-
IC/80/llH
INTERNATIONAL CENTRE FOR
THEORETICAL PHYSICS
VACUUM SOLUTIONS WITH DOUBLE DUALITY PROPERTIES
OF A QUADRATIC POINCARE GAUGE FIELD THEORY
INTERNATIONALATOMIC ENERGY
AGENCY
UNITED NATIONSEDUCATIONAL,
SCIENTIFICAND CULTURALORGANIZATION
Peter Baekler
Friedrich W. Hehl
and
Eckehard W. Mielke
1980 MIRAMARE-TRIESTE
-
IC/60/lll*
International Atomic Energy Agency
and
United Nations Educational Scientific and Cultural
Organization
IHTEHHATIOHAL CEHTRE Mffi THEORETICAL PKISICS
VACUUM SOLUTIONS WITH BOBBLE DUALITY PROPERTIES
OF A QUADRATIC POIHCARE GAUGE FIELD THEORY •
Peter Baekler, Friedrich W. Hehl
Institute for Theoretical Physics, University of Cologne,D-5000
Cologne kl, Federal Republic of Germany,
and
Eckehard V. Hielke
International Centre for Theoretical Physics, Trieste,
Italy.
SIBAIMRE - TRIESTE
July 1980
• Submitted for publication.
-
ABSTRACT
We look for exact vacuum solutions of the gauge
theory of the Poincarfe group with a lagrangian
quadratic in torsion and curvature. First we find
the trivial spherically symmetric solutions with
vanishing torsion, also knwon from the Stephen-
son-Kilmister-Yang gravitational theory (see Fig.l).
Then, by means of a double duality ansatz for the
curvature, we derive in a systematic way three
different spherically symmetric vacuum solutions
with dynamic torsion (see Fig. 2) all giving rise
to a Schwarzschild-de Sitter metric with a fixed
"cosmological" constant. We rederive the Baekler
solution, find a time-reflected "anti-Baekler"
solution, and discover a new solution with non-
vanishing translational and rotational energy.
CONTESTS
Abstract
Introduction
1. Field equations of the Poincarfe gauge field theory and
Bianchi
identities
2. A quadratic model lagrangian
3. The duals of the Bianchi identities
4. Rewriting the 1st field equation
5. The 2nd field equation fulfilled by a duality ansatz
6. Vanishing torsion: SKY-gravity
7. Solving the 1st field equation and the duality ansatz for
spheri-
cal symmetry
8. Outlook: Confining properties of Baekler's solution?
Acknowledgment sLiterature
INTRODUCTION
Within the last two decades, gauge theories of gravity have
been
developped as alternatives to the general relativity theory
of
Einstein (GR). The success of the gauge idea in electroweak
and
strong interactions is part of the motivation to try these
concepts
in gravitational theory, too, where they historically come
from,
aftenall. We have argued elsewhere (cf. [l] and refs.), why
the
Poincarfe group seems to be the moat natural starting point
for
setting up a gauge theory of gravity. In Sect. 1 we present
the
basic tools needed to formulate the two general field
equations
(1.7) and (1.8) of the Poincarfe gauge field theory (PG). They
con-
trol the torsion and the curvature of spacetime, respectively.
The
two Bianchi identities are also stated.
So far, the explicit form of the field lagrangian was left
open.
In Sect. 2 we start from the quadratic model lagrangian
(2.4),
the naturalness of which we have shown elsewhere (cf. [l]).
This
leads us to a quadratic Poincarfe gauge field theory (QPG).
Certain-
ly, the torsion-square part of the QPG-lagrangian yields, in
the
teleparallelism limit of vanishing curvature, a viable
macroscopic
gravitational theory, which is indistinguishable from GR for
pre-
sently feasible experiments (cf. [2-8]).
The curvature-square part, however, representing the dynamics
of
the Lorentz gauge potential and coupled to the spin of matter,
des-
cribes a new interaction of a Yang-Mills type, which may be
called
strong gravity and the mediating particles of which may be
named
"rotons" (see [1,2]). Whether the complete lagrangian, including
the
curvature-square part, has anything to do with nature, can only
be
decided by exhibiting exact solutions of the QPG and by working
out
their consequences.
The program of looking for exact solutions of the QPG was
started by
Baekler & Yasskin [9], see also Wallner [lO,ll]. They found,
in a
£j.rst step, all spherically symmetric vacuum solutions for
vanishing
- 2 -
-
torsion. As shown by Mielke [12], see also the literature
given
there, these solutions can be classified (see Fig. 1)
according
to their double duality properties in the curvature tensor.
We
rederive these solutions from this slightly more advanced
point
of view in Sect.6.In these solutions torsion is suppressed,
which
is responsible in QPG for (weak.) macroscopic gravity. Hence we
are
in need of non-trivial solutions carrying also torsion.
Recently Baekler [13] found such a spherically symmetric
vacuum
solution with dynamic torsion by explicitly integrating the
field
equations. To our knowledge, this is the first non-trivial
solu-
tion with dynamic torsion of any PGI Some of its properties
were
discussed in [14].
Soon it became clear that the curvature of Baekler's
solution,
apart from a piece of constant curvature, is anti-self double
dual.
