Ivan Maksymyk

Beyond S, T and U

The contribution to precision electroweak measurements due to TeV physics which couples primarily to the W ± and Z bosons may be parameterized in terms of the three ‘oblique correction’ parameters, S, T and U. We extend this parameterization to physics at much lower energies, > 100 GeV, and show that in this more general case neutral-current experiments are sensitive to only two additional parameters. A third new parameter enters into the W ± width. The standard electroweak theory has recently come of age, with experiments now probing its predictions with sufficient accuracy to test its r corrections in some detail. Besides providing a detailed test of the model, these precision measurements are also very useful for the constraints they impose on any potential new physics that might exist at energies higher than those that have been hitherto experimentally explored. A particularly interesting class of new physics that is constrained by these measure

Beyond [ital S], [ital T], and [ital U]

The contribution to precision electroweak measurements due to TeV physics which couples primarily to the W ± and Z bosons may be parameterized in terms of the three ‘oblique correction’ parameters, S, T and U. We extend this parameterization to physics at much lower energies, > 100 GeV, and show that in this more general case neutral-current experiments are sensitive to only two additional parameters. A third new parameter enters into the W ± width. The standard electroweak theory has recently come of age, with experiments now probing its predictions with sufficient accuracy to test its r corrections in some detail. Besides providing a detailed test of the model, these precision measurements are also very useful for the constraints they impose on any potential new physics that might exist at energies higher than those that have been hitherto experimentally explored. A particularly interesting class of new physics that is constrained by these measure

A global fit to extended oblique parameters

Abstract The STU formalism of Peskin and Takeuchi is an elegant method for encoding the measurable effects of new physics which couples to light fermions dominantly through its effects on electroweak boson propagation. However, this formalism cannot handle the case where the scale of new physics is not much larger than the weak scale. In this case three new parameters (V, W and X) are required. A global fit to precision electroweak data for these six parameters is performed. Our results differ from what is found for just STU. In particular we find that the preference for SThe STU formalism of Peskin and Takeuchi is an elegant method for encoding the measurable effects of new physics which couples to light fermions dominantly through its effects on electroweak boson propagation. However, this formalism cannot handle the case where the scale of new physics is not much larger than the weak scale. In this case three new parameters (V, W and X) are required. We perform a global fit to precision electroweak data for these six parameters. Our results differ from what is found for just STU. In particular we find that the preference for S<0 is not maintained.

Supersymmetric models with product groups and field dependent gauge couplings

We study the dilaton-dependence of the effective action for N = 1, SU(N1) × SU(N2) models with one generation of vectorlike matter transforming in the fundamental of both groups. We treat in detail the confining and Coulomb phases of these models writing explicit expressions in many cases for the effective superpotential. We can do so for the Wilson superpotentials of the Coulomb phase when N2 = 2, N1 = 2,4. In these cases the Coulomb phase involves a single U(1) gauge multiplet, for which we exhibit the gauge coupling in terms of the modulus of an elliptic curve. The SU(4) × SU(2) model reproduces the weak-coupling limits in a nontrivial way. In the confining phase of all of these models, the dilaton superpotential has a runaway form, but in the Coulomb phase the dilaton enjoys flat directions. Had we used the standard moduli-space variables: Tr k, k = 1, ... , N2, with the quark condensate matrix, to parameterize the flat directions instead of the eigenvalues of , we would find physically unacceptable behaviour, illustrating the importance to correctly identify the moduli.

