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**Simplicial Palatini action**

V.M. Khatsymovsky

(Submitted on 18 May 2017)

We consider the simplicial complex (piecewise flat spacetime) and a simplicial analog of the Palatini form of the general relativity action where the discrete Christoffel symbols are given on the tetrahedra (3-dimensional simplexes) as variables that are independent of the metric. Excluding these variables with the help of the equations of motion gives exactly the Hilbert-Einstein action or, in the present context, Regge action. The present paper continues our previous work. Now we include the parity violation term and the analogue of the Barbero-Immirzi parameter introduced in the Cartan-Weyl representation of the Einstein action with orthogonal connection. The path integral is considered and elementary areas are shown to be fixed at some Planck scale values.

https://arxiv.org/abs/1705.06711

**Local Lorentz covariance in finite-dimensional Local Quantum Physics**

Matti Raasakka

(Submitted on 18 May 2017)

We show that local Lorentz covariance arises canonically as the group of transformations between local thermal states in the framework of Local Quantum Physics, given the following three postulates: (i) Local observable algebras are finite-dimensional. (ii) Minimal local observable algebras are isomorphic to M2(C), the observable algebra of a single qubit. (iii) The vacuum restricted to any minimal local observable algebra is thermal. The derivation reveals a new and surprising relation between spacetime structure and local quantum states. In particular, we show how local restrictions of the vacuum can determine the connection between different local inertial reference frames.

https://arxiv.org/abs/1705.06407

**Spacetime has a `thickness'**

Samir D. Mathur

(Submitted on 18 May 2017)

Suppose we assume that (a) information about a black hole is encoded in its Hawking radiation and (b) causality is not violated to leading order in gently curved spacetime. Then we argue that spacetime cannot just be described as a manifold with a shape; it must be given an additional attribute which we call `thickness'. This thickness characterizes the spread of the quantum gravity wavefunctional in superspace -- the space of all 3-geometries. Low energy particles travel on spacetime without noticing the thickness parameter, so they just see an effective manifold. Objects with energy large enough to create a horizon do notice the finite thickness; this modifies the semiclassical evolution in such a way that we avoid horizon formation and the consequent violation of causality.