No Arabic abstract
We describe a class of diffeomorphism invariant SU(N) gauge theories in N^2 dimensions, together with some matter couplings. These theories have (N^2-3)(N^2-1) local degrees of freedom, and have the unusual feature that the constraint associated with time reparametrizations is identically satisfied. A related class of SU(N) theories in N^2-1 dimensions has the constraint algebra of general relativity, but has more degrees of freedom. Non-perturbative quantization of the first type of theory via SU(N) spin networks is briefly outlined.
In a diffeomorphism invariant theory, symmetry breaking may be a mask for coordinate choice.
We consider families of geometries of D--dimensional space, described by a finite number of parameters. Starting from the De Witt metric we extract a unique integration measure which turns out to be a geometric invariant, i.e. independent of the gauge fixed metric used for describing the geometries. The measure is also invariant in form under an arbitrary change of parameters describing the geometries. We prove the existence of geometries for which there are no related gauge fixing surfaces orthogonal to the gauge fibers. The additional functional integration on the conformal factor makes the measure independent of the free parameter intervening in the De Witt metric. The determinants appearing in the measure are mathematically well defined even though technically difficult to compute.
In this paper we use the covariant Peierls bracket to compute the algebra of a sizable number of diffeomorphism-invariant observables in classical Jackiw-Teitelboim gravity coupled to fairly arbitrary matter. We then show that many recent results, including the construction of traversable wormholes, the existence of a family of $SL(2,mathbb{R})$ algebras acting on the matter fields, and the calculation of the scrambling time, can be recast as simple consequences of this algebra. We also use it to clarify the question of when the creation of an excitation deep in the bulk increases or decreases the boundary energy, which is of crucial importance for the typical state
In $SU(N)$ gauge theory, it is argued recently that there exists a mixed anomaly between the CP symmetry and the 1-form $mathbb{Z}_N$ symmetry at $theta=pi$, and the anomaly matching requires CP to be spontaneously broken at $theta=pi$ if the system is in the confining phase. In this paper, we elaborate on this discussion by examining the large volume behavior of the partition functions of the $SU(N)/mathbb{Z}_N$ theory on $T^4$ a la t Hooft. The periodicity of the partition function in $theta$, which is not $2pi$ due to fractional instanton numbers, suggests the presence of a phase transition at $theta=pi$. We propose lattice simulations to study the distribution of the instanton number in $SU(N)/mathbb{Z}_N$ theories. A characteristic shape of the distribution is predicted when the system is in the confining phase. The measurements of the distribution may be useful in understanding the phase structure of the theory.
Pure gauge theories for de Sitter, anti de Sitter and orthogonal groups, in four-dimensional Euclidean spacetime, are studied. It is shown that, if the theory is asymptotically free and a dynamical mass is generated, then an effective geometry may be induced and a gravity theory emerges.