The causal approach to scalar QED via Duffin-Kemmer-Petiau equation

In this work we consider the scalar QED via Duffin-Kemmer-Petiau equation in the framework of Bogoliubov-Epstein-Glaser causal perturbation theory. We calculate the lowest order distributions for Compton scattering, vacuum polarization, the self energy and, by using a Ward identity, the vertex corre...

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Hauptverfasser: Lunardi, J.T., Manzoni, L.A., Pimentel, B.M., Valverde, J.S.
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spelling irk-123456789-794152015-04-02T03:02:10Z The causal approach to scalar QED via Duffin-Kemmer-Petiau equation Lunardi, J.T. Manzoni, L.A. Pimentel, B.M. Valverde, J.S. Quantum electrodynamics In this work we consider the scalar QED via Duffin-Kemmer-Petiau equation in the framework of Bogoliubov-Epstein-Glaser causal perturbation theory. We calculate the lowest order distributions for Compton scattering, vacuum polarization, the self energy and, by using a Ward identity, the vertex correction. The causal method provides a mathematically well defined and noneffective theory which determines, in a natural way, the propagator and the vertex of the usual effective theory. 2001 Article The causal approach to scalar QED via Duffin-Kemmer-Petiau equation / J.T. Lunardi, L.A. Manzoni, B.M. Pimentel, J.S. Valverde // Вопросы атомной науки и техники. — 2001. — № 6. — С. 25-29. — Бібліогр.: 13 назв. — англ. 1562-6016 PACS: 29.27.Hj 29.90. +r http://dspace.nbuv.gov.ua/handle/123456789/79415 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language English
topic Quantum electrodynamics
Quantum electrodynamics
spellingShingle Quantum electrodynamics
Quantum electrodynamics
Lunardi, J.T.
Manzoni, L.A.
Pimentel, B.M.
Valverde, J.S.
The causal approach to scalar QED via Duffin-Kemmer-Petiau equation
Вопросы атомной науки и техники
description In this work we consider the scalar QED via Duffin-Kemmer-Petiau equation in the framework of Bogoliubov-Epstein-Glaser causal perturbation theory. We calculate the lowest order distributions for Compton scattering, vacuum polarization, the self energy and, by using a Ward identity, the vertex correction. The causal method provides a mathematically well defined and noneffective theory which determines, in a natural way, the propagator and the vertex of the usual effective theory.
format Article
author Lunardi, J.T.
Manzoni, L.A.
Pimentel, B.M.
Valverde, J.S.
author_facet Lunardi, J.T.
Manzoni, L.A.
Pimentel, B.M.
Valverde, J.S.
author_sort Lunardi, J.T.
title The causal approach to scalar QED via Duffin-Kemmer-Petiau equation
title_short The causal approach to scalar QED via Duffin-Kemmer-Petiau equation
title_full The causal approach to scalar QED via Duffin-Kemmer-Petiau equation
title_fullStr The causal approach to scalar QED via Duffin-Kemmer-Petiau equation
title_full_unstemmed The causal approach to scalar QED via Duffin-Kemmer-Petiau equation
title_sort causal approach to scalar qed via duffin-kemmer-petiau equation
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
publishDate 2001
topic_facet Quantum electrodynamics
url http://dspace.nbuv.gov.ua/handle/123456789/79415
citation_txt The causal approach to scalar QED via Duffin-Kemmer-Petiau equation / J.T. Lunardi, L.A. Manzoni, B.M. Pimentel, J.S. Valverde // Вопросы атомной науки и техники. — 2001. — № 6. — С. 25-29. — Бібліогр.: 13 назв. — англ.
