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  Does a good path integral exist in Loop Quantum Gravity?

+ 6 like - 0 dislike

The Hamiltonian operator of Loop quantum gravity is a totally constraint system

$$H = \int_\Sigma d^3x\ (N\mathcal{H}+N^a V_a+G)$$

Here, $\Sigma$ is a 3-dimensional hypersurface; a slice of spacetime. Moreover, $\mathcal{H}$ is the Hamiltonian constraint, $V_a$ the diffeomorphism constraint, $G$ the Gauss law term and $N,N^a$ corresponding constraint generators. In research literature this Hamiltonian was criticized to be not hermitean and would not form a Lie algebra from its generators. The variables of the theory are Ashtekar's variable $A_a^i$ and the triad $E_a^i$. Therefore the Master constraint

$$M:=\int_\Sigma d^3x\ \mathcal{H}^2/\sqrt{\det q}$$

with 3-d-metric $q_{ab}$ was introduced that solves these issues. Loop quantum gravity can be treated canonically, but according to this paper:


one can derive a path integral from the Master constraint. I can't understand the derivation of it (especially with the measure factor). Question: Is there a plausible path integral in 4-d-spacetime that computes spin foam amplitudes?

What is if I treat Loop Quantum Gravity with the path integral with action

$$S = \int d^4x\ (E_a^i \dot{A_i^a}-N\mathcal{H}+N^a V_a+G) \tag{$\star$}$$ is it plausible (this action is mentioned in one of my introductory textbooks) despite the non-hermiticity of the Hamiltonian? Or would this action lead to significant errors?

P.S:: is the path integral $$\int d[E_a^i] d[A_i^a] d[N_{Master}] exp(i E_a^i \dot{A_i^a} - i\int dt N_{Master} M) $$ $$= \int d[E_a^i] d[A_i^a] exp(i E_a^i \dot{A_i^a}) \delta(M)$$ a better version than the path integral induced by the action $(\star)$?

This post imported from StackExchange Physics at 2016-12-24 22:42 (UTC), posted by SE-user kryomaxim

asked Dec 13, 2016 in Theoretical Physics by kryomaxim (65 points) [ revision history ]
edited Dec 25, 2016 by 40227

May be related: there is a covariant approach to Loop Quantum Gravity called the spinfoam formalism. Spinfoams are based on path integrals. They is still under active research, and it is yet unclear whether they give the same results as canonical LQG or not.

This post imported from StackExchange Physics at 2016-12-24 22:42 (UTC), posted by SE-user Solenodon Paradoxus

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