This, and the remarks above related to ref. [12], suggested to
us,
in analogy to the procedure of Belavin et al. [15] in SU(2)
gauge
field theory, to derive exact vacuum solutions of the QPG in
the
following systematic way: We make a double duality ansatz for
the
curvature, not forgetting the vital constant piece, and
solve
thereby the 2nd field equation of the QPG by reducing it to
the
2nd Bianchi identity. Left over is the 1st field equation and
the
duality ansatz, a system of equations which can be solved with
re-
lative ease in the case of spherical symmetry.
Our article is organized as follows: After the fundamental
equa-
tions of the QPG have been set up in the first two sections,
we
compute the duals of the Bianchi identities in Sect. 3 in
order
to have them available in a form which is more reminiscent of
the
field equations. In Sect. 4 we rewrite the symmetric part of
the
1st field equation in a pseudo-einsteinian form. In Sect. 5
a
double duality ansatz is employed and thereby the 2nd field
equation solved. In Sect. 6 the degenerate case of vanishing
torsion is treated and our results for the corresponding
spheri-
cally symmetric solutions are summarized in Pig. 1.
In Sect. 7 the symmetric part of the 1st field equation, by
means
of the duality ansatz, is reduced to an Einstein equation
with
"cosmological" constant acting in a riemannian spacetime.
For
spherical symmetry, this leads to a Schwarzschild-de Sitter
metric
inter alia. The anti-symmetric part of the 1st field equation
and
the duality ansatz yield, in the spherical case, four
differential
equations for the four unknown components of the torsion
tensor.
By integration we find three different special solutions and
col-
lect them in Fig. 2.
The conventions in this article are those of ref. [l] unless
sta-
ted otherwise (k = relativistic gravitational constant, fi *
modi-
fied Planck constant, c = velocity of light).
1. FIELD EQUATIONS OF THE POINCARE GAUGE FIELD THEORY AND
BIAHCHI IDENTITIES
In the PG (cf. [l]) spacetime is described by a
Riemann-Cartan
geometry. As independent geometrical variables we can take
the
tetrad coefficients et" and the connection coefficients P ; "
=
— — ["*•• . Here i,j ... = 0 ... 3 are holonomic (world)
indices and«,fj ... = O ... 3 anholonomic (Lorentz) indices.
The
tetrads are chosen orthonormal, i.e. the local metric 11—a
coincides with the Minkowski metric diag (-+++). The tetrad
co-
efficients e|* can be interpreted as translational and the
connec-
tion coefficients P-* "as rotational (or Lorentz) gauge
potentials.
The torsion
and the curvature
(12)U.2) P* * P ' *are the corresponding gauge field strengths,
respectively. The
operator D. represents the covariant exterior derivative with
re-
spect to a holonomic basis.
Let be given a matter field represented by a Poincare
spinor-ten-
sor WC**) an
-
det e"* , and 2C : = aL, whereas 1?": = eV is the gauge
field
lagrangian depending on some coupling constants K4 } K^ • • • }
on
the local metric, and on the anholonomic components of torsion
and
curvature, respectively; for a detailed discussion see ref.
[1].
Let be given the field momenta by
the momentum current of the gauge fields by
and the spin current of the gauge fields by
then the field equations of the PG read
(1.7)
(1.8)
The sources on the right hand sides are the canonical
momentum
current and the canonical spin current of the matter field.
The
field equs. (1.7, 1.8) are Yang-Mills type field equations. It
is_
specific to the PG, however, that the gauge currents ( £ ̂ } £ ̂
'» * )
have tensorial character. For simplicity we will concentrate
in
this article on the vacuum, i.e. we put the material sources
in
(1.7, 1.8) equal to zero.
The field equations are supplemented by the two Bianchi
identities
for torsion and curvature, respectively:
(1.9)r •'V3
(l.io) J) . (T
For the model lagrangian of our choice, see the next section,
the
field equations will turn out to be of fir3t differentiation
or-
der in torsion and curvature, similar as the Bianchi
identities.
2. A QUADRATIC MODEL LAGRANGIAN
If we insist that the field equations (1.7, 1.8) be linear in
the
2nd derivatives of the tetrad and the connection, i.e. that
they
are quasi-linear, then the field momenta ' * ) must be
linear in torsion and curvature. A particularly plausible
choice,
motivated toy the Gordon-decomposition of the momentum and the
spin
current of the Dirac field, reads (see [l])s
(2.1)
(2.2)
l e
at flIf we introduce the modified torsion tensor
(2.3)
then the corresponding gauge field lagrangian can written as
i.e. it consists of a translational part if .depending on
torsion,
with the Planck length Z = -/fcfic* as coupling constant, and of
a ro-
tational (or Lorentz) part ^ which depends on curvature and
is
characterized by a dimensionless strong coupling constant "it
.
Recently there have been 3ome objections against our model
lagran-
gian (2.4) by Sezgin and van Nieuwenhuizen [16], It should be
clear,
however, that these arguments, based on perturbative methods on
a
given Minkowaki background, do not necessarily apply to our
theory,
since Baekler's spherically symmetric vacuum solution [13],
for
example, is not asymptotically minkowskian, but rather has a
back-
ground of constant non-vanishing curvature.
