[Astro] [CAPT] CAPT Weekly Bulletin (w/c 16-02-26)

Mon Feb 16 08:15:13 GMT 2026

Monday 16th February at 3pm, A113 CAPT – Theoretical Physics Student Seminar

Mohammed Shafi

Oscillons in 1+1 Minkowski space

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Tuesdays at 11am, CAPT Foyer – Astro Coffee

Tuesdays at 11.30am, A113 CAPT – Astronomy Journal Club

Tuesday 17th February at 1pm, A113 CAPT – Particle Cosmology and Gravity Seminar

David Seery (Sussex)

The probability of rare fluctuations during inflation with stochastic instantons

In this talk, I will review why there has been recent interest in calculating the probability of extreme density perturbations produced during an inflationary phase, and briefly discuss the means by which such probabilities have been computed to date. I will the introduce a new approach, based on the use of "stochastic instantons". Such instantons have been widely applied in many other areas of physics, including turbulent fluid flow, reaction kinetics, climate modelling, and protein folding. The method has a number of advantages, including giving a spacetime picture for the assembly of a rare, extreme fluctuation. I will show how the method reproduces some known results but can also be applied to scenarios that were not previously accessible.

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 18th February at 1.30pm, A113 CAPT – Particle Cosmology and Gravity Whiteboard Talk

Sadra Jazayeri (Imperial)

Zooming Into the Ultraviolet with Primordial Features

In the next few years, galaxy surveys like Euclid and DESI are anticipated to improve the current CMB-driven bounds on primordial features in the power spectrum by roughly an order of magnitude (e.g. 1906.08758). Motivated by this observational prospect, I show that massive sectors during inflation, with energy scales parametrically larger than the Hubble rate, can leave characteristic scale-breaking signatures in primordial non-Gaussianity, in the presence of non-shift-symmetric couplings to the inflaton sector. As a benchmark example, I will consider sinusoidal modulations of the species masses, as in axion monodromy scenarios, which would trigger particle productions with exponentially larger rates than the Boltzmann-suppressed case in pure de Sitter. In these models, without a closed-form solution for the free massive theory, finding analytic templates using the in-in formalism for exchange processes that contribute to primordial non-Gaussianity(PNG) is a formidable challenge.  Circumventing the complexity of the corresponding in-in time integrals, I will build a novel bootstrap framework in which the exchange diagrams contributing to PNG can be solved using a set of integro-differential equations on the boundary implied by locality in the bulk of spacetime.

Note added: This is going to be a very informal white/black board talk based on the recent work 2511.00152.

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

Wednesday 18th February at 3.45pm, C4 Physics – Astronomy Seminar
Stephen Wilkins (Sussex)

Exploring the formation of the first stars, black holes, and galaxies

According to the Big Bang model, the Universe began in an extremely hot, dense state around 14 billion years ago. After a brief period of early evolution, it entered the cosmic dark ages, an era during which dark matter and gas slowly assembled into the first stars, black holes, and galaxies.

We are now entering a transformative period in observational extragalactic astronomy. The James Webb Space Telescope (JWST) has pushed our view of the cosmos to within a few hundred million years of the Big Bang providing observations of thousands of galaxies within the early Universe. JWST has also revealed surprising populations of early galaxies with unusual chemical enrichment patterns, and enigmatic compact sources known as “Little Red Dots”, which may offer new insight into the formation of the first supermassive black holes. JWST’s discoveries are being complemented by the wide-area Euclid mission, and will soon be augmented by the Square Kilometre Array Observatory, the Nancy Grace Roman Space Telescope, and the Extremely Large Telescope.

At the same time, cosmological simulations have become extraordinarily sophisticated, capable of modelling the growth of structure across cosmic time. Yet early JWST results reveal emerging tensions with these models, suggesting that key aspects of early galaxy formation may require revision.

In this talk, I will present recent work from my group and collaborators and discuss how these observations and simulations together are reshaping our understanding of the first billion years of cosmic history.

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Thursday 19th February at 1pm, A113 CAPT – Astronomy Lunch Talk

Marco Mirabile (ESO/INAF)

Globular Clusters as Probes of Galaxy Evolution: Insights from Ultra-Diffuse Galaxies

Globular clusters (GCs), as old and simple stellar systems, serve as important tracers of galaxy formation and evolution. By studying their properties—such as color, luminosity, spatial distribution, and kinematics—we gain insight into galaxy history, interactions, and dark matter content. Recent deep imaging has revealed ultra-diffuse galaxies (UDGs), a class of low-surface-brightness galaxies with unclear origins. Analyzing the GC populations in UDGs can help distinguish between their possible formation scenarios. I will present our study of GCs in UDGs within the Hydra I cluster, using combined data from MUSE at VLT and VIRCAM at VISTA.

Thursday 19th February at 2.45pm, 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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