Seminars
Winter term 2011/12
Date  Time  Speaker  Topic  Room 

11 October  12:00  Friedemann Queißer
(DuisburgEssen) 
SauterSchwinger like tunneling in tilted BoseHubbard lattices in the Mott phase  R 215 
18 October  12:00  Arbeitsgruppe

Bericht über besuchte Tagungen  R 215 
25 October  12:00  Roman Andree
(HumboldtUni, Berlin) 
Wilson loops in N = 4 and N = 2 supersymmetric YangMills theory  R 215 
8 November  12:00  Claus Kiefer

Bericht Tagung Montpellier  R 215 
15 November  12:00  Thomas Wotschke
(Bonn) 
Black Holes, BPS State Counting and Modularity  R 215 
22 November  12:00  Gianluca Calcagni
(Potsdam) 
Inflationary observables and observational constraints in loop quantum cosmology  R 215 
29 November  12:00  Yuri Obukhov
(Köln) 
Dirac fermion particle in the gravitational field  R 215 
13 December  12:00  Tim Koslowski
(Perimeter Institute) 
Shape Dynamics  R 215 
20 December  12:00  Christopher Max
(Köln) 
Bachelorkolloquium  R 215 
22 December  16:00  Alberto Favaro
(Imperial College, London) 
Closure relations for electromagnetism  R 215 
10 January  12:00  David Brizuela
(MPI, Potsdam) 
Semiclassical analysis of the quantum back reaction in a universe with positive cosmological constant  R 215 
24 January  12:00  Stefan Kurz
(Tampere, Finland) 
A new definition of a coordinate independent observer in relativistic electrodynamics  R 215 
31 January  12:00  Marco Scalisi
(MPI, Potsdam) 
Fractal and Noncommutative spacetimes: a connection  R 215 
10 February  11:00  Christian Schell
(Köln) 
Diploma colloquium: “Decoherence in Loop Quantum Cosmology with Fermions”  R 215 
16 March  10:00  HansThomas Elze
(Pisa) 
Quantumclassical hybrid dynamics  R 215 
Past seminars
Summer term 2011
Winter term 2010/11
Summer term 2010
Winter term 2009/10
Summer term 2009
Winter term 2008/09
Summer term 2008
Winter term 2007/08
Summer term 2007
Winter term 2006/07
Summer term 2006
Summer term 2005
Winter term 2004/05
Summer term 2004
Winter term 2003/04
Summer term 2003
Friedemann Queißer (DuisburgEssen)
SauterSchwinger like tunneling in tilted BoseHubbard lattices in the Mott phase
Within the BoseHubbard model, I establish a hierarchy of correlations via a controlled expansion into inverse powers of the coordination number 1/Z . Using this approach, I study the Mott phase of the BoseHubbard model on a tilted lattice. On the (Gutzwiller) meanfield level, the tilt has no effect  but quantum fluctuations entail particlehole pair creation via tunneling. For small potential gradients (longwavelength limit), I derive a quantitative analogy to the SauterSchwinger effect, i.e., electronpositron pair creation out of the vacuum by an electric field.
Close
SauterSchwinger like tunneling in tilted BoseHubbard lattices in the Mott phase
Within the BoseHubbard model, I establish a hierarchy of correlations via a controlled expansion into inverse powers of the coordination number 1/Z . Using this approach, I study the Mott phase of the BoseHubbard model on a tilted lattice. On the (Gutzwiller) meanfield level, the tilt has no effect  but quantum fluctuations entail particlehole pair creation via tunneling. For small potential gradients (longwavelength limit), I derive a quantitative analogy to the SauterSchwinger effect, i.e., electronpositron pair creation out of the vacuum by an electric field.
Close
Roman Andree (HumboldtUni, Berlin)
Wilson loops in N = 4 and N = 2 supersymmetric YangMills theory
Wilson loops provide properties to investigate the so called AdS/CFT correspondence. A correspondence between a type IIB string theory on an AdS_5 x S5 and a supersymmetric YangMills (SYM) theory with N = 4 supersymmetries on a 4 dimensional base manifold. In this talk I will consider the CFT side. An investigation of the pertubative behavior of an expectation value of a circular Wilson loop in an N = 4 and N = 2 SYM theory yields a difference term proportional to g6 in coupling constant and zeta function of 3, coming from the second loop order. This can be easily shown by a matrix model. I will show how to recover this result by standard perturbation theory and how simplify the extensive calculations.
