Seminars
Winter term 2011/12
| Date | Time | Speaker | Topic | Room |
|---|---|---|---|---|
| 11 October | 12:00 | Friedemann Queißer
(Duisburg-Essen) |
Sauter-Schwinger like tunneling in tilted Bose-Hubbard lattices in the Mott phase | R 215 |
| 18 October | 12:00 | Arbeitsgruppe
|
Bericht über besuchte Tagungen | R 215 |
| 25 October | 12:00 | Roman Andree
(Humboldt-Uni, Berlin) |
Wilson loops in N = 4 and N = 2 supersymmetric Yang-Mills 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 | Hans-Thomas Elze
(Pisa) |
Quantum-classical 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 (Duisburg-Essen)
Sauter-Schwinger like tunneling in tilted Bose-Hubbard lattices in the Mott phase
Within the Bose-Hubbard 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 Bose-Hubbard model on a tilted lattice. On the (Gutzwiller) mean-field level, the tilt has no effect -- but quantum fluctuations entail particle-hole pair creation via tunneling. For small potential gradients (long-wavelength limit), I derive a quantitative analogy to the Sauter-Schwinger effect, i.e., electron-positron pair creation out of the vacuum by an electric field.
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Sauter-Schwinger like tunneling in tilted Bose-Hubbard lattices in the Mott phase
Within the Bose-Hubbard 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 Bose-Hubbard model on a tilted lattice. On the (Gutzwiller) mean-field level, the tilt has no effect -- but quantum fluctuations entail particle-hole pair creation via tunneling. For small potential gradients (long-wavelength limit), I derive a quantitative analogy to the Sauter-Schwinger effect, i.e., electron-positron pair creation out of the vacuum by an electric field.
Close
Roman Andree (Humboldt-Uni, Berlin)
Wilson loops in N = 4 and N = 2 supersymmetric Yang-Mills 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 Yang-Mills (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 Yang-Mills 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 Yang-Mills (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 inverse-volume 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.
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Inflationary observables and observational constraints in loop quantum cosmology
In the inflationary scenario of loop quantum cosmology (LQC) in the presence of inverse-volume 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.
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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 Foldy-Wouthuysen representation. The quantum mechanical dynamics and the classical equations for particles with spin are compared.
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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 Foldy-Wouthuysen representation. The quantum mechanical dynamics and the classical equations for particles with spin are compared.
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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 CMC-volume and CFTs, ansaetze for quantization and/or current work on symmetry doubling from symmetry trading.
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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 CMC-volume 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
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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
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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 cyclicity-inducing measure of k-Minkowski. For larger scale, the averaged fractional measure can be obtained as the ciclicity-inducing measure from a certain nonlinear algebra. This fractional algebra is given a physical interpretation as an interpolating spacetime structure between k-Minkowski 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 cyclicity-inducing measure of k-Minkowski. For larger scale, the averaged fractional measure can be obtained as the ciclicity-inducing measure from a certain nonlinear algebra. This fractional algebra is given a physical interpretation as an interpolating spacetime structure between k-Minkowski and canonical noncommutativity.
Close
Hans-Thomas Elze (Pisa)
Quantum-classical hybrid dynamics
A new formulation of quantum-classical 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 quantum-classical 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 quantum-classical 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.
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Quantum-classical hybrid dynamics
A new formulation of quantum-classical 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 quantum-classical 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 quantum-classical 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