series Вопросы атомной науки и техники
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fulltext THE CAUSAL APPROACH TO SCALAR QED VIA DUFFIN-KEMMER-PETIAU EQUATION J.T. Lunardi*1, L.A. Manzoni2, B.M. Pimentel1 , J.S. Valverde1 1Instituto de Física Teórica, UNESP, Rua Pamplona 145, São Paulo, SP, Brazil 2Instituto de Física, USP, Caixa Postal 66318, São Paulo, SP, Brazil In this work we consider the scalar QED via Duffin-Kemmer-Petiau equation in the framework of Bogoliubov- Epstein-Glaser causal perturbation theory. We calculate the lowest order distributions for Compton scattering, vacu- um polarization, the self energy and, by using a Ward identity, the vertex correction. The causal method provides a mathematically well defined and noneffective theory which determines, in a natural way, the propagator and the ver- tex of the usual effective theory. PACS: 29.27.Hj 29.90. +r 1. INTRODUCTION∗ The usual way to approach scalar quantum electro- dynamics (SQED) is by performing the electromagnetic minimal coupling in the free Lagrangian of Klein-Gor- don (KG) scalar field theory [1]. An alternative way is to start from the free Duffin-Kemmer-Petiau (DKP) La- grangian instead of the KG one [2]. It is known that in the free field case the DKP and KG theories are equivalent, both in classical and quan- tum pictures [2,3,4]. However, there are still no general proofs of equivalence between these theories when inter- actions and decays of unstable particles are taken into account [5,6] (in this context see also references [7,8], which relate different results by using both DKP and KG formalisms with strong interactions). Some progress in this direction has been made recently. For instance, it was shown that this equivalence holds at the classical level when minimal interaction with electromagnetic [4,9] and gravitational [10] fields are present. Also, strict proofs of this equivalence were given for the quan- tized scalar field interacting with classical and quantized electromagnetic, Yang-Mills and external gravitational fields [6,11]. Perhaps the most evident advantages in working with DKP theory are the formal similarity with spinor QED, the fact that do not appear derivative couplings between DKP and the gauge field and that this theory allows an unified treatment of the scalar and vector fields. Despite this, the theory shares some difficulties with SQED based on KG one (SQED-KG), which are usually sur- passed by dealing with an effective theory [2,6]. In this work we shall consider SQED-DKP theory in the framework of Bogoliubov-Epstein-Glaser causal per- turbative method [12], which gives a mathematical rig- orous treatment of ultraviolet divergences in quantum  On leave from Departamento de Matematica e Estatistica, Universidad Estadual de Ponta Grossa, Ponta Grossa, PR, Brazil. field theory. Our goals are to obtain a non-effective and mathematically well defined theory for SQED-DKP, at the same time recovering the results of the effective the- ory already obtained in the usual perturbative approach. In addition, this work must be viewed as an initial step in the attempts to rigorously establish the renormaliz- ability of the theory. 2. THE DUFFIN-KEMMER-PETIAU THEO- RY The free DKP theory is given by the Lagrangian [2,4] ψψψβψ µ µ miL −∂= 2 , (1) where ψ is a multicomponent wave function, 0ηψψ += , and ( ) 12 200 −= βη . µβ are a set of matrices ( 3,2,1,0=µ ) satisfying the algebraic relations µ νρν ρµµνρρνµ ββββββββ gg +=+ . It is known that the above algebra has only three ir- reducible representations, whose degrees are 1, 5 and 10 [13]. The first one is trivial, having no physical content. The second and the third correspond, respectively, to scalar and vectorial representations. In this work we shall restrict us to the scalar case. The standard procedure of canonical quantization for the free lagrangian (1) gets [2] )(1)(),( yxS i yx abba −=    ++− ψψ and PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2001, № 6, p. 25-29. 