If we substitute (2.4) into (1.4-1.8), we find for the
vacuum
field equations of our quadratic PG (QPG) the expressions
(2.5) PifeT!*
(2.6)
with the momentum current of the translational field
-
and the momentum current of the rotational field
Observe the properties
(2.9) £ ' * = 0 ,
and
(2.10) e i. = o .
r.ROT£ r = 0.
Let us consider the symmetric and the antisymmetric part of
the
1st field equation separately. For this purpose we transvect
(2.5)
with :
fi
= DjCeT^f J -
The first term can be partially integrated. If we remember the
de-
finition of torsion (1.1) then we find (T- : = T' '. )
(2.12)
Hence the symmetric part ot (2.11) can be written as
(2.13)
with
(2.14), ±rpt£ rn _ L.
If we express £V a in terms of the modified torsion, we have
(2.;TR
Then X .„ , defined in (2.14), turns out to be
(2.16)
' fSe ' ' i) •Because of (2.9, 2.1O), the trace of (2.13)
reads
In an analogous way we can derive the antisymmetric part of
(2.11)
Using (2.9), a short calculation yields
(2.18)
Because of angular momentum conservation, equ. (2.18) can also
be
derived by differentiating (2.6) with D±. Because of J). J).
(ef~.'?
we immediately find (2.18).
In (2.13) as well as in (2.18), there appears a divergence of
the
type JLfeT**",,.) . For later purposes we transform such a
diver-
gence of an arbitrary 3rd rank tensor into the corresponding
holo-
noraic expression. Simple algebra yields
We substitute the equs. (2.42, 2.47) of ref. [l]:
(2.20, $ , 7 % - im*yDkCeT!^.V^ I- 'K + *\ t ' w h e r e *KHere
we used the abbreviation ^
the operator of covariant differentiation (see Schouten
[17]).
3. THE DUALS OF THE BIANCHI IDENTITIES
In the field equations there enter covariant divergencies,
whereas
in the Bianchi identities covariant curls show up. In order
to
bring the Bianchi identities into a similar form as the
field
equations, we will take their dual3.
- 8-
-
Let £** be the Levi-Civiti tensor density with £ = - i
(cf. MTW [IB], p. 87). Then 1£ ' "* k l •• •= G,' * L/-/~ g" is
an (orienta-
tion dependent) pseudo-tensor. The dual of an antisymmetric
2nd
rank covariant tensor A. . can then be defined as
u * " * * 1 j. /
U ** A I M Lr I m ™ 4 J1 1 A * * -̂ - —S" >ht d
' ~ X t kt •
We introduced the imaginary unit i here in order to guarantee
that
the operation of taking the dual is involutive, see (3.4)
below.
We define the reciprocal of the Levi-Civit^ tensor density by
the
relation
(3.2) ' ' ' *
where o
Of course, the formula (3.1) is also valid in anholonomic
coordi-
nates.
The duals of the torsion and the modified torsion read
respective-
ly:
(3.8) h
Their traces turn out to be
(3.9) F := F . V « = / •= ' . C it*and the reciprocal reads
(3.1O) C~2
By squaring we find the useful formula
The expression r* =• I plays a particular .role in our con-
siderations, since it vanishes identically for spherical
symmetry.
For the right, the left, and the double dual of the curvature
we
have, respectively:
(3.12)
(3.13)
(3-14) r # • u. u '
The double dual (3.14), in contrast to the single duals
(3.12,
3.13), is distinguished by the property of being a pure
(orienta-
tion independent) tensor (W. Kopczynski, priv. comm.).
The self double dual and the anti-self double dual of the
curva-
ture are defined according to
(3.15)
We have
(3.16)
+Ff? '•-i(
= • F *F* =-Obviously, the curvature splits into a sum as
follows:
(3.17) f = F + IF .
These notions, in the context of the curvature tensor, were
de-
veloped by Lanczos [19, 2O], Debever ^ J ^ a ] , Nomizu J 23]
,
- 10 -
-
others, see also Gu et al. [24] and Penrose & Rindler [25].
A
finer splitting of the curvature tensor than in (3.17) can
be
achieved by using also the left and the right (anti-) self
duals,
aee Xin [26].
Often one needs the explicit form of (3.14). If we define the
trace-
free Ricci tensor by
(3.18) /"„,. :*= F .
then the application of (3.2), after some algebra, yields
The first contraction of (3.19) reads
(3.2O) F ' **"
and the second contraction
(3.21) f. yf
Debever [21] has shown that in a riemannian 3pacetime V. the
curvature tensor ft P . *£ c a n ^e decomposed into its
irreducible
parts under the action of the Lorentz group by means of [R
and
IR . If we define the Weyl conformal curvature tensor as the
traceless part of jj by
(3.22) CV,
and note
(3.23)
- - 2 M ' c-
then the curvature tensor of a V4 can be written as
If we define the unit tensor in the space of bi-vectors "fl
then we can express (3.24) symbolically asX I -
.»> B -This is the irreducible decomposition looked for.
