5 Z → b ¯ . In this article we have extended our analysis by including the constraint form non decoupling oblique corrections as well; we note that for m$_{t}$ ′ < ∼ 500 GeV our previous constraints are largely unaffected but for m$_{t}$ ′ ≈ 600 GeV the oblique corrections start to have effect. With the inputs given in Table. (III) we have made the scan over the entire parameter space by a flat random number generator and obtained the constraints on various parameters of the 4 × 4 mixing matrix. In the following subsections we briefly discuss the various input parameters used in our analysis. The Z pole, W mass, and low-energy data can be used to search for and set limits on deviations from the SM. Most of the effects on precision measurements can be described by the three gauge self-energy parameters S , T and U . We assume these parameters to be arising from new physics only i.e they are equal to zero exactly in SM, and do not include any contributions from m$_{t}$ and M$_{H}$ . The effects of non-degenerate multiplets of chiral fermions can be described by just three parameters, S , T and U at the one-loop level [30, 31, 48–50]. T is proportional to the difference between the W and Z self-energies at Q 2 = 0, while S is associated with the difference between the Z self-energy at Q 2 = M 2 Z and Q 2 = 0 and ( S + U ) is associated with the difference between W self-energy at Q 2 = M 2 W and Q 2 = 0. A non-degenerate SU (2) doublet ( f 1 f 2 ) with masses m$_{1}$ and m$_{2}$ respectively yields the contributions [48] where Y is the hypercharge of the doublet. A heavy non-degenerate doublet of fermions contributes positively to T as where ρ ∗ 0 denotes the low-energy ratio of neutral to charged current couplings in neutrino interactions. S = 1 6 π [ 1 − Y ln( m 2 $_{1}$/m 2 $_{2}$) ] , (1) T = 1 16 πs 2 $_{W}$c 2 $_{W}$M 2 Z [ m 2 1 + m 2 − 2 m 2 $_{1}$m 2 m 2 1 − m 2 ln( m 2 $_{1}$/m 2 $_{2}$) ] , U = 1 6 π [ − 5 m 4 1 − 22 m 2 $_{1}$m 2 + 5 m 4 2 3( m 2 1 − m 2 $_{2}$) 2 + m 6 1 − 3 m 4 $_{1}$m 2 − 3 m 2 $_{1}$m 4 2 + m 6 2 ( m 2 1 m 2 $_{2}$) 3 ln( m 2 $_{1}$/m 2 $_{2}$) ] , ρ ∗ 0 − 1 = 1 1 − αT − 1 ≈ αT, (2) A. Oblique correction