instance in Grand Unified Theories. In this talk we present a model-independent calculation of the production cross section of scalar diquarks at the LHC for beam energies of √(s) = 14 TeV. The production of a single diquark is calculated up to next-to-leading order in the strong coupling constant αs, and the diquark pair production up to leading order.
[en] Pati-Salam GUTs are a first step in the direction of a complete fermion unification. As left-right-symmetric extensions of the SM they contain a right-handed neutrino. In addition the symmetry leads to a correlation between leptons and quarks. Thus they provide a framework to study mechanisms generating flavour structures simultaneously in quark and lepton sector. We study a SU(3) flavour symmetry and show how the spontaneous breaking of this symmetry by flavons may generate tribimaximal mixing for the leptons as well as nearly diagonal mixing in the quarks. Within this framework we present a supersymmetric model containing flavoured Higgs fields which may lead to a matter-Higgs-unification. We investigate which flavon representations are useful in constructing models leading to the desired CKM- and PMNS-mechanisms. Furthermore we discuss the problems of this approach and present possible solutions.
[en] As left-right-symmetric extensions of the SM, Pati-Salam GUTs contain right-handed neutrinos. By a multi-step breaking of the symmetry, their mass scale can be chosen near its best-fit value of ∝ 1014 GeV. We show in various cases that a full unification of all gauge couplings near the Planck scale is possible. In addition, we construct the Higgs parts of the Pati-Salam superpotential. We investigate the possibility of a strict Z2 symmetry between the left and right-handed part. This may lead to interesting new features such as massless states which are associated to the Goldstone modes.
[en] We construct models with a spontaneously broken SU(3)F flavour symmetry where three generations of Higgs multiplets transform in a flavour-triplet representation. The models are embedded in a supersymmetric Pati-Salam GUT framework, which includes left-right symmetry. We study the possible flavon representations and show that a model with flavons in the decuplet representation is able to reproduce the hierarchy structure of the quark and lepton mass and mixing matrices. This result requires no additional structure or fine-tunings except for an extra Z4 discrete symmetry in the superpotential. (orig.)
[en] The session on precision studies of electroweak interactions is summarized. The contributions address the bilinear, trilinear, quartic as well as heavy-quark interactions of the electroweak gauge bosons. This makes up a picture of the physics of electroweak symmetry and symmetry breaking which can be investigated with the proposed design of e+e- Linear Colliders and detectors
[en] We consider a grand unified theory based on the left-right symmetric Pati-Salam group. The maximal flavour symmetry of the gauge-kinetic terms, SU(3) x SU(3), is broken spontaneously by vacuum expectation values. The model contains additional fermionic quark (and lepton) partners, which introduce new sources of flavour violation in both, left- and right-handed quark transitions. These additional fermions cancel the flavour gauge anomalies and allow us to consider only renormalizable operators. The top and bottom partner can have a mass in the TeV range.
[en] We present an algorithm for a refined version of a final-state parton shower and a completely new one for an initial-state shower. These showers allow to reweight shower histories, as the complete weights for the showered events are explicitly known. We compare these algorithms using an implementation in the event generator WHIZARD to results from existing showers as well as data from the LEP, Tevatron and LHC colliders.
[en] Grand unified theories based on an E6 gauge symmetry are possible low energy scenarios of string theories. In addition to Quark and Lepton fields, the fundamental 27 of the E6 contains one up- and down-type Higgs superfield, a pair of exotic particles (''Leptoquarks''), and a NMSSM-like Singlet under the SM gauge group for each generation. The appearance of the Leptoquarks spoil simple gauge coupling unification. Embedding the SM into a Pati-Salam gauge group above 1016 GeV, one achieves full E6 unification below the Planck mass. Aside from model building aspects, implications for physics at the TeV scale will be presented. Three generations of Higgs fields may introduce a new type of dark matter in addition to the usual LSP. The signatures of TeV-scale Leptoquarks are studied using the event generator WHIZARD
[en] We investigate models where gauge unification (GUT) proceeds in steps that include Pati-Salam symmetry. Beyond the Standard Model, we allow for a well-defined set of small representations of the GUT gauge group. We show that all possible chains of Pati-Salam symmetry breaking can be realized in accordance with gauge-coupling unification. We identify, in particular, models with unification near the Planck scale, with intermediate left-right or SU(4) quark-lepton symmetries that are relevant for flavor physics, with new colored particles at accessible energies, and with an enlarged electroweak Higgs sector. We look both at supersymmetric and non-supersymmetric scenarios
[en] WHIZARD is a multi-purpose event generator for hadron- and lepton-colliders, considering the standard model as well as a multitude of BSM models. The current version of the program is only capable of automatically performing leading-order calculations, contributions of higher virtual orders being available for some specific kinds of processes. However, many applications require at least next-to-leading order accuracy. We present a first extension of WHIZARD which can also deal with processes at next-to-leading order, using the Frixione-Kunszt-Signer subtraction scheme. The program structure is briefly explained, focussing on the various components of the calculation and the corresponding interface to one-loop programs like GoSam. Finally, first results for NLO massless QCD are presented.