## Seminars

### Winter term 2013/14

Date | Time | Speaker | Topic | Room |
---|---|---|---|---|

October 11 | 10:00 | Thaisa Guio
(Köln/Bonn) |
Masterkolloquium: “Decoherence and the Arrow of Time in Quantum Cosmology” | Seminarraum
BCTP, Bonn |

October 15 | 12:00 | Tagungsberichte/Bachelorkolloquium | R 215 | |

October 22 | 12:00 | Sandipan Sengupta
(Bangalore, India) |
Topological parameters in gravity | R 215 |

October 25 | 12:00 | Bachelorkolloquium | R 215 | |

October 29 | 12:00 | David Brizuela
(Köln/Bilbao) |
A formalism based on statistical moments for classical and quantum mechanics (Part I) | R 215 |

November 5 | 12:00 | Felix Bischof
David Brizuela (Köln/Bilbao) |
Two-loop Form Factor in N=2 SYM
A formalism based on statistical moments for classical and quantum mechanics (Part II) |
R 215 |

November 12 | 12:00 | Biswajit Paul
(Kolkata, India) |
Symmetries in the Regge–Teitelboim Type Cosmology | R 215 |

November 26 | 12:00 | Claus Kiefer
(Köln) |
Journal Club | R 215 |

December 3 | 12:00 | Yakov Itin
(Jerusalem) |
Wave propagation in electromagnetic systems with a linear response | R 215 |

December 17 | 12:00 | Manuel Krämer
(Köln) |
Journal Club | R 215 |

January 14 | 12:00 | Thaisa Guio
(Köln) |
Journal Club | R 215 |

January 21 | 12:00 | Maxim Eingorn
(NCCU, Durham, NC, USA) |
Discrete cosmology: scalar perturbations and dynamics of galaxies | R 215 |

January 28 | 12:00 | Maxim Eingorn
(NCCU, Durham, NC, USA) |
Requiem for multidimensional Kaluza–Klein models | R 215 |

February 20 | 14:00 | Mairi Sakellariadou
(King’s College London) |
Particle Physics and Cosmology from Almost Commutative Manifolds | R 215 |

16:00 | Hans-Thomas Elze
(Pisa) |
Action principle for cellular automata and the linearity of quantum mechanics | R 215 |

## Past seminars

Summer term 2013

Winter term 2012/13

Summer term 2012

Winter term 2011/12

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

Friedrich W. Hehl (Köln/Missouri-Columbia)

In special relativity, quantum matter can be classified according to mass-energy and spin. The corresponding field-theoretical notions are the energy-momentum-stress tensor T and the spin angular momentum tensor S. Since each object in physics carries energy and, if fermionic, also spin, the notions of T and S can be spotted in all domains of physics, starting from the mechanical stress in engineering mechanics, over the Maxwell stress in electrodynamics to the energy-momentum tensor of matter in special and in general relativity. We discuss, in particular, asymmetric stress tensors, spin fluids, the Belinfante-Rosenfeld symmetrization of T, the improved energy-momentum of Callan, Coleman, and Jackiw. We discuss in how far Weyl's dictum that only general relativity leads to a proper definition of the energy concept is appropriate. This seminar is open ended and tries to build bridges to relativistic themodynamics.

Close

**On Energy–Momentum & Spin: the inertial currents in classical field theory**In special relativity, quantum matter can be classified according to mass-energy and spin. The corresponding field-theoretical notions are the energy-momentum-stress tensor T and the spin angular momentum tensor S. Since each object in physics carries energy and, if fermionic, also spin, the notions of T and S can be spotted in all domains of physics, starting from the mechanical stress in engineering mechanics, over the Maxwell stress in electrodynamics to the energy-momentum tensor of matter in special and in general relativity. We discuss, in particular, asymmetric stress tensors, spin fluids, the Belinfante-Rosenfeld symmetrization of T, the improved energy-momentum of Callan, Coleman, and Jackiw. We discuss in how far Weyl's dictum that only general relativity leads to a proper definition of the energy concept is appropriate. This seminar is open ended and tries to build bridges to relativistic themodynamics.

Close

Sandipan Sengupta (Bangalore, India)

Gravity theory in four dimensions has three independent topological parameters. In the Lagrangian, these show up as coefficients of three topological densities, namely Nieh-Yan, Pontryagin and Euler. We analyse the Hamiltonian theory based on this generalized Lagrangian. The resulting theory develops a nontrivial dependence on all three parameters, and is shown to admit a SU(2) gauge theoretic interpretation with a set of seven first class constraints corresponding to three SU(2) rotations, three spatial diffeomorphism and one to evolution in a timelike direction.

We also study how the topological parameters affect the gravity action with or without a cosmological constant for manifolds with boundaries. For both Dirichlet and locally AdS asymptotia, the Barbero-Immirzi parameter is shown to appear as the only independent topological coupling constant in the action principle.

