Upcoming Talks

I explore how cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements constrain cosmological models. The CMB angular scale provides robust constraints on the ratio of sound horizon to angular diameter distance, limiting possible deviations from the standard ΛCDM model. The null energy condition for a separate dark energy component imposes strict inequalities on BAO observables relative to ΛCDM predictions, restricting the freedom to fit new data within standard cosmological frameworks. I’ll discuss what this means for latest BAO results and other possible interpretations.

• Speaker: Antony Lewis (University of Sussex)
• Monday 20 October 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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In geophysical and astrophysical settings, rotating stratified flows often exhibit large-scale, nearly isolated vortices. Examples include the Mediterranean eddies in the Atlantic ocean, or the Great Red Spot (GRS) in Jupiter. These vortices have been widely studied using shallow-water or quasi-geostrophic models for decades. In particular, these models have successfully explained why these vortices maintain nearly lenticular shapes through time. However, prior reduced models have a blind spot when it comes to predicting the internal dynamics of such vortices, despite the fact that they are far from being motionless in their bulk (e.g. as observed for the GRS ). Various instabilities may sustain small-scale turbulence and accelerate the decay of large-scale vortices on long time scales.

Here, I will present a reduced model accounting for the bulk dynamics of large-scale pancake-like vortices. This model, which is developed in the framework of an interdisciplinary collaboration between pure and applied mathematics, is largely inspired by some ideas and methods pioneered by astrophysicists (e.g. S. Chandrasekhar or N. Lebovitz). First, I will describe the properties of the normal modes, because wave motions are often key to understanding the transition to turbulence in geophysical flows. As in the rotating non-stratified case, it will be shown that the wave spectrum solely consists of eigenvalues, and that the eigenvectors are all smooth. Moreover, it will be explained why some low-frequency waves/modes, which are governed by a mixed hyperbolic-elliptic problem for the velocity, can exist below the usual cutoff frequency of inertia-gravity waves. Next, by combining local and global stability methods, I will discuss whether some bulk instabilities could sustain small-scale bulk turbulence in strongly deformed stratified vortices.

• Speaker: Jérémie Vidal (ENS Lyon)
• Monday 20 October 2025, 16:00-17:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Mattias Brynjell-Rahkola.

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Hydrogen-deficient binary stars comprise one star which has been stripped of its hydrogen through mass transfer to a binary companion. Observations show that the companion is able to accrete several solar masses without spinning up to critical rotation, and so there must be a mechanism to drain spin angular momentum from the accretor. We test magnetically coupled winds and magnetic star-disc coupling as possible mechanisms and find that, while the disc coupling is negligible, the winds are sufficient to allow the accretor to gain mass without spinning up to critical rotation. However, in order to fully replicate observations, time-dependent scalings of the dynamo-generated magnetic field are needed.

• Speaker: David Bour / IoA
• Wednesday 22 October 2025, 13:15-13:40
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Sub-Neptunes are found around 50% of Sun-like stars in our galaxy. Despite their ubiquity, we lack a comprehensive understanding of their interior structure. I will present the first evolving interior structure model for sub-Neptunes that accounts for the expected miscibility between silicate magma and hydrogen. I will discuss the concept of “binodal surfaces”, which represent phase transitions within sub-Neptunes and provide a physically/chemically informed boundary between a planet’s “interior”’ and “envelope”. I will discuss the many implications of miscibility, and a potential observational route to testing its prevalence.

• Speaker: James Rogers / IoA
• Wednesday 15 October 2025, 13:15-13:40
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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We discuss modern formulations of the strong cosmic censorship conjecture (SCCC) and possible resolutions supported by rigorous non-linear results for the spherically symmetric Einstein-Maxwell-scalar field system. We show that the presence of a positive cosmological constant suggests a violation of the SCCC at a fundamental level of regularity. Indeed, the blueshift mechanism occurring at the Cauchy horizon can be counterbalanced by the dispersive effects encoded in the exponential Price law along (cosmological) black hole event horizons. On the other hand, we show that, if non-smooth black hole solutions are allowed, then the aforementioned violations are non-generic in a positive co-dimension sense.

