Bound states of the s-wave Klein-Gordon equation with equal scalar and vector Standard Eckart Potential Eser Ol˘gar, Ramazan Koc¸,∗ and Hayriye Tu¨tu¨ncu¨ler† Department of Physics, Faculty of Engineering University of Gaziantep, 27310 Gaziantep, Turkey‡ (Dated: February 1, 2008) A supersymmetric technique for the bound-state solutions of the s-wave Klein–Gordon equation with equal scalar and vector standard Eckart type potential is proposed. Its exact solutions are obtained. Possible generalization of ourapproach is outlined. PACSnumbers: 03.65.Ge; 03.65.Pm 6 INTRODUCTION 0 0 2 Relativisticquantummechanicsisrequiredtoobtainmoreaccurateresultsfortheparticleunderastrongpotential field. Whenweconsiderthiscondition,aparticleinthestrongpotentialfieldshouldbedescribedbytheKlein–Gordon n a equationandtheDiracequation.[1,2] Inordertoanalyserelativisticeffects onthespectrumofsuchaphysicalsystem, J one may construct the Klein–Gordon equation including adequate potentials and obtains their solutions. In recent 3 years, there have been many discussions about the Klein–Gordon equation with various types of potentials by using 2 differentmethodstoobtainthespectrumofthesystem. Someauthorshaveconsideredtheequalityofscalarpotential andvectorpotentialinsolvingtheKlein–GordonequationaswellastheDiracequationsforsomepotentialfields.[3−7] 1 Thes-wavebound-statesolutionsareobtainedinRefs.[5-8]. Similarly,thes-waveKlein–Gordonequationwithvector v 2 potentialandscalarRosen-Morsetype potentials[9,10] hasbeentreatedbythestandardmethod,[11] thesameproblem 5 with both the vector and scalar Hulthen-type potentials have been discussed analytically.[12] Energy spectrum of the 1 s-wave Schr¨odinger equation with the generalized Hulthen potential has been obtained by using the supersymmetric 1 quantum mechanics (SUSYQM) and supersymmetric Wentzel–Kramers–Brillouin (WKB) approach.[13] The bound- 0 state spectra for some physical problems has been studied by the quantization condition and the SUSYQM.[14−16] 6 0 InthisLetter,weconstructaKlein–GordonequationincludingtheEckartpotential[17] whosespectrumcanexactly / bedetermined. ForthispurposewetransformtheKlein–GordonequationintheformoftheSchr¨odinger-likeequation, h becausetherearemanypaperstotackletheprobleminthe frameworkofSchr¨odingerequations. Theeigenvaluesand p - eigenfunctions of the Eckart potential are obtained in terms of the SUSYQM. t n a u SUSYQM APPROACH TO BOUND STATE SOLUTION q : v Generally, the s-wave Klein–Gordon equation with scalar potential S(r) and vector potential V(r) can be written i [12,17] (h¯ =1,c=1) X ar d2 +[E−V(r)]2−[M +S(r)]2 f(r)=0, (1) (cid:26)dr2 (cid:27) where E is the energy, and M is the mass of the particle. Indeed, the original wavefunction can be expressed as R(r)=f(r)/r. We consider the standard Eckart potential in the form V(r)=V sech2(αr)−V tanh(αr). (2) 1 2 When we consider the case that the vector potential and the scalar potential are equal, i.e. V(r) = S(r), Eq.