Our analyses indicate that there might be nontrivial implications of the topological parameters in the quantum theory of gravity.

Close

**Topological parameters in gravity**Gravity theory in four dimensions has three independent topological parameters. In the Lagrangian, these show up as coefficients of three topological densities, namely Nieh-Yan, Pontryagin and Euler. We analyse the Hamiltonian theory based on this generalized Lagrangian. The resulting theory develops a nontrivial dependence on all three parameters, and is shown to admit a SU(2) gauge theoretic interpretation with a set of seven first class constraints corresponding to three SU(2) rotations, three spatial diffeomorphism and one to evolution in a timelike direction.

We also study how the topological parameters affect the gravity action with or without a cosmological constant for manifolds with boundaries. For both Dirichlet and locally AdS asymptotia, the Barbero-Immirzi parameter is shown to appear as the only independent topological coupling constant in the action principle.

Our analyses indicate that there might be nontrivial implications of the topological parameters in the quantum theory of gravity.

Close

Biswajit Paul (Kolkata, India)

Since their introduction, theories with higher derivatives are unavoidable and frequently arise in different contexts. Hamiltonian formulation for Higher derivative theories become necessary and is discussed in the first order formalism. This Hamiltonian formulation is applied to the minisuperspace cosmology following from the geodetic brane gravity model introduced by Regge and Teitelboim. The analysis is done using the equivalent first order approach. The constraint algebra is shown to realize a truncated Virasoro algebra. The gauge generator containing the exact number of gauge parameters is constructed. Equivalence between the gauge and reparametrization symmetries has been demonstrated. Complete gauge fixed computations have been provided and formal quantization is indicated.

Close

**Symmetries in the Regge–Teitelboim Type Cosmology**Since their introduction, theories with higher derivatives are unavoidable and frequently arise in different contexts. Hamiltonian formulation for Higher derivative theories become necessary and is discussed in the first order formalism. This Hamiltonian formulation is applied to the minisuperspace cosmology following from the geodetic brane gravity model introduced by Regge and Teitelboim. The analysis is done using the equivalent first order approach. The constraint algebra is shown to realize a truncated Virasoro algebra. The gauge generator containing the exact number of gauge parameters is constructed. Equivalence between the gauge and reparametrization symmetries has been demonstrated. Complete gauge fixed computations have been provided and formal quantization is indicated.

Close

Felix Bischof

It is known that there are close connections between certain amplitudes in supersymmetric theories and QCD. We aim to investigate whether such connections exist for the two-loop Higgs form factor in N=2 SYM and QCD. We hereby illustrate common techniques in two-loop computations.

Close

**Two-loop Form Factor in N=2 SYM**It is known that there are close connections between certain amplitudes in supersymmetric theories and QCD. We aim to investigate whether such connections exist for the two-loop Higgs form factor in N=2 SYM and QCD. We hereby illustrate common techniques in two-loop computations.

Close

Yakov Itin (Jerusalem)

A covariant description of a generic electromagnetic medium requires a set of 36 independent parameters, instead of two ordinary material parameters, epsilon and \mu. Such a set is arranged in a 4-th order constitutive tensor. Due to the group theory, this tensor is irreducibly decomposed into the sum of three independent sub-tensors. The first principal part is a substitution of the classical set of parameters. Two other tensors, skewon and axion, have no classical analogs and may represent some novel properties of media or artificial materials.

In my talk, I will describe how the generalized covariant dispersion relation is derived. The result is in a correspondence with the formula proposed by Hehl, Obukhov and Rubilar. I define the notion of optic tensor (an analog of acoustic tensor from elasticity) and describe its properties. With this new device, I show some new results about the skewon modified media. The most visual outcome is a proof that in the skewon modified vacuum the wave propagation is necessary superluminal. It means that the skewon is probably forbidden in vacuum, but not in material media.

Close

**Wave propagation in electromagnetic systems with a linear response**A covariant description of a generic electromagnetic medium requires a set of 36 independent parameters, instead of two ordinary material parameters, epsilon and \mu. Such a set is arranged in a 4-th order constitutive tensor. Due to the group theory, this tensor is irreducibly decomposed into the sum of three independent sub-tensors. The first principal part is a substitution of the classical set of parameters. Two other tensors, skewon and axion, have no classical analogs and may represent some novel properties of media or artificial materials.

In my talk, I will describe how the generalized covariant dispersion relation is derived. The result is in a correspondence with the formula proposed by Hehl, Obukhov and Rubilar. I define the notion of optic tensor (an analog of acoustic tensor from elasticity) and describe its properties. With this new device, I show some new results about the skewon modified media. The most visual outcome is a proof that in the skewon modified vacuum the wave propagation is necessary superluminal. It means that the skewon is probably forbidden in vacuum, but not in material media.

