# Talks

# 2017

# February

28. February 2017

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

Location: | ZARM, University of Bremen, Room 1280 |

When: | 14:30 |

Speaker: | Vittorio De Falco (ISSI, Bern, Switzerland) |

Title: | Approximate analytical calculations of photon geodesics in the Schwarzschild metric |

Topic: | In this talk, we show a method for deriving approximate analytical formulae. to integrate photon geodesics in a Schwarzschild spacetime. Based on this, we derive the approximate equations for light bending and propagation delay that have been introduced empirically already respectively by Beloborodov 2002 and Poutanen & Beloborodov 2006. We then derive for the first time an approximate analytical equation for the solid angle. We discuss the accuracy and range of applicability of the new equations and present a few simple applications of them to known astrophysical problems, that are: light curve from an emitting clump orbiting a black hole, emission line profile from an accretion disk around a black hole and light curve from a hot spot on the surface of a rotating neutron star. |

16 - 18 February 2017

**SEMINAR**

**7th Central European Relativity Seminar 2017**

Where: | Bremen "Haus der Wissenschaften" - Sandstraße 4/5, 28195 Bremen, Olbers Saal, first floor |

What: | This is the seventh seminar of a series initiated at the ESI (Vienna) January 27 - 29, 2011. This series of seminars is designed to provide a forum for younger researchers to present their work, and to expand their research horizons. The main geographical basin of attraction is Austria, the Czech Republic, Hungary, Poland and Germany. |

Topics: | The scientific program will include keynote lectures by D. Giulini and C. Lämmerzahl, as well as seminars by young researchers selected on the basis of submitted abstracts. The speakers will be chosen mainly amongst graduate students and post-docs. Anticipated are about 24 talks of 20 minutes each. A few longer talks might replace some of the shorter ones if scientifically or pedagogically desirable. The seminar will be accompanied by a public lecture (in english) by Jochen Liske, Hamburger Sternwarte, Universität Hamburg, on 18.02.2017, 15.30, entitled: "The World's Largest Telescope and the Acceleration of the Universe" |

Abstracts: | Abstracts submitted by January 15, 2017, will receive full consideration. Later submissions might be considered if the schedule allows. Abstract submission |

# January

25. January 2017

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

Location: | ZARM, University of Bremen, Room 1280 |

When: | 16:00 |

Speaker: | Dr. Souvik Banerjee (Uppsala University) |

Title: | 2. Lecture on Quantum Mechanics and General Relativity |

Topic: | The second of two lectures on black holes, the black hole information paradox, in general on the conflict between GR and QM, locality, a possible resolution of the information paradox, and on some further recent developments. |

24. January 2017

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

Location: | ZARM, University of Bremen, Room 1280 |

When: | 14:30 |

Speaker: | Dr. Souvik Banerjee (Uppsala University) |

Title: | 1. Lecture on Quantum Mechanics and General Relativity |

Topic: | The first of two lectures on black holes, the black hole information paradox, in general on the conflict between GR and QM, locality, a possible resolution of the information paradox, and on some further recent developments. |

# 2016

# December

6. December 2016

BREMEN - OLDENBURG RELATIVITY SEMINAR

Where: | ZARM, University of Bremen, Room 1280 |

When: | 14:00 |

Speaker: | Marko Toroš, Department of Physics University of Trieste |

Title: | Quantum Mechanics beyond Galileo" Time and Place |

Abstract: | We will discuss some problems related to combing relativity and quantum mechanics. We will first introduce Foldy's framework for quantum mechanics in Minkowski space-time. We will present some new results within the theory of relativistic open quantum systems. In particular, we will discuss dynamical maps, Lorentz covariance and non-inertial reference frames. In addition, we will also look at the implications for fundamental non-unitary modifications of quantum mechanics. |

2. December 2016

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

Where: | ZARM, University of Bremen, Room 1730 |

When: | 14:00 |

Speaker: | Anna Hedegaard Lukawska |

Title: | Correlation of cosmological observables in the effective field theory of inflation |

Abstract: | The temperature fluctuations in early universe are encoded in statistical properties of the CMB anisotropies. If the fluctuations follow a Gaussian statistics, then the connected three-point correlation function, four-point, and higher order correlation functions referred to as non-Gaussianities, are all vanishing, and all statistical information is given by the two-point correlation function. So far there are neither high statistical significance detections of a non-zero value for the three-point nor higher-order correlation functions. However, if non-Gaussianities of the primordial fluctuations are there, the correlations can provide valuable information on inflation. I will introduce this topic and present a study I have done on how big non-Gaussianities can be generated by single field models using the effective field theory of inflation. |

1. December 2016

BREMEN - OLDENBURG RELATIVITY SEMINAR

Where: | University of Oldenburg, Campus Wechloy, Room W2 3-349 |

When: | 16:15 |

Speaker: | Albert Samoilenko, Department of Theoretical Physics and Astrophysics, Belarusian State University, Minsk |

