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Trans precession

Cecilio Garcia-Quiros requested to merge waveforms/reviews/lalsuite:trans-precession into master

Description

@maria.haney

IMRPhenomXPHM allows choosing between different precessing prescriptions for the Euler angles: MSA and NNLO. In addition, there exist different prescriptions for the final spin (FS=0,1,2,3).

The default setting of XPHM uses MSA and FS3. However FS3 assumed that the final spin was always positive, that means beta<pi/2 i.e. there is no transitional precession. However, for some high mass ratios, high anti-aligned spins this phenomenon can occur. In this MR we take into account the sign of the final spin for FS3. The rest of FS options already tracked the sign.

A lal dictionary option allows to switch on and off this fix for FS3. To switch off do lalsim.SimInspiralWaveformParamsInsertPhenomXPTransPrecessionMethod(laldict, 0)

In addition, for the NNLO angles, we have that cos_beta is assumed to be positive, that means again, that there is no transitional precession and this was inherited from the IMRPhenomPv2 model. In this MR we also track the sign of cos_beta for XPHM. A second MR will be needed if one wants to fix also IMRPhenomPv2.

These fixes do not guarantee that transitional precession will be correctly modelled since particularly the NNLO badly behave for high mass ratios, but they will improve the behaviour of the model in this regime.

The function IMRPhenomXPCheckMaxOpeningAngle prints a warning message when beta is higher than pi/2 so transitional precession is happening. The call to this function has been moved from IMRPhenomXPGenerateFD to IMRPhenomXGetAndSetPrecessionVariables in order that XPHM also shows this warning message.

API Changes and Justification

Backwards Compatible Changes

  • This change introduces no API changes
  • This change adds new API calls

Backwards Incompatible Changes

  • This change modifies an existing API
  • This change removes an existing API

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

@cecilio.garcia-quiros has produced this wiki where the changes of the model have been tested and documented. The XPHM review team has given their approval on this.

Edited by Cecilio Garcia-Quiros

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