Einstein’s general relativity (GR) has passed all experimental examinations
for almost 100 years with flying colors. However, besides current puzzles on the
nature of dark matter and dark energy, there exist fundamental difficulties to
combine GR and quantum principles. A full theory of quantum gravity may settle
the issues, but such a theory is still missing. Some models of quantum gravity
suggest the breaking of local Lorentz invariance in the gravitational
interaction. This possibility lately raises enormous interests both for
theorists and experimenters in the gravity community.
In a series of papers that are published in Classical and Quantum Gravity
[1,2,3], Lijing Shao, a PhD student from School of Physics in Peking University,
and his collaborators proposed new tests of local Lorentz invariance and local
position invariance in gravity with pulsars. Pulsars are stably rotating
lighthouses in the sky that can be studied with great precision with large radio
telescopes on the ground. Shao and his collaborators did careful analysis with
real data from pulsar timing observations, and constrained tightly the
parameters in the parameterized post-Newtonian (PPN) formalism. Their limits
surpass previous limits by orders of magnitude, and are more promising to be
improved further in the future [1,2.3].
While PPN formalism is a generic framework that starts from the spacetime
metrics, there exists another generic framework, called standard-model extension
(SME), which roots in effective field theories. Recently, Shao used published
observations from an array of most precise millisecond pulsars, and achieved a
global constraints on the vacuum expectation values of the Lorentz-violating
tensor field in SME [4]. To be published in Physical Review Letters, his new
constraints are more stringent by orders of magnitude than the previous best
limits from Lunar Laser Ranging and atom interferometry experiments.
This work is supported by China Scholarship Council (CSC), and was carried
out when Shao was visiting the Max Planck Institute for Radio Astronomy in Bonn,
Germany.
[1] Shao & Wex, Class. Quantum Grav. 29 (2012) 215018. [arXiv:1209.4503]
[2] Shao et al., Class. Quantum Grav. 30 (2013) 165019. [arXiv:1307.2552]
[3] Shao & Wex, Class. Quantum Grav. 30 (2013) 165020. [arXiv:1307.2637]
[4] Shao, Phys. Rev. Lett. (2014) in press. [arXiv:1402.6452]