• Speaker: Flavio Rossetti (Gran Sasso Science Institute)
• Friday 24 October 2025, 13:00-14:00
• Venue: Potter Room / Zoom .
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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In some astrophysical flows known to be linearly stable, finite-amplitude perturbations with favourable spatial structure can nonlinearly trigger a transition from a non-magnetic, non-turbulent state to self-sustained dynamo action and turbulence. Such transitions are suspected to significantly impact spin-down in radiative stellar layers or accretion rates in stellar discs. I will first present numerical examples of nonlinearly-triggered Tayler-Spruit dynamos in a spherical shell and zero-net-flux MRI dynamos in a quasi-Keplerian plane flow. I will then discuss how optimal control can identify stable, nontrivial (M)HD equilibria without requiring prior knowledge of the transition mechanisms.

• Speaker: Florence Marcotte (Université Côte d'Azur, INRIA, CNRS)
• Monday 13 October 2025, 16:00-17:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Mattias Brynjell-Rahkola.

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Abstract not available

• Speaker: Antony Lewis (University of Sussex)
• Monday 20 October 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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Venerable Exoplanetary Systems, a brief history: Revelations from 100 years ago to some new discoveries via an unusual, entirely unanticipated, observational technique. The discussion will include the first ever observational evidence for the existence of an extrasolar planetary system, the first observational evidence for the existence of a differentiated extrasolar planet (i.e., one with a crust and mantle), and the remarkable discovery of objects with 100s of times larger abundances of the light elements Be and B than previously seen in any astronomical object.

• Speaker: Prof. Ben Zuckerman
• Tuesday 14 October 2025, 13:00-14:00
• Venue: HOYLE LECTURE THEATRE + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr. Mariona Badenas Agusti.

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M-theory provides a geometric framework to describe a variety of interesting quantum field theories in which the QFT ’s arise from Einstein metrics. We motivate a precise definition of this framework which (partly) takes the form of the space of complete, asymptotically conical Ricci flat manifolds in various dimensions. We show how this provides insights into various strongly coupled systems such as non-Abelian gauge theories in four and more dimensions and leads to confining string theories in four and five dimensions. The four dimensional strings can be compared to flux tubes in Yang-Mills theories.

• Speaker: Bobby Acharya (ICTP Trieste)
• Thursday 09 October 2025, 12:00-13:00
• Venue: MR9/Zoom https://cam-ac-uk.zoom.us/j/81827907718.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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Cosmological collapse, where gravitational pull overcomes the universe’s expansion, can create primordial black holes or other bound structures. The ultimate fate of such a collapse depends on the initial distribution of matter and its equation of state, as pressure counteracts the gravitational infall. Then, in the dust case, where there is no pressure, shouldn’t a black hole always form? In this talk, I will attempt to answer this question using numerical relativity simulations, discussing the challenges of this problem and the progress we have made so far. Additionally, as this is in full GR, it presents an opportunity to characterise the cosmological spacetime; therefore, I will also describe this using gravito-electromagnetism and Weyl invariants.

• Speaker: Robyn Munoz (Sussex University)
• Friday 17 October 2025, 13:00-14:00
• Venue: Potter Room / Zoom .
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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As the poster child of directly-imaged exoplanets, the HR 8799 system consists of four young gas giant planets that are likely to be in mean motion resonance. Their formation origin and evolutionary history remain uncertain but can be constrained by a rich set of archival and newly-obtained proprietary data. I will present the detection of key molecular species such as H2O and CO in the planetary atmosphere using the combination of high-contrast imaging and high-resolution spectroscopy. Despite solid detections, interpreting the data through spectral retrieval analysis has been controversial, largely due to systematics introduced by inhomogeneous data sets and differing underlying model assumptions. I will present a calibration procedure using benchmark brown dwarfs to understand the systematic errors. This leads to an accurate constraint of atmospheric composition, which in turn allows us to robustly trace the formation history. Moreover, using a sample of directly-imaged exoplanets including the HR 8799 planets, we convert their atmospheric metallicities to the accreted mass of solid during formation through a Bayesian framework that marginalizes the probabilities of disk conditions, formation locations, planetary interior structures, and accretion physics. We show that more than 50 M⊕ solid mass has been accreted, pointing to an extremely early formation time scale (

• Speaker: Ji Wang
• Thursday 06 November 2025, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: Jan Scholtz.

