STRONG SUPERSYMMETRIC QUANTUM EFFECTS ON THE TOP QUARK WIDTH

We compute the one-loop supersymmetric QCD quantum effects on the width $\Gamma (t\rightarrow W^{+}\, b)$ of the canonical main decay of the top quark within the framework of the MSSM. The corrections can be of either sign depending on whether the stop squark mass is above or below the top quark decay threshold into stop and gluino $\Gamma (t\rightarrow\tilde{t} \,\tilde{g})$. For $m_{\tilde{t}}$ above that threshold, the corrections are negative and can be of the same order (and go in the same direction) as the ordinary QCD corrections, even for stop and gluino masses of ${\cal O}(100)\,GeV$. Since the electroweak supersymmetric quantum effects turn out to be also of the same sign and could be of the same order of magnitude, the total MSSM correction to the top quark width could potentially result in a rather large ${\cal O}(10-25)\%$ reduction of $\Gamma (t\rightarrow W^{+}\, b)$ far beyond the conventional QCD expectations.Comment: 11 page

Tetra-, Tri-, and Mononuclear Manganese(II/III) Complexes of a Phenol-Based N2O2 Capping Ligand: Use of Carboxylates as Ancillary Ligands in Tuning the Nuclearity of the Complexes

Manganese(II/III) complexes of a phenol-based tetradentate ligand L2- [H2L ) N,N′-dimethyl-N,N′-bis(2-hydroxy- 3,5-dimethylbenzyl)-ethylenediamine], namely, [Mn4(L)2(PhCOO)6] (1), [Mn3(L)2(CH3CH2COO)2(OMe)2] · H2O (2), and [Mn(L){(CH3)3CCOO}(CH3OH)] · CH3OH (3), have been synthesized. The basicity and steric congestion provided by the carboxylate moiety used as an ancillary ligand have profound influence on tuning the nuclearity of these compounds. Results of X-ray crystallography, electronic spectroscopy, and variable-temperature (1.8-300 K) magnetic measurements have been used to characterize these compounds. Complex 1 has a very interesting centrosymmetric structure that involves two crystallographically equivalent binuclear [MnII-MnIII] units, connected together by a pair of syn-anti bridging benzoates to generate a “dimer of dimers” structural motif. Compound 2 with propionate as the ancillary ligand, on the other hand, has a nearly linear MnIII-MnII-MnIII core with antiferromagnetically coupled (J ) -0.13 cm-1) metal centers. Compound 1 has an ST ) 9 spin ground state with ferromagneticlly coupled metal centers (Jwb) 2.8(1) and Jbb ) 0.09(2) cm-1) that failed to function as a single molecule magnet due to the presence of low-lying excited states with smaller spin values and a weak magnetic anisotropy. The electron paramagnetic resonance spectrum of 1 in the frozen solution (12 K) displays two signals in the g ) 2 and g ) 4 regions, each split into six lines due to 55Mn (I ) 5/2) superhyperfine couplings. The use of bulky pivalate as a replacement for benzoate provides enough steric bulk to generate a mononuclear species [Mn(L){(CH3)3CCOO}(CH3OH)] · CH3OH (3). The lone manganese(III) center in this compound has an octahedral geometry, completed by the tetradentate ligand L2- together with an axially coordinated methanol molecule and a monodentate pivalate. The latter two are connected by a hydrogen bond, thus stabilizing the monodentate carboxylate moiety. Redox behaviors (CV) of 1 and 3 are grossly similar, each undergoing a quasi-reversible reduction process at E1/2 ) -0.03 and -0.11 V, respectively, versus a Ag/AgCl reference