Particle Physics

Besides providing a possible explanation to the strong CP problem and dark matter, the QCD axion possesses a rich cosmology. For example, if PQ breaking occurs after inflation, then axion cosmic strings form. Near the QCD phase transition, every axion string become attached to a domain wall which pull on the strings and cause the string-wall network to decay. While every string becomes attached to a domain wall, it is possible, though rare, to form an enclosed domain wall that is not attached to any axion string. These enclosed domain walls collapse under their own self tension, compressing a large amount of energy into a small volume and thereby potentially forming a primordial black hole. In this talk, I will discuss the abundance of enclosed domain walls, their dynamics of collapse, the efficiency of black hole formation, and their relic abundance. For sufficiently large axion decay constants, there may be an observable gravitational lensing signal at future lensing telescopes, especially in models with axion-like-particles.

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Particle production can occur in a curved spacetime like, for example, in the case of thermal emission of particles from black holes, otherwise known as Hawking radiation. The Unruh effect is a quantum field theory result that is closely connected to Hawking radiation. It states that accelerated observers associate a thermal bath of particles to the vacuum state of inertial observers. The Unruh effect has been given special attention because contrary to black hole evaporation, it is a prediction made in a flat (Minkowski) spacetime and therefore can be, in principle, tested in the laboratory. Recently, we have investigated the connection between the Unruh effect and classical radiation for a uniformly accelerated particle. This link seems counter-intuitive since the former is a purely quantum effect while the latter is a classic one. Nonetheless, we find that using a full quantum field treatment of the radiation exchanged by an accelerated charge with the surrounding Unruh thermal bath, the resultant power reduces at tree-level to the usual Larmor formula. The results are also consistent with the observation made by Unruh and Wald which states that the emission of a photon in the inertial frame corresponds to the emission or absorption of a photon in the accelerated frame. The fact that the derivation makes the link between the Unruh effect and the Larmor radiation from a uniformly accelerated charged particle clearer will perhaps help in resolving some of the controversies that have surrounded the Unruh effect since its discovery.

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Theories which spontaneously break spacetime parity can solve the strong CP problem. They usually have few free parameters and are therefore very predictive, but their landscape remains quite unexplored. I will present a construction based on a complete mirror copy of the standard model, linked to our world by colored portal fields. Those induce the partial spontaneous breaking of the color groups, yielding a vanishing theta angle at low energies. The lightest BSM fields could be found at colliders, and are either colored (pseudo-Goldstone or vector) bosons, or some of the vectorlike fermions predicted by parity. The lightest of the latter can actually play the role of thermal dark matter in our model, unlike what was previously found in similar constructions.

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This talk is virtual, but will also be broadcast in the Sky Room. 

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A cosmological network of axion strings in our Universe today may leave its imprint on the polarization pattern of the cosmic microwave background radiation through the phenomenon of axion-string-induced birefringence. I will explain how this signal arises, discuss how it depends on the properties of the string network and the axion-photon coupling, describe how existing measurements of anisotropic birefringence place constraints on axion strings, and discuss how the non-Gaussian nature of this signal could be leveraged in searches with future data.

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The implementation of optical astronomical interferometry presents several technical challenges, such as establishing a shared reference frame and conducting nonlocal measurements. This presentation aims to establish a connection between the theoretical framework developed in quantum information science and the schemes employed in astronomical interferometry. Our discussion will focus on the trade-offs between required resource and operational performance. We will categorize these methods into three types: nonlocal schemes, local schemes with a reference frame, and local schemes operating without a reference frame. By using this interdisciplinary connection, we also explore a generalized intensity interferometer. This approach achieves performance levels comparable to traditional intensity interferometers but introduces interesting fundamental distinctions.

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