Title: | Gauged Baby Skyrme Model with and without Chern-Simons Term |

Abstract: | The properties of the multisoliton solutions of the U(1) gauged modification of the 2+1 dimensional planar Skyrme model with and without Chern-Simons term are investigated numerically. Coupling to the Chern-Simons term allows for existence of the electrically charged solitons which may also carry magnetic fluxes. Two particular choices of the potential term are considered: (i) the weakly bounded potential and (ii) the double vacuum potential. In the absence of the gauge interaction in the former case the individual constituents of the multisoliton configuration are well separated, while in the latter case the rotational invariance of the configuration remains unbroken. We analyze the dependency of the structure of the solutions, the energies, angular momenta, electric and magnetic fields of the configurations on the gauge coupling constant g, and the electric potential. It is found that, generically, the coupling to the Chern-Simons term strongly affects the usual pattern of interaction between the skyrmions, in particular the electric repulsion between the solitons may break the multisoliton configuration into partons. On the other hand, in the strong coupling limit the coupling to the gauge field results in effective recovering of the rotational invariance of the configuration and both the magnetic flux and the electric charge of the solutions become quantized, although they are not topological numbers. |

# November

**Change of room**

**Now:** TAB Building, Entrance E, Second floor, Room: 2.63

28 November 2016

Replacement Seminar

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

Where: | ZARM, University of Bremen, TAB Building, Entrance E, Second floor, Room: 2.63 |

When: | 14:30 |

Speaker: | Andrea Fuster, Eindhoven University of Technology |

Title: | Finsler gravitational waves |

Abstract: | In this work we present a Finslerian version of the well-known gravitational pp-waves, which generalizes the very special relativity (VSR) line element. Our Finsler pp-waves are an exact solution of Finslerian Einstein’s equations in vacuum. |

21. November 2016

**PHYSICAL COLLOQUIUM**

Where: | University of Oldenburg, W2-1-148 |

When: | 21.11.16, 4.15 p.m. |

Speaker: | Dr. Erik Curiel (Munich Center for Mathematical Philosophy, Germany) |

Topic: | Can Black Holes be described by Thermodynamics? |

Abstract: | Serious problems have been raised about the idea that black holes "really are thermodynamical objects", for instance: that the Zeroth Law for black holes, constancy of surface gravity, is not equivalent to the deepest formulation of the Zeroth Law for ordinary thermodynamics, transitivity of equilibrium; that black?hole area is neither an extensive nor an additive quantity, as ordinary thermodynamical entropy is; that a lack of a general, localized expression for gravitational energy makes it difficult to construct a thermodynamical internal energy for black holes; and several more along the same lines. The fundamental concern is that the mere fact that the relevant black?hole quantities satisfy formal analogues of the Laws of ordinary thermodynamics does not by itself guarantee that enough of the structure of ordinary thermodynamics is thereby recovered. There is much more to thermodynamics, after all, than just the four Laws. Transitivity of equilibrium, for instance, normally grounds the construction of the state space of an ordinary thermodynamical system and the arguments that isolated systems spontaneously approach equilibrium. I argue in this talk that all these problems can be answered, and that black?hole can meaningfully be treated as thermodynamical objects. |

Please download the invitation here

16. November 2016

**Physics Colloquium**

Where: | Jacobs University, Lecture Hall in Research III Campusring 3 |

When: | 17:15 – 18.15h |

Speaker: | Prof. Dr. Johann Kroha (Professor of Theoretical Physics, Physikalisches Institut, Universität Bonn) Additional Information |

Topic: | Particle Creation in Coupled Bose-Einstein Condensates and in the Early Universe |

Abstract: | Common knowledge tells that many-body systems come to thermodynamic equilibrium by coupling to a heat reservoir. In classical physics, even ideally isolated, macroscopic systems thermalize due to the equivalence of the microcanonical and the canonical ensembles. However, in quantum dynamics it is a fundamental problem how an isolated quantum many-body system can eventually come to rest from an initial nonequilibrium state, and whether the final state is a thermal one. The problem arises because the time evolution of a quantum system is unitary, that is, a single (pure) quantum state will remain pure for all times and can never reach a thermal state. Contrary to this theorem, one typically observes quantum many-body systems behave in a thermal way. This paradox has recently become more and more pressing, as isolated quantum systems can be realized in ultracold atomic gases with unprecedented control. This problem is also central for the evolution of the universe as an ideally isolated system. It is closely related to the creation of elementary particles. In this talk we will review some attempts at resolving the thermalization paradox. As a prototype of an isolated quantum system we will then consider an atomic Bose-Einstein condensate performing Josephson oscillations in a double-well potential trap. We will show that this system thermalizes by a complex dynamics, covered by three different time regimes: an initial period of undamped Josephson oscillations, an intermediate period of avalanche-like creation of bosonic quasiparticles out of the condensate and a slow thermalization regime induced by quasiparticle collisions [1]. We will draw a detailed analogy to the dynamics of elementary particle creation and thermalization during and after the inflationary phase of the early universe. |

For further information please contact:

Prof. Dr. Stefan Kettemann, Professor of Physics, Physics & Earth Sciences

Email: s.kettemann(at)jacobs-university.de

Tel: +49 421 200-3521

Homepage: http://skettemann.user.jacobs-university.de

All are welcome!

