Vazha Loladze

Abstract:

The thermal confinement phase transition in $\mathrm{SU}(N)$ Yang-Mills theory is first order for $N\ge 3$ , with bounce action scaling as $N^2$ . Remarkably, lattice data for the action include a small coefficient whose presence likely strongly alters the phase transition dynamics. We give evidence, utilizing insights from softly broken supersymmetric Yang-Mills models, that the small coefficient originates from a deconfined phase instability just below the critical temperature. We predict the maximum achievable supercooling in $\mathrm{SU}(N)$ theories to be a few percent, which can be tested on the lattice. We briefly discuss the potentially significant suppression of the associated cosmological gravitational wave signals.

Abstract:

We explore the dynamics of the fermion-rotor system, a simple impurity model in d = 1 +1 dimensions consisting of a collection of purely right-moving fermions interacting with a quantum mechanical rotor localised at the origin. This was first introduced by Polchinski as a toy model for monopole-fermion scattering and is surprisingly subtle, with ingoing and outgoing fermions carrying different quantum numbers. We show that the rotor acts as a twist operator in the low-energy theory, changing the quantum numbers of excitations that have previously passed through the origin to ensure scattering consistent with all symmetries. We further show how generalisations of this model with multiple rotors and unequal charges can be viewed as a UV-completion of boundary states for chiral theories, including the well-studied 3450 model. We compute correlation functions between ingoing and outgoing fermions, and show that fermions dressed with the rotor degree of freedom act as local operators and create single-particle states, generalizing an earlier result obtained in a theory with a single rotor and equal charges. Finally, we point out a mod 2 anomaly in these models that descends from the Witten anomaly in 4d.

Abstract:

<jats:title>A<jats:sc>bstract</jats:sc> </jats:title> <jats:p>We study general properties of confinement phase transitions in the early universe. An observable gravitational wave signal from such transitions requires significant supercooling. However, in almost all understood examples of confining gauge theories the degree of supercooling is too small to give interesting gravitational wave signals. We review and highlight the evidence why supercooling is not generic in confining gauge theories. The exceptions are Randall-Sundrum models which define a strongly coupled gauge theory holographically by a 5D gravitational theory. We construct a simple illustrative model of a 4D gauge theory inspired by features of the Randall-Sundrum model. It is a large-<jats:italic>N</jats:italic> gauge theory in the conformal window coupled to a weakly coupled scalar field which undergoes a supercooled phase transition that breaks the conformal symmetry and triggers confinement. We show that there are interesting features in the gravitational wave spectra that can carry the imprint of the confining gauge theory.</jats:p>

Abstract:

We study the minimal requirements to obtain axion strings for axions with exponentially good quality. These ingredients appear in theories where an axion coming from a higher-form gauge field mixes with the phase of a complex scalar field. The resulting axion is perturbatively massless and inherits a high-quality shift symmetry from the global higher-form symmetry while being compatible with a post-inflationary axion scenario. Axions produced in this manner share features of both extra-dimensional and ordinary axions but are ultimately distinct from either. We refer to such axions as higher axions, as the mechanism responsible for the mixing is that of higher-groups. We present a simple toy model on a 5-dimensional manifold with boundary. The boundary hosts the complex scalar that provides axion strings through standard mechanisms. In addition, we study how these scenarios may arise in heterotic and type II string theory compactifications.