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Monday, September 16, 2019

Coarse Graining with SU(1,1)

This is the second post in a series about SU(1,1) techniques for coarse graining loop quantum cosmology. While the previous post was about the general idea of group quantisation techniques, this one will focus on coarse graining.

Friday, September 13, 2019

Public talk (in German)

Last year, I gave a public talk (in German) about quantum gravity in Regensburg. It is available on youtube:



It was done as an invited presentation to a talk series called Was-Ist-Wirklich (What is real), featuring various topics in science.

Friday, May 10, 2019

Quantum cosmology with SU(1,1)

This is the first post in an upcoming series covering some recent papers that deal with quantum cosmology models that are strongly relying on an SU(1,1), or equivalently SL(2,R), structure. In brief, one identifies classical phase space functions whose Poisson algebra is isomorphic to the Lie algebra su(1,1) and then quantises the cosmological model by promoting those functions to the generators of su(1,1) in some representation. The main advantage of this quantisation method is that the representation theory of the group under consideration is well known, so that the crucial "find a representation" step in constructing the quantum theory is essentially trivial.

Friday, May 3, 2019

Singularity resolution in LQG inspired black holes

It is expected that quantum gravity will somehow resolve the singularities that are generically present in classical gravitational theories. For example, this may be the Big Bang singularity that one encounters when applying Einstein's theory of General Relativity all the way to the beginning of the universe. An example of how this singularity is resolved in the context of loop quantum cosmology was discussed in this post.

Another place where singularities prominently occur is inside black holes. Matter that falls through the horizon of a black hole will eventually hit this singularity and the theory describing its propagation breaks down in this instant. On the other hand, a compete theory of quantum gravity should provide a well-defined description of such a process.

Penrose diagram of a maximally extended Schwarzschild spacetime. Physical motion bounded by the speed of light is possible only within the future light-cones drawn in orange. Due to the structure of the spacetime, any observer crossing the black hole horizon will eventually hit the black hole singularity.  

Friday, May 18, 2018

PhD Position available

A PhD Position in my group is available starting this fall. The full advertisement is below:

EDIT: The position has been filled.

Thursday, April 12, 2018

Quantum Gravity meets Lattice QFT

Together with some colleagues, I am organizing a workshop on the intersection of quantum gravity and lattice QFT at ECT* in Trento, Italy, September 3-7.

Click here for the conference website. 


The conference abstract goes as follows:

AdS/CFT has been one of the most fruitful approaches to analyse the qualitative aspects of the dynamics of strongly interacting QFTs, most prominently QCD. As an approach to understanding the early stage of high energy heavy ion collisions, but also proton-proton collisions at LHC, it is, in fact, one of very few systematic approaches. However, it is not clear how reliable the description is quantitatively, because QCD is not a N=4, supersymmetric, conformal, SU(N) gauge theory with infinite N and the QCD coupling constant is of limited size. Individual contributions exist on both sides of the duality calculating the size of the relevant corrections (like the perturbative calculation of quantum corrections on the gravity side for finite N and finite coupling strength, the lattice simulation of SU(N) gauge theories with N>3, the calculation of perturbative corrections from non conformality on the QFT side, lattice simulation with partial supersymmetry …) but no systematic effort. In addition, more general scenarios for gauge/gravity dualities have been studied, extending beyond the realms of AdS, CFT, and string theory. The probability is high that quantitative contact can only be made on the basis of non-perturbative calculations on both sides, which is a very tall order. On the QFT side, lattice QFT is the best established tool to do so, while on the quantum gravity side resummed string theory is the main approach. In addition, there is an increased recent interest within loop quantum gravity in holographic computations.

The aim of the workshop is to bring some of the internationally leading experts in these fields together, formulate a more systematic strategy, and realize a few projects in the direction of a quantitative application of quantum gravity techniques to QCD in subsequent months.

Monday, July 24, 2017

New group + PhD positions



The Elite Network of Bavaria recently awarded me with a grant to start my own research group at the University of Regensburg starting this fall. I am currently looking for PhD students to work with me on projects at the intersection of loop quantum gravity and string theory, more precisely in applying ideas about quantum gravity corrected geometries in the context of the gauge / gravity duality. The announcement for the positions can be found here.

EDIT: All currently open positions have been filled.