NRQCD matrix elements in polarization of J / Psi produced from b decay

We present the nonrelativistic QCD (NRQCD) prediction for the polarization of the J/{psi} promptly produced in b{r_arrow}J/{psi}+X, as well as the helicity-summed production rate. We propose that these observables can be of avail in measuring the three most important color-octet NRQCD matrix elements involved in J/{psi} production. Anticipating the measurement of the polarization parameter {alpha}, we determine its expected range given current experimental bounds on the color-octet matrix elements. We find that the leading-order NRQCD prediction for the polarization parameter {alpha} is expected to lie in the range {minus}0.33 to 0.05 whereas the color-singlet model prediction is {minus}0.40{plus_minus}0.04. {copyright} {ital 1997} {ital The American Physical Society}

Photoproduction of J / psi in the forward region

We study the phenomenology of fixed-target elastic J/{psi} photoproduction in the nonrelativistic QCD (NRQCD) factorization formalism. Our goal is to test an essential feature of this formalism{emdash}the color-octet mechanism. We obtain an order-of-magnitude estimate for a certain linear combination of NRQCD color-octet matrix elements. Our estimate is consistent with other empirical determinations and with the v-scaling rules of NRQCD. {copyright} {ital 1997} {ital The American Physical Society}

Fixing the dilaton with asymptotically expensive physics

Abstract We propose a general mechanism for stabilizing the dilaton against runaway to weak coupling. The method is based on features of the effective superpotential which arise for supersymmetric gauge theories which are not asymptotically free. Consideration of the 2PI effective action for bilinear operators of matter and gauge superfields allows one to overcome the obstacles to constructing a nonvanishing superpotential.

Hadronic J/ψ production calculated in the NRQCD factorization formalism

The NRQCD factorization formalism of Bodwin, Braaten, and Lepage prescribes how to write quarkonium production rates as a sum of products of short-distance coefficients times nonperturbative long-distance NRQCD matrix elements. We present a calculation of the inclusive cross section for hadronic {psi} production within the framework of the factorization formalism. Our method applies to the case in which the helicity of the {psi} is not measured. In addition to the well-known {ital color}-{ital singlet} production mechanisms, there are equally important mechanisms in which the {ital c{bar c}} pair that forms the {ital J}/{psi} is initially produced in a {ital color}-{ital octet} state, in either a {sup 3}{ital S}{sub 1}, {sup 1}{ital S}{sub 0}, {sup 3}{ital P}{sub 0}, or {sup 3}{ital P}{sub 2} angular-momentum configuration. In our presentation, we faithfully follow the {open_quote}{open_quote}matching{close_quote}{close_quote} procedure, thereby shedding light on the NRQCD factorization formalism. We determine the short-distance coefficients appearing in the factorization formula, and we point out how one may systematically include relativistic corrections in these calculations. {copyright} {ital 1996 The American Physical Society.}

Bounding anomalous gauge boson couplings

We investigate indirect phenomenological bounds on anomalous three-gauge-boson couplings. We do so by systematically determining their one-loop implications for precision electroweak experiments. We find that these loop-induced effects cannot be parametrized purely in terms of the parameters [ital S],[ital T], and [ital U]. Like some other authors, we find many cancellations among the loop-induced effects, and we show how to cast the low-energy effective theory into a form which makes these cancellations manifest at the outset. In a simultaneous fit of all [ital CP]-conserving anomalous three-gauge-boson couplings, our analysis finds only weak phenomenological constraints.

New physics and recent high precision electroweak measurements

Abstract We analyze LEP and SLC data from the 1995 Winter Conferences for signals of new physics. We compare the data with the Standard Model (SM) as well as a number of test hypotheses concerning the nature of new physics: (i) nonstandard Zb b couplings, (ii) nonstandard Zf f couplings for the entire third generation, (iii) nonstandard oblique corrections, (iv) nonstandard lepton couplings, (v) general nonstandard W and Z couplings to all fermions, as well as combinations of the above. In most of our analyses, we leave the SM variables αs and mt as free parameters to see how the various types of new physics can affect their inferred values. We find that the best fit ( χ 2 d.o.f. = 8.4 10 ) is obtained for the nonstandard Zb b couplings, which also give a ‘low’ value (0.112) for αs. The SM also gives a good description of the Z data, having χ 2 d.o.f. = 12.4 12 . If αs is held fixed to the low-energy value 0.112, then we find that a combination of the nonstandard Zb b couplings is fit to lie more than four standard deviations away from zero.