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Abstract not available

• Speaker: Houda Haidar (Newcastle)
• Friday 23 January 2026, 11:30-12:30
• Venue: Ryle Seminar Room, KICC + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Many presentations of quantum mechanics include a postulate that the state of a system undergoes an instantaneous change following a measurement. This is clearly incompatible with special and general relativity and raises questions concerning the description of measurement in quantum field theory (QFT).

Attempts to extend measurement postulates to QFT by hand have produced pathologies, such as the “impossible measurements” described long ago by Sorkin.

I will present a recent operational approach to these questions, which models measurement of one quantum field (the system) by coupling it to another (the probe). This is all accomplished in a model-independent way within algebraic quantum field theory (AQFT). The resulting framework provides a description of measurement in QFT that is causal, covariant and consistent, and includes state update rules that are derived from the formalism, and works equally well in flat or curved spacetimes. As well as covering the basics of the formalism and how it resolves Sorkin’s impossible measurement problem, I will touch on some more recent developments, including links to quantum reference frames.

I will not assume any prior knowledge of AQFT .

The talk is mostly based on joint work with Rainer Verch (Comm. Math. Phys. 378 (2020) 851-889 arXiv:1810.06512) and further work with Henning Bostelmann, Maximilian Ruep and Ian Jubb (see https://arxiv.org/abs/2304.13356 for a survey). I will also mention recent joint work with Daan Janssen, Leon Loveridge, Kasia Rejzner, James Waldron (Comm. Math. Phys. 406:19 (2025) https://arxiv.org/abs/2403.11973)

• Speaker: Professor Chris Fewster - York
• Wednesday 22 October 2025, 16:00-17:00
• Venue: MR3.
• Series: Theoretical Physics Colloquium; organiser: Amanda Stagg.

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Scalar fields are ubiquitous in string theory compactifications, arising both from geometric moduli and as descendants of higher-dimensional p-forms. In cosmology, they provide natural candidates to drive accelerated expansion, both during early (inflationary) and late (dark energy) time evolution of the Universe. In single-field models, scalar potentials are typically too steep to sustain slow-roll evolution. However, in multifield scenarios, accelerated expansion can occur even for steep potentials, when the scalar fields move along strongly non-geodesic trajectories in field space. Such dynamics not only enable inflation or dark energy but can also evade recent quantum gravity swampland constraints. In this talk, I will show how to extend the dynamical systems (DS) toolkit to include both kinetic and potential couplings between fields – features that naturally arise in string-theoretic constructions. Within this framework, I will present a compact and general expression for the non-geodesicity parameter, which offers a simple and transparent diagnostic of truly multifield evolution. I will also discuss connections with previous work on inflationary dynamics, where related mechanisms play a central role.

• Speaker: Ivonne Zavala (Swansea U.)
• Monday 13 October 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Gonzalo Villa.

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Planet formation unfolds in environments where stars are rarely alone: the majority of stellar systems are binaries, triples, or higher-order multiples. Hence, stellar multiplicity profoundly shapes the structure, evolution, and dynamics of protoplanetary discs. In this talk, we will explore how discs evolve under the gravitational influence of multiple stars and how this impacts planet formation. I will first summarise recent theoretical and numerical studies on disc dynamics in binary and triple systems, complemented by illustrative examples from observations (e.g. ALMA and VLT ) of young multiple stellar systems with discs and planets. Next, I will discuss our modelling efforts within the Stellar-MADE ERC project to investigate accretion, disc morphology, and orbital architecture in these complex systems. Finally, we will highlight the implications for dust evolution, planet formation, and long-term planetary stability.

• Speaker: Nicolás Cuello (IPAG Grenoble)
• Monday 27 October 2025, 16:00-17:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.

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Dust grains are key players of the evolution of the dense interstellar medium. The grain size distribution varies locally, modifying the thermodynamics and the chemistry of molecular clouds, the opacity of collapsing protostellar cores and the coupling between the gas and the magnetic field, and the solid content to form planetesimals in protoplanetary disks. Magnetohydrodynamical models are commonly used to study the formation of stars and disks, but they generally do not capture the complexity of the interactions with the dusty component.

