1,721,197 research outputs found
Third order corrections to the semileptonic b -> c and the muon decays
Full text linkWe compute corrections of order alpha(3)(s) to the decay b -> b -> cl ( nu) over bar taking into account massive charm quarks. In the on-shell scheme large three-loop corrections are found. However, in the kinetic scheme the three-loop corrections are below 1% and thus perturbation theory is well under control. We furthermore provide results for the order alpha(3)(s) corrections to b -> cl (nu ) over bar and the third-order QED corrections to the muon decay which will be important input for reducing the uncertainty of the Fermi coupling constant G(F)
Relation between the (MS)over-bar and the kinetic mass of heavy quarks
No full textWe compute the relation between the pole mass and the kinetic mass of a heavy quark to three loops. Using the known relation between the pole and the (MS) over bar mass we obtain precise conversion relations between the (MS) over bar and kinetic masses. The kinetic mass is defined via the moments of the spectral function for the scattering involving a heavy quark close to threshold. This requires the computation of the imaginary part of a forward-scattering amplitude up to three-loop order. We discuss in detail the expansion procedure and the reduction to master integrals. For the latter analytic results are provided. We apply our result both to charm and bottom quark masses. In the latter case we compute and include finite charm quark mass effects. Furthermore, we determine the large-beta(0) result for the conversion formula at four-loop order. For the bottom quark we estimate the uncertainty in the conversion between the (MS) over bar and kinetic masses to about 15 MeV which is an improvement by a factor of 2-3 as compared to the two-loop formula. The improved precision is crucial for the extraction of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar at Belle II
Differential effects of instructed and objective feedback reliability on feedback-related brain activity
No full textFeedback reliability refers to the probability that the same decision leads to the same positive or negative feedback in the future. Previous research has shown that unreliable feedback is associated with attenuated feedback-related brain activity in ERPs, represented by a reduced fronto-central valence effect (feedback-related negativity or reward positivity) and a reduced feedback-related P3. Here, we asked whether these effects reflect top-down mechanisms or whether they can be explained by implicit feedback-outcome contingency learning. In two experiments, participants performed a trial-and-error learning task while subjective or objective feedback reliability was varied across blocks. In Experiment 1, we manipulated instructed feedback reliability while holding objective feedback reliability constant. Low instructed feedback reliability led to an attenuation of the fronto-central valence effect and the P3. In Experiment 2, we manipulated objective feedback reliability while holding instructed feedback reliability constant. Here, no modulation of feedback-related brain activity was observed. These results suggest that effects of feedback reliability are driven by top-down mechanisms based on explicit knowledge. Specifically, effects on the fronto-central valence effect could indicate a devaluation of unreliable feedback or a bias on the generation or utilization of reward prediction errors
Four-loop singlet contribution to the electroweak rho parameter
No full textSchroeder Y, Steinhauser M. Four-loop singlet contribution to the electroweak rho parameter. Phys.Lett. B. 2005;622(1-2):124-130.We compute the four-loop QCD contribution to the electroweak rho parameter induced by the singlet diagrams of the Z-boson self-energy. The numerical impact on the weak mixing angle and the W-boson mass is small. (c) 2005 Elsevier B.V. All rights reserved
Four-loop decoupling relations for the strong coupling
No full textSchroeder Y, Steinhauser M. Four-loop decoupling relations for the strong coupling. Journal of High Energy Physics. 2006;2006(01):051.We compute the matching relation for the strong coupling constant within the framework of QCD up to four-loop order. This allows a consistent five-loop running (once the beta function is available to this order) taking into account threshold effects. As a side product we obtain the effective coupling of a Higgs boson to gluons with five-loop accuracy
Exact results for ZmOS and Z2OS with two mass scales and up to three loops
Full text linkWe consider the on-shell mass and wave function renormalization constants ZmOS and Z2OS up to three-loop order allowing for a second non-zero quark mass. We obtain analytic results in terms of harmonic polylogarithms and iterated integrals with the additional letters 1-tau 2 and 1-tau 2/tau which extends the findings from ref. [1] where only numerical expressions are presented. Furthermore, we provide terms of order O(E-2) and O(E) at two- and three-loop order which are crucial ingredients for a future four-loop calculation. Compact results for the expansions around the zero-mass, equal-mass and large-mass cases allow for a fast high-precision numerical evaluation
Kinetic Heavy Quark Mass to Three Loops
Full text linkWe compute three-loop corrections to the relation between the heavy quark masses defined in the pole and kinetic schemes. Using known relations between the pole and (MS) over bar quark masses, we can establish precise relations between the kinetic and (MS) over bar charm and bottom masses. As compared to two loops, the precision is improved by a factor of 2 to 3. Our results constitute important ingredients for the precise determination of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar at Belle II
Enhanced error-related negativity on flanker errors: Error expectancy or error significance?
