# Emergence of the Dirac equation in the solitonic

source of the Kerr spinning particle

###### Abstract

Gravitational and electromagnetic (EM) field of the Dirac electron is described by the Kerr-Newman (KN) solution. We elaborate a regular source of the KN solution which satisfies the requirement of flat space-time inside the source and realization of the exact KN solution outside the source. This requirement removes conflict between gravity and quantum theory and determines many details of the source structure. In particular, we obtain that the KN source should forms a gravitating bag model, similar to the known MIT and SLAC bag models. As opposite to the known bag models, the self-interacting Higgs field should be confined inside the bag, while outside the bag the gauge symmetry should be unbroken to provide the external KN gravity. We show that twistorial structure of the Kerr geometry (the Kerr theorem) determines structure of the Dirac equation, resulting in a variable mass term, which is generated inside the bag through interaction with the confined Higgs field. Similar to the other bag models, ellipsoidal deformations of the KN bag creates a string-like structure of the dressed electron – circular string positioned along perimeter of the KN bag.

## 1 Introduction

It has been discussed for long time that black holes (BH) have to be related with elementary particles [1]. However, spin and charge of particles prevent formation of the BH horizons. A BH looses the horizons if the charge or spin parameter exceeds the mass (in the dimensionless units ). For example, the electron charge exceeds the mass for 21 order, while its spin/mass ratio is about , and the BH threshold is exceeded for orders. Similar relations are valid for the other elementary particles, and besides the Higgs boson, which has neither spin nor charge, none of the elementary particles may be associated with a black hole. Meanwhile, it does not means that it concerns the over-rotating BH geometry without horizons.

As it was shown by Carter [2], the Kerr-Newman rotating BH solution has gyromagnetic ratio as that of the Dirac electron, and the four measurable parameters of the electron: spin, mass, charge and magnetic moment shows unambiguously that gravitational and electromagnetic field of the electron should correspond to over-rotating Kerr-Newman (KN) solution. The corresponding space has topological defect – the naked Kerr singular ring, which forms a branch line of space into two sheets: the sheet of advanced and sheet of the retarded fields. The Kerr-Schild form of metric

(1) |

in which is metric of
auxiliary Minkowski space and is a null vector
field, forming the Principal Null Congruence
(PNC) ^{1}^{1}1We use signature . These retarded
and advanced sheets are related by analytic transfer of the PNC
via disk spanned by the Kerr singular ring (see fig.1). So far as is the Kerr ellipsoidal
radial coordinate, the surface represents a disklike ”door”
from negative sheet to positive one . The null vector
fields differ on these sheets, and form the
different null congruences creating different
metrics

(2) |

on the same Minkowski background This mysterious twosheetedness caused search for different models of the source of Kerr geometry without negative sheet.

Singular metric conflicts with basic principles of quantum theory which is settled on the flat space-time and negligible gravitation. Resolution of this conflict requires ”regularization” of space-time, which has to be done before quantization, i.e. on the classical level. Singular region has to be excised and replaced by a regular core with a flat internal metric matching with external KN solution. Long-term search for the models of regular source (H. Keres (1966), W. Israel (I970), V. Hamity (1976), C. López (1984) at al.) [3, 4, 5, 6] resulted in appearance of the gravitating soliton model [7] which represents a domain-wall bubble, or a bag confining the Higgs field in a superconducting false-vacuum state. Such a matter regulates the KN electromagnetic (EM) field pushing it from interior of the bag to domain wall boundary and results in the consistency with flat internal metric required by Quantum theory. The Higgs mechanism of broken symmetry approaches this model with the known models of MIT- and SLAC- bags, and with the Coleman Q-ball models [8, 9], considered as electroweak soliton models in [10, 11, 12]. The used in MIT- and SLAC- bag models quartic potential for the self-interacting Higgs field ,

(3) |

describes a spontaneously broken theory, in which vacuum expectation value (vev) of the Higgs field vanishes inside the bag, and takes nonvanishing value outside the bag, The Dirac equation of the SLAC -bag theory in the presence of the classical -field takes the form

(4) |

where is a dimensionless coupling parameter. This expression shows that the Dirac field acquires effective mass from the vev of Higgs field . Inside the bag the Dirac field is massless, while outside the bag the wave function may acquire large mass The quarks are confined, preferring a more favorable energetic position inside the bag, which is the principal idea of the confinement mechanism.