**Change of room**

**Now:** 28. November, 14:30, TAB Building, Entrance E, Second floor, Room: 2.63

08 November 2016

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

Where: | ZARM, University of Bremen, TAB Building, Entrance E, Second floor, Room: 2.63 |

When: | 14:30 |

Speaker: | Andrea Fuster, Eindhoven University of Technology |

Title: | Finsler gravitational waves |

Abstract: | In this work we present a Finslerian version of the well-known gravitational pp-waves, which generalizes the very special relativity (VSR) line element. Our Finsler pp-waves are an exact solution of Finslerian Einstein’s equations in vacuum. |

# October 2016

31. October 2016

**Physical Colloquium**

Where: | University of Oldenburg, W2-1-148 |

When: | 31.10.16, 4.15 p.m. |

Speaker: | Dr. Felipe Guzman (ZARM, Zentrum für angewandte Raumfahrttechnologie und Mikrogravitation, Universität Bremen, Germany) |

Topic: | Laser measurement science and an overview of its groundbreaking applications |

Abstract: | Coherent light enables length measurements of exquisite sensitivity that lie at the core of fascinating observations in fundamental and quantum physics, astrophysics, geodesy and measurement science. In particular, observations from the Laser Interferometer Gravitational-Wave Observatory (LIGO) over the past year not only confirmed crucial gravitational physics effects, but have now also officially launched the era of Gravitational Wave Astronomy and Multi-Messenger observations. Similar laser-interferometric measurements have been demonstrated and are now flying on LISA Pathfinder, exceeding expectations and paving the way for a spaceborne Gravitational Wave Observatory that will allow us to survey the gravitational universe otherwise inaccessible to us from ground. Moreover, GRACE follow-on will continue to provide valuable information about fluctuations of the Earth’s gravitational field to the geophysical and climatology science community starting early 2018, whose observations will be greatly enhanced by interspacecraft laser gradiometric measurements. In the area of cavity optomechanics and novel compact and integrated photonics, the combination of low-loss devices and optomechanically coupled coherent light field is enabling us to reach unprecedented measurement accuracies at the quantum sensing limit, which is revolutionizing the state-of-the-art in several areas of measurement science. I will discuss the advances in coherent light measurements and some of its recent results and upcoming groundbreaking applications to the science community. |

26 October 2016

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

Where: | ZARM, University of Bremen, Room 1280 |

When: | 15:00 hrs |

Speaker: | Peter Hogan, University of Oldenburg |

Title: | Colliding Impulsive Gravitational Waves and a Cosmological Constant |

Abstract: | A space-time model is derived of the collision of two homogeneous, plane impulsive gravitational waves propagating in a vacuum before collision and for which the post collision space-time has constant curvature. The profiles of the incoming waves are Dirac delta functions multiplied by constants k and l respectively. The delta functions are singular on intersecting null hypersurfaces. The cosmological constant in the post collision region of the space-time is -6kl. |

20 October 2016

**BREMEN - OLDENBURG RELATIVITY SEMINAR **

Where: | University of Oldenburg, Room W2 3-349 |

When: | 12:15 hrs |

Speaker: | Sarah Kahlen, University of Oldenburg |

Title: | Five-dimensional wormholes at the core of rotating boson stars |

Abstract: | Wormholes are solutions of the Einstein equations which can be thought of as tunnels between distinct universes. In the presence of exotic matter wormholes become traversable, allowing travel between the universes. Although wormholes have not yet been observed in Nature, they attained an increasing interest in recent years. On the other hand, boson stars are hypothetical objects made up of self-gravitating Bose-Einstein condensates with self-interaction. The mixed system consists of a wormhole at the core of a boson star. In this talk I will present my studies of wormholes at the core of boson stars in five dimensions. The solutions have been constructed numerically for the non-rotating and rotating cases. Special focus lies on the domain of existence and the physical properties like mass, angular momentum and geometrical features. In particular I will show how rotation might stabilize the notoriously unstable wormhole solutions. |

18. October 2016

**BREMEN - OLDENBURG RELATIVITY SEMINAR **

Where: | University of Oldenburg, Room W2 3-349 |

When: | 14:15 hrs |

Speaker: | Prof. Syed Afsar Abbas, Centre for Theoretical Physics, JMI University, New Delhi, India |

Title: | Neutrinos in the Quantized Charge Standard Model |

Abstract: | Wormholes are solutions of the Einstein equations which can be thought of as tunnels between distinct universes. In the presence of exotic matter wormholes become traversable, allowing travel between the universes. Although wormholes have not yet been observed in Nature, they attained an increasing interest in recent years. On the other hand, boson stars are hypothetical objects made up of self-gravitating Bose-Einstein condensates with self-interaction. The mixed system consists of a wormhole at the core of a boson star. In the conventional Standard Model (SM) based on the group structure SU(3) _{C}XSU(2)_{L}XU(1)_{Y}, the electric charge is defined as Q=T_{3} + Y/2 ( or T_{3}+Y' ) where T_{3} is the diagonal generator of SU(2)_{L} and Y ( or Y' ) of U(1)_{Y}. Herein the electric charge is not quantized. We discuss and consistently derive another expression of the electric charge wherein the colour degree of freedom pops up in the expression of the electric charge itself. Moreover the electric charge is properly quantized as well. We call this model structure the Quantized Charge Standard Model (QCSM).This QCSM reproduces all the successes of the conventional SM. However the QCSM brings in some significant and major differences with respect to the SM. In particular it shows that the Right-Handed-Neutrino is a different kind of creature all together. This leads to a demand that the neutrinos behave differently in the "disappearance" and the "appearance" experiments. The QCSM predicts that the neutrinos in the disappearance experiments do travel with subluminal velocities while those that arise in the appearance experiments shall be observed to travel with superluminal velocities. As of now, all experiments have detected neutrino velocities only in disappearnce experiments. The experitmentalists are urged to confirm this unique prediction of the QCSM in appearance experiments in the future. |

