## About

44

Publications

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228

Citations

Introduction

Researching loop quantum gravity and spinfoam models... :-)

Additional affiliations

March 2016 - present

March 2013 - March 2016

March 2012 - March 2013

Education

October 2002 - July 2008

## Publications

Publications (44)

The higher category theory can be employed to generalize the BF action to the so-called 3BF action, by passing from the notion of a gauge group to the notion of a gauge three-group. In this work we determine the full gauge symmetry of the 3BF action. To that end, the complete Hamiltonian analysis of the 3BF action for an arbitrary semistrict Lie th...

We study a generalization of a 4-dimensional BF-theory in the context of higher gauge theory. We construct a triangulation independent topological state sum Z, based on the classical 3BF action for a general 3-group and a 4-dimensional spacetime manifold. This state sum coincides with Porter's TQFT for d=4 and n=3. In order to verify that the const...

We give a brief overview how to couple general relativity to the Standard Model of elementary particles, within the higher gauge theory framework, suitable for the spinfoam quantization procedure. We begin by providing a short review of all relevant mathematical concepts, most notably the idea of a categorical ladder, 3-groups and generalized paral...

The higher category theory can be employed to generalize the BF action to the so-called 3BF action, by passing from the notion of a gauge group to the notion of a gauge 3-group. In this work we determine the full gauge symmetry of the 3BF action. To that end, the complete Hamiltonian analysis of the 3BF action for a general Lie 3-group is performed...

This work overviews the single-particle two-way communication protocol recently introduced by del Santo and Daki\'c (dSD), and analyses it using the process matrix formalism. We give a detailed account of the violation of causal inequalities via this protocol and discuss the importance of the vacuum state -- in particular its role in the process ma...

We show that a categorical generalization of the the Poincar\'e symmetry which is based on the $n$-crossed modules becomes natural and simple when $n=3$ and that the corresponding 3-form and 4-form gauge fields have to be a Dirac spinor and a Lorentz scalar, respectively. Hence by using a Poincar\'e 4-group we naturally incorporate fermionic and sc...

We study the notion of causal orders for the cases of (classical and quantum) circuits and spacetime events. We show that every circuit can be immersed into a classical spacetime, preserving the compatibility between the two causal structures. Using the process matrix formalism, we analyse the realisations of the quantum switch using 4 and 3 spacet...

We provide several examples of higher gauge theories, constructed as generalizations of a BF model to 2BF and 3BF models with constraints. Using the framework of higher category theory, we introduce appropriate 2-groups and 3-groups, and construct the actions for the corresponding constrained 2BF and 3BF theories. In this way, we can construct acti...

The higher category theory can be employed to generalize the BF action to the so-called 3BF action, by passing from the notion of a gauge group to the notion of a gauge 3-group. The theory of scalar electrodynamics coupled to Einstein-Cartan gravity can be formulated as a constrained 3BF theory for a specific choice of the gauge 3-group. The comple...

The higher category theory can be employed to generalize the B F action to the so-called 3 B F action, by passing from the notion of a gauge group to the notion of a gauge 3-group. The theory of scalar electrodynamics coupled to Einstein–Cartan gravity can be formulated as a constrained 3 B F theory for a specific choice of the gauge 3-group. The c...

We study the notion of causal orders for the cases of (classical and quantum) circuits and spacetime events. We show that every circuit can be immersed into a classical spacetime, preserving the compatibility between the two causal structures. Within the process matrix formalism, we analyse the realisations of the quantum switch using 4 and 3 gates...

We perform the complete Hamiltonian analysis of the BFCG action for general relativity. We determine all the constraints of the theory and classify them into the first-class and the second-class constraints. We also show how the canonical formulation of BFCG general relativity reduces to the Einstein-Cartan and triad canonical formulations. The red...

We show that gravity and matter fields are always entangled, as a consequence of the local Poincar\'e symmetry. First, we present a generic argument, applicable to any particular theory of quantum gravity with matter, by performing the analysis in the abstract nonperturbative canonical framework, demonstrating that the scalar constraint allows for...