25 )(1)(),( xyS i yx baba −−=    −+− ψψ , where −ψ and +ψ contains only annihilation and cre- ation operators, respectively, and ( )[ ] )(1 xmii m S ab def ab ±± ∆+∂/∂/= , (2) where )(x±∆ are the positive (negative) frequency parts of the Pauli-Jordan distribution +∆=∆ + )()( xx )(x−∆ . This later distribution has causal support [12] and can be written as )()()( xxx advret ∆−∆=∆ , where )(xret∆ and )(xadv∆ has, respectively, retarded and advanced sup- ports with respect to the point x . Analogously we de- fine )()()()()( xSxSxSxSxS advret def −=+= −+ (3) where again )()( xS advret have retarded (advanced) support with respect to x and it is defined by equation (2) just replacing ±∆ by )(advret∆ . The above splitting of )(xS into retarded and advanced parts is not the unique possible, as we will see in the next sections. The interaction with the electromagnetic field is in- troduced by the minimal substitution µµµ ieA−∂→∂ in the Lagrangian (1), which becomes IF LLL += , where =FL is the free lagrangian (1) and µ µ ψβψ AeLI ::= . (4) is the interaction lagrangian. In this work we use 0>e . 3. THE BOGOLIUBOV-EPSTEIN-GLASER APPROACH In the Bogoliubov-Epstein-Glaser causal method [12] the S -matrix is introduced as an operator-valued functional given by the perturbative series )()( ),,( ! 11)( 1 1 1 4 1 4 n n nnn xgxg xxTxdxd n gS  ∑ ∫ ∞ = ×+= , (5) where )(xg is a c-number test function supposed to be- long to the Schwartz space, ∈)(xg S4( 4R ). The sym- metric n -point functions }),,{()( 1 n def n xxXXT = are distributions written in terms of free fields and are the basic building blocks to be inductively constructed from the knowledge of )(1 xT by means of the requirements of causality )()()( 2121 gSgSggS =+ , if supp >1g supp 2g and translational invariance. The above causality condi- tion implies that ),,(),,(),,( 111 nmmnmmnn xxTxxTxxT  +−= , if },,{},,{ 11 nmm xxxx  +> ; (6) Based on general arguments such as correspondence [3], we have that )1( 1 IiLT = , where )1( IL is the term of first order in the coupling constant in the interaction La- grangian. The inductive procedure works as follows. From the assumption that all )(XTm , with 1−≤ nm , are known and satisfy (6), we can construct the distributions ∑ −= 2 11 ),()(~),,( 1 ' P nnnnnn xYTXTxxA  , (7) ∑ −= 2 11 )(~),(),,( 1 ' P nnnnnn XTxYTxxR  , (8) where 2P stands for all partitions ,{: 12 xP }, 1−nx = 0, /≠/∪ XYX into disjoint subsets with 1nX = 2−= ≤ nY . In these expressions )(~ XTn refers to the n -point distributions corresponding to a series for the 1−S -matrix analogous to (5), which can be obtained from the formal inversion of )(gS . If in the above ex- pressions the sums are extended in order to include the empty set 0/=X we get ),,(),,( ),()(~),,( 11 ' 1 0 2 11 nnnn P nnnnnn xxTxxA xYTXTxxA   += = ∑ − (9) ),,(),,( )(~),(),,( 11 ' 1 0 2 11 nnnn P nnnnnn xxTxxR XTxYTxxR   += = ∑ − (10) where now 0 2P stands for all partitions ,,{: 1 0 2 xP YXxn ∪=− }1 . A glance at Eqs. (9) and (10) shows that nA and nR are not known because they contain the un- known nT . However, the distribution defined by '' 1 ),,( nnnn def nn ARARxxD −=−= (11) 26 is known. It can be proved that the supports of nR and nA are retarded and advanced with respect to nx , respectively. Then, nD has a causal support with re- spect to this point, i.e., supp )()(),( nnnnnn xxxXD −+ Γ∪Γ⊆ , After splitting nD