اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSome Basic Concepts of Perturbative QCD
142
0
0.0
(
0
)
تأليف
George Sterman
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
This is a brief review of some of the basic concepts of perturbative QCD, including infrared safety and factorization, relating them to more familiar ideas from quantum mechanics and relativity. It is intended to offer perspective on methods and terms whose use is commonplace, but whose physical origins are sometimes obscure.
قيم البحث
اقرأ أيضاً
Basic aspects of phononless resonant capture of monoenergetic electron antineutrinos (Moessbauer antineutrinos) emitted in boundstate beta-decay in the 3H - 3He system are considered. It is shown that stochastic magnetic relaxation phenomena as well
as the direct influence of solid-state effects on the energy of the electron antineutrino will cause line broadening by a factor of more than 10^(13). Lattice expansion and contraction after the transformation of the nucleus will drastically reduce the probability for phononless transitions. Thus, the observation of Moessbauer electron antineutrinos of the 3H - 3He system will most probably be unsuccessful. As a possible alternative, the Rare-Earth system 163Ho - 163Dy is briefly discussed.
What is a complex network? How do we characterize complex networks? Which systems can be studied from a network approach? In this text, we motivate the use of complex networks to study and understand a broad panoply of systems, ranging from physics a
nd biology to economy and sociology. Using basic tools from statistical physics, we will characterize the main types of networks found in nature. Moreover, the most recent trends in network research will be briefly discussed.
This tutorial outlines the basic theoretical concepts and tools which underpin the fundamentals of phase-coherent electron transport through single molecules. The key quantity of interest is the transmission coefficient T(E), which yields the electri
cal conductance, current-voltage relations, the thermopower S and the thermoelectric figure of merit ZT of single-molecule devices. Since T(E) is strongly affected by quantum interference (QI), three manifestations of QI in single-molecules are discussed, namely Mach-Zehnder interferometry, Breit-Wigner resonances and Fano resonances. A simple MATLAB code is provided, which allows the novice reader to explore QI in multi-branched structures described by a tight-binding (Huckel) Hamiltonian. More generally, the strengths and limitations of materials-specific transport modelling based on density functional theory are discussed.
We discuss some problems concerning the application of perturbative QCD to high energy processes. In particular for hard processes, we analyze higher order and higher twist corrections. It is argued that these effects are of great importance for unde
rstanding the behaviour of pion electromagnetic form factor at moderately large momentum transfers. For soft processes, we show that summing the contributions of the lowest twist operators leads to a Regge-like amplitude.
The predictive power of perturbative QCD (pQCD) depends on two important issues: (1) how to eliminate the renormalization scheme-and-scale ambiguities at fixed order, and (2) how to reliably estimate the contributions of unknown higher-order terms us
ing information from the known pQCD series. The Principle of Maximum Conformality (PMC) satisfies all of the principles of the renormalization group and eliminates the scheme-and-scale ambiguities by the recursive use of the renormalization group equation to determine the scale of the QCD running coupling $alpha_s$ at each order. Moreover, the resulting PMC predictions are independent of the choice of the renormalization scheme, satisfying the key principle of renormalization group invariance. In this letter, we show that by using the conformal series derived using the PMC single-scale procedure, in combination with the Pade Approximation Approach (PAA), one can achieve quantitatively useful estimates for the unknown higher-order terms from the known perturbative series. We illustrate this procedure for three hadronic observables $R_{e^+e^-}$, $R_{tau}$, and $Gamma(H to b bar{b})$ which are each known to 4 loops in pQCD. We show that if the PMC prediction for the conformal series for an observable (of leading order $alpha_s^p$) has been determined at order $alpha^n_s$, then the $[N/M]=[0/n-p]$ Pade series provides quantitatively useful predictions for the higher-order terms. We also show that the PMC + PAA predictions agree at all orders with the fundamental, scheme-independent Generalized Crewther relations which connect observables, such as deep inelastic neutrino-nucleon scattering, to hadronic $e^+e^-$ annihilation. Thus, by using the combination of the PMC series and the Pade method, the predictive power of pQCD theory can be greatly improved.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
