[Astro] [CAPT] CAPT Weekly Bulletin (w/c 07/10/24)

[Ella Batchelor]

Tuesdays at 11am, CAPT Foyer – Astro Coffee



Tuesday 8th October, A113 CAPT at 11am – Astronomy Journal Club



Tuesday 8th October, A113 CAPT at 1pm – Particle Cosmology Seminar
Theo Anton  (QMUL)
Generalised tests of gravity in cosmology

A plethora of modified theories of gravity have been proposed over the last several decades. Testing them all observationally is a considerable challenge, so it is advantageous to develop theory-independent approaches that constrain deviations from General Relativity in a systematic way. Many of the most precise such constraints to date are obtained from astrophysical measurements, for which deviations from GR are described by the parameterised post-Newtonian (PPN) parameters. Some attempts have been made to perform similarly general tests on cosmological scales, but it is not clear that they refer to the same couplings as the PPN formalism does, and so interpreting results from these disparate regimes physically is difficult and potentially misleading. With that problem in mind, I will introduce a framework, called parameterised post-Newtonian cosmology, that allows information from cosmological and astrophysical regimes to be combined consistently. I will present novel constraints on the evolution of the PPN parameters over cosmic history, using data from CMB anisotropies and Solar System experiments concurrently, and I will explain how these ideas can be further applied to test cosmological gravity to high precision.

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 9th October, C5 Physics at 3.45pm – Astronomy Seminar
Elke Roediger (Hull)

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Thursday 10th October at 1pm, A113 CAPT – Astronomy Lunch Talk
Omar Almaini
Investigating AGN activity in recently quenched galaxies at cosmic noon


We still do not understand the processes responsible for quenching star formation in massive galaxies, particularly in the distant Universe. AGN feedback is favoured by theoretical models, but so far direct observational evidence is limited. To tackle this problem, I will present a new Chandra X-ray analysis of AGN activity in a large sample of over 500 recently quenched galaxies at cosmic noon (1<z<3). Preliminary results reveal strong links between black hole activity and star formation, but the role of AGN in directly quenching star formation appears to be more subtle than current models predict.



Thursday 10th October, A113 CAPT at 3pm – Particle Cosmology Seminar
Kieran Wood (UoN)
Multi-metric black holes and the Gregory-Laflamme instability

Multi-metric gravity is the umbrella term for a class of modified gravitational theories, motivated by a number of problems at the interface between gravity and particle physics, that extend general relativity (GR) via the inclusion of additional interacting massive spin-2 fields beyond the single massless graviton of GR. Nonlinearly, the extra interactions manifest as a framework where multiple metric tensors interact with one another on the same spacetime manifold (hence the name). To date, black hole solutions of these multi-metric theories are only understood for the simplest case of bigravity (N=2 metrics) in 4 dimensions. It is, for example, known that one class of bigravity black holes is unstable for certain values of the graviton mass, with the instability taking the same form as the notorious Gregory-Laflamme (GL) instability plaguing higher dimensional black strings, although this feature has previously been viewed as little more than a peculiarity. In this talk, I will show how to generalise the 4d bigravity results to the full multi-metric theory in arbitrary dimension, constructing a wide class of black hole solutions of the general theory, and determine their linear stability. I will also elucidate the link between the instabilities of these multi-metric black holes and those of higher dimensional black strings. The result seems to suggest that the GL instability may be more fundamentally linked to the nature of massive spin-2 interactions.

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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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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