LittleZ′models

Abstract

We propose a new class of models called Little Z models in order to reduce the fine-tuning due to the current experimental limits on the Z mass in E 6 inspired supersymmetric models, where the Higgs doublets are charged under the extra U (1) gauge group. The proposed Little Z models allow a lower mass Z due to the spontaneously broken extra U (1) gauge group having a reduced gauge coupling. We show that reducing the value of the extra gauge coupling relaxes the experimental limits, leading to the possibility of low mass Z resonances, for example down to 200 GeV, which may yet appear in LHC searches. Although the source of tree level fine-tuning due to the Z mass is reduced in Little Z models, it typically does so at the expense of increasing the vacuum expectation value of the U (1) -breaking standard model singlet field, reducing the fine-tuning to similar levels to that in the Minimal Supersymmetric Standard Model.

Non-radiative inelastic processes in lithium-helium ion-atom collisions

“…On the other hand, non-adiabatic transition probabilities, inelastic cross-sections, and rate coefficients can be estimated within a model approach, especially when complete quantum-chemical information is not available. Such a model approach, the so-called branching probability current method, that requires information only about adiabatic potentials, has been recently proposed (Belyaev 2013a) and applied to inelastic aluminium-hydrogen collisions (Belyaev 2013a,b). The main assumption of the approach is that non-adiabatic transition probabilities can be estimated within the framework of the Landau-Zener (LZ) model (Landau 1932a,b;Zener 1932).…”

“…The method is similar to the branching classical trajectory method (Belyaev & Lebedev 2011), which is based on classical trajectories and determines LZ parameters along each trajectory. The branching probability current method determines LZ parameters beforehand and then varies an internuclear distance R without calculating any classical trajectories (see Belyaev 2013a).…”

“…The key point of the branching probability current method is a novel formula for a non-adiabatic transition probability within the LZ model, the so-called adiabatic-potential-based formula (Belyaev & Lebedev 2011;Belyaev 2013a). Positions of non-adiabatic regions R c are determined by minima of adiabatic splittings Z jk = |U j − U k | between adjacent adiabatic states with U j,k (R) being adiabatic potentials.…”

“…Positions of non-adiabatic regions R c are determined by minima of adiabatic splittings Z jk = |U j − U k | between adjacent adiabatic states with U j,k (R) being adiabatic potentials. In these regions, the LZ parameters are determined by the following formula (Belyaev & Lebedev 2011;Belyaev 2013a):…”

“…To get a first overview of the possible non-adiabatic effects in lithium-helium ion-atom interactions at different excitation levels, a model approach (Belyaev & Lebedev 2011;Belyaev 2013a) is applied here to estimate the cross-sections and rate coefficients in the corresponding non-radiative inelastic collisions.…”