Eliminating the Renormalization Scale Ambiguity for Top-Pair Production Using the Principle of Maximum Conformality

It is conventional to choose a typical momentum transfer of the process as the renormalization scale and take an arbitrary range to estimate the uncertainty in the QCD prediction. However, predictions using this procedure depend on the renormalization scheme, leave a non-convergent renormalon perturbative series, and moreover, one obtains incorrect results when applied to QED processes. In contrast, if one fixes the renormalization scale using the Principle of Maximum Conformality (PMC), all non-conformal $\{\beta_i\}$-terms in the perturbative expansion series are summed into the running coupling, and one obtains a unique, scale-fixed, scheme-independent prediction at any finite order. The PMC scale $\mu^{\rm PMC}_R$ and the resulting finite-order PMC prediction are both to high accuracy independent of the choice of initial renormalization scale $\mu^{\rm init}_R$, consistent with renormalization group invariance. As an application, we apply the PMC procedure to obtain NNLO predictions for the $t\bar{t}$-pair production at the Tevatron and LHC colliders. The PMC prediction for the total cross-section $\sigma_{t\bar{t}}$ agrees well with the present Tevatron and LHC data. We also verify that the initial scale-independence of the PMC prediction is satisfied to high accuracy at the NNLO level: the total cross-section remains almost unchanged even when taking very disparate initial scales $\mu^{\rm init}_R$ equal to $m_t$, $20\,m_t$, $\sqrt{s}$. Moreover, after PMC scale setting, we obtain $A_{FB}^{t\bar{t}} \simeq 12.5$, $A_{FB}^{p\bar{p}} \simeq 8.28$ and $A_{FB}^{t\bar{t}}(M_{t\bar{t}}>450 \;{\rm GeV}) \simeq 35.0$. These predictions have a $1\,\sigma$-deviation from the present CDF and D0 measurements; the large discrepancy of the top quark forward-backward asymmetry between the Standard Model estimate and the data are thus greatly reduced.Comment: 4 pages. Detailed derivations for the top-quark pair total cross-sections and forward-backward asymmetry can be found in Refs.[arXiv:1204.1405; arXiv:1205.1232]. To match the published version. To be published in Phys.Rev.Let

The effects of contract detail and prior ties on contract change : a learning perspective

Despite the large literature on alliance contract design, we know little about how transacting parties change and amend their underlying contracts during the execution of strategic alliances. Drawing on existing research in the alliance contracting literature, we develop the empirical question of how contract detail and prior ties influence the amount, direction, and type of change in such agreements during the collaboration. We generated a sample of 115 joint ventures (JVs) by distributing a survey to JV board members or top managers and found that the amount of contract change is negatively associated with the level of detail in the initial contract but is positively associated with the number of prior ties between alliance partners. In relation to the direction of contract change, we find that the level of detail of the initial agreements negatively correlates with the likelihood of removing or weakening existing provisions and that prior collaborative experience positively correlates with the likelihood of strengthening of existing provisions or adding of new ones. We also find that prior ties affect the type of change in that JV parents prefer to change enforcement provisions more so than the coordination provisions in the contract. Our paper generates new insights on the complementarities between relational governance and transaction cost economics perspectives on alliance contracting