On the possibility to fix ill posed Cauchy problems for alternative theories of gravity

Néstor Ortíz (ICN-UNAM)

RESUMEN: Gravitational wave astronomy opens the possibility to test alternative theories of gravity in the non-linear regime. Numerical simulations are required in order to obtain predictions that could be confronted with observations. Unfortunately, the field equations' structure of many of such theories do not guarantee the possibility to define a well posed initial value problem. Inspired by the Israel-Stewart treatment of relativistic viscous hydrodynamics, I will introduce a pragmatic strategy capable to alleviate the typical pathologies of ill posed Cauchy problems. I will show implementation examples of this strategy in toy models, and I will discuss current efforts to implement it in actual evolution systems of gravity theories. Based on arXiv:1706.07421 and ongoing work.