## 2 Supersymmetric phase transition and formation of false-vacuum bubble.

Such a structure of the broken symmetry is not appropriate for the gravitating KN soliton model, since the vev of Higgs field breaks also the gauge symmetry the gravitational and electromagnetic (EM) external KN fields, turning them into short-range ones. An opposite (dual) geometry is realized in the Coleman’s Q-ball models [8, 9], in which the Higgs field is confined inside the ball, and the external vacuum state is unbroken. However, formation of the corresponding potential turns out to be a very non-trivial problem, and we have showed in [7] that this type of broken symmetry may be obtained by using a supersymmetric scheme of phase transition containing the three chiral fields [22]. One of this fields, say has the required radial dependence, and we chose it as the Higgs field setting the additional notations in accord with

(5) |

The required potential

(6) |

is obtained from the superpotential (suggested by J.Morris in [23])

(7) |

where are real constants. The condition

(8) |

determines two vacuum states separated by a spike of the potential at :

(I) external vacuum, , with vanishing Higgs field , and

(II) internal vacuum state, , which is indeed a false vacuum state, since the Higgs field is not vanish, and therefore symmetry is broken.

Domain wall boundary of the phase transition between the states (I) and (II) is determined by matching the external KN metric where

(9) |

with flat internal metric It fixes the boundary at or Since is the Kerr oblate coordinate, the bag forms an oblate disk of the radius with thickness so that

## 3 Advanced fields and two sheets outside the KN source.

The KN solution may be represented in the Kerr-Schild (KS) form via the both Kerr congruences or but not via the both ones simultaneously, [17, 18]. Vector potential of the KN solution is also to be aligned with the Kerr congruence, and by the use of or congruence, it turns out to be either retarded, , or advanced, For the physical sheet of the KN solution we chose the outgoing Kerr congruence corresponding to the retarded EM field The fields and cannot reside on the same physical sheet, because each of them should be aligned with the corresponding Kerr congruence. Considering the retarded sheet as a basic physical sheet, we fix the congruence and the corresponding metric , which are not allowed for the advanced field The field is to be compatible with another congruence positioned on the separate sheet which different metric . It should be emphasized, that this problem disappears inside the bag, where and the space is flat, and the difference between two metrics disappears. Therefore, the regulated KN space-time takes the twosheeted structure outside the bag, as it is illustrated on Fig.2.

We obtain that removing the twosheetedness related with the source of KN solution, we meet it
again from another side related with advanced potentials outside the regulated bag-like source of KN solution.
^{2}^{2}2Following Dirac and Feynman [15, 16], the
retarded potentials can be split into a half-sum and half-difference
with advanced ones with setting correspondence of the half-difference
with radiation reaction and the half-sum with a self-interaction of the source.
We discuss here this new effect in details, because it turns out to be related with solutions of
the Dirac equation on the KS background.

The Kerr congruences are determined by the Kerr theorem, [19, 20, 21, 14], which presents for the KN solution two different congruences [13, 14]. The considered in sec.1 twosheeted structure of the source was related with one of the congruences, The second sheet of metric was created by analytic extension of this congruence to negative sheet of the KN solution corresponding to The considered now twosheeted structure has another origin. The two congruences are now related with two different solutions of the Kerr theorem.

## 4 The Kerr theorem

Kerr theorem determines all the geodesic and shear free congruences as analytical solutions of the equation

(10) |

where is an arbitrary holomorphic function of the projective twistor variables

(11) |

where are null Cartesian coordinates of the auxiliary Minkowski space.

We notice, that the first twistor coordinate is also a projective spinor coordinate

(12) |

and it is equivalent to two-component Weyl spinor which defines the null direction^{3}^{3}3We use the spinor notations
of the book [22], where the -matrixes has the form
and
.

It is known, [19, 13, 14], that function for the Kerr and KN solutions may be represented in the quadratic in form,

(13) |

In this case (10) can explicitly be solved, leading to two solutions

(14) |

where It has been shown in [14], that these solutions are antipodally conjugate,

(15) |

Therefore, the solutions (14) determine two Weyl spinor fields and , which in agreement with (15) are related with two antipodal congruences

(16) |

(17) |

In the Debney-Kerr-Schild (DKS) formalism [19] function is also a projective angular coordinate It gives to spinor fields and an explicit dependence on the Kerr angular coordinates and

For the congruence this dependence takes the form

(18) |

In agreement with (15) we have and from the Lorentz invariant normalization we obtain which yields

(19) |

These massless spinor fields can be connected to the left-handed and right-handed congruence, and only one of them, say “left”, is “retarded” and corresponds to the external KN solution. In DKS formalism, the vector field is determined by the differential form

(20) |

where may be considered as a normalizing factor for the time-like component , Antipodal map (15) transforms the normalized field in the field which retains the time-like direction and reflects the space orientation. Therefore, the spinor fields created by the Kerr theorem and correspond to the left out-field and right-in fields, i.e. to the retarded and advanced fields correspondingly.

