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A less formal approach to kaluza-klein formalism
Authors:M A McKiernan
Institution:(1) University of Waterloo, Waterloo, Ont., Canada
Abstract:The lsquoactionrsquo integrals (a) 
$$\lambda (\tau _1 ) = \int\limits_{\tau _0 }^{\tau _1 } {\surd g_{ij} \dot y^i \dot y^j d\tau } $$
and 
$$\lambda (\tau _1 ) = \int\limits_{\tau _0 }^{\tau _1 } {\{ \surd h_{ij} \dot x^i \dot x^j  - B_i \dot y^i \} d\tau } $$
, corresponding respectively to gravitational and gravitational-electromagnetic phenomena, are shown to be related under continuous groups of null translations. This relation motivates a modified Kaluza—Klein formalism for which the classical cylindrical metric preserving transformations (c)y 5 = =x 5 +f 5(x j ),y i =f i (x j ) fori = 1, 2, 3, 4 are replaced by (d)y 5 =x 5,y i =f i (x j ,x 5). The cylindrical metric of V5 is nevertheless preserved under (d), since it is assumed thatV 5 admits a metric of the form 
$$(\dot y^5 )^2  - g_{ij} (y^k )\dot y^i \dot y^j $$
(corresponding to (a)) and that (d) defines a continuous group of null translations in theV 4 metric defined byg ij whenx 5 is considered the group parameter. Application of (d) leads to the cylindrical metric 
$$(\dot x^5  + B_i \dot x^i )^2  - h_{ij} \dot x^i \dot x^j $$
corresponding to (b). The resulting electromagnetic fieldsF ij =B i,j B j,i are then related to the curvatures of theV 4 corresponding tog ij andh ij ; in particular it is shown that 
$$B_i B_j \mathop R\limits_g ^{ij}  =  - \tfrac{1}{4}F_{ij} F^{ij} $$
and 
$$F_{,j}^{ij}  = B_j \mathop R\limits_g ^{ij} $$
. When 
$$\mathop {R_{ij} }\limits_g  = 0$$
it is shown thatF ij is a null electromagnetic field which is generally non-trivial. Some physical and geometric interpretations of the mathematical results are also presented.Dedicated to Professor A. Ostrowski on the occasion of his 75th birthday
Keywords:
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