fourth generation physics, see for example Ref. [@overview].

In this paper, we will focus mainly on the fourth generation of leptons and comment only briefly on inclusion of the extra quark family toward the end. If we assume the flavor symmetry of the lepton sector is described correctly at tree level by an $A_4$ model [@Ma:2001dn; @Altarelli:2005yp; @Zee:2005ut; @He:2006dk; @King:2006np; @Morisi:2007ft; @Bazzocchi:2007na; @Frampton:2008ci], we then need to reconcile the prospects of a heavy fourth generation of leptons with the results known for the neutrinos in the first three generations. This requires that we extend the successful results of $A_4$ models, such as tribimaximal mixing (TBM), to the four generation model. The simplest approach is to demand a model where the $A_4$ model can be minimally embedded. The simplest extension of this type is based on $A_5$ where surprisingly many new features arise, some of which will be immediately testable in the next round of neutrino experiments or at the LHC.

In the literature there has been numerous discussions of three generation lepton flavor symmetry using the $A_{5}$ group. It is well known that the tribimaximal value of the solar mixing angle $\theta^{\rm TBM}_{12} = \tan^{-1}(\frac{1}{\sqrt{2}}) = 35.26\,^{\circ}$, which is very 