Academic literature on the topic 'Qt-subtraction'

We present a 10-year-old boy with syncope who was found to have long-QT syndrome and severe Pulmonary Hypertension (PH) both in the absence of a secondary cause; to our knowledge, this is the first report with this unusual coexistence. His genetic tests were positive for hereditary hemorrhagic telangiectasia and Long QT Syndrome (LQTS) without any family history of PH or LQTS. We demonstrated that digital subtraction pulmonary angiography was more useful compared to CT angiogram to demonstrate pulmonary vascular changes which correlated with a noresponse to acute vasoreactivity testing during right heart catheterization. He has been stable for the last 2 years on Ambrisentan, Sildenafil, and Nadolol without recurrence of symptoms.

Introduction: Ventricular pacing (VP) may impact the accuracy of QT interval measurement, as it increases the QT by increasing the QRS duration amongst other mechanisms. We aimed to investigate the accuracy of the commonly used clinical practice of subtracting 50 ms from the corrected QT (QTc) in ventricular paced rhythms. Methods: We conducted a prospective observational study on 23 consecutive pacemaker patients. Four ECGs were recorded for each subject, 2 in their native rate and 2 following an atrial paced, atrial sensed and inhibited response to sensing and then a dual pacing, dual sensing and dual response pacing of 100 bpm to allow for an intrinsic and a ventricular paced QRS, respectively. The averaged QTc in the ventricular paced rhythm was then compared with the non-ventricular-paced QTc for individual subjects. Results: At a mean spontaneous heart rate of 66 bpm (SD ±8), the mean difference in QTc between the ventricular paced and nonpaced QRS was 48.27 ms (95% CI = 32-64.6 ms, p < 0.001). At faster paced rates, the mean QTc difference was 81.3 ms (95% CI = 35.8-126.8 ms, p = 0.002). Conclusions: The QTc measurement during VP confirms the current 50-ms subtraction assumption rule within a range of ±16 ms at an average heart rate of 66 bpm. However, at faster heart rates, the 50-ms adjustment may underestimate the QTc discrepancy between a wide and normal QRS.

In this article, we report phenomenological studies about the impact of O(α) corrections to diphoton production at hadron colliders. We explore the application of the Abelianized version of the qT-subtraction method to efficiently compute NLO QED contributions, taking advantage of the symmetries relating QCD and QED corrections. We analyze the experimental consequences due to the selection criteria and we find percent-level deviations for Mγγ>1TeV. An accurate description of the tail of the invariant mass distribution is very important for new physics searches which have the diphoton process as one of their main backgrounds. Moreover, we emphasize the importance of properly dealing with the observable photons by reproducing the experimental conditions applied to the event reconstruction.

Large cerebral aneurysms are considered more dangerous than their smaller counterparts, with higher risk of subarachnoid hemorrhage. Understanding the hemodynamics of large aneurysms has potential to predict their response to treatment. Digital subtraction angiography images for patients with intracranial aneurysms over a seven-year period were reviewed. Unruptured solitary aneurysms of the internal carotid artery (ICA) proximal to the terminus and posterior communicating artery were included. Contrast intensity over time was analyzed at the center of the M1 segment of the middle cerebral artery distal to the aneurysm and compared to the contralateral side. Analysis included time to peak (TP)10%–100% (time needed for contrast to change from 10% intensity to 100%), washout time (WT)100%–10% (time for 100% intensity to 10%), and quartile time (QT)25%–25% (time for 25% intensity during vessel filling to 25% during emptying). Fifty patients met the inclusion criteria. Analysis over the ipsilateral M1 segment revealed a significant increase in QT25%–25% (8.5 vs 7.6 seconds, p = 0.006) compared to the contralateral side. There was a correlation between TP10%–100% and QT25%–25% with aneurysm size (Pearson’s r = 0.37, p = 0.007 and r = 0.43, p = 0.001, respectively). Larger ICA aneurysms were associated with delayed contrast intensity times . A plausible mechanism is that large aneurysms act as a capacitance chamber (Windkessel effect) that slow the arrival of contrast distal to the aneurysm. This may be of significance for large aneurysms after treatment, where the loss of the Windkessel effect places the distal circulation at greater risk for hemorrhage, and warrants further study.

