School of Physical Sciences

Simplicial volume is a homotopy invariant for compact manifolds introduced by Gromov that measures the complexity of a manifold in terms of singular simplices. A celebrated question by Gromov (~’90) asks whether all oriented closed connected aspherical manifolds with zero simplicial volume also have vanishing Euler characteristic. In this talk, we will describe the problem and we will show counterexamples to some variations of the previous question. Moreover, we will describe some new strategies to approach the problem as well as the relation between Gromov’s question and other classical problems in topology. This will include joint works with Clara Löh and George Raptis, and with Alberto Casali.

• Speaker: Marco Moraschini (Università di Bologna)
• Wednesday 19 February 2025, 16:00-17:00
• Venue: CMS, MR15.
• Series: Differential Geometry and Topology Seminar; organiser: Oscar Randal-Williams.

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Coarse graph theory is a developing area, which focuses on the large-scale geometric structure of graphs, particularly through the lens of quasi-isometry. A central goal here is to find coarse analogues of classical graph-theoretic results. We discuss some initial steps in this direction. Joint work with Tung Nguyen and Paul Seymour.

• Speaker: Alexander Scott (Oxford)
• Thursday 20 February 2025, 14:30-15:30
• Venue: MR12.
• Series: Combinatorics Seminar; organiser: ibl10.

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Abstract not available

• Speaker: Speaker to be confirmed
• Wednesday 07 May 2025, 14:30-15:30
• Venue: Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.
• Series: Theory - Chemistry Research Interest Group; organiser: Lisa Masters.

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With a planet teaming with life all around us, it is tempting to think that any life on other worlds must be like Earth life. But is that true, and if it is not, what limits can we place on where we might look for life on other worlds? Starting from the still-controversial possibility of the presence of phosphine in the clouds of Venus, I will discuss what we know (not much) can model (some) and speculate about how the chemistry of life might work on other worlds under conditions very different from Earth. In particular, different atmospheres give different chemistries, possibly chemistries that use solvents other than water as their base. Alternative solvents open up the possibility of life on many bodies previously considered uninhabitable, such as the clouds of Venus, the surface of Mars, even the Moon. I will end with some thoughts on complex, even intelligent, life and where we might find it.

https://teams.microsoft.com/l/meetup-join/19%3ameeting_N2YxZjU5NTgtYzIwNi00MTY2LThkY2ItZjQyMTJmNjdkMWQw%40thread.v2/0?context=%7b%22Tid%22%3a%2249a50445-bdfa-4b79-ade3-547b4f3986e9%22%2c%22Oid%22%3a%2253b919d9-f8a7-4f56-9bb0-baaf0ba7404d%22%7d

• Speaker: William Bains
• Tuesday 18 February 2025, 11:00-12:00
• Venue: Chemistry Dept, Unilever Lecture Theatre and Zoom.
• Series: Centre for Atmospheric Science seminars, Chemistry Dept.; organiser: Dr Megan Brown.

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This talk presents an overview of past, current, and future contributions to the ATLAS experiment, spanning from Standard Model precision measurements to new physics searches and the development of advanced luminosity detectors.

The discussion begins with ATLAS forward detectors, focusing on the LUCID system for luminosity monitoring. The evolution from LUCID -2 to LUCID -3 is explored, highlighting the challenges posed by HL-LHC conditions and the new detector prototypes under development: LUCID JF , LUCID JN, and Fiber. Performance studies demonstrate their potential to ensure robust and precise luminosity measurements across various beam conditions.

The second part of the talk delves into key ATLAS physics analyses, emphasising precision measurements of Standard Model processes, including W and Z boson cross sections and their role in PDF constraints. The importance of V+jets and V+ heavy-flavor jets final states is also discussed. Additionally, I will present a search for long-lived particles based on dE/dx measurements and the identification of low-β signatures, providing a potential signature of physics beyond the Standard Model

Finally, the talk will conclude with an outreach project conducted in Bologna aimed at children aged 5 to 11, designed to study gender bias in STEM fields and promote equal opportunities in science from an early age.

