The group of causal automorphisms

The group of causal automorphisms on Minkowski space-time is given and its structure is analyzed

D0 dimuon charge asymmetry from B_s system with Z' couplings and the recent LHCb result

The D0 collaboration has announced the observation of the like-sign dimuon charge asymmetry since 2010, which has more than 3\sigma deviation from the Standard Model prediction. One of the promising explanation is considering the existence of flavor changing Z' couplings to the b and s quarks which can contribute to the off-diagonal decay width in the B_s - \bar{B}_s mixing. Model construction is highly constrained by the recent LHCb data of 1fb^{-1} integrated luminosity . In this paper, we analyze the experimental constraints in constructing new physics models to explain the dimuon charge asymmetry from the CP violation of the B_s system. We present limits on Z' couplings and show that it is impossible to obtain the 1\sigma range of the dimuon charge asymmetry without the new contribution in the B_d system. Even with arbitrary contribution in the B_d system, the new couplings must be in the fine tuned region.Comment: 34 pages, 12 figures, Additional analyses and references are updated. (Conclusion unchanged.

Radiatively Generated Maximal Mixing Scenario for the Higgs Mass and the Least Fine Tuned Minimal Supersymmetric Standard Model

We argue that given the experimental constraints on the Higgs mass the least fine tuned parameter space of minimal supersymmetric standard model is with negative stop masses squared at the grand unification scale. While stop mass squared is typically driven to positive values at the weak scale, the contribution to the Higgs mass squared parameter from the running can be arbitrarily small, which reduces fine tuning of electroweak symmetry breaking. At the same time the stop mixing is necessarily enhanced and the maximal mixing scenario for the Higgs mass can be generated radiatively even when starting with negligible mixing at the unification scale. This highly alleviates constraints on possible models for supersymmetry breaking in which fine tuning is absent.Comment: 5pages, 1 color figur