(1) becomes a well-known Schr¨odinger equation d2 +(E2−M2)−2(E+M)[V sech2(αr)−V tanh(αr)] f(r)=0, (3) (cid:26)dr2 1 2 (cid:27) with the effective potential V (r)=2(E+M)[V sech2(αr)−V tanh(αr)]. (4) eff 1 2 2 Then Eq. (3) takes the form d2 − +V (r) f(r)=λf(r), (5) (cid:26) dr2 eff (cid:27) where λ=E2−M2 is the redefined energy parameter. In order to solve Eq. (5), in the frameworkof the SUSYQM, we introduce the following ground-state wave function f (r)=Nexp W(r)dr , (6) 0 (cid:20)Z (cid:21) where N is a normalization constant, and W(r) refers to a super-potential. Substituting Eq. (6) into Eq. (5), we obtain W2(r)−W′(r)=V (r)−λ , (7) eff 0 where λ is the ground-state energy, and Eq. (7) is a nonlinear Riccati equation which gives the wavefunction of the 0 system. Our task is now,to obtainthe super potentialW(r), whichis helpful to express the super partnerpotentialsV (r) + and V (r). After some straightforwardcalculation, we obtain the super potential W(r), which can be written as − W(r)=A−Btanh(αr), (8) where A and B are the constant coefficients. Notice that the result Eq. (8) shows that the problem can be treated in the framework of the SUSYQM. The super-symmetric partner potentials are given by V (r)=W2(r)±W′(r). (9) ± Substituting Eq. (8) into Eq. (9), we obtain the following partner potentials V (r) = A2+B2−B(B+α)sech2(αr)−2ABtanh(αr), (10a) + V (r) = A2+B2−B(B−α)sech2(αr)−2ABtanh(αr). (10b) − In order to obtain λ and the relations of A and B with V and V , we compare Eqs.(3), (7), (10a),and (10b). As a 0 1 2 consequence, one can easily obtain the following relations λ = A2+B2, (11a) 0 1 B = α± 8(E+M)V +α2 , (11b) 1 2 h p i 2(E+M)V 2 A = . (11c) α± 8(E+M)V +α2 1 p It is well known that the potentials are shape invariant., that is, V (r) has the same functional form as V (r) but + − different parameters except for an additive constant. shape invariant condition can be expressed as V (r,a )=V (r,a )+R(a ), (12) + 0 − 1 1) wherea anda representsthepotentialparametersinthesupersymmetricpartnerpotentials,andR(a )isaconstant. 0 1 1 This property permits an immediate analytical determination of eigenvalues and eigenfunctions. It is obvious that the potentials are invariant when the following conditions hold AB a = − , 0 α−B a = −α+B, 1 R(a ) = a2+a2−(A2+B2). 1 0 1 Thus, the energy eigenvalues of Hamiltonian which includes V (r) partner potential − d2 +V (r) are given by − dr2 − λ(−) = 0, (13) 0 AB 2 λ(−) = R(a )= − +(−αn+B)2−(A2+B2). (14) n k (cid:18) αn−B(cid:19) X 3 Therefore, the complete energy spectrum are obtained by 2 AB λ = λ(−)+λ = − +(−αn+B)2, n n 0 (cid:18) αn−B(cid:19) n = 1,2,3,···. (15) Substituting the values of coefficients A, B, and λ into Eq. (15), we obtain the required relativistic bound-state 0 energy spectrum (E +M)2V2 1 M2−E2 = n 2 +α2(n+δ)2, (16) n α2 (n+δ)2 where the parameters δ is defined by δ =−1 + 1 1+ 8(En+M)V1. 2 2q α2 The corresponding unnormalized ground-state wavefunction is determined by Eq. (6), f (r)=Nexp(−Ar)(cosh(αr))B/α. (17) 0 By using the parameters of A, B, and f (r), we obtain the wavefunction in the form 0 1 R (r)= [cosh(αr)](p+w)exp(α[w−p]r)), (18) 0 r where 1 2(E+M)V 1 2 p = n+δ+ , 2(cid:20) α2 n+δ(cid:21) 1 2(E+M)V 1 w = n+δ− 2 . 2(cid:20) α2 n+δ(cid:21) The unnormalized wavefunction of the related Hamiltonian can be obtained by a similar mathematical procedure presentedinRef.[11]. Byusingthis method, the wavefunctioncanbe expressedinterms ofthe Jacobipolynomialas 1 R(r)= [cosh(αr)](p+w)exp[α(w−p)r]×P−2p,−2w[−coth(αr)]. (19) r n This equation gives the required wavefunction of the standard Eckart potential with the Klein–Gordon equation. CONCLUSIONS In summary, we have discussed the exact solution of the Klein–Gordon equation including the equal scalar and vector Eckart potentials by using the SUSYQM. We have shown that both the eigenvalues and eigenfunctions of the Klein–Gordon equation can be obtained in the closed form for the Eckart potential. 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