Project  Title and Abstract 

ÄFriedrich(2003  2006) 
Analysis of asymptotically flat spacetimesThe goal of project A1 is to further develop the theory of asymptotically flat spacetimes as models for the gravitational fields of isolated bodies, Black Holes and the nonlinear selfinteration of vacuum fields. One has to distinguish between two different regions of spacetime: the interior, in which violent interactions between vacuum and matter fields can arise, and the exterior, in which the gravitational wave signal takes shape. Further idealization leads quite naturally to an asymptotic description of this signal as a radiation field on the hypersurface S that one can think of as being the set of endpoints of outgoing lightlike geodesics. 
ÄFrauendiener(2003  2006) 
Numerical Calculation of Gravitational Waves for Isolated SystemsThe work within project A2 over the last years has been concerned to a large part with the investigation of various general fundamental issues for the discretisation of the Einstein equation motivated by the growing experience with the conformal field equations approach. In the application we have outlined five topics of research. The topics are a) the construction of initial data, b) the implementation of an evolution code, c) the investigation of compatible boundary conditions, d) the problem of the constraint propagation and e) the choice of gauge. It should be stressed that most of these topics are not specific to the conformal approach but appear in almost any formulation of the Einstein equations. 
ÄSchäfer(2003  2014) 
Analytical Approximation MethodsProject A4 aims at developing schemes and constructing approximate analytical solutions of the equations of motion resulting from the higher order postNewtonian (PN) Hamiltonians of spinning binary systems derived in recent years. Another aim is the construction of approximate analytical or semianalytical solutions of damped inspiraling orbits. 
Ä Brügmann
(2007  2014)

Numerical Methods for General RelativityGoal of project A5 is the development of robust and efficient methods for the numerical solution of the Einstein equations. Gravitational wave astronomy requires numerical solutions of high reliability and accuracy for the theoretical prediction and analysis of gravitational waves. Focus areas are reformulations of the Einstein equations as a first order in time and second order in space system, numerical methods for the Einstein evolution problem including structure preservation, efficient elliptic solvers for adaptive meshes and black hole geometries, and the adaptation of these numerical algorithms to wave problems. 
ÄAnsorg(2011  2014) 
Pseudospectral methods for the Einstein equations on hyperboloidal slicesThis Project is concerned with the development of novel numerical techniques for the solution of constraint and time evolution equations in general relativity. Three aspects are central: (i) the incorporation of future null infinity, (ii) the use of pseudospectral methods for spatial directions, and (iii) the introduction of appropriate coordinates related to conformal mappings known from complex analysis. 
Ä Ansorg
(2003  2010)

Rotating Neutron Stars and Black HolesThe project B1 is concerned with two major problems: The investigation of axisymmetric and stationary configurations and the calculation of physically relevant initial data of binary systems. The first issue deals with selfgravitating equilibrium configurations that are composed of black holes and/or perfect fluid bodies. In the past years, the second one has led to advancements in the multidomain pseudospectral methods used to solve the constraint equations for binary systems. In the future, a further development and an appropriate adaptation of the numerical methods to the specific problem being considered is necessary for both subjects. 
Ä Ruder
(2003  2006)

Oscillation Modes of Rotating Neutron StarsThe goal of this project is the analysis of the oscillation modes of rotating Neutron Stars. We plan to go beyond the linear studies and follow the oscillations through fully nonlinear methods, including the full variation of the spacetime. We intend to extract accurate oscillation frequencies and eigenfunctions, and obtain limits on the nonlinear saturation amplitudes of the oscillations. 
ÄMüller(2003  2014) 
Gravitational Collapse of Compact Astrophysical ObjectsThe aim of project B3 is to provide gravitational wave templates of nonradial stellar core collapse to neutron stars or black holes by means of multidimensional generalrelativistic hydrodynamic and magnetohydrodynamic simulations. The availability of such templates enhances the detectability of the expected weak signals and helps to exploit their information content of the event. The focus of the project is on the appropriate treatment of general relativistic effects including the latest available or to be developed computational tools. 
ÄSchäfer(2003  2010) 
Inspiraling Black Holes and Neutron StarsProject B4 aims to provide accurate and efficient description for various aspects involved in the dynamics of compact binaries of arbitrary mass ratio, invoking postNewtonian (PN) framework to solve twobody problem in general relativity. It includes the development of gravitational wave templates for compact binaries. 
Ä Rezzolla
(2003  2010)