## 5 Dirac equation and two solutions of the Kerr theorem.

The KN solution belongs to the class of algebraically special Kerr-Schild (KS) solutions, for which all the tensor quantities are to be aligned with null directions of the Kerr congruence In means that the consistent solutions of the Dirac equation on the KS background should be aligned with the Kerr congruence. It has been showed in [24] that the Dirac field aligned with KS background should satisfy the linearized Dirac equations

(21) |

in which gravity drops out. For the Dirac bispinor the alignment conditions turn into equations for eigenfunctions of the helicity operator [25],

(22) |

and one sees that the spinor fields and have opposite helicity, forming the ”left-handed” and ”right-handed” helicity states, aligned with out-going direction and in-going direction correspondingly. In Kerr geometry, these fields should be placed on different sheets corresponding to two antipodal congruences obtained from the Kerr theorem. Authors of the paper [24] concluded that these solutions “are not consistent unless the mass vanishes…”. Indeed, the left-handed part of the Dirac equation is aligned with physical sheet of the KN geometry, while the right-handed parts is aligned with the second sheet obtained under parity inversion of the Kerr null congruence. For the zero mass, the left- and right-hand parts of the Dirac equations decouple, leading to solutions with opposite helicity which are consistent with different sheets of the KN geometry. In the same time, the both null congruences coexist without conflict on the flat space-time, where the massive Dirac equation is consistent with the both Kerr congruences.

In particular, there exist in flat space-time the massive plane wave solutions [25] (v.1, sec. 16 and sec. 23), identified as the spherical helicity states

(23) |

where , is 4-momentum and is the normalized bispinor formed from (18) and (19).

Therefore, the massive Dirac solutions aligned with the both Kerr null directions exist only inside the bag, where the spice-time is flat. Outside the bag, the KN gravitational field breaks parity of the left- and right-handed spinors, and the Dirac bispinor splits into the massless left- and right- Weyl spinors which should be placed on the different sheets of the KN solution, as it is illustrated in Fig.2.

## 6 Variable mass and the bag model conception

We arrive at the Dirac equation with a variable mass term which changes for different regions of the space-time. We notice that it is a proper feature of the MIT- and SLAC- bag models related with principal idea of the quark confinement [26, 27]. The quark wave function, solution of the Dirac equation with a variable mass term, is deformed tending to avoid the regions with a large bare mass, and get an energetically favorable position, concentrating inside or on the boundary of the bag.

The bag conception should be applied for the Dirac wave function on the KN background. Taking into account the discussed in sec.1. peculiarities of the gravitating KN bag model, the self-interacting Higgs field should be confined inside the bag. In agreement with (4), the vev of the Higgs field should give the mass term to the Dirac equation through the Yukawa coupling between the left-handed and right-handed spinor field inside the bag, in full consistency with the results of previous section. The corresponding Hamiltonian is

(24) |

and the energetically favorable wave function has to be determined by minimization of the averaged Hamiltonian Similar to results of the SLAC-bag model, the one expected that the Dirac wave function will be pushed from the region inside the bag, where the bare mass is large, towards a narrow zone at the bag border. Similarly to the case of the MIT and SLAC bags, the narrow concentration of the Dirac wave function is admissible for scalar potential, since it does not lead to the Klein paradox. Concrete form of the wave function will depend on the ratio of the parameters and . In the strong coupling limit the wave function will concentrate on the shell of the bag. The exact solutions of this kind are known only for two-dimensional case, and the corresponding variational problem for the KN soliton should apparently be solved numerically by using the ansatz where is a variable factor of the deformation, and the Dirac bispinor is formed by the Weyl spinors (18) and (19) aligned with two null congruences given by the Kerr theorem.