The cardiac late Na+ current is generated by a small fraction of voltage-dependent Na+ channels that undergo a conformational change to a burst-gating mode, with repeated openings and closures during the action potential (AP) plateau. Its magnitude can be augmented by inactivation-defective mutations, myocardial ischemia, or prolonged exposure to chemical compounds leading to drug-induced (di)-long QT syndrome, and results in an increased susceptibility to cardiac arrhythmias. Using CytoPatch™ 2 automated patch-clamp equipment, we performed whole-cell recordings in HEK293 cells stably expressing human Nav1.5, and measured the late Na+ component as average current over the last 100 ms of 300 ms depolarizing pulses to -10 mV from a holding potential of -100 mV, with a repetition frequency of 0.33 Hz. Averaged values in different steady-state experimental conditions were further corrected by the subtraction of current average during the application of tetrodotoxin (TTX) 30 μM. We show that ranolazine at 10 and 30 μM in 3 min applications reduced the late Na+ current to 75.0 ± 2.7% (mean ± SEM, n = 17) and 58.4 ± 3.5% (n = 18) of initial levels, respectively, while a 5 min application of veratridine 1 μM resulted in a reversible current increase to 269.1 ± 16.1% (n = 28) of initial values. Using fluctuation analysis, we observed that ranolazine 30 μM decreased mean open probability p from 0.6 to 0.38 without modifying the number of active channels n, while veratridine 1 μM increased n 2.5-fold without changing p. In human iPSC-derived cardiomyocytes, veratridine 1 μM reversibly increased APD90 2.12 ± 0.41-fold (mean ± SEM, n = 6). This effect is attributable to inactivation removal in Nav1.5 channels, since significant inhibitory effects on hERG current were detected at higher concentrations in hERG-expressing HEK293 cells, with a 28.9 ± 6.0% inhibition (mean ± SD, n = 10) with 50 μM veratridine.

Abstract In this work we extend the qT -subtraction formalism, originally developed for QCD corrections, to the case of mixed QCD⊗QED corrections, and apply it to the fully exclusive calculation of the $$ \mathcal{O}\left({\alpha}_s\alpha \right) $$ O α s α contribution to the production of an off-shell Z boson in hadronic collisions. We present explicit results for the subtraction term and the hard factor, therefore providing all the ingredients needed for the application of the formalism up to $$ \mathcal{O}\left({\alpha}_s\alpha \right) $$ O α s α . To study the phenomenological impact we consider the decay of the off-shell Z boson into a pair of neutrinos, and present kinematical distributions for the final-state leptons at LHC energies.

Abstract We compute the quark and gluon transverse momentum dependent parton distribution functions at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. Our calculation is based on an expansion of the differential Drell-Yan and gluon fusion Higgs production cross sections about their collinear limit. This method allows us to employ cutting edge multiloop techniques for the computation of cross sections to extract these universal building blocks of the collinear limit of QCD. The corresponding perturbative matching kernels for all channels are expressed in terms of simple harmonic polylogarithms up to weight five. As a byproduct, we confirm a previous computation of the soft function for transverse momentum factorization at N3LO. Our results are the last missing ingredient to extend the qT subtraction methods to N3LO and to obtain resummed qT spectra at N3LL′ accuracy both for gluon as well as for quark initiated processes.

Abstract We report on the first fully differential calculation of the next-to-next-to-leading-order (NNLO) QCD radiative corrections to the production of bottom-quark pairs at hadron colliders. The calculation is performed by using the qT subtraction formalism to handle and cancel infrared singularities in real and virtual contributions. The computation is implemented in the Matrix framework, thereby allowing us to efficiently compute arbitrary infrared-safe observables in the four-flavour scheme. We present selected predictions for bottom-quark production at the Tevatron and at the LHC at different collider energies, and we perform some comparisons with available experimental results. We find that the NNLO corrections are sizeable, typically of the order of 25–35%, and they lead to a significant reduction of the perturbative uncertainties. Therefore, their inclusion is crucial for an accurate theoretical description of this process.

Abstract We consider the production of a colourless system at next-to-leading order in the strong coupling constant $$\alpha _{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{S}}$$αS. We impose a transverse-momentum cutoff, $$q_{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{T}}^{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{cut}}$$qTcut, on the colourless final state and we compute the power corrections for the inclusive cross section in the cutoff, up to the fourth power. The study of the dependence of the cross section on $$q_{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{T}}^{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{cut}}$$qTcut allows for an understanding of its behaviour at the boundaries of the phase space, giving hints on the structure at all orders in $$\alpha _{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{S}}$$αS and on the identification of universal patterns. The knowledge of such power corrections is also a required ingredient in order to reduce the dependence on the transverse-momentum cutoff of the QCD cross sections at higher orders, when the $$q_{\mathrm{T}}$$qT-subtraction method is applied. We present analytic results for both Drell–Yan vector boson and Higgs boson production in gluon fusion and we illustrate a process-independent procedure for the calculation of the all-order power corrections in the cutoff. In order to show the impact of the power-correction terms, we present selected numerical results and discuss how the residual dependence on $$q_{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{T}}^{{\displaystyle } {\scriptstyle } {\scriptscriptstyle } {\scriptscriptstyle } \mathrm{cut}}$$qTcut affects the total cross section for Drell–Yan Z production and Higgs boson production via gluon fusion at the LHC.

