Meike List

Rotating boson stars and Q-balls

We consider axially symmetric, rotating boson stars. Their flat-space limits represent spinning Q-balls. We discuss their properties and determine their domain of existence. Q-balls and boson stars are stationary solutions and exist only in a limited frequency range. The coupling to gravity gives rise to a spiral-like frequency dependence of the boson stars. We address the flat-space limit and the limit of strong gravitational coupling. For comparison we also determine the properties of spherically symmetric Q-balls and boson stars.

MICROSCOPE Mission: First Results of a Space Test of the Equivalence Principle

According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10^{-15} precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)=[-1±9(stat)±9(syst)]×10^{-15} (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.

New powerful thermal modelling for high-precision gravity missions with application to Pioneer 10/11

The evaluation of about 25 years of Doppler data has shown an anomalous constant deceleration of the deep space probes Pioneer 10 and 11. This observation became known as the Pioneer anomaly (PA) and has been confirmed independently by several groups. Many disturbing effects that could cause a constant deceleration of the craft have been excluded as possible source of the PA. However, a potential asymmetric heat dissipation of the spacecraft surface leading to a resulting acceleration still remains to be analysed in detail. We developed a method to calculate this force with very high precision by means of finite element (FE) modelling and ray tracing algorithms. The elaborated method is divided into two separate parts. The first part consists of the modelling of the spacecraft geometry in FE and the generation of a steady state temperature surface map of the craft. In the second part, this thermal map is used to compute the force with a ray-tracing algorithm, which gives the total momentum generated by the radiation emitted from the spacecraft surface. The modelling steps and the force computation are presented for a simplified geometry of the Pioneer 10/11 spacecraft including radioisotope thermoelectric generators (RTG), equipment/experiment section and the high gain antenna. Analysis results how that the magnitude of the forces to be expected are non-negligible with respect to the PA and that more detailed investigations are necessary. The method worked out here for the first time is not restricted to the modelling of the Pioneer spacecraft but can be used for many future fundamental physics (in particular gravitational physics) and geodesy missions like LISA, LISA Pathfinder or MICROSCOPE for which an exact disturbance modelling is crucial.

Rotating boson stars and Q-balls. II. Negative parity and ergoregions

We construct axially symmetric, rotating boson stars with positive and negative parity. Their flat space limits represent spinning Q-balls. Q-balls and boson stars exist only in a limited frequency range. The coupling to gravity gives rise to a spiral-like frequency dependence of the mass and charge of boson stars. We analyze the properties of these solutions. In particular, we discuss the presence of ergoregions in boson stars and determine their domains of existence.

Rotating boson stars in five dimensions

We study rotating boson stars in five spacetime dimensions. The boson fields consist of a complex doublet scalar field. Considering boson stars rotating in two orthogonal planes with both angular momenta of equal magnitude, a special ansatz for the boson field and the metric allows for solutions with nontrivial dependence on the radial coordinate only. The charge of the scalar field equals the sum of the angular momenta. The rotating boson stars are globally regular and asymptotically flat. For our choice of a sextic potential, the rotating boson star solutions possess a flat spacetime limit. We study the solutions in flat and curved spacetime.

Charged boson stars and black holes

Abstract We consider boson stars and black holes in scalar electrodynamics with a V-shaped scalar potential. The boson stars come in two types, having either ball-like or shell-like charge density. We analyze the properties of these solutions and determine their domains of existence. When mass and charge become equal, the space–times develop a throat. The shell-like solutions need not be globally regular, but may possess a horizon. The space–times then consist of a Schwarzschild-type black hole in the interior, surrounded by a shell of charged matter, and thus a Reissner–Nordstrom-type space–time in the exterior. These solutions violate black hole uniqueness. The mass of the black hole solutions is related to the mass of the regular shell-like solutions by a mass formula of the type first obtained within the isolated horizon framework.

Boson Shells Harbouring Charged Black Holes

We consider boson shells in scalar electrodynamics coupled to Einstein gravity. The interior of the shells can be empty space, or harbor a black hole or a naked singularity. We analyze the properties of these types of solutions and determine their domains of existence. We investigate the energy conditions and present mass formulae for the composite black hole-boson shell systems. We demonstrate that these types of solutions violate black hole uniqueness.

Stability of self-gravitating Bose-Einstein-Condensates

ZARM, University of Bremen, Am Fallturm, 28359 Bremen, Germany(Dated: July 23, 2015)We study the ground state and the first three radially excited states of a self-gravitating Bose-Einstein-Condensate with respect to the influence of two external parameters, the total mass and the strength of in-teractions between particles. For this we use the so-called Gross-Pitaevskii-Newton system. In this context weespecially determine the case of very high total masses where the ground state solutions of the Gross-Pitaevskii-Newton system can be approximated with the Thomas-Fermi limit. Furthermore, stability properties of thecomputed radially excited states are examined by applying arguments of the catastrophe theory.I. INTRODUCTION

Modelling of Solar Radiation Pressure Effects: Parameter Analysis for the MICROSCOPE Mission

Modern scientific space missions pose high requirements on the accuracy of the prediction and the analysis of satellite motion. On the one hand, accurate orbit propagation models are needed for the design and the preparation of a mission. On the other hand, these models are needed for the mission data analysis itself, thus allowing for the identification of unexpected disturbances, couplings, and noises which may affect the scientific signals. We present a numerical approach for Solar Radiation Pressure modelling, which is one of the main contributors for nongravitational disturbances for Earth orbiting satellites. The here introduced modelling approach allows for the inclusion of detailed spacecraft geometries, optical surface properties, and the variation of these optical surface properties (material degradation) during the mission lifetime. By using the geometry definition, surface property definitions, and mission definition of the French MICROSCOPE mission we highlight the benefit of an accurate Solar Radiation Pressure modelling versus conventional methods such as the Cannonball model or a Wing-Box approach. Our analysis shows that the implementation of a detailed satellite geometry and the consideration of changing surface properties allow for the detection of systematics which are not detectable by conventional models.

DEVELOPMENT OF MODELS FOR HIGH PRECISION SIMULATION OF THE SPACE MISSION MICROSCOPE

MICROSCOPE is a French space mission for testing the Weak Equivalence Principle (WEP). The mission goal is the determination of the Eotvos parameter with an accu- racy of 10 15 . This will be achieved by means of two high-precision capacitive differential accelerometers, that are built by the French institute ONERA. At the German institute ZARM drop tower tests are carried out to verify the payload performance. Additionally, the mission data evaluation is prepared in close cooperation with the French partners CNES, ONERA and OCA. Therefore a comprehensive simulation of the real system in- cluding the science signal and all error sources is built for the development and testing of data reduction and data analysis algorithms to extract the WEP violation signal. Cur- rently, the High Performance Satellite Dynamics Simulator (HPS), a cooperation project of ZARM and the DLR Institute of Space Systems, is adapted to the MICROSCOPE mission for the simulation of test mass and satellite dynamics. Models of environmen- tal disturbances like solar radiation pressure are considered, too. Furthermore detailed modeling of the on-board capacitive sensors is done.