Responses of the Brans-Dicke field due to gravitational collapses

Authors: Hwang, Dong-il; Yeom, Dong-han

Source: Classical and Quantum Gravity, Volume 27, Number 20, 21 October 2010 , pp. 205002-205023(22)

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Abstract:

We study responses of the Brans-Dicke field due to gravitational collapses of scalar field pulses using numerical simulations. Double-null formalism is employed to implement the numerical simulations. If we supply a scalar field pulse, it will asymptotically form a black hole via dynamical interactions of the Brans-Dicke field. Hence, we can observe the responses of the Brans-Dicke field by two different regions. First, we observe the late time behaviors after the gravitational collapse, which include formations of a singularity and an apparent horizon. Second, we observe the fully dynamical behaviors during the gravitational collapse and view the energy-momentum tensor components. For the late time behaviors, if the Brans-Dicke coupling is greater (or smaller) than −1.5, the Brans-Dicke field decreases (or increases) during the gravitational collapse. Since the Brans-Dicke field should be relaxed to the asymptotic value with the elapse of time, the final apparent horizon becomes time-like (or space-like). For the dynamical behaviors, we observed the energy-momentum tensors around ω ~ −1.5. If the Brans-Dicke coupling is greater than −1.5, the T_uu component can be negative at the outside of the black hole. This can allow an instantaneous inflating region during the gravitational collapse. If the Brans-Dicke coupling is less than −1.5, the oscillation of the T_vv component allows the apparent horizon to shrink. This allows a combination that violates weak cosmic censorship. Finally, we discuss the implications of the violation of the null energy condition and weak cosmic censorship.

Document Type: Research article

DOI: http://dx.doi.org/10.1088/0264-9381/27/20/205002

Publication date: 2010-10-21