Close

Maxim Eingorn (Odessa, Ukraine)

The mechanical approach to cosmological problems inside the cell of uniformity represents a very promising scientific research direction in modern cosmology. It may be also associated with discrete cosmology in the nonrelativistic limit. In its framework the observable inhomogeneous Universe is described in the first order approximation with respect to its deviation from the averaged homogeneous FLRW one, the gravitational potentials of separate inhomogeneities (galaxies) are found and their relative motion (particularly, the motion of the Milky Way and Andromeda as well as the dwarf galaxies around our Local Group) is investigated in detail. It turns out that the characteristic features of scalar perturbations (including, for example, singularities in the places of gravitating masses locations and beyond them) are sensitive to spatial topology and composition of the Universe. Thus, the discrete cosmology screens powerfully different cosmological models and sheds light on the spacetime structure and its filling.

Close

**Discrete cosmology: scalar perturbations and dynamics of galaxies**The mechanical approach to cosmological problems inside the cell of uniformity represents a very promising scientific research direction in modern cosmology. It may be also associated with discrete cosmology in the nonrelativistic limit. In its framework the observable inhomogeneous Universe is described in the first order approximation with respect to its deviation from the averaged homogeneous FLRW one, the gravitational potentials of separate inhomogeneities (galaxies) are found and their relative motion (particularly, the motion of the Milky Way and Andromeda as well as the dwarf galaxies around our Local Group) is investigated in detail. It turns out that the characteristic features of scalar perturbations (including, for example, singularities in the places of gravitating masses locations and beyond them) are sensitive to spatial topology and composition of the Universe. Thus, the discrete cosmology screens powerfully different cosmological models and sheds light on the spacetime structure and its filling.

Close

Mairi Sakellariadou (King’s College London)

The unification of the four fundamental forces remains one of the most important issues in theoretical particle physics. In this talk, I will first give a short introduction to noncommutative spectral geometry, a bottom-up approach that unifies the (successful) Standard Model of high energy physics with Einstein's General theory of Relativity. The model is build upon almost-commutative spaces and I will discuss the physical implications of the choice of such manifolds. I will show that even though the unification has been obtained only at the classical level, the doubling of the algebra may incorporate the seeds of quantisation. I will then briefly review the particle physics phenomenology and highlight open issues and current proposals. In the last part of my talk, I will explore consequences of the gravitational-Higgs part of the spectral action formulated within such almost-commutative manifolds. In particular, I will study modifications of the Friedmann equation, propagation of gravitational waves and the onset of inflation. I will show how current measurements (Gravity Probe B and pulsars) can constrain free parameters of the model. I will conclude with a short discussion on open questions.

Close

**Particle Physics and Cosmology from Almost Commutative Manifolds**The unification of the four fundamental forces remains one of the most important issues in theoretical particle physics. In this talk, I will first give a short introduction to noncommutative spectral geometry, a bottom-up approach that unifies the (successful) Standard Model of high energy physics with Einstein's General theory of Relativity. The model is build upon almost-commutative spaces and I will discuss the physical implications of the choice of such manifolds. I will show that even though the unification has been obtained only at the classical level, the doubling of the algebra may incorporate the seeds of quantisation. I will then briefly review the particle physics phenomenology and highlight open issues and current proposals. In the last part of my talk, I will explore consequences of the gravitational-Higgs part of the spectral action formulated within such almost-commutative manifolds. In particular, I will study modifications of the Friedmann equation, propagation of gravitational waves and the onset of inflation. I will show how current measurements (Gravity Probe B and pulsars) can constrain free parameters of the model. I will conclude with a short discussion on open questions.

Close

Hans-Thomas Elze (Pisa)

We introduce an action principle for a class of integer valued cellular automata and obtain Hamiltonian equations of motion. Employing sampling theory, these discrete deterministic equations are invertibly mapped on continuum equations for a set of bandwidth limited harmonic oscillators, which encode the Schroedinger equation. Thus, the linearity of quantum mechanics is related to the action principle of such cellular automata and its conservation laws to discrete ones.

Reference: Phys. Rev. A (2014), to appear (arXiv:1312.1615).

Close

**Action principle for cellular automata and the linearity of quantum mechanics**We introduce an action principle for a class of integer valued cellular automata and obtain Hamiltonian equations of motion. Employing sampling theory, these discrete deterministic equations are invertibly mapped on continuum equations for a set of bandwidth limited harmonic oscillators, which encode the Schroedinger equation. Thus, the linearity of quantum mechanics is related to the action principle of such cellular automata and its conservation laws to discrete ones.

Reference: Phys. Rev. A (2014), to appear (arXiv:1312.1615).

Close