The coefficients of the operators of an effective field theory(EFT) are constrained to satisfy certain inequalities, under the (mild) assumption that the ultraviolet(UV) completion satisfies general requirements of causality and unitarity. These “positivity” constraints have been the subject of intense investigation in the last 15 years, since they prove rigorously that some low energy theories cannot be UV completed. The speaker will discuss the extension of these ideas to theories where the Lorentz symmetry is spontaneously broken, as it happens in cosmology and condensed matter physics. As a starting point he will focus on a conformal field theory at finite charge. The low energy excitations of this system are described by an EFT for the Goldstone of the spontaneously broken charge: a conformal superfluid. The speaker will show that the coefficients of this EFT are constrained since, in analogy with what happens in the Lorentz invariant case, one can run a dispersive argument for the 2-point function of the conserved current and of the stress-energy tensor.
頻道：(網上講授)Zoom ID:421-480-1692 ← cosmology
講者：Paolo Creminelli(International Centre for Theoretical Physics)
“Copernicus Webinar and Colloquium Series”: To promote scientific discussions during this pandemic, they are organizing an online seminar series, i.e. Copernicus Webinar Series, seeking the most outstanding speakers to introduce innovative ideas and important progress in the field of gravity and cosmology. This series is named after the famous Polish Astronomer, Nicolaus Copernicus, whose discovery eventually marked the dawn of modern science.