into its advanced and retarded parts we can obtain nT from the relations (9) or (10). The above splitting is the nontrivial step of the in- ductive procedure. In dealing with this problem we need only to consider the numerical distribution d associated with nD (i.e., we neglect the operator field distributions that appear as factors in the causal distribution nD ). Then, we write ard −= , where r and a are respec- tively the associated retarded and advanced numerical distributions. To solve the splitting problem we must de- termine the singular order ω of a distribution. We have to consider two distinct cases: i) 0<ω - in this case the solution of the splitting problem is unique and the r and a distributions can be found by multiplication of d by step functions; ii) 0≥ω - now the solution can be no longer obtained by multiplying d by step functions and, after a careful mathematical treatment, it may be shown that the retarded distribution (which suffices to deter- mine nT ) is given, in momentum space, by the central splitting solution ∫ + ∞ ∞− + +−− = )01()0( )(ˆ 2 )(ˆ 1 itit tpddtipr ωπ , (12) where the symbol ^ denotes the Fourier transform. How- ever, in contrast with the case 0<ω , this expression does not give a unique solution for the splitting problem. By assuming that the splitting procedure cannot raise the singular order of d , it can be shown that the general so- lution in momentum space is given by ∑ = += ω 0 )(ˆ)(~ a a a pCprpr , (13) where the aC are constant coefficients which are not fixed by the causal structure - we need additional physi- cal conditions in order to determine them. We now apply the inductive steps above to construct the two point distributions for SQED-DKP theory. Looking for (4) we see that the one-point distribution for the DKP field interacting with electromagnetic field is given by )(:)()(:)(1 xAxxiexT µ µ ψβψ= , where e is the physical charge. To go from 1=n to 2=n we con- struct the distribution ),( 212 xxD , which in this case is given by )](),([),( 2111212 xTxTxxD = :)(:)(::)()({: 1122 2 xxxxe ψβψψβψ µν= (14) )()(:})()(::)()(: 212211 xAxAxxxx νµ νµ ψβψψβψ− We can verify explicitly that this distribution is causal from the fact that 0)](),([ 2111 =xTxT if 0)( 2 21 <− xx . 4. APPLICATIONS We now apply the formalism sketched above to de- termine some lowest order processes in SQED, namely the Compton scattering, vacuum polarization, self-ener- gy of the scalar particle and the vertex correction at the limit of zero transferred momentum. 4.1. COMPTON SCATTERING By using Wick's theorem [12] we normally expand (14) and keep only those terms contributing to Compton scattering, given by )(:)()(: :)()(:),( 2121 21 2 212 xxSxAxA xxiexxD bc dacdab I − ×ψψββ= νµ νµ (15) )}({:)()(: :)()(:),( 1221 21 2 21 xxSxAxA xxiexxD da cbcdab II −− ×ψψββ= νµ νµ (16) In both these terms, the numerical distribution we have to split is )(xS , which is causal. Thus, a splitting solution is trivially obtained from (3). But it can be shown that )(xS has singular order 0=ω , which im- plies that this splitting is not unique. The general solu- tion for the numerical retarded distribution in configura- tion space is )()()(~ xCxSxr ret δ+= , where C is an ar- bitrary constant. The general result for the numerical distribution ),( 21 xxt I is )()(),( 212121 xxCxxSxxt FI −+−−= δ , (17) where we have defined )()()( 1 xmiixS F m def F ∆+∂/∂/−=− ( )(xF∆ is the usual scalar Feynman propagator). In a similar way we find +−−= )(),( 1221 xxSxxt FII )(' 12 xxC −δ . The condition of charge conjugation in- variance of the theory requires that 'CC = . The gauge invariance requirement yields m IC = , where I is the 5 × 5 identity matrix. Turning this result into (17) we ob- tain ),()(),( 122121 xxtxxTxxt IICI =−−= , (18) where we have defined )()()( 1 xxSxT m FC δ−≡ . It is straightforward to see that this distribution is the Green function for DKP equation, i. e., )()()( xxTmi C δ=−∂/ . So, in this sense the causal approach gives, in a natural ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2000, №2. Серия: Ядерно-физические исследования (36), с. 3-6. 