We study Polchinski’s “fermion-rotor system” as an accurate description of charged Weyl fermions scattering on a magnetic monopole core in the limit of zero gauge coupling. Traditionally it was thought such scattering could lead to fractional particle numbers (“semitons”). By direct calculations we show those semitonic processes are in fact free propagation, facilitated by composite fermion-rotor operators interpolating the “forbidden” states, effectively “recovering” both ingoing and outgoing states in every lowest partial wave. Nonsemitonic Callan-Rubakov processes are unchanged. Published by the American Physical Society 2025

We study the possibility of production of primordial black holes (PBHs) from bubble collisions during a first-order phase transition. While typical colliding bubbles are small and irrelevant for PBH production, we find that those that can produce PBHs must have a macroscopically thick fluid shell and have been born much before the typical nucleation time. Particularly large uncertainties arise from an exponential sensitivity of the nucleation rate on the required duration of bubble growth which depends on the details of the collisions and the evolution of the spacetime metric toward the end of the phase transition. We introduce a few parameters to be obtained from future numerical simulation to represent those unknowns, and estimate the PBH abundance in an Abelian Higgs benchmark model and show that it can be significant. We predict an approximately monochromatic PBH mass spectrum, and find regions in the parameter space where the PBHs can constitute entire dark matter or even overclose the Universe. Our result thus shows that models with a first-order phase transition can be constrained by overabundant PBHs or null results of other PBH searches. Published by the American Physical Society 2024

Reading and math are related due to many codeveloping skills. Historically, theorizing in these two areas has progressed separately, despite well-documented empirical evidence for a range of shared underlying developmental processes subserving these learning domains. The purpose of this paper is to describe the links between the Triple Code Model, an influential model of numerical cognition, and the Triangle Framework, a dominant model of learning to read. We describe several parallels between the theoretical models and discuss how the cognitive mechanisms posited by the Triangle Framework might be used to understand the commonalities in learning processes across these learning domains In particular, we discuss how the cognitive mechanisms implemented in the Triangle Framework can be used to understand linguistic aspects of numerical cognition, specifically, learning the connections among numerals (e.g., 24) and words (e.g., twenty-four), and linking those to semantic representations of magnitude. Following from these commonalities between the two models, we discuss several ways that interdisciplinary work integrating both models can benefit math cognition research.

Here we report muon spin rotation (μSR) experiments on the temperature and field dependence of the effective magnetic penetration depth λ(T) in the η-carbide-type suboxide Ti4Ir2O, a superconductor with a considerably high upper critical field. The temperature dependence of λ(T), obtained from transverse-field (TF)-μSR measurements, is in perfect agreement with an isotropic fully gaped superconducting state. Furthermore, our ZF μSR results confirm that the time-reversal symmetry is preserved in the superconducting state. We find, however, a remarkably small ratio of Tc/λ0−2∼1.22. This value is close to most unconventional superconductors, showing that a very small superfluid density is present in the superconducting state of Ti4Ir2O. The presented results will pave the way for further theoretical and experimental investigations to obtain a microscopic understanding of the origin of such a high upper critical field in an isotropic single-gap superconducting system. Published by the American Physical Society 2024