Collision and Merger of Black Holes and Neutron StarsThis project will provide the first systematic description in full general relativity of the dynamics of matter in a blackhole plus neutronstar binary system which undergoes a progressive inspiral and merger as it loses energy and angular momentum through the emission of gravitational radiation. 
ÄJanka(2003  2014) 
Merging of Neutron StarsMerging binary neutron stars are among the strongest known sources of gravitational waves (GWs) and are widely favored as astrophysical events with properties suitable for explaining gammaray bursts (GRBs) of the class of short, hard bursts. This project is on the way of developing improved computational tools and numerical models for the very last stages of the binary evolution, the final plunge and merging of the neutron stars, and the early stages of the remnant formation. The goal is a better understanding of the link between the characteristics of the observable signals  gravitational waves as well as GRBs , and the binary and neutron star properties. 
ÄBrügmann(2005  2014) 
Orbiting Black HolesProject B7 is aimed at the computation of the orbital motion of two black holes shortly before their collision and merger. One major goal is to model the gravitational waves that are generated in the process. This requires the numerical solution of the Einstein equations of general relativity in the regime of highly dynamic and highly nonlinear gravitational fields. 
ÄKokkotas(2007  2014) 
Gravitational Waves from Oscillations and Instabilities of Relativistic StarsThe aim of project B8 is the study of linear and nonlinear oscillations of relativistic stars, with and without magnetic fields. The oscillations and possible instabilities of relativistic stars can reveal a wealth of information for their internal structure and dynamics via the emitted gravitational waves. In this project a detailed study of the dynamics of both old and newly born stars (uniformly or differentially rotating) will provide the means to develop what is called gravitational wave asteroseismology. 
Ä Kokkotas
(2010  2014)

MagnetarsMagnetars are neutron stars with a magnetic field greatly exceeding B > 10^14 G. Sporadic "giant flares" are believed to be associated with starquakes caused by the rearrangement of the huge magnetic field. During these giant flares huge amounts of energy are released in only a few seconds (gamma and xrays) and in addition, it is expected that gravitational waves should be generated. The plan is to simulate the magnetar dynamics in order to reveal the actual strength of the emitted gravitational waves, while in addition a Bayesian approach will be used for the detection of as yet unnoticed high frequency oscillations of magnetars. 
Ä Rezzolla
(2010  2014)

Electromagnetic Counterparts to Supermassive Black Hole MergersMerging supermassive black holes (SMBHs) are possibly the strongest gravitational waves (GWs) sources and important candidates for future spaceborne gravitationalwave observatories of the LISA (Laser Interferometer Space Antenna) type. If the gravitationalwave (GW) information can be combined with the corresponding electromagnetic (EM) one, then the simultaneous EM and GW observation would have enormous consequences and open completely new scientific opportunities in astrophysics, cosmology and fundamental physics. The purpose of this project is to investigate whether these links between EM and GW signals are possible, to determine their realistic impact on the physics of binary BHs and thus to take the first steps towards a multimessenger GW astronomy. 
Ä Lück
(2003  2010)

Iterative Design of the Sensitivity Curve of Gravitational Wave DetectorsThe aim of this project is the analysis of synchronous tracking of signals from inspiralling binary systems in continuation of the work started in Project C1 in the last funding period. The signal from an inspiralling binary system of two compact objects spans a wide frequenc range over the whole inspiral process but only occupies a well predicted, narrow frequency space per unit of time for most of the event. Instead of using a detector with a stationary tuning we investigate the response if the tuning is changed during the inspiral event. When the tuning frequency of a signal recycled gravitational wave detector is suddenly changed the response of the interferometer can no longer be described by the steady state filter functions. We will develop a code for modelling the dynamical response of a dual recycled detector and compute the improvement of dynamical tuning in comparison to fixedfrequency detection. Furthermore we want to optimize the detection efficiency and parameter estimation accuracy for GEO HF (a series of sequential upgrades of GEO600 in the time frame 20072014) for likely interferometer configurations and for scientifically interesting sources in close cooperation with the GEO HF design team to weigh scientifically beneficial sensitivity curves against technical, financial and time constraints. The configurations considered include the injection of squeezed light, changing from detuned to tuned operation and a change from heterodyne readout to DC readout. 
Ä Schutz
(2003  2014)

Interpretation of Gravitational Wave SignalsThe goal of this project is the development of methods for the extraction of information from gravitational wave signals. In the next phase of this project, methods for eliminating spurious coincidences with great confidence will be extended to the implementation of optimal methods for signal detection and parameter extraction from networks of both interferometric and bar detectors. The search methods for gravitational wave pulsars will be optimized in the context of the Einstein search engine. 
Ä Tuennermann
(2003  2014)

High resolution interferometer based on reflective optical componentsProject C3 aims for the reduction of thermal noise in gravitational wave detectors that results from the transmission of laser light through optical components. In C3, new optical components based on allreective gratings are designed, fabricated and tested in order to replace conventional beam splitters and cavity couplers. The intense research of the previous funding periods yields a variety of theoretical and experimental achievements including a test in a prototype gravitational wave detector. The new funding period is required to solve remaining problems which are the combination of the techniques developed here with coatingfree mirror surfaces, the additional phase noise associated with diffractive optics, and the reduction of scattered light. 
Ä Nawrodt
(2003  2014)

Quality Factor Measurements at Cryogenic TemperaturesOne of the fundamental sensitivity limits of gravitational wave detectors is the thermal noise of the test masses. An extensive improvement would be achieved by decreasing the operating temperature down to cryogenic temperatures while using test masses with high quality factors in this region. Therefore, measurements of the Qfactor of promising materials are done in project C4 in a temperature range from 300 K down to 5 K. These measurements reveal different kinds of damping mechanisms. In conjunction with the theoretical interpretation this contribution to the understanding of mechanical losses in solids leads to a controlled lowering of thermal noise. 
Ä Schnabel
(2007  2014)