27 way, the correct effective propagator for the DKP scalar particle, which agrees with the results of [2,6]. 4.2. VACUUM POLARIZATION Considering now those terms contributing to vacuum polarization we have :)()(:)}()({),( 21212 xAxAyPyPxxDVac νµ ν µµ ν −−= (19) where 21 xxy def −= and ×−= µµ ν β{)( 2TreyP def )}()( ySyS −−+ νβ . It turns out that the expression into curl brackets in the above expression is the numerical distribution we have to split, which have singular order 2=ω . Using the central splitting formula (12) to deter- mine its retarded part )(ˆ kr we can determine the corre- sponding numerical distribution )(ˆ kt . The final result for the complete two-point distribution for the vacuum polarization in configuration space is given by :)()()(:),( 2211212 xAxxxAixxT Vac ν µ ν µ −Π−= , where )(ˆ 2 1)(ˆ 24 kg k kkk Π        −=Π µ ν νµ µ ν π ; 2/32 4 2 4 2 41 )0( 1 12 )(ˆ 2     − +− =Π ∫ ∞ s m isks dskek m . However, from the fact that the singular order of the distribution we had to split was 2=ω , the above result is not unique. The most general solution is given by 2 20)(ˆ)(~ kCkCCkk +++Π=Π µ µ , where the normaliza- tion constants 0C , µC and 2C are not determined by causality, but from the requirements of parity invariance, zero mass for the gauge field, and the identification of e with the physical charge. These conditions imply that 020 === CCC µ . 4.3. SELF-ENERGY AND VERTEX CORRECTION Now, the terms in (14) contributing to the scalar self- energy are )()([)(:),( 120211 2 21 xxDxxSxexxD self I −−−= +−µβψ :)()]()( 221021 xxxDxxS ψβ−−+ µ ++ ; (20) )()([)(:)( 120122 2 2,1 xxDxxSxexxD self II −−= ++µβψ :)()]()( 121012 xxxDxxS ψβ−−+ µ +− . (21) The numerical distributions we have to split are the terms into brackets, which have singular order 1=ω . The final general solution, involving two arbitrary con- stants, is given by :)()()(:),( 2211 2 21 xxxxiexxT self I ψψ −Σ= :)()()(: 1122 2 xxxxie ψ−Σψ+ (22) where ( )[ ]{ 222 4 2 1log )2(4 )(ˆ mpibiep −−−=Σ π θ π ×     /++/−           −/+     − pCC b p b p b m 10242 2 11 2 11 . (23) By considering the complete propagator for the scalar particle and by requiring its normalized mass to be m , we find that these constants satisfy the condition      −= 10 2 1 CmC , which can be used to eliminate one of them, say 0C . The remaining constant 1C is related to another one, which appears in the splitting of the vertex causal distri- bution, by the following Ward identity )(ˆ )2( 1),(ˆ 2 p p pp Σ ∂ ∂=Λ µ µ π , (24) where µΛ is the vertex numerical distribution. Substi- tuting the explicit form of the self-energy (23) into this identity we obtain ( )[ ]{ 222 6 2 1log )2(4 ),(ˆ mpibiepp −−−=Λ π θ π µ ×              −+     /+ 424 11 2 12 bmb p mb p µµ β    +     −    −− − + 2 2 22 11)1( 1 1..2 b mbi b VP m p π δ µ     +−/+        −/ µ µµ β β 12424 2 11 2 C bbm pp b p (25) This result is well defined at 0=p , but it is singular on mass shell 22 mp = due to the logarithmic term. The above form of the vertex function suffices to study the physical meaning of the constant 1C , which is done in 28 connection to charge normalization. The physical charge is defined in the scattering of a scalar particle by an ex- ternal electromagnetic field at low energies. Thus we must consider the