Measuring Multijet Structure of Hadronic Energy Flow Or What IS A Jet?

Ambiguities of jet algorithms are reinterpreted as instability wrt small variations of input. Optimal stability occurs for observables possessing property of calorimetric continuity (C-continuity) predetermined by kinematical structure of calorimetric detectors. The so-called C-correlators form a basic class of such observables and fit naturally into QFT framework, allowing systematic theoretical studies. A few rules generate other C-continuous observables. The resulting C-algebra correctly quantifies any feature of multijet structure such as the "number of jets" and mass spectra of "multijet substates". The new observables are physically equivalent to traditional ones but can be computed from final states bypassing jet algorithms which reemerge as a tool of approximate computation of C-observables from data with all ambiguities under analytical control and an optimal recombination criterion minimizing approximation errors.Comment: PostScript, 94 pp (US Letter), 18 PS files, [email protected]

Towards a standard jet definition

In a simulated measurement of the $W$-boson mass, evaluation of Fisher's information shows the optimal jet definition to be physically equivalent to the $k_\mathrm{T}$ algorithm while being much faster at large multiplicities.Comment: version to appear in Phys. Rev. Lett., 4 page

Semileptonic decays in the limit of a heavy daughter quark

The rate of the semileptonic decay b to c l v is calculated with order alphas^2 accuracy, as an expansion around the limit of equal masses of the b and c quarks. Recent results obtained around the limit of the c-quark much lighter than b are confirmed. Details of the new expansion method are described.Comment: 7 pages, 5 figure

Landau equations and asymptotic operation

The pinched/non-pinched classification of intersections of causal singularities of propagators in Minkowski space is reconsidered in the context of the theory of asymptotic operation as a first step towards extension of the latter to non-Euclidean asymptotic regimes. A highly visual distribution-theoretic technique of singular wave fronts is tailored to the needs of the theory of Feynman diagrams. Besides a simple derivation of the usual Landau equations in the case of the conventional singularities, the technique naturally extends to other types of singularities e.g. due to linear denominators in non-covariant gauges etc. As another application, the results of Euclidean asymptotic operation are extended to a class of quasi-Euclidean asymptotic regimes in Minkowski space.Comment: 15p PS (GSview), IJMP-A (accepted

Effective Field Theory Dimensional Regularization

A Lorentz-covariant regularization scheme for effective field theories with an arbitrary number of propagating heavy and light particles is given. This regularization scheme leaves the low-energy analytic structure of Greens functions intact and preserves all the symmetries of the underlying Lagrangian. The power divergences of regularized loop integrals are controlled by the low-energy kinematic variables. Simple diagrammatic rules are derived for the regularization of arbitrary one-loop graphs and the generalization to higher loops is discussed.Comment: 22 pages, 11 figures and 1 tabl

Weak antilocalization in HgTe quantum wells and topological surface states: Massive versus massless Dirac fermions

HgTe quantum wells and surfaces of three-dimensional topological insulators support Dirac fermions with a single-valley band dispersion. In the presence of disorder they experience weak antilocalization, which has been observed in recent transport experiments. In this work we conduct a comparative theoretical study of the weak antilocalization in HgTe quantum wells and topological surface states. The difference between these two single-valley systems comes from a finite band gap (effective Dirac mass) in HgTe quantum wells in contrast to gapless (massless) surface states in topological insulators. The finite effective Dirac mass implies a broken internal symmetry, leading to suppression of the weak antilocalization in HgTe quantum wells at times larger than certain t_M, inversely proportional to the Dirac mass. This corresponds to the opening of a relaxation gap 1/t_M in the Cooperon diffusion mode which we obtain from the Bethe-Salpeter equation including relevant spin degrees of freedom. We demonstrate that the relaxation gap exhibits an interesting nonmonotonic dependence on both carrier density and band gap, vanishing at a certain combination of these parameters. The weak-antilocalization conductivity reflects this nonmonotonic behavior which is unique to HgTe QWs and absent for topological surface states. On the other hand, the topological surface states exhibit specific weak-antilocalization magnetoconductivity in a parallel magnetic field due to their exponential decay in the bulk.Comment: 14 pages, 10 figures, version as publishe

ДОСВІД ВИКОРИСТАННЯ ЛАПАРОСКОПІЧНОГО ТРЕНАЖЕРА З МЕТОЮ ПОКРАЩЕННЯ ПРАКТИЧНИХ НАВИЧОК СТУДЕНТІВ-МЕДИКІВ

During the last years an exponential increase of technical equipment role is being observed in surgical practice. Minimally invasive surgical interventions are widely integrated and require specialists to acquire specific skills. Considering inconsistency between educational programs and modern tendencies, there is a need to create new training courses. The article describes experience of laparoscopic trainer box application for improving medical students’ practical skills, who had no laparoscopic experience in the past. Participants completed training course, consisting of seven exercises, on constructed by us laparoscopic box trainer. Assessment of skill improvement was performed, comparing participants’ results at the beginning and end of the course. All participants were able to successfully complete each of the seven laparoscopic exercises, with accomplishment of target level up to the last set. All students refined upon their results in the average from 1.6 to 4.65 times, depending on the exercise. Constructed in the clinic laparoscopic box trainer with the suite of exercises is useful and reasonable for effective increase of practical skills level and motivation of medical students. Early introducing future specialists with standards of mini-invasive surgery is an important part of their educational process and helps to create innovation oriented professional thinking.В останні роки спостерігається експоненціальне збільшення ролі технічного оснащення в практиці лікаря хірургічного профілю. Міні-інвазивні хірургічні втручання зазнають широкої інтеграції та потребують від спеціаліста оволодіння певними специфічними навичками. Враховуючи наявність невідповідності навчальних програм сучасним тенденціям, виникає необхідність створення нових навчальних курсів. У статті показано досвід використання лапароскопічного тренажера для покращення практичних навичок студентів-медиків, які не мали попереднього досвіду лапароскопічної хірургії. На сконструйованому нами бокс-тренажері учасники пройшли навчальний курс, що складається з семи вправ. Оцінка покращення навичок була здійснена шляхом порівняння результатів учасників на початку і в кінці проходження курсу. Всі учасники змогли успішно виконати вправи, з досягненням поставленого цільового рівня. Всі студенти після проходження курсу покращили свої результати в середньому від 1,6 до 4,65 раза, залежно від вправи (p<0,05). Використання самостійно сконструйованих лапароскопічних бокс-тренажерів з розробленим у клініці комплексом вправ є доцільним задля ефективного підвищення практичної підготовки і вмотивованості студентів-медиків. Раннє ознайомлення майбутніх спеціалістів із стандартами міні-інвазивної хірургії є важливою складовою навчального процесу і допомагає створити інноваційно орієнтоване професійне мислення

The resultant parameters of effective theory

This is the 4-th paper in the series devoted to a systematic study of the problem of mathematically correct formulation of the rules needed to manage an effective field theory. Here we consider the problem of constructing the full set of essential parameters in the case of the most general effective scattering theory containing no massless particles with spin J > 1/2. We perform the detailed classification of combinations of the Hamiltonian coupling constants and select those which appear in the expressions for renormalized S-matrix elements at a given loop order.Comment: 21 pages, 4 LaTeX figures, submitted to Phys. Rev.