We study top-antitop pair production and top spin correlations in a model with an electrically neutral massive gauge boson, Z, at the Large Hadron Collider. In addition to the Standard Model processes, the Z contributes to the top-antitop pair produc
tion process in the s-channel. Choosing a kinematical region of top invariant mass around the Z resonance pole, we find sizable deviations of the top-antitop pair production cross section and the top spin correlations from those of the Standard Model.
We investigate supersymmetry breaking meta-stable vacua in N=2, SU(2)times U(1) gauge theory with N_f=2 massless flavors perturbed by the addition of small N=1 preserving mass terms in a presence of a Fayet-Iliopoulos term. We derive the low energy e
ffective theory by using the exact results of N=2 supersymmetric QCD and examine the effective potential. At the classical level, the theory has supersymmetric vacua on Coulomb and Higgs branches. We find that supersymmetry on the Coulomb branch is dynamically broken as a consequence of the strong dynamics of SU(2) gauge symmetry while the supersymmetric vacuum on the Higgs branch remains. We also estimate the lifetimes of the local minima on the Coulomb branch. We find that they are sufficiently long and therefore the local vacua we find are meta-stable.
Stringent restrictions for model building are imposed by a no-go theorem in noncommutative gauge field theory. Circumventing this theorem is crucial for the construction of realistic models of particle interactions. To this end, the noncommutative co
nstruction of tensor representations of gauge groups using half-infinite Wilson lines is extended to allow for gauge groups consisting of an arbitrary number of $U_*(N)$ factors. This as well allows representations other than the ones permitted by the no-go theorem.
We address the construction of four-dimensional N=2 supersymmetric nonlinear sigma models on tangent bundles of arbitrary Hermitian symmetric spaces starting from projective superspace. Using a systematic way of solving the (infinite number of) auxil
iary field equations along with the requirement of supersymmetry, we are able to derive a closed form for the Lagrangian on the tangent bundle and to dualize it to give the hyperkahler potential on the cotangent bundle. As an application, the case of the exceptional symmetric space E_6/SO(10) times U(1) is explicitly worked out for the first time.
We review the projective-superspace construction of four-dimensional N=2 supersymmetric sigma models on (co)tangent bundles of the classical Hermitian symmetric spaces.
