Improved Renormalization of Lattice Operators: A Critical Reappraisal

We systematically examine various proposals which aim at increasing the accuracy in the determination of the renormalization of two-fermion lattice operators. We concentrate on three finite quantities which are particularly suitable for our study: the renormalization constants of the vector and axial currents and the ratio of the renormalization constants of the scalar and pseudoscalar densities. We calculate these quantities in boosted perturbation theory, with several running boosted couplings, at the "optimal" scale q*. We find that the results of boosted perturbation theory are usually (but not always) in better agreement with non-perturbative determinations of the renormalization constants than those obtained with standard perturbation theory. The finite renormalization constants of two-fermion lattice operators are also obtained non-perturbatively, using Ward Identities, both with the Wilson and the tree-level Clover improved actions, at fixed cutoff ($\beta$=6.4 and 6.0 respectively). In order to amplify finite cutoff effects, the quark masses (in lattice units) are varied in a large interval 0<am<1. We find that discretization effects are always large with the Wilson action, despite our relatively small value of the lattice spacing ($a^{-1} \simeq 3.7$ GeV). With the Clover action discretization errors are significantly reduced at small quark mass, even though our lattice spacing is larger ($a^{-1} \simeq 2$ GeV). However, these errors remain substantial in the heavy quark region. We have implemented a proposal for reducing O(am) effects, which consists in matching the lattice quantities to their continuum counterparts in the free theory. We find that this approach still leaves appreciable, mass dependent, discretization effects.Comment: 54 pages, Latex, 5 figures. Minor changes in text between eqs.(86) and (88

DEPENDENCE OF THE CURRENT RENORMALISATION CONSTANTS ON THE QUARK MASS

We study the behaviour of the vector and axial current renormalisation constants $Z_V$ and $Z_A$ as a function of the quark mass, $m_q$. We show that sizeable $O(am_q)$ and $O(g_0^2 a m_q)$ systematic effects are present in the Wilson and Clover cases respectively. We find that the prescription of Kronfeld, Lepage and Mackenzie for correcting these artefacts is not always successful.Comment: Contribution to Lattice'94, 3 pages PostScript, uuencoded compressed

'To trust or not to trust': The impact of social media influencers on the reputation of corporate brands in crisis

Corporates often partner with social media influencers to bolster brand image after crises. Although existing evidence suggests that influencers have a largely positive effect on brands, yet there is paucity of research on the role of influencers in corporate crisis communications. Across two studies, we examine the impact of influencers on consumers’ perception of corporate brand in crisis. Drawing on persuasion knowledge theory, we identify pitfalls associated with influencers, such as inferences of manipulative intent, which negatively affect perceived trustworthiness and corporate reputation. The downside of engaging influencers in crisis communications can, however, be offset by influencer and the brand communicating values-driven motives of their partnership. Our findings imply that corporate brands should respond to crises through a bolstering strategy that promotes existing corporate goodwill, without influencer’s involvement. When leveraging on influencers’ support, however, brands should endeavor to inoculate manipulative inferences by communicating the values-driven motives behind the brand-influencer partnership

'To trust or not to trust': The impact of social media influencers on the reputation of corporate brands in crisis

Corporates often partner with social media influencers to bolster brand image after crises. Although existing evidence suggests that influencers have a largely positive effect on brands, yet there is paucity of research on the role of influencers in corporate crisis communications. Across two studies, we examine the impact of influencers on consumers’ perception of corporate brand in crisis. Drawing on persuasion knowledge theory, we identify pitfalls associated with influencers, such as inferences of manipulative intent, which negatively affect perceived trustworthiness and corporate reputation. The downside of engaging influencers in crisis communications can, however, be offset by influencer and the brand communicating values-driven motives of their partnership. Our findings imply that corporate brands should respond to crises through a bolstering strategy that promotes existing corporate goodwill, without influencer’s involvement. When leveraging on influencers’ support, however, brands should endeavor to inoculate manipulative inferences by communicating the values-driven motives behind the brand-influencer partnership

Non-perturbative Renormalization of the Complete Basis of Four-fermion Operators and B-parameters

We present results on the B-parameters $B_K$, $B^{3/2}_7$ and $B^{3/2}_8$, at $\beta=6.0$, with the tree-level Clover action. The renormalization of the complete basis of dimension-six four-fermion operators has been performed non-perturbatively. Our results for $B_K$ and $B^{3/2}_7$ are in reasonable agreement with those obtained with the (unimproved) Wilson action. This is not the case for $B^{3/2}_8$. We also discuss some subtleties arising from a recently proposed modified definition of the B-parameters.Comment: Talk presented at Lattice '97, Edinburgh (UK), July 1997. LaTeX 3 pages, uses espcrc

Non-perturbative renormalization in kaon decays

We discuss the application of the MPSTV non-perturbative method \cite{NPM} to the operators relevant to kaon decays. This enables us to reappraise the long-standing question of the $\Delta I=1/2$ rule, which involves power-divergent subtractions that cannot be evaluated in perturbation theory. We also study the mixing with dimension-six operators and discuss its implications to the chiral behaviour of the $B_K$ parameter.Comment: Talk presented at LATTICE96(improvement), LaTeX 3 pages, uses espcrc2, 2 postscript figure

Ischemic preconditioning of the muscle reduces the metaboreflex response of the knee extensors

Purpose: This study investigated the effect of ischemic preconditioning (IP) on metaboreflex activation following dynamic leg extension exercise in a group of healthy participants. Method: Seventeen healthy participants were recruited. IP and SHAM treatments (3 × 5 min cuff occlusion at 220 mmHg or 20 mmHg, respectively) were administered in a randomized order to the upper part of exercising leg’s thigh only. Muscle pain intensity (MP) and pain pressure threshold (PPT) were monitored while administrating IP and SHAM treatments. After 3 min of leg extension exercise at 70% of the maximal workload, a post-exercise muscle ischemia (PEMI) was performed to monitor the discharge group III/IV muscle afferents via metaboreflex activation. Hemodynamics were continuously recorded. MP was monitored during exercise and PEMI. Results: IP significantly reduced mean arterial pressure compared to SHAM during metaboreflex activation (mean ± SD, 109.52 ± 7.25 vs. 102.36 ± 7.89 mmHg) which was probably the consequence of a reduced end diastolic volume (mean ± SD, 113.09 ± 14.25 vs. 102.42 ± 9.38 ml). MP was significantly higher during the IP compared to SHAM treatment, while no significant differences in PPT were found. MP did not change during exercise, but it was significantly lower during the PEMI following IP (5.10 ± 1.29 vs. 4.00 ± 1.54). Conclusion: Our study demonstrated that IP reduces hemodynamic response during metaboreflex activation, while no effect on MP and PPT were found. The reduction in hemodynamic response was likely the consequence of a blunted venous return

Status and Perspective of Non-perturbative Renormalization in Weak Decays

We discuss the status and the problems related to the application of the off-shell non-perturbative renormalization method in a fixed gauge to operators relevant to weak decays. In particular, we critically reappraise the method recently proposed for the $\Delta I=1/2$ rule. We also present a general analysis of the renormalization for the $\Delta I=3/2$ operators, and apply it to the $\Delta S=2$ operator.Comment: Invited talk at the International Workshop ``Lattice QCD on Parallel Computers'', 10-15 March 1997, Tsukuba (Japan). LaTeX 12 pages, uses espcrc2, 6 figure