This complexity requires analytical and numerical methods that offer complementary levels of detail. In the first part of the talk, I present a multifluid approach that models the dynamics of a dust size distribution in interaction with the gas and the magnetic field. We explore its fundamental physics in the linear regime. We discuss the consequences of the coupling of the dust with the magnetic field on dust enrichment within the protostellar envelope and on magnetic braking (Verrier et al, in prep). In a second part of the talk, I present our new multifluid numerical method that allows us to simulate 3D dusty protostellar collapses (Verrier et al, 2025). This method is designed to capture all the coupling regimes between the gas and the neutral dust grains, including the terminal velocity regime (Lebreuilly et al, 2019). We find that millimeter dust grains enrich the first hydrostatic core and some locations of the envelope, promoted by the initial turbulence of the dense core, setting favourable conditions to early planet formation scenarios. Finally, we present perspectives that connect dust dynamics in turbulence and dust growth.

• Speaker: Gabriel Verrier (CEA Saclay, France)
• Wednesday 15 October 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.

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Understanding the generation of large-scale magnetic fields and flows in MHD turbulence remains one of the most challenging problems in astrophysical fluid dynamics. The well-studied kinematic theory ignores the possibility of small-scale dynamo action, which is prevalent at high magnetic Reynolds number. Here, we thus examine the possibility of large-scale field (and flow) arising from a fully MHD basic state — as may arise from the saturation of a small-scale dynamo. Under this new theory, four mean field tensors now come into play. In certain cases, such as “short-sudden” turbulence, these tensors may be calculated explicitly. More generally, the (nonlinear) mean field theory works well for mildly turbulent flows, but can fail in strongly disordered systems. This leads us to address the more general dynamical systems question of whether a linear response can be detected following a  small (linear) perturbation to a chaotic system.

• Speaker: David Hughes (Leeds)
• Monday 17 November 2025, 16:00-17:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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Our recent work (2509.13307) demonstrated the performance of GPU -accelerated nested sampling for efficient high-dimensional Bayesian inference in cosmology. Using JAX -based emulators and likelihoods we can leverage the parallel computing of GPUs to achieve orders of magnitude speed-ups against CPU -based analyses, and bring robust evidence calculations up to GPU -speed. This puts nested sampling back on equal footing with Markov Chain Monte Carlo (MCMC) methods, which use auto-diff gradients to achieve their speed-ups. In particular a Euclid-like mock Cosmic Shear likelihood has been considered, an analysis which previously took 8 months on a CPU instance, and we bring the time to constrain both ΛCDM and w0wa down to only 2 days on a single GPU . This talk explores a few options for pushing our methodology even further, in preparation for joint analyses of next generation of cosmlogical surveys.

• Speaker: Toby Lovick / IoA
• Wednesday 08 October 2025, 13:15-13:40
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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I will introduce a Python package called ECHO21 for modelling the global 21-cm signal from the dark ages through cosmic dawn to the end of reionization. Leveraging its analytical framework, ECHO21 generates a single model in O(1) s, allowing a large number of signals to be generated efficiently by distributing models across multiple cores. Thus, it is ideal for performing astrophysical or cosmological inference from a given 21-cm dataset. We offer six astrophysical parameters that control the Lyman-α emissivity, X-ray emissivity, emissivity of ionizing photons, and star formation rate. Beyond its efficiency, some of the attractive and novel features in ECHO21 relative to previously published codes are the inclusion of Lyα heating, the ability to vary the standard cosmological parameters as easily as the astrophysical parameters, different models of star formation rate density (physically-motivated, a semi-empirical, and an empirically-motivated), and modelling the global signal for a Coulomb-like interacting DM (IDM) framework. This IDM model incorporates cooling of baryons as well as a delay in star formation. With several 21-cm experiments soon to provide cosmic dawn 21-cm data, ECHO21 is a flexible and extensible new open-source package for making quick and sufficiently realistic astrophysical inferences.

• Speaker: Shikhar Mittal / Battcock Centre
• Wednesday 08 October 2025, 13:40-14:05
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Abstract not available

• Speaker: Toby Lovick / IoA
• Wednesday 08 October 2025, 13:15-13:40
• Venue: Hoyle Lecture theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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