# On geometry influence on the behavior of a quantum mechanical scalar particle with intrinsic structure in external magnetic and electric fields

###### Abstract

Relativistic theory of the Cox’s scalar not point-like particle with intrinsic structure is developed on the background of arbitrary curved space-time. It is shown that in the most general form, the extended Proca-like tensor first order system of equations contains non minimal interaction terms through electromagnetic tensor and Ricci tensor .

In relativistic Cox’s theory, the limiting procedure to non-relativistic approximation is performed in a special class of curved space-time models. This theory is specified in simple geometrical backgrounds: Euclid’s, Lobachevsky’s, and Riemann’s. Wave equation for the Cox’s particle is solved exactly in presence of external uniform magnetic and electric fields in the case of Minkowski space. Non-trivial additional structure of the particle modifies the frequency of a quantum oscillator arising effectively in presence if external magnetic field. Extension of these problems to the case of the hyperbolic Lobachevsky space is examined. In presence of the magnetic field, the quantum problem in radial variable has been solved exactly; the quantum motion in z-direction is described by 1-dimensional Schrödinger-like equation in an effective potential which turns out to be too difficult for analytical treatment. In the presence of electric field, the situation is similar. The same analysis has been performed for spherical Riemann space model.

O.V. Veko^{1}^{1}1Kalinkovichi Gymnasium,
Belarus,vekoolga@mail.ru, K.V. Kazmerchuk^{2}^{2}2Mosyr State
Pedagogical University, Belarus, kristinash2@mail.ru,
E.M. Ovsiyuk^{3}^{3}3Mosyr State Pedagogical University, Belarus, e.ovsiyuk@mail.ru,
V.V. Kisel^{4}^{4}4Belarusian State University of Informatics and
Radioelectronics,
V.M. Red’kov^{5}^{5}5B.I. Stepanov Institute of Physics, NAS of Belarus, redkov@dragon.bas-net.by

PACS numbers: 02.30.Gp, 02.40.Ky, 03.65Ge, 04.62.+v

MSC 2010: 33E30, 34B30

KeywordsIntrinsic structure, scalar particle, curved space-time, generalized Schrödinger equation, magnetic field, electric field, Minkowski, Lobachevsky, Riemann space models

## 1 Scalar Cox’s particle with intrinsic structure

In 1982 W. Cox [1] proposed a special wave equation for a scalar particle with a larger set of tensor components than the usual Proca’s approach includes: he used the set of a scalar, 4-vector, antisymmetric and (irreducible) symmetric tensor, thus starting with the 20-component wave function (see Section 13).

First, let us consider the system of Cox’s equations [1] in the Minkowski space. We will use a Proca-like generalized system obtained after elimination from the initial system of Cox’s equations two second-rank tensors (see Section 13):

(1.1) |

is a tensor inverse to ( stands for additional parameter responsible for non-trivia intrinsic structure of a scalar particle in Cox’s approach):

(1.2) |

are expressed through electromagnetic invariants (for more technical details see Section 13).

In geometrical models with metrics of special type one cap perform non-relativistic approximation and derive extended Schrödinger type equation (see Section 13):

(1.3) |

where the notation is used

It is a generalized Schrödinger equation for the particle with intrinsic structure.

In presence of a pure magnetic field, the above equation (1.3) takes a more simple form

(1.4) |

where the notation is used (let )

In presence of a pure electric field, the above equation (1.3) takes the form

(1.5) |

where

## 2 Cox’s particle in the magnetic field, Minkowski space

Let the homogeneous magnetic field be directed along the axis :

Recalculating the potential to cylindrical coordinates by the formulas

we obtain

(2.1) |

The metric tensor in these coordinates and field variables are determined by

(2.2) |

The Schrödinger equation for this case reads

where

below we will use the notation

We compute

(2.3) |

After using the substitution for the wave function

we get the radial Schrödinger equation

(2.4) |

By physical reasons parameter must be purely imaginary (see Section 13): ; so the radial equation reads

(2.5) |

With the use of notation equation (2.5) can be written as

(2.6) |

which coincides with the equation arising in the problem of the usual particle in the magnetic field. Its solutions are known. We present here only an expression for the energy spectrum

(2.7) |

from this after translating to ordinary units we obtain

(2.8) |

With the use of notation the formula for the energy levels can be written as

(2.9) |

Thus, the intrinsic structure of the Cox’s particle modifies the frequency of the quantum oscillator (in fact, this result was firstly produced in different formalism by Kisel [2]).

(2.10) |

## 3 Cox’s particle in the magnetic field in the Lobachevsky space

In a special (cylindrical) coordinate system in the Lobachevsky space, analogue of the uniform magnetic field is determined by the relations (we use dimensionless coordinate obtained by dividing on the curvature radius ):

(3.1) |

The wave equation in this case reads

(3.2) |

where

Below the notation is used:

We compute

After using the substitution for the wave function:

(3.4) |

the Schrödinger equation (3.2) gives (the function must be imaginary, )

(3.5) |

In this equation, the variables are separated:

(3.6) |

The radial equation for the function reads

(3.7) |

the equation for is (remember that )

## 4 Analysis of the equation in the variable

In equation (3), let us eliminate the first derivative term:

(4.1) |

Eq. (4.1) can be viewed as the Schrödinger equation in the effective potential field . The corresponding effective force is

(4.2) |

We find the points of local extremum: and the roots of a quadratic equation

(4.3) |

When considering the bound states (for motion in the variable ) we have . This means that the square root in (4.3) is an imaginary number. Consequently, the point of zero force (equilibrium points) except cannot exist. The situation is illustrated in the Fig. 1.

After the change of variables , the differential equation (4.1) reads

(4.4) |

Note that singular points are located outside the physical range of the variable. Further progress in analytical treatment of eq. (4.4) (with 5 singular points) is hardly possible.

## 5 Solution of the radial equation

Let us turn to the radial equation (3.7) for the function . It is solvable in hypergeometric functions – see more detail [4]. Below we will write done only final results on energy spectrum. There exist only finite series of bound states, defined by relations

(5.1) |

obeys the restriction
In usual units the last relation can be written as:

In the limit of vanishing curvature, we obtain the known result in the flat space

## 6 Cox’s particle in the electric field, Minkowski space

Schrödinger equation for Cox’s particle in the electric field has the form (see Section 13)

the notation is used:

Let us use cylindric coordinates

(6.2) |

First, we get (let it be )

(6.3) |

Next, we consider the Hamiltonian

(6.4) |

In explicit form, the extended Schrödinger equation looks as follows (to allow for the imaginary character of , we make formal change )

With the substitution and the notation

we get

(6.5) |

After separation of the variables ( stands for the separation constant) we derive

(6.6) |

where

In fact, (6.6) coincide with the well known equations for an ordinary particle in the uniform electric field. Equation in the variable looks as a one-dimensional Schrödinger equation in the potential of the form :

(6.7) |

The form of the curve says that any particle moving from the right must be reflected by this barrier in vicinity of the point (we assume that electric force acts in positive direction of the axis ).

Mathematic solutions of the equation (6.7) can be expressed in Airy function. Indeed, let us change the variable

let it be (for definiteness )

(6.8) |

then we arrive at the Airy equation

(6.9) |

to the turning point there corresponds the value .

Eq. (6.9) can be related to the Bessel equation. Indeed, let us introduce the variable

then Airy equation gives

Applying the substitution , we arrive at the Bessel equation [8]

(6.10) |

with two linearly independent solutions

(6.11) |

Thus, general solutions of Airy equation can be constructed as linear combinations of

where

and with the notation , one expresses two independent solutions of the Schrödinger equation as follows