## 7 String from deformation of a bag

Taking the bag
model conception, we should also accept the dynamical point of
view that the bags may easily be deformed [27, 28], and
deformations of the bag create stringy structures. The
deformations considered in the bag models are typically formations
of the bag into an open flux-tube string with radial and
rotational excitations. The known Dirac’s model of an ”extensible”
spherical electron [29] may be considered as a prototype
of the bag model. Under vanishing rotation, the KN
disk-like bag turns into the spherical Dirac ”extensible” electron
model. The non-rotating spherical KN bag has just the Dirac
radius corresponding to classical radius of the electron,
In fact, the disk-like bag of the KN rotating
source may be considered as a bag obtained by the rotational
stretch from the Dirac ”extensible” spherical bag. Kerr’s
parameter of rotation stretches the spherical bag to the
disk of the Compton radius which indicates that
the KN bag should correspond to the zone of vacuum polarization of
a “dressed” electron. Since the degree of oblateness of the KN
bag turns out to be very close to the fine
structure constant acquires in the KN bag a geometrical
interpretation. Under stringy deformations the bag may acquire
oscillations similar to excitation of the strings, [28].
For the KN bag-like source, concentration of the wave function at
the border of the KN disk results in the appearance of the
circular light-like string, similar to obtained by Sen
fundamental string to low energy heterotic string theory
[30]. ^{4}^{4}4The real and complex stringy structures of the
Kerr geometry were discussed in [31, 32, 33].
It may be shown that the lowest excitation of the Kerr closed
string creates a circulating singular point which may be
interpreted as a confined quark in the conception of the bag
models, or as a point-like bare electron with zitterbewegung of
the Dirac theory, either as an end point of an open circular
string (D0-brane [32]) in the conception of string
theory.

## 8 Conclusion

Considering the problem of source of the KN solution we arrive at a gravitating soliton model based on the Higgs model of broken symmetry, which is similar to many other models of solitons, bags and Q-balls. However, the requirement to retain the long-range KN gravitational field outside the source enforces us to refuse from the usual quadratic term of self-interaction and introduce especial supersymmetric scheme of phase transition, in which symmetry is to be broken only inside the source where it realizes a supersymmetric false-vacuum state. As a result, we automatically obtain the flat space-time inside the source, avoiding contradictions between gravity and the standard quantum theory. The consequent treatment of the Dirac equation on the regularized KN background exhibited three important peculiarities:

1) structure of the Dirac equation is close related with two-sheeted structure of the Kerr geometry,

2) the Weyl components of the Dirac wave function are close related with twistor structure of the Kerr geometry determined by the Kerr theorem,

3) the Dirac equation acquires a variable mass term which find a strong theoretical interpretation in the frame of bag models.

We conclude that the source of KN solution should be considered as a gravitating bag model, and its further development should be based on theory of the bag models.

The KN bag represents a gravitating extension of the Q-ball models, which were suggested in [10, 11, 12] for electroweak sector of the standard model, and therefore, the gravitating KN bag can be considered as a step beyond the standard model towards its unification with gravity.

Comment added on December 20, 2014:

Jim Bogan informed me today that a geometrical model of the electron and its spin was published only just by the distinguished mathematician, Sir Michael Atiyah & colleagues, http://arxiv.org/pdf/1412.5915.pdf but they take a different path than in my paper. I could note that their work is based on the remarkable properties of self-duality of the Taub-NUT solution and its connection with Dirac theory is defined by twistorial structure. All these properties are present also in the Kerr-Newman solution, and the most part of their mathematical construction is to be related to the Kerr-Newman solution, too. Indeed, there is a remarkable common basis – the Kerr-NUT solution which lies beyond of the both lines of consideration, and we consider ideed different parts of this basic solution. The Kerr-Newman solution is considered in this paper in the Kerr-Schild form of metric which has an auxiliary Minkowski background, allowing us to present geometry of the extended electron in the real physical space-time. The NUT-part is apparently important, but it cannot be represented in the Kerr-Schild form, and so far it drops out from my consideration. On the other hand, the treatment of Sir Michael Atiyah et al is based on the NUT-part of the Kerr-NUT solution which requires a more abstract mathematical treatment and turns out to be far from our physical space-time. In my opinion the spin of the electron is related basically with the Kerr-Newman geometry, while the NUT-part may be important for self-interaction. I am thankful to Jim Bogdan for paying my attention to this paper.

### Acknowledgments

This work is supported by the RFBR grant 13-01-00602. Author thanks Theo M. Nieuwenhuizen, Yuri Rybakov and Bernard Whiting for interest to this work and useful conversations.

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