DESY Theory Seminar

The tune of Love and the nature(ness) of spacetime

by Rafael Porto (ICTP Sao Paolo)

Europe/Berlin
Seminar room 2, building 2A (DESY Hamburg)

Seminar room 2, building 2A

DESY Hamburg

Description
I discuss the properties of compact objects in non-trivial gravitational backgrounds using an effective field theory (EFT) description. I show that certain higher dimensional operators —allowed by diff invariance— have zero matching coefficients for the case of black holes (BHs) in general relativity (GR), and in four dimensions. These (Wilson) coefficients are known as ‘Love numbers’. Their values are consistent with naive dimensional analysis for compact objects (e.g. neutron stars) other than BHs. I argue —due to short-distance sensitivity— that the vanishing of Love numbers for BHs implies a fine tuning from the EFT side, already at the classical level. While a generalized version of the no-hair theorem(s) may explain this behavior, it also suggests that an emergent symmetry of GR (in black hole backgrounds) could be the ultimate culprit. The situation worsen in the quantum realm, where we expect renormalization effects to drive the Love numbers of BHs away from zero. Hence, either (quantum) black holes have non-trivial Love numbers at the end of the day, or plausibly a —yet to be found— symmetry protects these coefficients against quantum corrections. (I briefly discuss this idea also in the context of cosmology.) Finally, I discuss the future steps towards probing the Love numbers of black holes (and neutron stars) —in binary systems— with the next generation of gravitational wave detectors.