Let us now turn to the Bianchi identities. Transvect (1.9)
with
i- € '*kl and finda
Dk(e s eor, by multiplication with e^ and partial
integration,
(3.27)
Decomposed into symmetric and antisymmetric part, (3.27)
reads:
C3.28
The equs. (3.28) should be compared with (2.13) and (2.18),
respectively.
In an analogous way we treat the 2nd Bianchi identity (1.10).
We
transvect it first with j £'*** .
^ = 0 .Then we multiply by -j ^ **P >* ' ;
(3.30)
Equs. (3.29) and (3.30) should be compared with (2.6)!
4. REWRITING THE FIRST FIELD EQUATION
Before one makes use of the analogous form of the field
equations
and of the corresponding Bianchi identities, ohne should
rewrite
the 1st field equation in two respects. To this end we first
put
it into a quasi-einsteinian form by decomposing the curvature
ten-
sor R,«,» C*) of the Riemann-Cartan spacetime U. into its
rie-
mannian part R a » * : = ^A* (* */ a n d into its torsion
depen-
-dent terms, ̂ "he'respective Einstein tensors read:
- J l - t -
-
(4.1)
Then a straightforward but tedious calculation, the result of
which
we may take from equ. (3.78) of ref. [27], leads to
(4.3) G -
-
Symmetrization of (4.11) yields
_ i
(4.13)
The explicit form of the last term we find by substituting
the
definition (3.11) twice and by applying contractions of
(3.2):
(4.14)
Collecting our results, we have for a U.
ROT
(4.15)
3e c' H-»*~~ -Jt (Cot
f ror more specifically for a
(4 16) V m^ If '
The translational energy can be put into a similar form,
(4.17) T £ A = £-%
but this formula will not turn out to be as useful as
(4.15).
On substitution of (4.15) into (4,6), the symmetric part of
the
1st field equation finally reads
(4.18)
5. THE SECOND FIELD EQUATION FULFILLED BY A DUALITY ANSATZ
A strategy for finding exact solutions in a Yang-Mills
theory
has been developped by Belavin et al. [15]. It consists in
sol-
ving the field equations by means of a duality ansatz, see
also
Actor [28], Certainly our 2nd field equation (2,6), i.e.
(5.1)
being very similar to a pure Yang-Mills equation, should be
most
appropiate for such an undertaking.
The modified torsion tensor T '. M a enters (5.1). We recall
(cf.[l](
equ. (2.43))
(5.2) e I - / s
The unit tensor if —(
self double dual:
in the space of bivectors is
(3.3) or
The antisymmetric tensor'JO s (if',* **) • perhaps surprisingly,
has
the same property:
Because of (5.1)-(5.4), we may take the 2nd Bianchi identity
in
it3 equivalent form (3.3O), i.e.
(5 si TV (e F" J «) — 0.
We compare (5.1) and (5.5) and remember (5.2). We try to
solve
(5.1) by the double duality ansatz
(5.6)
with the unknown constants (_ ^ if) ^''
We take the double dual of (5.6) and substract the result from
(5.6):
(5.7) • •
-
For ̂ £ - 1 , the curvature of the solutions ia self double
dual:
p = 0 . If we add or subtract (5.1) and (5.5), we have
instead
of (5.1) the two equations
(5.8) ?:*i.e. any solution with self double dual or anti-self
double dual
curvature leads to the trivial case of vanishing torsion:
T] r -a 3=fr ==t> F;'i* ** * 0. A look at the 1st field
equation
(2.5) cum (4.15) then shows, since |F = 0 or F 3 &t that it
is fulfil-
led identically. Consequently we find the
PROPOSITION 1: The subclass of solutions of the QPG with
self
or anti-self double dual curvature tensors resides in a rie-
mannian spacetime V^, - We will discuss these solutions in Sect.
6.
Comming back to (5.7), we conclude that the only non-trivial
case
with dynamic torsion, which we can find by means of the
ansatz
(5.6), i3 represented by
(5.9) £ = - 1 .
Then we can write (5.6) alternatively as
? : ? « - £ S *e:ra,e:•fil
For the duality ansatz (5.6) with £ = -1 we calculate the left
hand
side of (5.1) ,
(5.12)= - 5.
or, because of (5.5), and after some algebra:
T). ft* F'* ^(5.13)
In this article we will put 0 = 0; 6 ^ 0 will be studied
elsewhere.
Of course, the field equation (5.1) can be solved for HP, A ' =
0
a=* F"J1 ' s ff . Then the right hand side of (5.13) vanishes.
This" I *
is again the trivial case of a V̂ ,, see Sect. 6.
For 0 = 0, non-vanishing torsion can only be achieved for / -
T.
Hence, as can be seen from (5.1) and (5.13), the 2nd field
equa-
tion is non-trivially solved for
(5.14) ={ >
(5.15)
(5.15a,b)
It is remarkable that the constant curvature term in (5.1)
yields
a non-trivial solution only for a specific choice of the
constant
/.namely for / = 1/2.
Let us study some properties of the duality ansatz (5.15).
