Application of the Principle of Maximum Conformality to the Top-Quark Charge Asymmetry at the LHC

The Principle of Maximum Conformality (PMC) provides a systematic and process-independent method to derive renormalization scheme- and scale- independent fixed-order pQCD predictions. In Ref.\cite{pmc3}, we studied the top-quark charge asymmetry at the Tevatron. By applying the PMC, we have shown that the large discrepancies for the top-quark charge asymmetry between the Standard Model estimate and the CDF and D0 data are greatly reduced. In the present paper, with the help of the Bernreuther-Si program, we present a detailed PMC analysis on the top-quark pair production up to next-to-next-to-leading order level at the LHC. After applying PMC scale setting, the pQCD prediction for the top-quark charge asymmetry at the LHC has very small scale uncertainty; e.g., $A_{\rm C}|_{\rm 7 TeV;PMC} =\left(1.15^{+0.01}_{-0.03}\right)\%$, $A_{\rm C}|_{\rm 8 TeV;PMC} =\left(1.03^{+0.01}_{+0.00}\right)\%$, and $A_{\rm C}|_{\rm 14 TeV;PMC} =\left(0.62^{+0.00}_{-0.02}\right)\%$. The corresponding predictions using conventional scale setting are: $A_{\rm C}|_{\rm 7 TeV;Conv.} =\left(1.23^{+0.14}_{-0.14}\right)\%$, $A_{\rm C}|_{\rm 8 TeV;Conv.} =\left(1.11^{+0.17}_{-0.13}\right)\%$, and $A_{\rm C}|_{\rm 14 TeV;Conv.} =\left(0.67^{+0.05}_{-0.05}\right)\%$. In these predictions, the scale errors are predicted by varying the initial renormalization and factorization scales in the ranges $\mu^{\rm init}_r\in[m_t/2,2m_t]$ and $\mu_f\in[m_t/2,2m_t]$. The PMC predictions are also in better agreement with the available ATLAS and CMS data. In addition, we have calculated the top-quark charge asymmetry assuming several typical cuts on the top-pair invariant mass $M_{t\bar{t}}$. For example, assuming $M_{t\bar{t}}>0.5 ~ {\rm TeV}$ and $\mu_f=\mu^{\rm init}_r =m_t$, we obtain $A_{\rm C}|_{\rm 7 TeV;PMC}=2.67\%$, $A_{\rm C}|_{\rm 8 TeV;PMC}=2.39\%$, and $A_{\rm C}|_{\rm 14 TeV;PMC}=1.28\%$.Comment: 10 pages, 4 figures. Discussion improve

Pramanicin analog induces apoptosis in human colon cancer cells: critical roles for Bcl-2, Bim, and p38 MAPK signaling

Pramanicin (PMC) is an antifungal agent that was previously demonstrated to exhibit antiangiogenic and anticancer properties in a few in vitro studies. We initially screened a number of PMC analogs for their cytotoxic effects on HCT116 human colon cancer cells. PMC-A, the analog with the most potent antiproliferative effect was chosen to further interrogate the underlying mechanism of action. PMC-A led to apoptosis through activation of caspase-9 and -3. The apoptotic nature of cell death was confirmed by abrogation of cell death with pretreatment with specific caspase inhibitors. Stress-related MAPKs JNK and p38 were both activated concomittantly with the intrinsic apoptotic pathway. Moreover, pharmacological inhibition of p38 proved to attenuate the cell death induction while pretreatment with JNK inhibitor did not exhibit a protective effect. Resistance of Bax -/- cells and the protective nature of caspase-9 inhibition indicate that mitochondria play a central role in PMC-A induced apoptosis. Early post-exposure elevation of cellular Bim and Bax was followed by a marginal Bcl-2 depletion and Bid cleavage. Further analysis revealed that Bcl-2 downregulation occurs at the mRNA level and is critical to mediate PMC-A induced apoptosis, as ectopic Bcl-2 expression substantially spared the cells from death. Conversely, forced expression of Bim proved to significantly increase cell death. In addition, analyses of p53-/- cells demonstrated that Bcl-2/Bim/Bax modulation and MAPK activations take place independently of p53 expression. Taken together, p53-independent transcriptional Bcl-2 downregulation and p38 signaling appear to be the key modulatory events in PMC-A induced apoptosis

Case Study: Pan-Mass Challenge

The Pan-Mass Challenge (PMC), a nonprofit organization based in Needham, Mass., is the nation's original fundraising bike-a-thon, and today raises more money for charity than any other single athletic fundraising event in the country. As donors increasingly turned to online giving, PMC began offering credit cards as a payment option and this is now the most common tool for making donations. However, PMC also recognized that card processing fees were reducing the amount of each donation it received.Identifying an opportunity to both reduce transaction fees and tap the growing number of donors with donor-advised funds, PMC launched the DAF Direct application in 2013 (which appears as an option when donors choose their giving method) to enable DAF donors to conveniently support individual riders directly from their DAF. Unlike credit card donations, DAF grants are not subject to a processing fee, which means 100 percent of the grant go tothe charity

Differential electrophysiological response during rest, self-referential, and non-self-referential tasks in human posteromedial cortex

The electrophysiological basis for higher brain activity during rest and internally directed cognition within the human default mode network (DMN) remains largely unknown. Here we use intracranial recordings in the human posteromedial cortex (PMC), a core node within the DMN, during conditions of cued rest, autobiographical judgments, and arithmetic processing. We found a heterogeneous profile of PMC responses in functional, spatial, and temporal domains. Although the majority of PMC sites showed increased broad gamma band activity (30-180 Hz) during rest, some PMC sites, proximal to the retrosplenial cortex, responded selectively to autobiographical stimuli. However, no site responded to both conditions, even though they were located within the boundaries of the DMN identified with resting-state functional imaging and similarly deactivated during arithmetic processing. These findings, which provide electrophysiological evidence for heterogeneity within the core of the DMN, will have important implications for neuroimaging studies of the DMN

