Effective Field Theories in Frontline Science
Theory Frameworks Behind Black Hole and Neutron Star Collisions
The detection of gravitational waves from colliding black holes (left) and, furthermore, the discovery of gravitational waves from neutron stars this past October were spectacular in many ways, but one in particular was the large number of people around the world who contributed to the discovery. Indeed, members of the Physics Department at CMU can claim their share of the credit for this remarkable triumph. The initial story mentioned the counterpart detection by the Dark Energy Survey (DES), of which Scott Dodelson is one of the science leaders.
Perhaps the most important CMU contribution, however, was hidden as a reference in the recent discovery paper. This reference, number 13 in the list at the end of the paper, links to the work of CMU Professor Ira Rothstein and his collaborator Walter Goldberger at Yale University which created an effective field theory that describes the gravitational radiation emitted by inspiraling neutron stars. Their theoretical results were used by the collaboration not only to help detect the signal but also to extract information from it such as the masses of the colliding stars.
Anyone who attended last month’s THEORY CENTER TALK by Alberto Nicolis will recognize many of the key ideas articulated in the paper. Effective field theory is exciting not only because it can be used to attack such a wide variety of problems (as demonstrated by the Goldberger-Rothstein paper), but also because it is not usually employed as a cookbook. The Goldberger-Rothstein paper uses elementary physical intuition to identify the degrees of freedom and the terms in the theory that need to be considered, ordering them by the ratio of the neutron stars’ relative velocity to the speed of light. This is yet one example of why the Physics Department is looking to hire another expert in field theory this year. Who knows where field theory will next lead us to new discoveries?