Ruxandra Bondarescu

The astrophysics simulation collaboratory portal: a framework for effective distributed research

We describe the motivation, architecture, and implementation of the Astrophysics Simulation Collaboratory (ASC) portal. The ASC project provides a web-based problem solving framework for the astrophysics community that harnesses the capabilities of emerging computational grids.

Evolution of 3D Boson Stars with Waveform Extraction

Numerical results from a study of boson stars under nonspherical perturbations using a fully general relativistic 3D code are presented together with the analysis of emitted gravitational radiation. We have constructed a simulation code suitable for the study of scalar fields in space-times of general symmetry by bringing together components for addressing the initial value problem, the full evolution system and the detection and analysis of gravitational waves. Within a series of numerical simulations, we explicitly extract the Zerilli and Newman–Penrose scalar Ψ4 gravitational waveforms when the stars are subjected to different types of perturbations. Boson star systems have rapidly decaying nonradial quasinormal modes and thus the complete gravitational waveform could be extracted for all configurations studied. The gravitational waves emitted from stable, critical and unstable boson star configurations are analysed and the numerically observed quasinormal mode frequencies are compared with known linear perturbation results. The superposition of the high frequency nonspherical modes on the lower frequency spherical modes was observed in the metric oscillations when perturbations with radial and nonradial components were applied. The collapse of unstable boson stars to black holes was simulated. The apparent horizons were observed to be slightly nonspherical when initially detected and became spherical as the system evolved. The application of nonradial perturbations proportional to spherical harmonics is observed not to affect the collapse time. An unstable star subjected to a large perturbation was observed to migrate to a stable configuration.

Testing scalar-tensor theories and parametrized post-Newtonian parameters in Earth orbit

We compute the PPN parameters

Numerical Simulations of Oscillating Soliton Stars: Excited States in Spherical Symmetry and Ground State Evolutions in 3D

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Finite Mirror Effects in Advanced Interferometric Gravitational Wave Detectors

and

Spin evolution of accreting neutron stars: Nonlinear development of the r -mode instability

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Spinning down newborn neutron stars: Nonlinear development of the r-mode instability

for general scalar-tensor theories in the Einstein frame, which we compare to the existing PPN formulation in the Jordan frame for alternative theories of gravity. This computation is important for scalar-tensor theories that are expressed in the Einstein frame, such as chameleon and symmetron theories, which can incorporate hiding mechanisms that predict environment-dependent PPN parameters. We introduce a general formalism for scalar-tensor theories and constrain it using the limit on

The Astrophysics Simulation Collaboratory portal: A framework for effective distributed research

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Depressing de Sitter in the Frozen Future

given by the Cassini experiment. In particular we discuss massive Brans-Dicke scalar fields for extended sources. Next, using a recently proposed Earth satellite experiment, in which atomic clocks are used for spacecraft tracking, we compute the observable perturbations in the redshift induced by PPN parameters deviating from their general relativistic values. Our estimates suggest that

Women in Science: Surpassing Subtle and Overt Biases through Intervention Programs

|\gamma - 1| \sim |\beta -1| \sim 10^{-6}