# September 2016

12 September 2016

**BREMEN - OLDENBURG RELATIVITY SEMINAR **

Where: | University of Bremen, ZARM, Rm 1730 |

When: | 16:15 hrs |

Speaker: | Rico Berner, TU Berlin |

Title: | Kinematic constraints in parametrized nonlinear electrodynamics |

Abstract: | The aim of the talk is to give a concise introduction to the parametrization approach by Kucha and present its application to nonlinear electrodynamics. We show how the motion of physical fields, in particular the electromagnetic potential, is connected with the choice of a space and time decomposition of the background spacetime manifold. The relation of the field dynamics and its kinematic description is derived. With regard to generally covariant theories, the arising kinematic constraints are investigated for the class of nonlinear electrodynamics. We address the problem of finding the explicit form of the super-Hamiltonian constraint and reduce it to the problem of solving two nonlinear equations. By this, a plug-and-play approach to find the whole set of constraints for an arbitrary theory of nonlinear electrodynamics is provided and applied to selected examples. |

# August 2016

16 August 2016

**BREMEN-OLDENBURG-RELATIVITY SEMINAR **

Where: | University of Bremen, ZARM, Room 1280 |

When: | 14:30 hrs |

Speaker: | Dr. Marco Maceda, UAM-I, Mexico City |

Title: | Noncommutative Landau problem in Podolsky's generalized electrodynamics |

Abstract: | We discuss the Landau problem in Podolsky's electrodynamics at the classical level and also within the context of noncommutative quantum mechanics. For the latter, we use Bopp shifts to obtain corrections to the standard expressions for the energy eigenvalues; their consequences are then analyzed. |

# July 2016

29 July 2016

**BREMEN-OLDENBURG RELATIVITY SEMINAR **

Where: | University of Bremen, ZARM, Room 1280 |

When: | 11:00 hrs |

Speaker: | Prof. Dr. Alfredo Macias, UAM-I, Mexico |

Title: | Do Black Holes exist? |

26 July 2016

**BREMEN-OLDENBURG RELATIVITY SEMINAR**

Where: | University of Bremen, ZARM, Room 1280 |

When: | 2:30 hrs |

Speaker: | Jiri Ryzner, Charles University Prague |

Title: | Majumdar-Papapetrou: special cases |

Abstract: | One of important analytical solutions of Einstein-Maxwell equations is the Majumdar-Papapetrou solution, which consists of extremal sources of gravitational and electromagnetic field. We investigate the properties of two particular cases: two extremal Reissner-Nordström black holes in equilibrium and the field of an infinitely long, straight, extremally charged string. |

21 July 2016

**BREMEN-OLDENBURG-RELATIVITY SEMINAR**

Where: | University of Bremen, ZARM, Room 1280 |

When: | 04:00 hrs |

Speaker: | Dr. Elias Castellanos |

Title: | Ouasi-Bound scalar field configurations in curved geometries |

Abstract: | One of the most interesting ideas suggested in recent years is that scalar fields can be relevant candidates to describe dark matter in the Universe. Moreover, the possible existence of super-massive black holes located at the center of galaxies, imposes that these scalar field configurations must be stable, at least for enough time, in the presence of these super massive objects, if these scalar clouds want to be interpreted as a dark matter halo. Furthermore, if the dark matter particle is assumed as a 0-spin boson, this opens the door to the existence of scalar field dark matter as a some kind of Bose-Einstein condensate. In this talk we will discuss some issues related with scalar fields configurations in two specific curved geometries. Also, we wil explore the properties of the scalar cloud when the system can be viewed as some type of trapped Bose-Einstein condensate. |

# June 2016

24 June 2016

**BREMEN-OLDENBURG RELATIVITY SEMINAR**

**- Field Theory, Gravity, Relativity -**

Where: | University of Oldenburg, Room W2 3-349 |

When: | 11:15 hrs |

Speaker: | Anastasia Golubtsova, Laboratory of Theoretical Physics JINR, Dubna |

Title: | "Holographic Wilson loops in Lifshitz-like backgrounds" |

Abstract: | In this talk we discuss the evolution of Wilson loops in Lifshitz-likebackgrounds which can describe anisotropic quark-gluon plasma using theholographic approach. We evaluate the Wilson loops in both static andtime-dependent cases. The anisotropic time-dependent plasma is dual toLifshitz-Vaidya background, while we use a black brane in theLifshitz-like spacetime for a finite temperature plasma in equilibrium.To probe the system we calculate Wilson loops oriented in differentspatial directions. We find that anisotropic effects in the Lifshitz-likebackgrounds are more visible for the Wilson loops lying in thetransversal direction unlike the Wilson loops partially oriented inthe longitudinal one. |

16 June 2016

**Physikalisches Kolloquium **

Wo: | Universität Bremen, Hörsaal H3, Gebäude NW 1, Otto-Hahn-Allee |

Wann: | 16 hrs |

Sprecher/in: | Prof. Dr. Manfred Stöckler |

Titel: | "EPR, Schrödingers Katze, Bellsche Ungleichung: das Rätsel der Nicht-Lokalität der Quantenmechanik" |