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

Reconsideration of the QCD corrections to the ηc\eta_c decays into light hadrons using the principle of maximum conformality

In the paper, we analyze the $\eta_c$ decays into light hadrons at the next-to-leading order QCD corrections by applying the principle of maximum conformality (PMC). The relativistic correction at the ${\cal{O}}(\alpha_s v^2)$-order level has been included in the discussion, which gives about $10\%$ contribution to the ratio $R$. The PMC, which satisfies the renormalization group invariance, is designed to obtain a scale-fixed and scheme-independent prediction at any fixed order. To avoid the confusion of treating $n_f$-terms, we transform the usual $\overline{\rm MS}$ pQCD series into the one under the minimal momentum space subtraction scheme. To compare with the prediction under conventional scale setting, $R_{\rm{Conv,mMOM}-r}= \left(4.12^{+0.30}_{-0.28}\right)\times10^3$, after applying the PMC, we obtain $R_{\rm PMC,mMOM-r}=\left(6.09^{+0.62}_{-0.55}\right) \times10^3$, where the errors are squared averages of the ones caused by $m_c$ and $\Lambda_{\rm mMOM}$. The PMC prediction agrees with the recent PDG value within errors, i.e. $R^{\rm exp}=\left(6.3\pm0.5\right)\times10^3$. Thus we think the mismatching of the prediction under conventional scale-setting with the data is due to improper choice of scale, which however can be solved by using the PMC.Comment: 5 pages, 2 figure

An analysis of H→γγH \to \gamma \gamma up to three-loop QCD corrections

The principle of maximum conformality (PMC) provides a convenient way for setting the optimal renormalization scales for high-energy processes, which can eliminate the conventional renormalization scale error via an order-by-order manner. At present, we make a detailed PMC analysis on the Higgs decay $H\rightarrow \gamma\gamma$ up to three-loop QCD corrections. As an important point of deriving reliable PMC estimation, it is noted that only those $\{\beta_i\}$-terms that rightly determine the running behavior of coupling constant via the renormalization group equation should be absorbed into the coupling constant, and those $\{\beta_i\}$-terms that pertain to the quark mass renormalization and etc. should be kept as a separate. To avoid confusion of separating and absorbing different types of $\{\beta_i\}$-terms into the coupling constant, we first transform the decay width in terms of top quark $\overline{\rm MS}$ mass into that of on-shell mass and then apply the PMC scale setting. After applying PMC scale setting, the final estimation is conformal and is scheme-independent and scale-independent. Up to three-loop QCD corrections, we obtain a PMC scale $\mu^{\rm PMC}_{r}=242.3$ GeV $\sim 2M_H$, which is optimal and highly independent of any choice of initial scale. Thus, we obtain a more accurate scale-independent prediction by taking the Higgs mass as the same as that of ATLAS and CMS measurements, i.e., $\Gamma(H\rightarrow \gamma\gamma)|_{\rm ATLAS}=9.504^{+0.226}_{-0.252}$ keV and $\Gamma(H\rightarrow \gamma\gamma)|_{\rm CMS}=9.568^{+0.195}_{-0.191}$ keV, where the error is caused by the measured Higgs mass, i.e. the Higgs mass $M_{H}$ is taken as $125.5\pm0.2^{+0.5}_{-0.6}$ GeV for ATLAS and $125.7\pm0.3\pm0.3$ GeV for CMS, respectively.Comment: 16 pages, 2 figures. References updated and discussion improved, to be published in J.Phys.

Reanalysis of the BFKL Pomeron at the next-to-leading logarithmic accuracy

We apply the principle of maximum conformality (PMC) to the Balitsky-Fadin-Kuraev-Lipatov (BFKL) Pomeron intercept at the next-to-leading logarithmic (NLL) accuracy. The PMC eliminates the conventional renormalization scale ambiguity by absorbing the non-conformal $\{\beta_i\}$-terms into the running coupling, and a more accurate pQCD estimation can be obtained. After PMC scale setting, the QCD perturbative convergence can be greatly improved due to the elimination of renormalon terms in pQCD series, and the BFKL Pomeron intercept has a weak dependence on the virtuality of the reggeized gluon. For example, by taking the Fried-Yennie gauge, we obtain $\omega_{\rm MOM}^{\rm PMC}(Q^{2},0)\in [0.149,0.176]$ for $Q^2\in[1,100]\;{\rm GeV}^2$. This is a good property to apply to the high-energy phenomenology. Further more, to compare with the data, it is found that the physical ${\rm MOM}$-scheme is more reliable than the $\overline{\rm MS}$-scheme. The ${\rm MOM}$-scheme is gauge dependent, which can also be greatly suppressed after PMC scale setting. We discuss the MOM-scheme gauge dependence for the Pomeron intercept by adopting three gauges, i.e. the Landau gauge, the Feynman gauge and the Fried-Yennie gauge, and we obtain $\omega_{\rm MOM}^{\rm PMC}(Q^{2}=15\;{\rm GeV}^2,0) = 0.166^{+0.010}_{-0.017}$; i.e. about $10\%$ gauge dependence is observed. We apply the BFKL Pomeron intercept to the photon-photon collision process, and compare the theoretical predictions with the data from the OPAL and L3 experiments.Comment: 18 pages, 6 figures. References updated and discussions improve