Experimental constraints on supersymmetric theories

We extended the analyses of Fayet, and Fayet and Farrar, of experimental searches for gluinos, the sypersymmetric partners of gluons. Because of their large production cross sections, present data appears to exclude gluino masses below 3.5–6 GeV/c2 and may be more restrictive. Since gluinos remain very light in many models, they will either be detected soon or many supersymmetric theories will be excluded.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87578/2/196_1.pd

Effective charges and expansion parameters in QCD

The momentum subtraction scheme MOM has been empirically successful in producing small QCD corrections to physical quantities at one loop order. By explicit calculations, we show that with a suitable shift in the renormalization scale, the minimal subtraction scheme coupling constant αMS coincides with typical momentum scheme coupling constants at both one and two loop order.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87888/2/107_1.pd

Experimental constraints on gluino masses and supersymmetric theories

We extend the analyses of Fayet, and Fayet and Farrar, of experimental searches for gluinos, the supersymmetric partners of gluons. Because of their large production cross sections, present data appears to exclude gluino masses below 3.5-6 GeV/c2 and may be more restrictive. Lifetime considerations give an upper limit on scalar quark masses and on the scale of supersymmetry breaking, and experiments sensitive to missing energy will provide interesting limits on the latter. Since gluinos remain very light in many models, they will either be detected soon or many supersymmetric theories will be excluded.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23982/1/0000231.pd

The two-loop axial anomaly in N = 1 supersymmetric Yang-Mills theory

We calculate the two loop correction to the divergence of the axial current inN = 1 supersymmetric Yang-Mills theory. We find that, if we use supersymmetric dimensional regularization, the anomaly is proportional to the [beta]-function, a result we interpret as evidence that the supermultiplet nature of the trace, axial and supersymmetry anomalies persists at the two- loop level. Thus it appears that the Adler-Bardeen theorem is not valid in supersymmetric theories.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24036/1/0000285.pd

Dimensional regularization and the two-loop axial anomaly in abelian, non-abelian and supersymmetric gauge theories

The two-loop corrections to the axial anomaly are calculated for a non-abelian gauge theory with fermions using both conventional and supersymmetric dimensional regularization. In both cases we find results consistent with the Adler-Bardeen theorem if we use non-anticommuting [gamma]5 of 't Hooft and Veltman. Expectations (based on the supermultiplet structure of the anomalies) that there exists in N = 1 supersymmetric Yang-Mills theory an axial current J5 such that are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23832/1/0000071.pd

Observations on horizontal symmetries and flavor changing neutral currents

We present a detailed study of the possibility of having a horizontal gauge symmetry, in addition to SU(3)c x SU(2)L x U(1). Grand unification is not used as a constraint. We concentrate on the horizontal group SU(3)H. There are two main results. (i) The horizontal symmetry might break on two mass scales, one heavy and the other of order mz or a few mz. The KL-KS mass difference and other rare kaon and muon transitions are protected by a residual symmetry, but other flavor changing processes not involving the lightest fermion of each charge can be orders of magnitude larger, e.g. and some others are forbidden). Some sectors should have relatively large flavor changing neutral currents. (ii) There is not enough new physics in the approach to explain fermion masses, but the structure of the model suggests that the lighter masses and the KM quark mixing angles might be generated radiatively. Unfortunately, careful analysis shows that the same symmetry that protects the KL-KS mass difference requires that the Cabibbo angle be identically zero to all orders. This suggests that it may be extremely difficult to make a realistic fundamental or effective SU(3) horizontal symmetry. While the model fails to generate the CKM angles, it is consistent with all low energy data and suggests a number of interesting reactions that might occur.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24006/4/1-s2.0-0550321382905430-main.pd

Estimating inclusive [psi] and [psi][eta]c production in e+e- annihilation

The reaction e+e- --> [psi] + X provides (i) a test of perturbative QCD, and (ii) a way to study even C states (such as [eta]c, [chi], Higgs) recoiling against the [psi]. Estimates of the cross section using QCD, a simple non-perturbative model, and a calculation of the contribution from two-body final states, suggest small but not unmeasurable cross sections. If m[eta]c [approximate] m[psi], this may be a good way to find the [eta]c.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23524/1/0000479.pd