Abstract: | Eigentlich wollten Einstein, Podolsky und Rosen in ihrem Gedankenexperiment aus dem Jahre 1935 die Unvollständigkeit der Quantentheorie zeigen. Heute ist diese Arbeit aber interessant, weil darin die Nicht-Lokalität der Quantentheorie eine zentrale Rolle spielt. Im EPR-Paradoxon wird ein Zustandstyp verwendet, den wir heute verschränkt nennen. Er wurde dann von Schrödinger analysiert und zur Formulierung des Gedankenexperiments mit der Katze benutzt. Seit den sechziger Jahren konzentriert sich die Diskussion um die Nicht-Lokalität im Anschluss an einen Beweis von J.S. Bell auf die Besonderheiten der Korrelationen von Messungen an verschränkten Systemen mit weit voneinander entfernten Messgeräten. Diese belegen, dass (entgegen einer zentralen Prämisse von Einstein) die Quantentheorie nicht lokal ist, und darüber hinaus, dass jede beliebige Theorie, die die gleichen Korrelationen wie die Quantenmechanik vorhersagt, nicht lokal sein kann. Mittlerweile sind die von der Quantentheorie vorhergesagten Korrelationen empirisch hoch bestätigt. Damit ist das von EPR aufgeworfene Problem aber nicht gelöst, weil es keine dynamische Erklärung für den Messprozess an verschränkten Systemen zu geben und die Nicht-Lokalität der Quantentheorie der Relativitätstheorie zu widersprechen scheint. Die genaue Bedeutung der Nicht-Lokalität, insbesondere die Frage, ob sich daraus ein Konflikt mit der Relativitätstheorie ergibt, haben in der Philosophie der Physik eine bis heute offene Kontroverse ausgelöst. Der Sprecher berichtet über einschlägige Einsichten, Missverständnisse und mehr oder weniger verzweifelte Lösungsvorschläge. |

14 June 2016

**BREMEN-OLDENBURG RELATIVITY SEMINAR**

**- Field Theory, Gravity, Relativity -**

Where: | University of Bremen, ZARM, Room 1280 |

When: | 14:30 hrs |

Speaker: | Dr. Dennis Raetzel, University Potsdam |

Title: | "How light gravitates: a brief exploration" |

Abstract: | As Einstein's equations tell us that all energy is a source of gravity, light must gravitate. However, because changes of the gravitational field propagate with the speed of light, the gravitational effect of light differs significantly from that of massive objects. In particular, the gravitational force induced by a light pulse is due only to its creation and annihilation and decays with the inverse of the distance to the pulse. We can expect the gravitational field of light to be extremely weak. However, the properties of light are premisses in the foundations of modern physics: they were used to derive special and general relativity and are the basis of the concept of time and causality in many alternative models. Studying the back-reaction of light on the gravitational field could give new fundamental insights to our understanding of space and time as well as classical and quantum gravity. In this talk, a brief overview is given of the gravitational field of light pulses in the framework of general relativity. A glimpse is caught of the gravitational interaction of two single photons which turns out to depend on the degree of their polarization entanglement. |

02. June 2016

**Theory colloquium **

Where: | University of Oldenburg, W2 1-143 |

When: | 14:15 hrs |

Speaker: | Prof. Dr. Wolfgang Duschl (Kiel) |

Title: | The Evolution of Active Galactic Nuclei - Individually and as an Ensemble |

Abstract: | Quasars, and Active Galactic Nuclei (AGN, for short) in general, are among the most efficient energy sources in the Universe. They balance their energy budget by liberating potential energy through accretion of matter into super-massive black holes. Due to their high luminosity, they are ideal test bodies which can be observed almost throughout the entire Universe's history. As ever so often in astrophysics, we are confronted with the problem of exceedingly long evolutionary timescales of individual objects which are not accessible to direct observation. In the talk, the speaker will adress several problems related to the evolution of individual objects as well as that of entire ensembles of AGN, an example being, for instance, the processes limiting the mass growth of black holes. |

# Mai 2016

19 May 2016

**Theory Colloquium**

Where: | University of Oldenburg, W2 1-143 |

When: | 14:15 hrs |

Speaker: | Dr. Christian Pfeifer, University of Bremen, University of Hannover |

Title: | "The Potential in General Linear Electrodynamics: Causal Structure, Propagators and Quantization" |

Abstract: | From an axiomatic point of view, the fundamental input for a theory of electrodynamics are Maxwell's equations dF=0 (or F=dA) and dH=J, and a constitutive law H=# F, which relates the field strength 2-form F and the excitation 2-form H. In this talk we consider general linear Electrodynamics, the theory of Electrodynamics which is defined through a liner constitutive law. The best known application of this theory is the effective description of Electro-dynamics inside (linear) media including for example birefringence. We will analyze the classical theory of the electromagnetic potential A thoroughly before we use methods familiar from mathematical quantum field theory in curved spacetimes to quantize it. Our analysis of the classical theory contains the inversion of the principal symbol of the field equations, the construction of the causal structure on the basis of the constitutive law, which replaces the metric one uses in Maxwell Electrodynamics, the construction of the inverse of the field equations and the Puli-Jordan propagator and the classification of the classical symplectic phase space of the theory. This classical analysis then sets the stage for the construction of the quantum algebra of observables and quantum states. |

