[Astro] [CAPT] CAPT Weekly Bulletin (w/c 03-11-25)

Tue Nov 4 08:31:59 GMT 2025

Tuesdays at 11am, CAPT Foyer – Astro Coffee

Tuesday 4th November at 1pm, A113 CAPT – Particle Cosmology and Gravity Seminar

Usama Aqeel

Matter Sourced Bubble Nucleation in the Asymmetron Scalar Tensor Theory

We investigate how matter density distributions affect thin-wall bubble formation in the asymmetron mechanism, a scalar-tensor theory with a universal coupling to matter and explicit symmetry-breaking and analyse the stability of its metastable state. We show that the screening mechanism of the asymmetron inside dense objects induces a surface tension associated with the boundary of the screening object, leading to a richer class of bubble solutions than the standard Coleman-Callan bulk nucleation. These boundary surface tensions are used to modify the Nambu-Goto action for instantons, allowing for the computation of the corresponding Euclidean action for bubbles nucleating on flat planes, as well as on concave and convex cylindrical surfaces. We find that the smallest Euclidean action occurs for bubbles nucleating along the edge of a concave spherical surface. Comparing this edge nucleation channel with the bulk one, we determine the maximum curvature radius for which concave edge nucleation is preferred. Since the maximum radius of curvature is exponentially suppressed by the action of a bulk bubble, we find that within the regime of the instanton approximation, edge nucleation is always preferred. This is largely due to the weak couplings of the asymmetron. We apply these findings to determine the maximum curvature radius of a cosmic void and discuss how our results affect the seeding of N-body simulations of asymmetron domains, showing that domain wall nucleation preferentially occurs at the edges of cosmological voids. We also demonstrate that the presence of a homogeneous gas around the dense substrates reduces the maximum curvature radius, enabling bulk bubbles to form preferentially as the asymmetron undergoes a density-driven phase transition.

Link to join:  https://teams.microsoft.com/l/meetup-join/19%3ameeting_OGM3OTk5NzQtZWEwZS00ZmUyLTk3MGUtZjFhY2M5OTU2MjI1%40thread.v2/0?context=%7b%22Tid%22%3a%2267bda7ee-fd80-41ef-ac91-358418290a1e%22%2c%22Oid%22%3a%22f3250584-4b5f-48fa-a897-08e77f2246b7%22%7d
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Wednesday 5th November at 11am, A113 CAPT – CAPT Coding Club

Wednesday 5th November at 3:45pm, C4 Physics – Astronomy Weekly Seminar

Romeel Davé (Edinburgh)

How massive galaxies quench in the Simba simulations

Cosmological simulations of galaxy formation have matured rapidly in the last few years, with recent models combining structure formation, hydrodynamics, stellar and black hole growth, and associated feedback processes to accurately reproduce key demographical properties observed in the galaxy population.  Our group's Simba simulation suite includes unique input physics that have dramatic implications particularly for the growth and quenching of massive galaxies.  I will show how Simba's AGN jet feedback impacts the surrounding circum-galactic and intergalactic medium on surprisingly large scales.  Using the Hyenas zoom simulations based on Simba, I will further show how Simba's jets blow X-ray cavities as observed, depositing energy and evacuating halo gas, the first time this has been demonstrated within a full hierarchical galaxy formation context.  Such feedback also goes helps explain some puzzling trends seen in the stellar-to-halo mass relation and the matter power spectrum.

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Thursday 6th November at 1pm, A113 CAPT – Astronomy Lunch Talk

Candela Zerbo
Minding the Gap Between Scales: Insights from Simulations on the Role of Local Density and the Cosmic Web on Galaxy Evolution

The evolution of galaxies is strongly influenced by their surrounding environment, from the local density of neighbouring systems to their position within the cosmic web. In this work, we aim to disentangle the relative importance of these factors using simulated galaxies. Building on the observational framework of O’Kane et al. (2024), we classify simulated galaxies into six environmental categories to explore how their baryonic properties and star formation activity vary with local density and cosmic-web location. As a first step, we focus on two test clusters from The Three Hundred project. We examine the spatial distribution of their galaxies and the stellar mass function in each environment. We will later incorporate star formation rates and compare different density estimators. Future stages will include contrasting results between hydrodynamical (GIZMO–SIMBA) and semi-analytic (SAG) models, and evaluating the impact of different filament identification methods. This ongoing work will provide new insights into how local and large-scale structures jointly drive galaxy evolution.

Thursday 6th November at 3pm, A113 CAPT – Particle Cosmology Journal Club
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Fridays at 4pm, CAPT Foyer – CAPT Cakes
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If you have any events/visitors you would like included in next week’s bulletin, please let me know.

Best wishes

Ella

Ella Batchelor (she/her)
Administrator

School of Physics & Astronomy

University of Nottingham
A112a Centre for Astronomy & Particle Theory
University Park
Nottingham, NG7 2RD

+44 (0) 115 74 86778 |  nottingham.ac.uk<http://nottingham.ac.uk/>

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