We perform the complete Hamiltonian analysis of the BFCG action for General Relativity. We determine all the constraints of the theory and classify them into the first-class and the second-class constraints. We also show how the canonical formulation of BFCG General Relativity reduces to the Einstein-Cartan and triad canonical formulations. The red...

We describe a theory of quantum gravity which is based on the assumption that the spacetime structure at small distances is given by a piecewise linear (PL) 4-manifold corresponding to a triangulation of a smooth 4-manifold. The fundamental degrees of freedom are the edge lengths of the triangulation. One can work with finitely many edge lengths, s...

We study the derivation of the effective equation of motion for a pointlike particle in the framework of quantum gravity. Just like the geodesic motion of a classical particle is a consequence of classical field theory coupled to general relativity, we introduce the similar notion of an effective equation of motion, but starting from an abstract qu...

We perform a complete Hamiltonian analysis of the BFCG action for a general Lie 2-group by using the Dirac procedure. We show that the resulting dynamical constraints eliminate all local degrees of freedom which implies that the BFCG theory is a topological field theory.

We perform the full Hamiltonian analysis of the topological BFCG action based on the Poincaré 2-group. The Hamiltonian of the theory is constructed, and the algebra of constraints is computed. The Dirac brackets are evaluated, and the second class constraints are then eliminated from the theory. The results are contrasted with those of the topologi...

We argue that Hartle-Hawking states in the Regge quantum gravity model generically contain non-trivial entanglement between gravity and matter fields. Generic impossibility to talk about "matter in a point of space" is in line with the idea of an emergent spacetime, and as such could be taken as a possible candidate for a criterion for a plausible...

We study the implications of the simplicity constraint in the spincube model
of quantum gravity. By relating the edge-lengths to the integer areas of
triangles, the simplicity constraint imposes very strong restrictions between
them, ultimately leading to a requirement that all 4-simplices in the
triangulation must be almost mutually identical. As...

We give a brief review of the problem of quantum gravity. After the
discussion of the nonrenormalizability of general relativity, we briefly
mention the main research directions which aim to resolve this problem. Our
attention then focuses on the approach of Loop Quantum Gravity, specifically
spinfoam models. These models have some issues concernin...

We show that it is possible to solve the cosmological constant (CC) problem
in a discrete quantum gravity theory based on Regge calculus by using the
effective action approach and a special path-integral measure. The effective
cosmological constant is a sum of 3 terms: the classical CC, the quantum
gravity CC and the matter CC. Since observations c...

We study the quantum contributions to the classical cosmological constant in
a Regge state-sum model of quantum gravity in the effective action approach. We
use a special path-integral measure and we include matter, in the form of a
massive scalar field. The effective cosmological constant is given as a sum of
3 terms: the classical CC, the quantum...

We calculate the classical limit effective action of the EPRL/FK spinfoam
model of quantum gravity coupled to matter fields. By employing the standard
QFT background field method adapted to the spinfoam setting, we find that the
model has many different classical effective actions. Most notably, these
include the ordinary Einstein-Hilbert action co...

We show that the EPRL/FK spin foam model of quantum gravity has an absolutely
convergent partition function if the vertex amplitude is divided by an
appropriate power $p$ of the product of dimensions of the vertex spins. This
power is independent of the spin foam 2-complex and we find that $p>2$ insures
the convergence of the state sum. Determining...

Classical dynamics of a brane-like object in Riemann-Cartan geometry is ob- tained from the conservation law of its stress-energy and spin tensors. We apply the general world-sheet equations to the Nambu-Goto type of membrane with totally antisymmetric spin tensor parallel to the world-sheet. The resulting equations are recognized as the 3- dimensi...

We show that General Relativity can be formulated as a constrained
topological theory for flat 2-connections associated to the Poincar\'e 2-group.
Matter can be consistently coupled to gravity in this formulation. We also show
that the edge lengths of the spacetime manifold triangulation arise as the
basic variables in the path-integral quantizatio...

We show that a natural modification of the EPRL/FK vertex amplitude gives a
finite spin foam model whose effective action gives the Einstein-Hilbert action
in the limit of large spins and arbitrarily fine spacetime triangulations. The
first-order quantum corrections can be easily computed and we show how to
calculate the higher-order corrections.