# April 2016

22 April 2016

**BREMEN-OLDENBURG RELATIVITY SEMINAR - Field Theory, Gravity, Relativity - **

Where: | University of Oldenburg, W02-3-349 |

When: | 11:15 hrs |

Speaker: | Michael Kalisch, Friedrich-Schiller-Universität, Jena |

Title: | "Pseudo-spectral construction of highly deformed non-uniform black string solutions " |

Abstract: | Black strings are static solutions to Einstein's vacuum field equations in spacetimes with a compactified dimension. The horizon of such an object wraps the compact dimension. I will explain in detail how we constructed black string solutions in a critical regime, in which the horizion is close to pinching off. The use of an appropiately designed pseudo-spectral scheme allowed us to obtain very accurate and unprecedented results. In particular, we observed three clearly pronounced turning points in the curves of thermodynamic quantities, resulting in a spiral curve in the black string's phase diagram. |

19 April 2016

**BREMEN-OLDENBURG RELATIVITY SEMINAR - Field Theory, Gravity, Relativity - **

Where: | University of Bremen, ZARM, Room 1280 |

When: | 2:30 hrs |

Speaker: | Dr. Maxim Eingorn, North Carolina Central University, Durham, NC, USA |

Title: | "All-scale cosmological perturbations and screening of gravity in inhomogeneous Universe" |

Abstract: | Without exceeding the limits of the concordance cosmological model, all-scale scalar and vector perturbations of the homogeneous background are derived analytically for arbitrarily distributed inhomogeneities (discrete gravitating masses) as their nonrelativistic sources. The obtained expressions for the metric corrections are gauge-invariant, converge everywhere in voids, have zero average values, and conform to Minkowski background limit and Newtonian cosmological approximation as particular cases. Moreover, the uniform matter distribution limit as one more crucial test is easily passed as well. It is rigorously proven that gravitational attraction between inhomogeneities is governed by Yukawa law, covering the whole space and coming up to take place of Newtonian gravitation, which is restricted exclusively to sub-horizon distances. The finite time-dependent screening length (amounting to 3.7 Gpc at present) is determined by the average rest mass density of nonrelativistic matter and provides natural estimates of the homogeneity scale, the upper limit of the cosmic structure dimension, and the bound to a spatial domain of probable structure development. The definition of Yukawa interaction range is generalized to the extended cosmological model with extra continuous perfect fluids and nonzero spatial curvature. |

14 April 2016

**Physics Colloqium **

Where: | University of Bremen, Hörsaal H3, Geb. NW1, Otto-Hahn-Allee |

Speaker: | Prof. Dr. Wiesendanger, Universität Hamburg |

Title: | "Magnetische Knoten auf der Nanometerskala: von der Grundlagenforschung zu neuen Datenspeicherkonzepten" |

Abstract: | Nanoskalige Knoten in der Magnetisierung, sogenannte Skyrmionen, sind zum Gegenstand intensiver weltweiter Forschungsanstrengungen geworden, da man mit ihnen neuartige Konzepte der hochdichten magnetischen Datenspeicherung realisieren kann. Neben ihrer geringen Größe zeichnen sich Skyrmionen durch nicht-triviale topologische Eigenschaften verbunden mit einem ausgezeichneten Drehsinn der Magnetisierung aus, verursacht durch eine zugrundeliegende chirale spinabhängige Wechselwirkung, welche diese nanoskaligen magnetischen Objekte äußerst stabil werden lässt. Die Entdeckung von Skyrmionengittern und insbesondere einzelner nanoskaliger Skyrmionen in ultradünnen metallischen Schichten liefert die Basis für Anwendungen in Form von neuartigen magnetischen Datenspeichern, Logikelementen und Sensoren unter Nutzung der Technologie, welche in den vergangenen Jahrzehnten auf dem Gebiet der Riesen- und Tunnelmagnetowiderstands-Sensoren etabliert wurde. Dieser Vortrag widmet sich sowohl den grundlegenden physikalischen Aspekten dieser neuartigen nanoskaligen Magnetisierungsstrukturen in ultradünnen Schichten und Multilagensystemen als auch deren Anwendungsperspektiven. |

7 April 2016

**Theory Colloquium**

Where: | University of Oldenburg, W2 1-143 |

When: | 14:15 hrs |

Speaker: | Dr. Roman Konopolya |

Title: | "Detection of gravitational waves from black holes: Is there a window for alternative theories?" |

Abstract: | Recently the LIGO and VIGRO collaborations reported the observation of gravitational-wave signal corresponding to the inspiral and merger of two black holes, resulting into formation of the final black hole. It was shown that the observations are consistent with the Einstein theory of gravity with high accuracy, limited mainly by the statistical error. Angular momentum and mass of the final black hole were determined with rather large allowance of tens of percents. Here we shall show that this indeterminacy in the range of the black-home parameters allows for some non-negligible deformations of the Kerr spacetime leading to the same frequencies of the black-hole ringing. This means that at the current precision of the experiment there remains some possibility for alternative theories of gravity. |

# March 2016

11 March 2016

**BREMEN - OLDENBURG RELATIVITY SEMINAR**

** - Field Theory, Gravity, Relativity -**

Where: | University of Oldenburg, Room W2 3-349 |

When: | 12:15 hrs |

Speaker: | Christian Knoll, University of Oldenburg |

Title: | "Dirac equation in Myers-Perry black hole geometry with equal angular momenta" |

