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SUMMARY:The propagation of gravitational waves through matter - Nigel Bish
 op\, Rhodes University
DTSTART:20221104T130000Z
DTEND:20221104T140000Z
UID:TALK179099@talks.cam.ac.uk
CONTACT:Prahar Mitra
DESCRIPTION:The modification of gravitational waves (GWs) passing through 
 matter is normally treated as very weak. We have re-investigated this matt
 er using linearized perturbations within the Bondi-Sachs formalism\, and f
 ind that\, while the effect is normally very weak\, there are special astr
 ophysical circumstances in which it can be significant\n\nWe consider a GW
  source surrounded by a spherical shell of matter. We find that the shell 
 causes the GWs to be modified both in magnitude and phase\; and that if th
 e shell is viscous\, then the shear induced in the velocity field results 
 in an energy transfer so damping the magnitude of the GWs. Both effects ca
 n be significant if the shell radius is much smaller than the GW wavelengt
 h\, and there are astrophysical scenarios for which the modification to th
 e GW signal is large enough to be measurable. These scenarios include core
  collapse supernovae (CCSNe)\, quasinormal mode emission from the remnant 
 of a binary neutron star (BNS) merger\, and primordial GWs. In particular\
 , there are feasible values of the CCSNe parameters for which viscous damp
 ing of the GW signal would be almost complete.\n\nIn numerical relativity\
 , an evolution of the full Einstein and matter field equations with GW ext
 raction far from the source will properly include all effects described ab
 ove. However\, in situations such as CCSNe and BNS shear viscosity is not 
 included in the modeling\, and GW extraction is handled approximately. Res
 ults obtained in these cases would need to be corrected.\n\nThe presentati
 on is based on:\n1. N.T. Bishop\, M. Naidoo\, and P.J. van der Walt (2020)
 \, Gen. Rel. Grav. 52:92\, https://doi.org/10.1007/s10714-020-02740-9 arXi
 v:1912.08289\n2. M. Naidoo\, N.T. Bishop\, and P.J. van der Walt (2021)\, 
 Gen. Rel. Grav. 53:97\, https://doi.org/10.1007/s10714-021-02841-z arXiv:2
 102.00060\n3. N.T. Bishop\,  P.J. van der Walt and M. Naidoo (2022)\, arXi
 v:2206.15103
LOCATION:Potter room/Zoom
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