Highreflection waveguide coatings of detector test massesProject C5 invents and researches techniques for the reduction of ‘coating thermal noise’ of gravitational wave detector test mass mirrors. Coating thermal noise stems from the currently used thick highreflectivity dielectric multilayer coatings. Within the previous funding period highreflectivity surfaces were designed and fabricated that rely on thin waveguide structures. The first fully monolithic, singlecrystalline mirror was designed and high reflectivities of up to 99.8% were demonstrated. The intent of the next funding period is to further push monolithic mirrors towards their theoretical limit of 100% reflectivity, to demonstrate monolithic antireflection coatings, to supply an insitu experimental confirmation of a decreased thermal noise level of these devices, and to investigate their optical performance at cryogenic temperatures. 
Ä Schutz
(2007  2014)

LISA Data Analysis MethodsThe ESANASA joint space detector LISA, which is expected to be launched in 2015, will have great sensitivity in detecting gravitational waves. But LISA presents new challenges for data analysis. It will return an immense amount of data. However, LISA's high sensitivity creates a problem: signals have to be extracted from a background dominated by other signals. The problem for LISA is a {it source confusion} problem. 
Ä Neuhaeuser
(2007  2014)

Populations of Astrophysical SourcesWe will investigate very young, oscillating neutron stars (NS), precessing NS, and old binary NS, the most prominent sources of gravitational waves. We will consider a nonhomogeneous spatial distribution of the birth rate of very young NS over the sky due to the nearby Gould Belt, a toruslike structure around the Sun younger than 50 Myrs with several thousand stars including both young NS (one of them shows precession) and supernova progenitors. The goal is a clear prediction of the NS birth rate in the Gould Belt and the fraction of NSNS binaries in the Belt. (Project Part 1)Isolated NS are potential sources for constraining the equationofstate of matter at ultrahigh densities. The determination of the mass can be achieved by measuring the surface gravity or gravitational redshift from absorption lines. Here, strong magnetic fields and polarization effects become important, so that we will investigate radiation transfer through the geometrically thin NS atmosphere. The goal is to construct a new generation of nonLTE model atmospheres for neutron stars. (Project Part 2) 
Ä Schnabel
(2010  2014)

Nonclassical readout for gravitational wave detectorsThe new project C8 researches and experimentally demonstrates nonclassical readout schemes based on quantum entangled light. The goal is the sensitivity improvement of future groundbased gravitational wave detectors using ultrahigh laser powers. When increasing the laser power a problem arises because the amount of scattered photons at the interferometer readout port also increases. Current readouts are not able to distinguish between signals arising from scattered photons and signals arising from gravitational waves. In this project entangled light will be used to experimentally demonstrate an interferometer readout that is able to distinguish between scattered photons and gravitational wave signals without deteriorating the overall detector sensitivity that might already be enhanced with squeezed light. 
Ä Nawrodt
(2010  2014)

Optical Properties of SiliconBased Test MassesThe new project C9 experimentally researches the optical properties and prospects of siliconbased test masses. Two novel setups will be developed allowing the determination of the optical absorption of silicon test masses at the laser wavelength of 1550 nm in a wide temperature range from 5 to 300K. At the Leibniz Universität Hannover interferometric measurements based on the temperature dependence of the refractive index will provide precise absorption data near room temperature. At the FriedrichSchillerUniversität Jena a microcalorimetric experiment will provide precise absorption data at cryogenic temperatures. Another concern of this project is the optical quality of silicon test mass surfaces. Reflectivities and optical absorption of dielectric SiSiO_{2}coatings will be investigated in view of an adoption in future gravitational wave detectors. 
Ä(2011  2014) 
Coherent Quantum Noise Cancellation for Optomechanical Sensing and Gravitational Wave DetectorsIn the new project C10 we will explore coherent feedforward control for quantum noise cancellation (QNC) in optomechanical sensing. Quantum noise provides the limit to measurement precision in various physical systems ranging from atomic spin measurements, via displacement sensing in microoptomechanical setups to gravitational wave detectors. Techniques for coherent quantum noise cancellation will allow to improve on and surpass these limitations. Our project will experimentally investigate QNC techniques in quantum optical systems. In tabletop experiments on interferometer subsystems  such as the laser system or suspended cavity mode cleaners  we will provide valuable results guiding the way to coherent control of gravitational wave detectors. We will explore generalisations and applications of QNC techniques which have been put forward in the context of interferometric displacement sensing. The research performed in this project will serve to enhance the sensitivity of next generation interferometric gravitational wave detectors. 
Ä Bruegmann
(20072010)

Public outreachProject Ö on public outreach communicates the science of the SFB/TR7 to the general public. A central part of its activities is the operation of a mobile exhibition, the "EinsteinWellenMobil". The "EinsteinWellenMobil" can be booked by schools for several days of weeks. It consists of various stations and exhibits designed for student interaction. Furthermore, various events are organized highlighting general relativity and gravitational waves. 