By
means of (3.15), (3.19), and (5.15), we have
F r f , «or, by contraction,
1 r 3X
A ,decomposition of (5.17) into its anti-symmetric and its
sym-
metric parts yields, respectively,
(5-18> F c < t / n = 0 ,
(5.19) p - -
The property (5.18) looks very riemannian-like, of course.
To-
gether with the contraction of the first Bianchi identity,
it
yields
(5.2O) -ff
-il-
-
or, together with (2.IB),
(5.2D Dk (e I ) =
-
logical" constant and equ. (6.11) a HordstrgJm type vacuum
theory
(cf. MTW, p. 429). However.it should toe stressed that (6,10),
say,
does not really correspond to Einstein's theory with
cosmological
constant since, afterjall, the source of (6.2) is the spin of
matter
and the arbitrary "cosmologieal" constant is of a strong
gravityorigin.
If we relate (6.1O, 6.11) to (6.9), then we recognize that
every
spherically symmetric solution of (6.1, 6.2) is either a
solution
of Einstein's vacuum theory with arbitrary "cosmological"
constant
or of Nordstrfrfm's vacuum theory. Consequently, in order to
classify
all spherically symmetric solutions of SKY-gravity, we have
to
look for the corresponding solutions of Einstein's and
Nordstromps
theories, respectively.
In Einstein 's theory with coamological constant .A.,one has to
be a4
bit careful in ennunciating Birkhoff's theorem . It states
{Kra-
sinski & Plebanski [40], cf. Bonnor [41]) that all
spherically •
symmetric solutions can be reduced to either the
Schwarzschild-de
Sitter (SdS) metric
{cf. MTW, p. 843 for a discussion,
-
IR:V-
IR =fR =
00
vanishing energySKY-equation
A
0
7
IR = 0 or fR = 0self I anti-self
Einstein with A
SdS (6.12)Nariai(6.13) Ni (6.20)
Fig. 1: SKY-gravity and solutions with double duality
properties (the symbol ̂ ) means spherical
symmetry).
-II'
(7.
where the tensor t,,. = tftt»j , depends solely on the
modified
torsion, as can be seen by substituting (4.8):
Let us now use the duality ansatz (5.15) and its
consequences
(5.18, 5.19, 5.23). From (7.2) we find:
(7.4) '*/»
The energy tensor ~t « vanishes together with the totally
anti-
symmetric part F t i , r t = T^v*.*l of the torsion. Hence,
because
of (5.15a, b ) , we have
(7.5) *., = " (ffl 9*,i.e. torsion drops out altogether and we
are left with an Einstein
equation with the "cosmological" constant -A.: — ~ A*ffi acting
in a
riemannian spacetime V*.
Accordingly, the symmetric part of the 1st field equation (2.5)
is
reduced to (7.5), whereas its antisymmetric part stays the
same,
see (2.18):
(7.6) Dk (e T . Cot(3
The 2nd field equation (2.6) is solved by the duality ansatz
(5.15,
5.15a, 5.15b):
Consequently (7.5, 7.6, 7.7) are the remnants of the two
field
equations (2.5, 2.6). The equations (7.5, 7.6, 7.7) need to
be
solved.
Because of (7.7), the totally antisymmetric part of the torsion
is
required to vanish identically. Therefore we would not be able
to
find axially symmetric solutions with the duality ansatz
(7.7),
-
since in this case torsion has certainly a leading F ^ j y ]
-part.
Perhaps & =£ (T is a way out in this case. Let us
concentrate in
the present article on the simplest case compatible with
(7.7),
namely on spherical symmetry, where £•[,*a»1 ~ ̂ • S o far we
have net
completed the proof that the duality ansatz (7.7) encompasses
all
spherically symmetric solutions, but we know already that it
does
include most cases.
We start off from the most general spherically symmetric
metric
(cf. ',40j, equ. (2.13),and MTW, p. 361)
-xx(7.8)
with the unknown functions U =• yM CR,TJ , X - -1 ̂ ff,~O,and r
= r(R,T).
Differentiation with respect to R and T will be denoted by a
prime
and a dot, respectively. A tetrad field which is naturally
asso-
ciated with this metric reads
i \'x X «(7.9) (no summation!).
Now we impose O(3) symmetry and space reflection symmetry on
tor-
sion and curvature. We find 4 nonvanishing anholonomic
components
of the torsion and 6 components of the curvature. We display
them
in two matrices, where the antisymmetric index pairs (Ol, O2,
O3,
23, 31, 12) are numbered by (1,2 .
(7.1O)
361):
(7.11) (F.7") =
/A . . . . .\
. C . . . G
. . C . -G .
D . -H .
\. -D . . . -Sj
We have f = f(R,T) etc. and A = A(R,T) etc. Simple
calculations
yield for the modified torsion
-15-
(7.12)
and for the (anti-)self dual parts of the curvature
f-2q
•
V •
2k
•
h+k
•
f - g
h+X
-f+g
(7.13)
and
(7.14)
(?;.'% iA-L ^
C-H . . . -D+G
C-H . D-G
A-L
D-G . C-H
t . -D+G . . . C-H
•A+L
C+H . . . D+G
C+H . -D-G
. -A-L
D+G . -C-H
-D-G . . . -C-H
, i.e. IF is then a diagonal matrix.