contributions to S matrix (in the limit of zero transferred momentum) from the terms contain- ing 1C in both the self-energy and vertex distributions. Because of the above mentioned mass shell singularity, we must be care in taking the adiabatic limit. Making so, we can prove that all these contributions cancel them- selves and conclude that this constant has no physical meaning. Nevertheless it can be specified by requiring the vertex function to satisfy the central splitting condi- tion, i.e., )0,0(ˆ µΛ . Using this condition into (25) we ob- tain 4 1 1 =C . 5. CONCLUSIONS AND FINAL REMARKS In this work we considered SQED-DKP theory in the framework of Bogoliubov-Epstein-Glaser causal method. The starting point was the identification of the one point distribution )(1 xT , which was determined by the interaction Lagrangian (4) written in terms of free fields. The causal method thus dictated completely the form of the interaction, giving us a non-effective and mathematically well-defined theory. In calculating the two-point distribution for Compton scattering, and by using the requirements of charge conjugation and gauge invariance, we recovered in a natural way the scalar propagator of the DKP usual effective theory. At one loop level we calculate the vacuum polarization, the scalar self-energy and the vertex correction in the limit of zero transferred momentum. We determined the phys- ically meaningful normalization constants by using physical requirements, as charge and mass normaliza- tion, parity and gauge invariance. All our results agree with those obtained in the context of the effective SQED-DKP theory as well as in the context of SQED- KG, what corroborates the belief about the equivalence of KG and DKP theories. A complete analysis at one loop level, as well as the study of the renormalizability of the theory, is in course. As future perspectives we can quote the use of the causal approach to study DKP field interacting with external fields. ACKNOWLEDGMENT J.T.L. and B.M.P. thank respectively to CAPES- PICDT and CNPq for partial support. L.A.M. and J.S.V. thank FAPESP for full support. REFERENCES 1. C. Itzykson and J. B. Zuber. Quantum Field Theory. Singapore: Mc-Graw Hill, 1980. 2. A. I. Akhiezer and V. B. Berestetskii. Quantum Electrodynamics. New York: Interscience, 1965. 3. N. N. Bogoliubov and D. V. Shirkov. Introduction to the Theory of Quantized Fields. New York: Wi- ley, 1980. 4. J. T. Lunardi, B. M.Pimentel, R. G. Teixeira and J. S. Valverde. Remarks on Duffin-Kemmer-Petiau the- ory and gauge invariance // Phys. Lett. A, 2000, v. 268, p. 165-173. 5. R. A. Krajcik and M. M. Nieto. Historical develop- ment of the Bhabha first order relativistic wave equations for arbitrary spin // Am. J. Phys. 1977, v. 45, p. 818-822. 6. V. Ya. Fainberg and B. M. Pimentel. On equivalence of Duffin-Kemmer-Petiau and Klein-Gordon equa- tions // Theor. Math. Phys. 2000, v. 124, p. 1234-1249. 7. B. C. Clark, S. Hama, G. R. 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A. 2000, v. 271, p. 16-25. 12.G. Scharf. Finite Quantum Electrodynamics: the Causal Approach. Berlin: Springer, 2nd ed., 1995. 13.J. Géhéniau // Acad. R. Belg. Cl. Sci. Mém. Collect 8, 1938, v. 18, №1, p. 15-19. ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2000, №2. Серия: Ядерно-физические исследования (36), с. 3-6. 29 J.T. Lunardi*1, L.A. Manzoni2, B.M. Pimentel1 , J.S. Valverde1 1Instituto de Física Teórica, UNESP, Rua Pamplona 145, São Paulo, SP, Brazil 2Instituto de Física, USP, Caixa Postal 66318, São Paulo, SP, Brazil PACS: 29.27.Hj 29.90. +r 1. INTRODUCTION 2. THE DUFFIN-KEMMER-PETIAU THEORY 3. THE BOGOLIUBOV-EPSTEIN-GLASER APPROACH acknowledgment REFERENCES