Gauge gravitation theory explained

In quantum field theory, gauge gravitation theory is the effort to extend Yang–Mills theory, which provides a universal description of the fundamental interactions, to describe gravity.

Gauge gravitation theory should not be confused with the similarly named gauge theory gravity, which is a formulation of (classical) gravitation in the language of geometric algebra. Nor should it be confused with Kaluza–Klein theory, where the gauge fields are used to describe particle fields, but not gravity itself.

Overview

The first gauge model of gravity was suggested by Ryoyu Utiyama (1916–1990) in 1956^[1] just two years after birth of the gauge theory itself.^[2] However, the initial attempts to construct the gauge theory of gravity by analogy with the gauge models of internal symmetries encountered a problem of treating general covariant transformations and establishing the gauge status of a pseudo-Riemannian metric (a tetrad field).

X . Any such connection is a sum K = \Gamma + \Theta of a linear world connection \Gamma and a soldering form \Theta = \Theta ^{a} _{\mu} dx ^{\mu ⊗ \vartheta} _{a} where \vartheta _{a=\vartheta} ^{λ \partial} ^{λ} is a non-holonomic frame. For instance, if K is the Cartan connection, then \Theta = \theta = dx ^{\mu ⊗ \partial} _{\mu} is the canonical soldering form on X . There are different physical interpretations of the translation part \Theta of affine connections. In gauge theory of dislocations, a field \Theta describes a distortion.^[4] At the same time, given a linear frame \vartheta _{a} , the decomposition \theta = \vartheta ^{a ⊗ \vartheta} _{a} motivates many authors to treat a coframe \vartheta ^{a} as a translation gauge field.^[5] P\to X leaving its base X fixed. On the other hand, gravitation theory is built on the principal bundle FX of the tangent frames to X . It belongs to the category of natural bundles T\to X for which diffeomorphisms of the base X canonically give rise to automorphisms of .^[6] These automorphisms are called general covariant transformations. General covariant transformations are sufficient in order to restate Einstein's general relativity and metric-affine gravitation theory as the gauge ones.

In terms of gauge theory on natural bundles, gauge fields are linear connections on a world manifold

X , defined as principal connections on the linear frame bundle FX , and a metric (tetrad) gravitational field plays the role of a Higgs field responsible for spontaneous symmetry breaking of general covariant transformations.^[7] G of a principal bundle P\to X is reducible to a closed subgroup H , i.e., there exists a principal subbundle of P with the structure group H .^[8] By virtue of the well-known theorem, there exists one-to-one correspondence between the reduced principal subbundles of P with the structure group H and the global sections of the quotient bundle . These sections are treated as classical Higgs fields.

The idea of the pseudo-Riemannian metric as a Higgs field appeared while constructing non-linear (induced) representations of the general linear group, of which the Lorentz group is a Cartan subgroup.^[9] The geometric equivalence principle postulating the existence of a reference frame in which Lorentz invariants are defined on the whole world manifold is the theoretical justification for the reduction of the structure group of the linear frame bundle to the Lorentz group. Then the very definition of a pseudo-Riemannian metric on a manifold

X as a global section of the quotient bundle leads to its physical interpretation as a Higgs field. The physical reason for world symmetry breaking is the existence of Dirac fermion matter, whose symmetry group is the universal two-sheeted covering of the restricted Lorentz group, .^[10]

Bibliography

• I. . Kirsch . 2005 . A Higgs mechanism for gravity . Phys. Rev. D . 72 . 024001 . hep-th/0503024.
• Sardanashvily . G. . Gennadi Sardanashvily . 2011 . Classical gauge gravitation theory . Int. J. Geom. Methods Mod. Phys. . 8 . 1869–1895 . 1110.1176.
• Yu. . Obukhov . 2006 . Poincaré gauge gravity: Selected topics . Int. J. Geom. Methods Mod. Phys. . 3 . 95–138 . gr-qc/0601090.

Notes and References

1. Utiyama . R. . 1956 . Invariant theoretical interpretation of interaction . Physical Review . 101 . 1597 . 10.1103/PhysRev.101.1597.
2. Book: Milutin . Blagojević . Friedrich W. . Hehl . 2013 . Gauge Theories of Gravitation: A Reader with Commentaries . World Scientific . 978-184-8167-26-1.
3. F. . Hehl . J. . McCrea . E. . Mielke . Y. . Ne'eman . 1995 . Metric-affine gauge theory of gravity: Field equations, Noether identities, world spinors, and breaking of dilaton invariance . Physics Reports . 258 . 1 . 10.1016/0370-1573(94)00111-F. gr-qc/9402012.
4. Malyshev . C. . 2000 . The dislocation stress functions from the double curl (3)-gauge equations: Linearity and look beyond . Annals of Physics . 286 . 249 . 10.1006/aphy.2000.6088. cond-mat/9901316 .
5. Book: Blagojević, M. . 2002 . Gravitation and Gauge Symmetries . Bristol, UK . IOP Publishing.
6. Book: I. . Kolář . P.W. . Michor . J. . Slovák . 1993 . Natural Operations in Differential Geometry . Springer-Verlag . Berlin & Heidelberg.
7. Dmitri Ivanenko . D. . Ivanenko . Gennadi Sardanashvily . G. . Sardanashvily . 1983 . The gauge treatment of gravity . Physics Reports . 94 . 1 . 10.1016/0370-1573(83)90046-7.
8. Nikolova . L. . Rizov . V. . 1984 . Geometrical approach to the reduction of gauge theories with spontaneous broken symmetries . Reports on Mathematical Physics . 20 . 287 . 10.1016/0034-4877(84)90039-9.
9. M. . Leclerc . 2006 . The Higgs sector of gravitational gauge theories . Annals of Physics . 321 . 708 . 10.1016/j.aop.2005.08.009. gr-qc/0502005 .
10. Book: Gennadi Sardanashvily . G. . Sardanashvily . O. . Zakharov . 1992 . Gauge Gravitation Theory . Singapore . World Scientific.