Recent direct measurement of the Top quark mass and quasi-infrared fixed point

We note that the recent direct measurement of the top quark mass at 173.3±5.6 (stat)±6.2 (syst) by DØ collaboration severely constrains the theoretically attractive infra-red fixed point scenario of the top quark Yukawa coupling in supersymmetric GUTs. For one-step unified models the above mentioned measurement bounds the arbitrary but experimentally determinable parameter tanβ to the range 1.3 ≤ tan β ≤ 2.1. Further crunch on the top quark mass may determine tan β even more accurately within the fixed point scenario. On the other hand an experimental value of tan β > 2.1 will rule out the fixed point scenario bounding ht (MX)/4π to 0.022 from above.