Close
Wilson loops in N = 4 and N = 2 supersymmetric YangMills theory
Wilson loops provide properties to investigate the so called AdS/CFT correspondence. A correspondence between a type IIB string theory on an AdS_5 x S5 and a supersymmetric YangMills (SYM) theory with N = 4 supersymmetries on a 4 dimensional base manifold. In this talk I will consider the CFT side. An investigation of the pertubative behavior of an expectation value of a circular Wilson loop in an N = 4 and N = 2 SYM theory yields a difference term proportional to g6 in coupling constant and zeta function of 3, coming from the second loop order. This can be easily shown by a matrix model. I will show how to recover this result by standard perturbation theory and how simplify the extensive calculations.
Close
Thomas Wotschke (Bonn)
Black Holes, BPS State Counting and Modularity
For a certain class of supersymmetric black holes, Strominger and Vafa showed how to compute the microscopic entropy by using string theory methods. Determining the microscopic entropy boils down to a counting problem of so called BPS states. This counting can often be organized by using the mathematical language of modular forms. In recent years it was observed that the new class of mock modular forms is needed in order to take care of decays of the black hole microstates. We review these results and comment on the interplay between mathematics and physics with a special focus on modular forms.
Close
Black Holes, BPS State Counting and Modularity
For a certain class of supersymmetric black holes, Strominger and Vafa showed how to compute the microscopic entropy by using string theory methods. Determining the microscopic entropy boils down to a counting problem of so called BPS states. This counting can often be organized by using the mathematical language of modular forms. In recent years it was observed that the new class of mock modular forms is needed in order to take care of decays of the black hole microstates. We review these results and comment on the interplay between mathematics and physics with a special focus on modular forms.
Close
Gianluca Calcagni (MPI, Potsdam)
Inflationary observables and observational constraints in loop quantum cosmology
In the inflationary scenario of loop quantum cosmology (LQC) in the presence of inversevolume corrections, we study the power spectra of scalar and tensor perturbations convenient to confront with observations. Using the recent data of cosmic microwave background (CMB) and other cosmological experiments, for the first time we place experimental bounds on the LQC quantum corrections for several inflaton potentials.
Close
Inflationary observables and observational constraints in loop quantum cosmology
In the inflationary scenario of loop quantum cosmology (LQC) in the presence of inversevolume corrections, we study the power spectra of scalar and tensor perturbations convenient to confront with observations. Using the recent data of cosmic microwave background (CMB) and other cosmological experiments, for the first time we place experimental bounds on the LQC quantum corrections for several inflaton potentials.
Close
Yuri Obukhov (Köln)
Dirac fermion particle in the gravitational field
The dynamics of the Dirac fermions in arbitrary gravitational fields is discussed. The general Hermitian Dirac Hamiltonian is derived and then we transform it to the FoldyWouthuysen representation. The quantum mechanical dynamics and the classical equations for particles with spin are compared.
Close
Dirac fermion particle in the gravitational field
The dynamics of the Dirac fermions in arbitrary gravitational fields is discussed. The general Hermitian Dirac Hamiltonian is derived and then we transform it to the FoldyWouthuysen representation. The quantum mechanical dynamics and the classical equations for particles with spin are compared.
Close
Tim Koslowski (Perimeter Insitute)
Shape dynamics
Shape Dynamics is a reformulation of GR that trades refoliation invariance for local spatial conformal invariance (symmetry trading). The proof of equivalence with GR is based on Barbour's Machian ideas. I will discuss the construction of Shape Dynamics. Then I will show how it can be coupled to standard matter. Depending on individual interest I will discuss Shape Dynamics in 2+1 dimensions, theclassical correspondence between large CMCvolume and CFTs, ansaetze for quantization and/or current work on symmetry doubling from symmetry trading.
Close
Shape dynamics
Shape Dynamics is a reformulation of GR that trades refoliation invariance for local spatial conformal invariance (symmetry trading). The proof of equivalence with GR is based on Barbour's Machian ideas. I will discuss the construction of Shape Dynamics. Then I will show how it can be coupled to standard matter. Depending on individual interest I will discuss Shape Dynamics in 2+1 dimensions, theclassical correspondence between large CMCvolume and CFTs, ansaetze for quantization and/or current work on symmetry doubling from symmetry trading.