Incidentally, the (6x6)-unit matrix reads ^ o ^ op ) —
= diag (1,1,1,1,1,1).
In a V4 we have always D=G
For writing out (7.11) and (7.6) explicitly, we will need
the
anholonomic components of the connection. We express the
connec-
tion in terms of the metric (7.8) and the torsion (7.10) [see
[l]
equ. (2.51)]:
(7.15)
/
T
-
Then, by means of its definition {1.2), we can compute the
curva-
ture in terms of metric and torsion:
fB- • 6 —
« Vi W= -H - - ̂ f,r - r'^y- ( h + 1
(7.16)
Now everything is prepared for solving the equations (7.5,
7.6,
7.7). Using the metric (7.8) and Schwarzschild coordinates r »
Rt
t=T, equ. (7.5), via Birkhoff's theorem, leads to the
SdS-metric
(6.12) with _/\- - -
Here we have e — S — fl. JJ . The case of the Nariai metric,
which emerges also in this context, will be left to a
separate
study.
Equ. (7.6) has only one independent component. By means of
(7,8,
7.9, 7.12, 7.15), it can be put quite generally into the
form
e * - / • •(7.18)
If we restrict ourselves to static solutions in the torsion,
i.e.
g = f = h = k = O , and use the SdS-metric (7.17), then (7.18)
re-
duces to
Let us now turn to the duality ansatz (7.7): The relation
K-L
is fulfilled identically for spherical symmetry, as can be
seen
from (7.1O). The set (7,7) corresponds to 3 different
equations.
This can be read off from (7.13) in a most direct way. If we
again assume staticness in torsion and use the SdS-metric
(7.17),
eqs. (7.7, 7.13. 7.16) yield:
(7.20) A~L- 2JL3-
(7.21) C-H =
(7.22) D_i
- hfr
= 0 = )
The metric is already determined in (7.17). We should
remember
that in (7.19) to (7.22) we always have e'* = e'^sfl"? The
four
unknown torsion functions (g, f, h, k) are governed by the
four
ordinary first order differential equations (7.19, 7.20, 7.21,
7.22).
Addition and subtraction of (7.19) and (7.22) yield,
respectively,
if we remember (7.17):
±L? + k) = Or ,(7.23)
(7.24)
Equ. (7.23) leads to two different cases: Either to
h = -k (case I),(7.25)
or to
(7.26)»" ~,
-X(case II).
Let us first follow up case I. For the specific choice g =
f,
equ. (7.24) results in
(7.27) = - k
-
with tft» iHLgyiation constant to. On substituting (7.27) into
(7.2O,
7.21), we find
Sit(7.26) = -
-
The other components look similarly. Clearly, the tetrad field
al-
ways carries 3pin. The spin current (1.6) cum (2.1) turns out
to
be
(7.37a,
,--f/st
= ± • •tall other components = o.
Whereas the mass dipol moment density £^*° stays the same
for
both solutions (7.31a,b), the corresponding flux in
r-direction
reverses it3 sign.
The case II of (7.26) has different characteristics. We
eliminate
from (7.2O) and from (7.22) multiplied by e ̂ the term
OFe'O.Thia
leads to a second order differential equation for k(r)
alone:
(7.34) [ ~ax (t* k)']'A specific solution of (7.34) is
(7.35) k* = - | ^ f ; OC = with
-
de Sitter metric with the associated torsion and curvature
struc-
tures could lead to a classical model for confinement. Some
of
our ideas presented in this section ate frankly speculative,
but
we hope that they have at least some plausibility. - In any
re-
lativistic theory of particles possessing quarks as building
blocks, a mechanism of (at least partial) confinement of the
basic
constituents has to be inherent in the model.
In quantum chroroodynamics (QCD, see [47] for a review),
nowadays
the moat prominent model, such a confining phase is suspected
to
occur by taking non-pertubative effects properly into
account.
Despite much efforts, this has not yet been demonstrated. A
classi-
cal analysis does not yield encouraging hints either. On the
con-
trary: It is known [48 j that pure Yang-Mills fields cannot
form
classical glue-balls. The reason being that nearby small
portions
of the vector gauge fields must always point in the some
direc-
tion in internal space and therefore must repel each other
similar
as charges of the same sign. Therefore, in phenomenological
devi-
ces, such as the MIT-bag model [49], see also [50], a color
sen-
sitive "bag constant" - B has been included ad hoc into the
la-
grangian in order to compensate for the pressure of the quark
gas.
This, and appropriate conditions for the Dirac spinor at the
boundary of the bag, yield a reasonable description for
hadrons
with confined quarks.
On the other hand a mechanism of confinement, which is
intrinsic
and in accordance with gauge ideas, emerges if we adopt the
hypothesis that strong interactions are (at least partially)
mediated by tensor gauge fields. In the f-g theory of
gravity,
modeled after Einstein's theory in a V4, Salam and Strathdee
[51]
have shown that there exist a completely confining
configuration:
the anti-de Sitter space. Usually this space is obtained as a
so-
lution of the Einstein equation with (scaled)
negative"cosmologi-
cal" term. In the f-g theory such a term can be simulated by
adding a mixing term Jf ? to the Einstein-Hilbert lagrangian
for the f and ̂ ^v tensor fields. For a X -^ -term of the
Pauli-Fierz form, however, f̂ ,y represents a massive spin-2
par-
ticle. This is inconsistent with the aim to achieve
confinement
by (tensor) gluons, which have to stay massless.
