[Astro] [CAPT] CAPT Weekly Bulletin (w/c 10-03-25)

Mon Mar 10 10:45:01 GMT 2025

Monday 10th March at 3pm, A113 Physics – Theoretical Physics Student Seminar

Benjamin Muntz

Geometric Amplitudes and the Swampland Distance Conjecture

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Tuesdays at 11am, CAPT Foyer – Astro Coffee

Tuesday 11th March at 1pm, A113 Physics – Particle Cosmology and Gravity Seminar

Diksha Jain (DAMTP, Cambridge)

The S-matrix and boundary correlators in flat space

We consider the path integral of a quantum field theory in Minkowski spacetime with fixed boundary values (for the elementary fields) on asymptotic boundaries. We define and study the corresponding boundary correlation functions obtained by taking derivatives of this path integral with respect to the boundary values. The S-matrix of the QFT can be extracted directly from these boundary correlation functions after smearing. We interpret this relation in terms of coherent state quantization and derive the constraints on the path-integral as a function of boundary values that follow from the unitarity of the S-matrix. We then study the locality structure of boundary correlation functions. In the massive case, we find that the boundary correlation functions for generic locations of boundary points are dominated by a saddle point which has the interpretation of particles scattering in a small elevator in the bulk, where the location of the elevator is determined dynamically, and the S-matrix can be recovered after stripping off some dynamically determined but non-local ``renormalization'' factors. In the massless case, we find that while the boundary correlation functions are generically analytic as a function on the whole manifold of locations of boundary points, they have special singularities on a sub-manifold, points on which correspond to light-like scattering in the bulk. We completely characterize this singular scattering sub-manifold, and find that the corresponding residues of the boundary correlations at these singularities are precisely given by S-matrices. This analysis parallels the analysis of bulk-point singularities in AdS/CFT and generalizes it to the case of multi-bulk point singularities.

Reference: https://inspirehep.net/literature/2719839

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 12th March at 3pm, C14 Physics – Postgraduate Poster Competition

The competition is sponsored by Cerca Magnetics. Posters will be judged by representatives from Cerca Magnetics and by staff from the school. Public viewing is from 3-4pm, with prize-giving at around 4pm.

Wine, soft drinks and snacks will be provided. All staff and students are encouraged to attend.

Wednesday 12th March at 3.45pm, C4 Physics – Astronomy Seminar
Dr Ting-Yun (Sunny) Cheng (Durham)

Needles in Haystacks: Searching for Rare Primordial Systems with Deep Learning

Primordial systems are unique archeological sites, commonly hidden within vast observational datasets yet offering invaluable insights into the story of our Universe. In this talk, I will present efforts in searching for two kinds of (potentially) primordial systems — (1) low-metallicity dwarf galaxies and (2) Lyman limit deuterium systems — using deep learning techniques.

Extremely metal-poor dwarf galaxies (XMPs) are often regarded as the “living fossils” of the earliest galaxies. These relics in the local Universe are ideal laboratories for studying the environmental conditions and chemical enrichment processes of early galaxies, as well as their impact on the evolution of early Universe. However, these systems are exceedingly rare; despite extensive searches over the past two decades, only a few hundred have been identified among millions of galaxy samples. This talk will present my recent work on developing an effective deep learning pipeline for identifying XMPs and report some exciting new discoveries from our ongoing search.

The second part of the talk will introduce the search for Lyman limit deuterium systems in the Lyman-alpha forest of quasar spectra. Deuterium, primarily produced during Big Bang nucleosynthesis, has been largely consumed by stellar processes, making these systems rare and invaluable tracers for understanding the early Universe. In particular, Lyman limit deuterium systems are even rarer, with only three well-known systems in literature. I will present newly discovered systems from this search and our investigation of the temperature-density relation in these systems.

Wednesday 12th March at 6pm, Arts Lecture Theatre – Gravitational Waves and Human Choices
£3 (Free Concessions)
Running time: 1 hour

Join Professor Thomas Sotiriou, University of Nottingham and artist Matthew Woodham for this informative evening.

Uncover the nature of gravitational waves: how ripples in spacetime reveal secrets about the Universe’s most violent events, challenge Einstein’s General Relativity, and even connect to human consciousness.

Click here<https://www.lakesidearts.org.uk/event/gravitational-waves-and-human-choices/> to book.
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Thursday 13th March at 1pm, A113 CAPT – Astronomy Lunch Talk

Jen Feron
The Peculiar Velocity Effect in 21cm Lightcones

The 21cm brightness temperature during the Epoch of Reionisation is widely modelled using semi-numeric simulations. They are used for their computational speed and flexibility to test different astrophysical and cosmological parameters. However, these simulations often make assumptions in order to reduce computational costs. In particular the peculiar velocity effect is considered separately to lightcone effects. We highlight the importance of considering these effects in conjunction with each other. Especially when looking at the 1D power spectrum at large k scales. Here we see a boost in power of >300 % (>70%) in the Epoch of Reionisation (Cosmic Dawn), which is recoverable after the addition and removal of diffuse radio foregrounds and SKAO-like instrumental noise.

Thursday 13th March at 3pm, A113 CAPT – Special Seminar

Bruno Valexio Bento (IFT Madrid)

Tests and exploitations of String Theory: From Dark Energy to Gravitational Waves

Although string theory is famously hard to connect with observations, a lot of work is currently done with the aim of both testing it and exploiting its features to address observational puzzles. For instance, the nature of Dark Energy is one of the current big questions in cosmology--within string theory it is intimately tied to the search for de Sitter vacua within its vast landscape of solutions. As an example of exploitation, I will outline a concrete and previously unexplored setup using Casimir energies on extra dimensions that are Riemann flat compact manifolds, where one can look for such de Sitter solutions. I will then turn to Gravitational Waves as probes of extra dimensions and discuss how common ingredients in string compactifications might be key to their observability. We will look at a simple example of a binary system source in the context of a warped braneworld scenario, where we can compare the signals sourced by localised and extended sources, and how these relate to fifth force constraints.
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Fridays at 4pm, CAPT Foyer – CAPT Cakes
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Visitors
Ting-Yun (Sunny) Chen from Durham will be visiting on Wednesday and Thursday this week.

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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