Close
Alberto Favaro (Imperial College, London)
Closure relations for electromagnetism
Link to abstract as PDF
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Closure relations for electromagnetism
Link to abstract as PDF
Close
David Brizuela (MPI, Potsdam)
Semiclassical analysis of the quantum back reaction in a universe with positive cosmological constant
We will present a systematic method to analyze the quantum back reaction of any system with one degree of freedom. The key ingredients of our approach are a decomposition of the wave function in terms of moments and an intensive use of computer algebra tools. The equations of motion for the moments form an infinite set of coupled diffential equations. Nevertheless, under appropriate semiclassical conditions, this system can be truncated at a given order and still will accurately described its quantum dynamics. Finally, we will apply these general tools to the analysis of a homogeneous universe with a positive cosmological constant and show the physical consequences of the quantum back reaction.
Close
Semiclassical analysis of the quantum back reaction in a universe with positive cosmological constant
We will present a systematic method to analyze the quantum back reaction of any system with one degree of freedom. The key ingredients of our approach are a decomposition of the wave function in terms of moments and an intensive use of computer algebra tools. The equations of motion for the moments form an infinite set of coupled diffential equations. Nevertheless, under appropriate semiclassical conditions, this system can be truncated at a given order and still will accurately described its quantum dynamics. Finally, we will apply these general tools to the analysis of a homogeneous universe with a positive cosmological constant and show the physical consequences of the quantum back reaction.
Close
Stefan Kurz (Tampere, Finland)
A new definition of a coordinate independent observer in relativistic electrodynamics
Link to abstract as PDF
Close
A new definition of a coordinate independent observer in relativistic electrodynamics
Link to abstract as PDF
Close
Marco Scalisi (MPI, Potsdam)
Fractal and Noncommutative spacetimes: a connection
We examine, in parallel, fractal and noncommmutative spacetimes. Focusing on the action functional and on its nontrivial measure, we find a mapping between them. Depending on the scale at which the relation is estabilished, two possibilities arise. Near a fractional fundamental scale, identified with the Planck scale, the effective measure coincides with a cyclicityinducing measure of kMinkowski. For larger scale, the averaged fractional measure can be obtained as the ciclicityinducing measure from a certain nonlinear algebra. This fractional algebra is given a physical interpretation as an interpolating spacetime structure between kMinkowski and canonical noncommutativity.
Close
Fractal and Noncommutative spacetimes: a connection
We examine, in parallel, fractal and noncommmutative spacetimes. Focusing on the action functional and on its nontrivial measure, we find a mapping between them. Depending on the scale at which the relation is estabilished, two possibilities arise. Near a fractional fundamental scale, identified with the Planck scale, the effective measure coincides with a cyclicityinducing measure of kMinkowski. For larger scale, the averaged fractional measure can be obtained as the ciclicityinducing measure from a certain nonlinear algebra. This fractional algebra is given a physical interpretation as an interpolating spacetime structure between kMinkowski and canonical noncommutativity.
Close
HansThomas Elze (Pisa)
Quantumclassical hybrid dynamics
A new formulation of quantumclassical hybrid dynamics is presented, which concerns the direct coupling of classical and quantum mechanical degrees of freedom  of interest for approximation schemes and for the foundations of quantum mechanics, in particular at the quantumclassical border. The present linear theory differs from the nonlinear ensemble theory of Hall and Reginatto, but shares with it to fulfill all consistency requirements discussed in the literature, while earlier attempts failed to do this. Our work is based on a representation of quantum mechanics in the framework of classical analytical mechanics, showing that notions of states in phase space, observables, Poisson brackets, and related canonical transformations can be naturally extended to quantum mechanics and generalized for quantumclassical hybrids (arXiv:1111.2276 and 1202.3448). Classically induced decoherence, backreaction, separable interactions, enlarged algebra of observables, (non)locality, and “free will” can be discussed here.
Close
Quantumclassical hybrid dynamics
A new formulation of quantumclassical hybrid dynamics is presented, which concerns the direct coupling of classical and quantum mechanical degrees of freedom  of interest for approximation schemes and for the foundations of quantum mechanics, in particular at the quantumclassical border. The present linear theory differs from the nonlinear ensemble theory of Hall and Reginatto, but shares with it to fulfill all consistency requirements discussed in the literature, while earlier attempts failed to do this. Our work is based on a representation of quantum mechanics in the framework of classical analytical mechanics, showing that notions of states in phase space, observables, Poisson brackets, and related canonical transformations can be naturally extended to quantum mechanics and generalized for quantumclassical hybrids (arXiv:1111.2276 and 1202.3448). Classically induced decoherence, backreaction, separable interactions, enlarged algebra of observables, (non)locality, and “free will” can be discussed here.
Close