Abstract: | This talk is the defense of the Speakers' Master Thesis. The main result is the solution of the angular part of the Dirac equation in the geometry of the five dimensional Myers-Perry black hole with equal angular momenta. The Speaker will begin to introduce the formalism and fix the notation for the Dirac equation in curved spacetimes. After that the Speaker briefly consider the Dirac equation in the geometry of the Kerr black hole. The decoupled Dirac equation of Chandrasekhar is reproduced using a method from the literature. A minimal example is constructed and some physical interpretations are discussed. One set of special solutions to the angular equations is derived. Next is the Dirac equation in the geometry of the five dimensional Myers-Perry black hole with equal angular momenta. Again, the equations are decoupled using a method from the literature. A minimal example is constructed with which some physical interpretations are discussed. The angular equations are solved. The last part involves possible future work. A possible condition for physical solutions to the complete equations considered before is discussed. The Dirac equation in the Myers-Perry black hole geometry with equal angular momenta in any uneven dimension is formulated. |

# February 2016

12 February 2016

**Colloquium talk **

Where: | Max Planck Institute for Astrophysics, Garching |

When: | 16 Uhr c.t. |

Speaker: | Eiichiro Komatsu |

# January 2016

14 January 2016

**Physikalisches Kolloquium **

Wo: | Universität Bremen, Hörsaal H3, Geb. NW1, Otto-Hahn-Allee |

Wann: | 16 Uhr c.t. |

Sprecher/in: | Dr. Jan Ingo Flege |

Titel: | "Four (or Five) Quarks for Muster Mark?" - Zur Existenz von Tetra- und Pentaquarks |

Abstract: | Etwa 50 Jahre nach der Aufstellung wesentlicher Grundlagen des Standardmodells zum Aufbau massiver Teilchen aus Elementarbausteinen, sogenannten Quarks, herrscht in der Teilchenphysik eine neue Aufbruchsstimmung: Neueste experimentelle Ergebnisse vom Large Hadron Collider (LHC) in der Schweiz zeigen ungeahnte Einblicke in den subatomaren Mikrokosmos und erhärten die Hypothese, dass es neben den etablierten hadronischen Teilchen wie Mesonen und Baryonen, die aus je zwei bzw. drei Quarks bestehen, auch Teilchen aus einer größeren Anzahl dieser Elementarbausteine gibt. Obzwar nicht die ersten ihrer Art - erste Hinweise auf ein Pentaquark aus fünf Teilchen wurden bereits 2003 veröffentlicht - so sind die aktuellen Funde im Gegensatz zu früheren (teils voreiligen) Meldungen von dramatisch gesteigerter statistischer Signifikanz. Im Vortrag wird zunächst der akzeptierte Wissenstand zum strukturellen Aufbau der Hadronen und ihrer Wechselwirkungen kompakt dargestellt. Aufbauend auf den sich daraus ergebenden Möglichkeiten ihrer experimentellen Untersuchung werden anschließend die jüngsten Befunde der LHCb-Experimente zum Nachweis von Tetra- [1] und Pentaquarks [2] erläutert und ein Überblick über den gegenwärtigen Stand der (sicherlich noch nicht abgeschlossenen) Diskussion um ihre Bedeutung für die Teilchenphysik gegeben. [1] R. Aaij et al. (LHCb Collaboration), Phys. Rev. Lett./ *112*, 222002 (2014). [2] R. Aaij et. al. (LHCb Collaboration), Phys. Rev. Lett. / *115*, 072001 (2015). |

7 January 2016

**Talk: Ralf Lehnert**

Where: | University of Oldenburg |

When: | 14:15 hrs |

Speaker: | Dr. Ralf Lehnert (University of Hannover) |

Title: | "Does Relativity Theory Hold Exactly?" |

Abstract: | Relativity Theory is a cornerstone of physics. Since its conception over a century ago, it has beem scrutinized experimentally with ever increasing precision, but no credible evidence for departures from its underlying symmetry - Lorentz invariance - has been found to date. However, recent theoretical research has established that minute violations of Lorentz symmetry can be accommodated in various approaches to physics beyond the Sandard Model. This seminar provides a brief overview of our group's efforts in this research field. A variety of mechanisms for Lorentz breakdown are reviewed, the effective-field-theory test framework for the emerging low-energy effects is introduced, and a number of present-day and near-future experimental measurements in this context are surveyed. |

# December 2015

18 December 2015

**BREMEN-OLDENBURG RELATIVITY SEMINAR**

**- Field Theory, Gravity Relativity -**

Where: | University of Oldenburg, Lecture Hall W2 3-349 |

When: | 16:00 hrs |

Speaker: | Philipp Heinrich - University of Oldenburg |

Title: | "Analysis of UV and EUV emission from impacts on the Sun after 2011 June 7 eruptive flare" |

Abstract: | On 2011 June 7 debris from a large filament eruption fell back to the Sun causing bright ultraviolet (UV) and extreme ultraviolet (EUV) splashes across the surface. These impacts may give clues on the process of stellar accretion. I will give an introduction to the subject and subsequently discuss how the impact emission is influenced by structures in the falling ejecta and at the solar surface. |

