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New paper with @jmezquiagabravo, new framework, new GW effects & new GR tests: https://arxiv.org/abs/2009.12187
We find that a gravitational lens can split a GW signal in theories beyond GR, much like birefringence in some materials.
Let me walk you through our main results [1/n]
![New paper with @jmezquiagabravo, new framework, new GW effects & new GR tests: https://arxiv.org/abs/2009.12187 We find that a gravitational lens can split a GW signal in theories beyond GR, much like birefringence in some materials. Let me walk you through our main results [1/n]](https://pbs.twimg.com/media/Ei_MZldXkAAh0Gi.jpg "New paper with @jmezquiagabravo, new framework, new GW effects & new GR tests: https://arxiv.org/abs/2009.12187 We find that a gravitational lens can split a GW signal in theories beyond GR, much like birefringence in some materials. Let me walk you through our main results [1/n]")
We find that a gravitational lens can split a GW signal in theories beyond GR, much like birefringence in some materials.
Let me walk you through our main results [1/n]
A gravitational lens spontaneously breaks symmetries, allowing couplings between GWs and scalar fields forbidden in homogeneous space.
Around the lens +,x & scalar polarizations combine into propagation eigenstates, which evolve independently and may have different speed [2/n]
![A gravitational lens spontaneously breaks symmetries, allowing couplings between GWs and scalar fields forbidden in homogeneous space.Around the lens +,x & scalar polarizations combine into propagation eigenstates, which evolve independently and may have different speed [2/n]](https://pbs.twimg.com/media/Ei_L2pXXYAEHhvM.jpg "A gravitational lens spontaneously breaks symmetries, allowing couplings between GWs and scalar fields forbidden in homogeneous space.Around the lens +,x & scalar polarizations combine into propagation eigenstates, which evolve independently and may have different speed [2/n]")
Around the lens +,x & scalar polarizations combine into propagation eigenstates, which evolve independently and may have different speed [2/n]
The different speed leads to a time delay between the different states. In many cases the two metric polarizations h_+, h_x (slightly mixed w/ scalar) can pick a different speed.
This splits a signal (e.g. a BH merger) into separate echoes [3/n]
![The different speed leads to a time delay between the different states. In many cases the two metric polarizations h_+, h_x (slightly mixed w/ scalar) can pick a different speed.This splits a signal (e.g. a BH merger) into separate echoes [3/n]](https://pbs.twimg.com/media/Ei_PN4ZXcAAIdm2.png "The different speed leads to a time delay between the different states. In many cases the two metric polarizations h_+, h_x (slightly mixed w/ scalar) can pick a different speed.This splits a signal (e.g. a BH merger) into separate echoes [3/n]")
This splits a signal (e.g. a BH merger) into separate echoes [3/n]
If the time delay is small enough, the two polarizations interfere with each other in the detector, scrambling the waveform.
This type of test does not require an electromagnetic counterpart to the event. Any LIGO signal is sensitive at the ~ms level [4/n]
![If the time delay is small enough, the two polarizations interfere with each other in the detector, scrambling the waveform.This type of test does not require an electromagnetic counterpart to the event. Any LIGO signal is sensitive at the ~ms level [4/n]](https://pbs.twimg.com/media/Ei_Pa0xXcAE6aEr.png "If the time delay is small enough, the two polarizations interfere with each other in the detector, scrambling the waveform.This type of test does not require an electromagnetic counterpart to the event. Any LIGO signal is sensitive at the ~ms level [4/n]")
This type of test does not require an electromagnetic counterpart to the event. Any LIGO signal is sensitive at the ~ms level [4/n]
GW lensing tests will become much more effective with growing number of GW detections (higher chance of good source-lens orientation).
Our forecast suggest a factor ~10 improvement with @LIGO design sensitivity and ~100 with 3rd generation detectors [5/n]
![GW lensing tests will become much more effective with growing number of GW detections (higher chance of good source-lens orientation).Our forecast suggest a factor ~10 improvement with @LIGO design sensitivity and ~100 with 3rd generation detectors [5/n]](https://pbs.twimg.com/media/Ei_P-soXsAAlgxU.png "GW lensing tests will become much more effective with growing number of GW detections (higher chance of good source-lens orientation).Our forecast suggest a factor ~10 improvement with @LIGO design sensitivity and ~100 with 3rd generation detectors [5/n]")
Our forecast suggest a factor ~10 improvement with @LIGO design sensitivity and ~100 with 3rd generation detectors [5/n]
GW birefringence allows detection in lensing set-ups that do not contribute in "traditional" lensing.
In particular, the metric (Shapiro) and geometric (deflection angle) contributions to the time delay can dominate for different lens redshift or mass (here example th.) [6/n]
![GW birefringence allows detection in lensing set-ups that do not contribute in "traditional" lensing.In particular, the metric (Shapiro) and geometric (deflection angle) contributions to the time delay can dominate for different lens redshift or mass (here example th.) [6/n]](https://pbs.twimg.com/media/Ei_RPD4X0AA21r1.png "GW birefringence allows detection in lensing set-ups that do not contribute in \"traditional\" lensing.In particular, the metric (Shapiro) and geometric (deflection angle) contributions to the time delay can dominate for different lens redshift or mass (here example th.) [6/n]")
In particular, the metric (Shapiro) and geometric (deflection angle) contributions to the time delay can dominate for different lens redshift or mass (here example th.) [6/n]
After discussing the framework in general we applied it to a specific theory of gravity in the Horndeski class.
GW lensing tests via birefringence can go much deeper into the parameter space of the theory than limits from GW170817 (average difference in GW vs EM speed)
[7/n]
![After discussing the framework in general we applied it to a specific theory of gravity in the Horndeski class. GW lensing tests via birefringence can go much deeper into the parameter space of the theory than limits from GW170817 (average difference in GW vs EM speed)[7/n]](https://pbs.twimg.com/media/Ei_TCTWWoAIlFu3.png "After discussing the framework in general we applied it to a specific theory of gravity in the Horndeski class. GW lensing tests via birefringence can go much deeper into the parameter space of the theory than limits from GW170817 (average difference in GW vs EM speed)[7/n]")
GW lensing tests via birefringence can go much deeper into the parameter space of the theory than limits from GW170817 (average difference in GW vs EM speed)
[7/n]
These constraints would be achieved by a binary merger in a very dense environment, such as the vicinity of a super-massive black hole. Events like #GW190521 could be a smoking gun for such environments (e.g. EM counterparts, hierarchical formation, multi-band observation) [8/n]
![These constraints would be achieved by a binary merger in a very dense environment, such as the vicinity of a super-massive black hole. Events like #GW190521 could be a smoking gun for such environments (e.g. EM counterparts, hierarchical formation, multi-band observation) [8/n]](https://pbs.twimg.com/media/Ei_Tx4NXsAETs-9.png "These constraints would be achieved by a binary merger in a very dense environment, such as the vicinity of a super-massive black hole. Events like #GW190521 could be a smoking gun for such environments (e.g. EM counterparts, hierarchical formation, multi-band observation) [8/n]")
![Many more details on the paper itself [9/n] https://inspirehep.net/literature/1819285](https://pbs.twimg.com/media/Ei_Tu7fXYAYFUaL.jpg "Many more details on the paper itself [9/n] https://inspirehep.net/literature/1819285")
or on our recent talks in remote conferences:
and of course, questions comments are most welcome! [10/n]
and of course, questions comments are most welcome! [10/n]
