Status  Confirmed 
Seminar Series  APCTH 
Subjects  hepth 
Date  Tuesday 24 October 2017 
Time  14:00 
Institute  APC 
Seminar Room  483 A  Malevitch 
Speaker's Last Name  Julié 
Speaker's First Name  Félix 
Speaker's Email Address  
Speaker's Institution  APC, Université Paris Diderot 
Title  Twobody problem in modified gravities and EOB theory 
Abstract  The effectiveonebody (EOB) approach has proven to be a very powerful framework to describe analytically the coalescence of compact binary systems in general relativity (GR). In this seminar, we address the question of extending it to the frame of modified gravities, focussing on the first building block of the EOB approach; that is, mapping the conservative part of the twobody dynamics to the Hamiltonian of a single test particle in effective external fields. We first consider the example of massless scalartensor (ST) theories, whose twobody dynamics is known at second post Keplerian (2PK) order. Two distinct STEOB Hamiltonians will be proposed : (i) a STdeformation of the general relativistic EOB Hamiltonian, which allows to incorporate scalartensor (2PK) effects as parametrized corrections to GR (parametrized EOB, or PEOB), and (ii) the Hamiltonian of a ST testbody problem, which is well suited to regimes that depart strongly from GR. Both STEOB Hamiltonians lead to simple (yet canonically equivalent) formulations of the conservative 2PK twobody problem, but also define two distinct resummations of the dynamics that may provide information on the strongfield regime; in particular, the ISCO location and associated orbital frequency. The class of EinsteinMaxwelldilaton (EMD) theories, which provide simple examples of « hairy » black holes, will also be discussed. In particular, we compute the associated postKeplerian twobody Lagrangian, and show that it can, as well, be incorporated within the parametrized effectiveonebody (PEOB) framework. 
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