We give a brief review of the problem of quantum gravity. After the discussion of the nonrenormalizability of general relativity, we briefly mention the main research directions which aim to resolve this problem. Our attention then focuses on the approach of Loop Quantum Gravity, specifically spinfoam models. These models have some issues concernin...

We define an effective action for spin-foam models of quantum gravity by adapting the background field method from quantum field theory. We show that the Regge action is the leading term in the semi-classical expansion of the spin-foam effective action if the vertex amplitude has the large-spin asymptotics which is proportional to an exponential fu...

We analyze the large-spin asymptotics of a class of spin-network wavefunctions of Euclidean loop quantum gravity, which corresponds to a flat spacetime. A wavefunction from this class can be represented as a sum over the spins of an amplitude for a spin network whose graph is a composition of the wavefunction spin network graph with the dual one-co...

We study the classical limit of the ELPR/FK spin foam models by analyzing the
large-distance asymptotics of the corresponding graviton propagators. This is
done by examining the large-spin asymptotics of the Hartle-Hawking wavefunction
which is peaked around a classical flat spatial geometry. By using the
stationary phase method we determine the wa...

We study the problem of semiclassical limit of Loop Quantum Gravity theory
defined by the new spin foam models. This is done by analyzing the large-spin
asymptotics of the Hartle-Hawking wavefunction. By using the stationary phase
method we determine the wavefunction asymptotics, which then determines the
large-distance asymptotics of the correspon...

We analyze the large-spin asymptotics of a class of spin-network
wavefunctions of Euclidean Loop Quantum Gravity, which corresponds to a flat
spacetime. A wavefunction from this class can be represented as a sum over the
spins of an amplitude for a spin network whose graph is a composition of the
the wavefunction spin network graph with the dual on...

The dynamics of brane-like extended objects in spacetimes with torsion is derived from the conservation equations of stress-energy and spin tensors. Thus obtained world-sheet equations are applied to macroscopic test membranes made of spinning matter. Specifically, we consider membranes with maximally symmetric distribution of stress-energy and spi...

We use the conservation law of the stress-energy and spin tensors to study the motion of massive brane-like objects in Riemann-Cartan geometry. The world-sheet equations and boundary conditions are obtained in a manifestly covariant form. In the particle case, the resultant world-line equations turn out to exhibit a novel spin-curvature coupling. I...

We use the conservation law of the stress-energy and spin tensors to study the motion of massive zero-size objects in Riemann-Cartan geometry. The resultant world line equations turn out to exhibit a novel spin-curvature coupling. In particular, the spin of the Dirac particle does not couple to the background curvature. This is a consequence of its...

Classical dynamics of spinning zero-size objects in an external gravitational
field is derived from the conservation law of the stress-energy and spin
tensors. The resulting world line equations differ from those in the existing
literature. In particular, the spin of the Dirac particle does not couple to
the background curvature. As a check of cons...

Within the framework of generalized Papapetrou method, we derive the effective equations of motion for a string with two particles attached to its ends, along with appropriate boundary conditions. The equations of motion are the usual Nambu-Goto-like equations, while boundary conditions turn out to be equations of motion for the particles at the st...

Within the framework of generalized Papapetrou method, we derive the effective equations of motion for a string with two particles attached to its ends, along with appropriate boundary conditions. The equations of motion are the usual Nambu-Goto-like equations, while boundary conditions turn out to be equations of motion for the particles at the st...

Within the framework of generalized Papapetrou method, we derive the effective equations of motion for a string with two particles attached to its ends, along with appropriate boundary conditions. The equations of motion are the usual Nambu-Goto-like equations, while boundary conditions turn out to be equations of motion for the particles at the st...

The dynamics of a classical branelike object in a curved background is derived from the covariant stress-energy conservation of the brane matter. The world sheet equations and boundary conditions are obtained in the pole-dipole approximation, where nontrivial brane thickness gives rise to its intrinsic angular momentum. It is shown that intrinsic a...

The Mathisson-Papapetrou method is originally used for derivation of the particle world line equation from the covariant conservation of its stress-energy tensor. We generalize this method to extended objects, such as a string. Without specifying the type of matter the string is made of, we obtain both the equations of motion and boundary condition...

## Projects

Project (1)