17 December 2015

**Talk: Harry Braden**

Where: | University of Oldenburg, W01 0-012 (Wechloy) |

When: | 16:00 hrs |

Speaker: | Harry Braden (University of Edinburgh) |

Title: | "Spectral Curves are Transcendental" |

Abstract: | The modern approach to integrable systems typically proceeds via a curve, the parameters of the curve encoding the actions and its Jacobian (or possibly some related Prym) encoding the angles. Physically relevant families of curves are often described by fixed relations amongst differentials on the curve. We shall look at number theoretic properties of these curves. For many integrable systems the curves are transcendental. |

17 December 2015

**Physics K****olloquium**

Wo: | Universität Bremen, Hörsaal H3, Geb. NW 1, Otto-Hahn-Allee |

Wann: | 16:15 Uhr c.t. |

Sprecher/in: | Prof. Dr. Matthias Günther, MEVIS, Bremen |

Titel: | "Physik-Nobelpreis 2015: Die Entdeckung der Neutrinomasse" |

Abstract: | Der Physik-Nobelpreis geht dieses Jahr an zwei Teilchen-Physiker, den Japaner Takaaki Kajita und den Kanadier Arthur B. McDonald. Sie haben mit ihren Experimenten den Beweis liefern können, dass Neutrinos eine Masse besitzen. Neutrinos sind ungeladene Elemntarteilchen, die nach dem Standardmodell der Teilchenphysik in drei verschiedenen Arten (Flavors) vorkommen undeigentlich masselos sein sollten. Der Nachweis der Neutrino-Oszillationen, bei denen Neutrino ihren Flavor ändern, (und der nun zur Verleihung des Physiknobelpreises an Kajita und McDonald geführt hat) hat nun zweifelsfrei bewiesen, dass Neutrinos nicht masselos sind (zumindest zwei der drei Flavor nicht). In dem Vortrag sollen Neutrinos "greifbar" werden. Die Beschreibung der Neutrino-Eigenschaften wird deutlich machen, vor welchen Herausforderungen die Neutrino-Forscher standen (und stehen). Die faszinierenden Möglichkeiten der Neutrinoforschung werden kurz dargestellt. *Hinweis*: Wie schon ein wenig traditionell werden wir die Nobelvorlesung mit hochadventlichem Glühwein und Weihnachtsgebäck begleiten. Sie werden *ab ca. 16 Uhr *vor dem Hörsaal H3 einen entsprechenden Ausschank vorfinden. Selbstverständlich haben wir auch einige Kannen Tee vorrätig für diejenigen, denen Glühwein nicht zusagt. |

10 December 2015

**Talk: ****Chris Eilbeck**

Where: | University of Oldenburg, W01 0-012 (Wechloy) |

When: | 16:00 hrs |

Speaker: | Chris Eilbeck (Heriot-Watt University) |

Title: | "Generalizations of the Weierstrass sigma function, discriminants, and heat equations" |

Abstract: | The solutions of many interesting nonlinear wave equations can be written down in terms of Weierstrass $\wp$ functions and their generalizations to higher genus. In turn the $\wp$ functions are just the 2nd logarithmic derivatives of a entire function, the Weierstrass $\sigma$ function generalized to genus $g$. We discuss the properties of the $\sigma$ function associated with a plane curve of genus $g$. These functions satisfy sets of interesting linear parabolic PDEs. These PDEs can be used to form linear but complicated recurrence relations for the coefficients of the sigma expansion. A connection with the discriminant of the associated curve is also highlighted. |

# November 2015

26 November 2015

**Talk: ****Victor Enolski **

Where: | University of Oldenburg, W01 0-012 (Wechloy) |

When: | 16:00 hrs |

Speaker: | Victor Enolski (Kiew) |

Title: | "Lesser known Nahm Ansatz in algebro-geometric description of monopole fields" |

Abstract: | In the ADHMN-construction (Atiyah-Drinfeld-Hitchin-Manin-Nahm) calculation of the monopole fields- Higgs field and gauges - reduced to solving linear ODE - Weyl equations with "potentials'" are given by the so called Nahm data. Even in the case of charge two, when the Nahm data represent elliptic functions, the analytic expressions for the monopole fields are unknown until now. We overcome the problem using a lesser known Nahm Ansatz (compared to the ADHMN construction), whose implementation leads to a complete description of monopole fields in terms of algebraic functions and incomplete elliptic integrals. |

26 November 2015

**Physikalisches K****olloquium**

Wo: | Universität Bremen, Hörsaal H3, Geb. NW 1, Otto-Hahn-Allee |

Wann: | 16:00 Uhr |

Sprecher/in: | Prof. Dr. Christopher Kyba |

Titel: | "Artificial light at a crossroads during the International Year of Light" |

Abstract: | For centuries, increases in the luminous efficiency of lamps have resulted in corresponding increases in light use, rather than energy savings. This has resulted in an exponential growth of light pollution, to the point where true night no longer occurs in most of Europe. Will LEDs be the final nail in the coffin for the night, or will they allow us to save energy and bring the stars back over our cities? This talk will touch on concepts and results from remote sensing, lighting design, physiology of vision, biology, ecology, energy economics, and lighting policy, in order to discuss the role of LEDs in the Energiewende, and in the worldwide transition to sustainable and healthy lighting. |