La tesi si occupa delle correzioni di potenza calcolate su un parametro-soglia di momento trasverso che interessano calcoli perturbativi di ordine superiore nella costante di accoppiamento forte. In particolare, si impone un parametro-soglia di momento trasverso, qt_cut, su uno stato finale bianco e si calcolano le correzioni di potenza sul parametro-soglia, fino alla quarta potenza, per la sezione d'urto inclusiva al primo ordine sottodominante in QCD. Inoltre, si considera lo stesso processo al secondo ordine sottodominante in QCD, limitandosi al contributo reale-virtuale, e si calcolano le correzioni di potenza per la sezione d'urto inclusiva sino alla seconda potenza sul parametro-soglia. Lo studio della dipendenza della sezione d'urto dal parametro-soglia permette di approfondire il comportamento della prima nei limiti dello spazio delle fasi, dando indizi sulla struttura a tutti gli ordini nella costante di accoppiamento forte e sull'identificazione di caratteristiche universali. La conoscenza delle correzioni di potenza è poi un ingrediente fondamentale per ridurre la dipendenza delle sezioni d'urto di QCD dal parametro-soglia quando viene applicato un metodo slicing come la sottrazione-qt. Si presentano, quindi, risultati analitici per la produzione di un bosone vettore e per la produzione di un bosone di Higgs al primo ordine sottodominante in QCD, e per la parte reale-virtuale del canale qg per la produzione di un bosone vettore al secondo ordine. Nel dettaglio, si illustra una procedura generale per il calcolo delle correzioni di potenza sul parametro-soglia. Per mostrare l'impatto numerico di tali correzioni, si presentano dei risultati numerici e si discute di come la dipendenza residuale da qt_cut interessi la sezione d'urto totale della produzione di un bosone Z o di un bosone di Higgs presso LHC. La seconda parte della tesi, complementare alla prima, è dedicata allo sviluppo di un'interfaccia tra MadGraph5_aMC@NLO e POWHEG BOX, al fine di coniugare la flessibilità di MadGraph quando genera gli elementi di matrice per processi del Modello Standard o di sue estensioni, con tutte le caratteristiche di POWHEG BOX. Tra di esse, la possibilità di generare eventi con peso positivo è fondamentale e rende POWHEG uno dei metodi più usati quando sono necessari campioni molto numerosi. Al fine di testare l'interfaccia, si studia la produzione di un bosone di spin 0 assieme a due getti, con accoppiamenti che violano CP. Si discutono delle distribuzioni che caratterizzano le proprietà del bosone e alcuni risultati ottenuti con la funzione di ripesamento di POWHEG BOX. Infine, si presentano alcune distribuzioni ottenute con il metodo MiNLO.
The thesis deals with the power corrections in a transverse-momentum cutoff that affect perturbative calculations at higher orders in the strong coupling constant. In particular, we impose a transverse-momentum cutoff, qt_cut, on a colourless final state and we compute the power corrections for the inclusive QCD next-to-leading-order cross section in the cutoff, up to the fourth power. We also consider the same production process at next-to-next-to-leading order in QCD, restricting ourselves to the real-virtual contribution, and we compute the power corrections up to the second power in the cutoff for the inclusive cross section. The study of the dependence of the cross section on qt_cut allows for an understanding of its behaviour at the boundaries of the phase space, giving hints on the structure at all orders in the strong coupling constant and on the identification of universal patterns. The knowledge of such power corrections is also a required ingredient in order to reduce the dependence on the transverse-momentum cutoff of the QCD cross sections at higher orders, when the qt-subtraction method, i.e. a slicing scheme, is applied. We present analytic results for both Drell-Yan vector-boson and Higgs-boson production in gluon fusion at next-to-leading order in QCD, and for the real-virtual part of the qg-initiated channel of vector-boson production at NNLO in QCD. In particular, we illustrate a process-independent procedure for the calculation of the all-order power corrections in the cutoff. In order to show the impact of the power-correction terms, we present selected numerical results and discuss how the residual dependence on qt_cut affects the total cross section for Drell-Yan Z production and Higgs boson production via gluon fusion at the Large Hadron Collider. A second and complementary part of the thesis is devoted to the development of an interface between MadGraph5_aMC@NLO and the POWHEG BOX framework, in order to match the flexibility of MadGraph for the generation of matrix elements for Standard-Model processes and for several of its extensions, to all features of the POWHEG BOX framework. Among those, it is essential the possibility, via the POWHEG method, to generate events with positive weights, which makes it the method of choice when large samples of events are needed. As a proof of concept, we provide a phenomenological study for the production of a spin-0 Higgs-like boson, in association with up to two jets, with CP-violating couplings. We discuss a few distributions able to characterise the spin-0 boson CP properties, and discuss a few results obtained using the POWHEG BOX reweighting feature. We also present a few distributions obtained with the MiNLO method.