دانلود کتاب Elementary Particles and Their Currents

The plan of the book is as follows. The first chapter contains a brief reviewof the elements of field theory, especially of the free fields. Apart from fixingconventions on the Lorentz metric and the like, a sophisticated reader will notlearn much by reading it. In Chapter 2 the currents are introduced in a generalway and the connection between current conservation and an invariance groupis illustrated with the classical case of the group of invariances of a Lagrangiancontaining two degenerate scalar fields the group SU2. Although this chapterdeals only with free fields we use throughout the LSZ technique for constructingone-particle states via the asymptotic condition. The formulas are then easilygeneralized to the interacting field case, and, in fact, the third chapter deals withSU2 in the context of interacting pion-nucleon fields. In the fourth chapter weturn on the electromagnetic field and study SU2 as a "broken symmetry."With Chapter 5 the real work of the book gets underway. Here we beginthe study of electron-proton scattering. As the reader will discover, there is adetailed analysis of the form factor structure of the matrix elements of thecurrents as they are limited by Lorentz, parity, time reversal, and charge conjugationinvariance. I have chosen to treat the latter symmetries here, ratherthan in the beginning of the book, since my own experience in reading textsis that it is more convenient to have a general concept and its concrete applicationsin close juxtaposition, whereas otherwise one tends to forget the formerbefore corning to grip with the latter. In Chapter 6 the experimental electronprotonsituation is treated in a preliminary way and it is here that we first meetthe vector mesons. Historically the existence of the vector mesons was firstconjectured to explain the electron-proton scattering data. Only later were thesemesons actually found. In the seventh chapter there is a brief discussion ofdispersion relations, which are introduced mainly to give a logical foundationto some of the formulas introduced in the previous chapters. I do not think thatdispersion relations "explain" anything in electron-proton scattering, but theydo provide a formalism for considering the structure of certain matrix elementsand for connecting one matrix element to another.The next five chapters deal with the weak interactions of nonstrange particles.The discussion divides naturally into the two parts of leptonic interactionsand semileptonic interactions. The former provide a perfect example ofthe present impasse in theoretical elementary particle physics. The theory, asis discussed in detail in the text, involves the coupling of currents to currentsand is in splendid agreement with experiment, but it suffers from an almostcomplete absence of logical foundation. Leptons do not have strong interactionsbut if we attempt to treat the current-current couplings in anything but lowestorderperturbation theory, we are bedeviled by infinities of the worst sort.Moreover, since the "weak photon" has not yet been observed, the basic roleof the currents must be regarded as mysterious.It should be emphasized that even if the weak vector meson is found, thiswill still leave open the mathematical problem of the structure of its theory,especially in higher orders. In fact, the success of the lowest-order theory issomething of a handicap since, so far, experiment has not given any guidanceon how to construct the full theory. These matters are discussed, in some detail,in Chapters 7 through 9.The semileptonic weak interactions, such as ordinary 0-decay, involveboth lepton and baryons in initial and final states. Because of this, semileptonicdecays combine aspects of both the strong and the weak interactions. Chapter10 treats the vector current part of the semileptonic coupling, which is given,as we shall see, by the isotopic vector part of the electromagnetic current. Thevector current is conserved so long as SU2 is an approximately valid symmetrygroup. In this chapter I review the consequences of this property of the current.Because the vector current can be identified with the isotopic spin currentone is spared the problem of the details of the strong couplings, since one maytake the unknown form factors in 0-decay matrix elements from electronprotonscattering experiments. However, with the axial vector current there isno such luck, and in Chapters 11 and 12 I review the various attempts at makingdynamical models for the axial current. I have included a selection of "proofs"of the Goldberger-Treiman relation and an introduction to the current algebraof SU2 X SU2. An exploitation of this algebra leads to the discovery of thecelebrated Adler-Weisberger sum role, which is derived in Chapter 12.The rest of the book deals with the weak and electromagnetic interactionsof strange particles. Chapter 13 is a general introduction to SU3, which nowappears to be the correct approximate symmetry group of the elementaryparticle Lagrangian. Chapter 14 contains a review of some of the calculationsusing naive quark models. Chapter 15 considers the Cabibbo theory of strangeparticle decays and some of the results of the SU3 X SU3 current algebra. Atthe very end of the book the reader will find a discussion of CP violation inthe K°, K° system