Particle Physics

I will introduce how to incorporate loop contributions into positivity bounds in a massless scalar theory with shift symmetry. The allowed region of Wilson coefficients is called the EFT-hedron. With loop contributions, the n=4 null constraint, which plays an important role in determining the allowed region for g3–g4 (the Wilson coefficients of dimension-10 and dimension-12 operators, respectively), is modified. This modification of the null constraint reveals new features of the EFT-hedron. We obtained a much stronger bound for g2 (the Wilson coefficient of dimension-8 operators) without using the full unitarity condition. Furthermore, we found a negative g4, which is not possible under the tree-level bound. It would be interesting to generalize our method to more complicated theory and test our results.

The measurement of the electron magnetic moment (g-2)_e has reached the spectacular precision of sub-parts-per-trillion, and is currently the highest-precision measurement of a property of a fundamental particle. The next iteration of the measurement is expected to improve the precision by almost an order of magnitude, at which point the leading systematic uncertainty will be the “cavity shift”: the modification of the electron energy levels due to the conducting walls of the cavity in which the electron is trapped. This quantity cannot be directly measured at the required precision, and must be calculated. I will review the setup of the (g-2)_e experiment and present a new calculation of the cavity shift using the full machinery of quantum mechanics and quantum electrodynamics, which improves upon previous classical calculations with a consistent renormalization scheme while allowing for individual quality factors for each cavity mode.

It is usually assumed that 4D instantons can only arise in non-Abelian theories. One can, however, explicitly construct instantons for QED in the background of a Dirac monopole. This is the low-energy effective field theory for fermions interacting with a 't Hooft-Polyakov monopole. This theory posesses both a topological instanton number and 't Hooft zero modes. I will show how such instantons provide the underlying mechanism for the Callan-Rubakov process: monopole-catalyzed baryon decay with a cross section that saturates the unitarity bound. 

Various models of physics beyond the Standard Model predict the existence of ultralight bosons. These particles can be produced through superradiant instabilities, which create boson clouds around rotating black holes, forming so-called "gravitational atoms". In this talk, I review a series of papers that study the interaction between a gravitational atom and a binary companion. The companion can induce transitions between bound states of the cloud (resonances), as well as transitions from bound to unbound states (ionization). These processes back-react on the binary’s dynamics and leave characteristic imprints on the emitted gravitational waves (GWs), providing direct information about the mass of the boson and the state of the cloud. However, some of the resonances may destroy the cloud before the binary enters the frequency band of future gravitational wave detectors. This destruction leaves a mark on the binary’s eccentricity and inclination, which can be identified through a statistical analysis of a population of binary black holes.

Gravitational waves were detected in 2015 after 100 years of their prediction. Coalescence of black holes and neutron stars have been studied giving birth to a new way of studying our Universe. The coincidence of the gravitational signal with a gamma ray burst has been identified as the beginning of multi-messenger astronomy. In order to move from the limited statistics, allowed by the actually running interferometers (LIGO and VIRGO), to a huge sample a new generation of detectors has to be designed , built and operated. Einstein Telescope is the project for a third generation detector, supported by a large European collaboration. It is going to be formed by a combination of a Low Frequency Cryogenic interferometer and an High Frequency high laser power interferometer both located underground in order to minimise the noise. Laser technology, seismic noise attenuation, quantim squeezing are a few of the keys to success. The experiment is going to produce results in several field of research like astronomy, astrophysics, nuclear physics, cosmology. It is going to be in competition and cooperation with the US project Cosmic Explorer.