No full textThe present study investigated whether the error-related negativity, an electrophysiological marker for performance monitoring, reflects (1) the expectancy of errors, or (2) the significance of errors for the current task goal. In the first case, a larger error-related negativity is predicted for less expected errors, whereas in the second case, a larger error-related negativity is predicted for errors with greater significance. To test these predictions, we varied flanker size in a flanker task. With large flankers, more errors occurred by executing the response associated with the flankers (flanker errors) leading to a greater expectancy of flanker errors. As revealed by a multinomial model, these additional flanker errors represented highly significant attention errors, leading to an increased error significance. The error-related negativity was larger for flanker errors with large flankers, which supports the error significance account
Are errors detected before they occur? Early error sensations revealed by metacognitive judgments on the timing of error awareness
Full text linkErrors in choice tasks are not only detected fast and reliably, participants often report that they knew that an error occurred already before a response was produced. These early error sensations stand in contrast with evidence suggesting that the earliest neural correlates of error awareness emerge around 300 ms after erroneous responses. The present study aimed to investigate whether anecdotal evidence for early error sensations can be corroborated in a controlled study in which participants provide metacognitive judgments on the subjective timing of error awareness. In Experiment 1, participants had to report whether they became aware of their errors before or after the response. In Experiment 2, we measured confidence in these metacognitive judgments. Our data show that participants report early error sensations with high confidence in the majority of error trials across paradigms and experiments. These results provide first evidence for early error sensations, informing theories of error awareness
Errors can elicit an error positivity in the absence of an error negativity: Evidence for independent systems of human error monitoring
No full textErrors in human behavior elicit a cascade of brain activity related to performance monitoring and error detection. Whereas the early error-related negativity (Ne/ERN) has been assumed to reflect a fast mismatch or prediction error signal in the medial frontal cortex, the later error positivity (Pe) is viewed as a correlate of conscious error processing. A still open question is whether these components represent two independent systems of error monitoring that rely on different types of information to detect an error. Here, we investigated the prediction that the Ne/ERN but not the Pe requires a representation of the correct response to emerge. To this end, we created a condition in which no information about the correct response was available while error detection was still possible. We hypothesized that a Pe, but no Ne/ERN should be obtained in this case. Participants had to classify targets but ignore flankers that were always associated with an incorrect response. Targets but not flankers were masked with varying target-masking intervals. Crucially, on some trials no target at all was presented, thus preventing the representation of a correct response and the emergence of an Ne/ERN. However, because flankers were easily visible and responses to the flankers were always incorrect, detection of these flanker errors was still possible. In line with predictions of a multiple-systems account, we observed a robust Pe in the absence of an Ne/ERN for these errors. Moreover, this Pe relied on the same neural activity as that on trials with a visible target, as revealed by multivariate pattern analysis. These findings demonstrate that the mechanisms reflected by the two components use different types of information to detect errors, providing evidence for independent systems of human error monitoring
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