With respect to this issue, the QPG is claimed to be
conceptual
superior as compared to other tensor gauge theories. Without
having
included it from the beginning, we obtain for our modified
anti-
self double dual solutions an effective bag constant
(8.1) B - X £+ )which is of microscopic origin. Furthermore, as
a promissing new
feature, a Schwarzschild-de Sitter solution (7.31a,b) with
dynamic
torsion is the result.(Other choices of the QPG lagrangian
would
yield also massive spin-2 mesons (see [16]) without the need
to
introduce a Pauli-Fierz mass term if«r.)
In order to exhibit the confining property of this solution,
we
may adopt here the crude physical picture that the hadron is
re-
presented by a Schwarzschild-de Sitter microuniverse, with a
-=-=•
singularity at the center originating from a "source" quark
of
mass1 OC . Into this world one can think of putting an
additional
quark-treated as a test particle, in so far as its
contribution
to the source is ignored - in order to complete the hadronic
structure.
For the case of scalar test (and source) "quarks", we will
solve
the Klein-Gordon equation
(8.2) C a -in the curved background given by (7.17) with 0£= O.
Here
is the generally covariant Laplace-Beltramic operator (for
the
following discussion See also Mielke [52 ]). Stationary,
radial
solutions of (8.2) may be obtained by using the familiar
separa-
tion ansatz
(8.4)
In this ansatz
(8.5) S • = ~^£
denotes a dimensionless radial coordinate. After introducing
the
"tortoise coordinate" (MTW, p. 663)0
{8.6) § ' " J ~T~L—"5 - ardanQ {=? Avtn $) for+
-
equ. (8.2) reduces to the Schrodinger type equation
(8.7, C *) +f*] C -afor the radial function R U M
formulae the quantity
. In this and the following
(8-8) I* =has been used. It denotes the (dimensionless} ratio of
the re-
duced Compton wave length Xu. of the test particle and the
Planck length JL, modified by our strong constant 3C .
Formally, the curved background affects the wave equation only
via
an effective curvature potential (compare with MTW, p. 868)
which
in the de Sitter case is implicitly given by
for ie > o Cte * eO.It is instructive to consider the
particular simple case of zero
angular momentum states (L = 0) for yt> 0 . Then the
curvature
potential of the anti-de Sitter space reads explicitly
This potential belongs to a family of examples studied by
Poschl
and Teller [53] for the oscillations of diatomic molecules
(see
also [54], p. 89). For ft9"< 0. . it gives rise to a smooth
"wall"M It-infinite at Q - 3 , which the test "quark" can never
penetrate.
Equ. (8.7) can be exactly solved [55,51] in terms of
hypergeo-
metric functions. The regular, square-integrable solutions
form
a discrete set having quantized energy values
(8.11, C2N | + VIApart from the zero-point term, these are
exactly the energy
levels of the 3-dimensional non-relativistie harmonic
oszillator
([54], p.70). The result (8.1O) may be interpreted as a
prototype
mass spectrum for an excited hadron of integer spin. This
spec-
trum has discrete eigenstates, no continuum, and thus no
disso-
ciation of the "quarks".
In a sense, the confinement in an anti-de Sitter
microuniverse
incorporates the features of both, the bag and the potential
model in QCD (see Sect. 1.3.5 of [47]). It should be noted
that
the Schwarzschxld-type source term -=£- in the solution
(7.31a,b)
is necessary for the observed asymptotic freedom of the
consti-
tuents at short distances. By treating this term as a
pertuba-
tion, it can be shown [51 in the limit Ur* 0 of the scalar
test
mass that the degeneracy of the energy levels of (8.1O) in
the
parameter (2N 4- L) is removed.
For a more realistic analysis of the implications of the
solution
(7.31a,b) for the confinement problem, we may consider its
effect
on a spin-1/2 test particle. In an l?4 not only the
Schwarzschild-
de Sitter metrical background occurs in the generally
covariant
Dirac equation, but also the dynamic torsion of the vacuum
solu-
tion is expected to yield essential contributions. Morover, in
a
QPG theory coupled to Dirac fields, the completely
antisymmetric
part of the torsion induces a nonlinar term of the axial
vector
type into the spinor equation (see [56]). Therefore, the
analysis
of the spinor solutions in Baekler's background presents a
high-
ly interesting but formidable task in itself, which we will
defer
to a later publication.
The main problem for a realistic description of hadrons within
the
QPG paradigm, which must be also solved, concerns the
incorpora-
tion of color and, needless to say, of flavor. We need to
make
a distinction between quarks and antiquarks and also
introduce
a color selectivity in order to obtain only the physical
hadronic
states.
