Testing Weak Equivalence Principle with Strongly Lensed Cosmic Transients

Understand

Current constraints on Einstein's weak equivalence principle (WEP) utilize the observed time delay between correlated particles of astronomical sources.

• However, the intrinsic time delay due to particle emission time is impossible to measure and is simply assumed to be zero in previous studies.
• Here we propose a robust method to test WEP for relativistic messengers using strongly lensed cosmic transients, which can naturally overcome the intrinsic time delay problem.
• This can be achieved in two ways: by comparing the time delays between lensed images seen in different energy bands or in gravitational waves (GWs) and their electromagnetic (EM) counterparts.