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 17 3.3 +/- 5.6 (stat) +/- 6.2(syst) by DO collaboration severely constrai ns the theoretically attractive infrared fixed point scenario of the t op quark Yukawa coupling in supersymmetric GUTs. For one-step unified models the above-mentioned measurement bounds the arbitrary but experi mentally determinable parameter tan beta to the range 1.3 less than or equal to tan beta less than or equal to 2.1. Further crunch on the to p quark mass may determine tan beta even more accurately within the fi xed point scenario. On the other hand, an experimental value of tan be ta > 2.1 will rule out the fixed point scenario bounding h(t)(2)(M-X)/ 4 pi to 0.022 from above.