In the vierbein description of the tensor fields, the
(covering)
symmetry of the PG includes a group of local SL(2,C)
transfor-
mations. This local group can easily be enlarged to
incorporate
a color symmetry via the subgroup chain SL( 2 ,C)C SL(2 ,C) ®SU
C ( 3)
-
to obtain only one anti-de Sitter "microuniverse" with
absolute
confinement for all kind of test particles and no outside
space-
time, a color sensitivity has to be built into the theory.
Similar
as in the colored extension [51] of the f-g theory, this has to
be
achieved in such a way that for color singlet states the
tele-
parallelism limit ?C —* 0 will be obtained. '
Expressed differently, the observed hadronic states should
not
feel the strong Yang-Mills type gravity ("rotona") and,
unlike
their constituents, should not participate in the
geometrodynamical
confinement mechanism.
ACKNOWLEDGMENTS
One of the authors (FWH) is most grateful to Professor Remo
Ruffini for- the invitation to present some aspects of the
QPG
at the 2nd Marcel Grossmann Meeting in Trieste. We all are
very
much obliged to Professor Hubert Goenner for his advice on
the
Birkhoff theorem and on related questions, and to Dr. Phil
Yasskin
for most interesting critical remarks and for sharing with
us
hia knowledge in solving the field equations of QPG. One of
us
(EWM) would like to thank Professor Abdus Salam, the
International
Atomic Energy Agency, and UNESCO for hospitality at the ICTP
in
Trieste. This work was supported by the Deutsche
Forschungsge-
meinschaft, Bonn.
found implicitly in Baekler & Yasskin [9]: Take the
discussion
following their equ. (64). The 6 cases are reduced to the
cases
I and II, i.e. to Nordstrom's theory comprising anti-self
double
dual solutions, cf. our equ. (6.11), and to case VI, i.e. to
Einstein's theory with "cosmological" constant comprising
self
double dual solutions, cf. our equ. (6.10).
Goenner [36] gave a careful exposition of the Birkhoff
theorem
with references to the original literature. Birkhoff type
theo-
rems in theories with torsin were investigated by Yasskin
[37],
Ramaswamy & Yasskin [38], and Neville [39].
This proposition subsumes in a unified way and in a
hopefully
final form results of different authors on SKY-gravity, see
Thomson [45], Pavelle [46], Ni [33], Olesen [34], Gu et al.
[24],
Mielke [12], and Baekler & Yasskin [9]. In the past
several
spherically symmetric solutions of the SKY-equation (6.2)
have
been given. We turn first to the solution of Thomson [45]
and
Pavelle [46]:
"
)~
For (F.I) we find R = 0, i.e. it also fulfills (6.1) and is
a
special case of (6.20). The examples of Ni [33], see also
Pavelle [46],
(F.2) Js*- - dix +and of Thomson [45]
( F . 3 ) d $a = - r f < " *
both have no double duality properties, i.e. they do not
fulfill
(6.1).6 It ia always understood that (1 -~- + TfcT1}'* -/ f'^
etc.
FOOTNOTES
We have changed our conventions in the meantime. The
holonomic
torsion now reads • p; - — y? 'Ci^l •
An additional term t(*F '.^JA + ~̂ .7*/*) does not seem to
work,
even being a self dual combination, 3ince there is no
Bianchi
identity for the right dual, see also [24,26].
Compare in this context Ni [33], Olesen [34], Mielke [12J,
andthe literatur cited there. The proof of our assertion can be
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IC/80/30 B. NOJAROV, E. NADJAKOV and V. ANTONOVA: High spin
structure in acoupled bands model.
rc/6o/31 AHMED OSMAH: Rearrangement collisions between four
identical part iclesas a four-body problem.
IC/80/53 R. BECK, H.V. MIHAILOVIC and M. POWSAK: Calculation of
nuclear reactionparameters with tk« generator co-ordinate method
»nd their i t t t i
IC/60/3U I.Zh. PETKOV and M.V. STOITSOV: On a generalisation of
the Thomas-FermiINT.REP.• method to finite Fermi systems.
IC/80/58INT.HEP.•
IC/80/59INT.REP.•
IC/80/fiOIDT.REP.*
3. YOKSAN: Spatial variations of order parameter wahiM fondo
impurityfor T 4 Tc.
J.K.A. AMUZU: Sliding friction of some metallic glaseas.
Zi-Zhao GAB and Guo-Zhen YANG: A theory of coherent propagation
ofl ight Have in semiconductors.
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iWTTf.f •'* 1
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IC/8O/61INT.REP.•
K.G. AKDENIZ and 0. OGUZ: A nev class of meronic solutions.
IC/80/63 H.B. SIHQH and K. HAUO: Optical absorption spectrum of
highly excitedINT.REP.* direct gap samiconductora.
IC/SO/fiU W. KLON0WSKI: Living protein iwcromolecule as a
non-equilibriumINT.HEP.• metdatable system,
IC/8O/65 H.Q. HEIK: An approximation to the ground state of E ®
E and fg ©INT.HEP.* Jahn-Teller system* based on Judd's isolated
exact solutions.
IC/80/66 A.H. ERMLOV, A.S. KIREEV and A.M. KURBATOV: Spio
glaaees with ncm-INT.REP.* Gaussian distributions. Frustration
model.
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