• Speaker: Laura Fabbri, University of Bologna
• Tuesday 18 February 2025, 11:00-12:00
• Venue: Ryle Seminar Room.
• Series: Cavendish HEP Seminars; organiser: Dr. Aashaq Shah.

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Simplicial volume is a homotopy invariant for compact manifolds introduced by Gromov that measures the complexity of a manifold in terms of singular simplices. A celebrated question by Gromov (~’90) asks whether all oriented closed connected aspherical manifolds with zero simplicial volume also have vanishing Euler characteristic. In this talk, we will describe the problem and we will show counterexamples to some variations of the previous question. Moreover, we will describe some new strategies to approach the problem as well as the relation between Gromov’s question and other classical problems in topology. This will include joint works with Clara Löh and George Raptis, and with Alberto Casali.

• Speaker: Marco Moraschini (Università di Bologna)
• Sunday 16 February 2025, 16:00-17:00
• Venue: CMS, MR15.
• Series: Differential Geometry and Topology Seminar; organiser: Henry Wilton.

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Since any Fano variety can be recovered from its derived category up to isomorphism, we ask whether less information determines the variety – this is called a categorical Torelli question. In this talk, we consider an n-fold cover X → Y ramified in a divisor Z. The cyclic group of order n acts on X. We study how a certain subcategory of Db(X) (the Kuznetsov component) behaves under this group action. We combine this with techniques from topological K-theory and Hodge theory to prove that this subcategory determines X for two new classes of Fano threefolds which arise as double covers of (weighted) projective spaces. This is joint work with Augustinas Jacovskis and Franco Rota (arXiv:2310.13651).

• Speaker: Hannah Dell, University of Bonn
• Wednesday 19 February 2025, 14:15-15:15
• Venue: CMS MR13.
• Series: Algebraic Geometry Seminar; organiser: Dhruv Ranganathan.

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Mayer Vietoris presenations of rings let us relate the coherence properties of the rings involved, simplicial presentations conjecturally extend the Mayer Vietoris principles, allowing us to lift up in dimension the corresponding coherency relations.

• Speaker: Vincenzo di Bartholo, University of Cambridge
• Wednesday 19 February 2025, 16:30-17:30
• Venue: MR12.
• Series: Algebra and Representation Theory Seminar; organiser: Adam Jones.

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The Weddell Gyre mediates carbon exchange between the abyssal ocean and atmosphere, which is critical to global climate. This region also features large and highly variable freshwater fluxes due to seasonal sea ice, net precipitation, and glacial melt; however, the impact of these freshwater fluxes on the regional carbon cycle has not been fully explored. Using a novel budget analysis of dissolved inorganic carbon (DIC) mass in the Biogeochemical Southern Ocean State Estimate and revisiting hydrographic analysis from the ANDREX cruises, we highlight two freshwater-driven transports. Where freshwater with minimal DIC enters the ocean, it displaces DIC -rich seawater outwards, driving a lateral transport of 75±5 Tg DIC /year. Additionally, sea ice export requires a compensating import of seawater, which carries 48±11 Tg DIC /year into the gyre. Though often overlooked, these freshwater displacement effects are of leading order in the Weddell Gyre carbon budget in the state estimate and in regrouped box-inversion estimates. Implications for evaluating basin-scale carbon transports are considered. [Time permitting, I’ll also share some results on the role of heat addition in driving circulation change and warming patterns in the Indian sector of the Southern Ocean.]

• Speaker: Benjamin Taylor, Scripps Institution of Oceanography
• Wednesday 26 February 2025, 15:30-16:30
• Venue: BAS Seminar Room 1.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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Abstract not available

• Speaker: Flaviano Della Pia, University of Cambridge
• Wednesday 21 May 2025, 15:00-15:30
• Venue: Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.
• Series: Theory - Chemistry Research Interest Group; organiser: Lisa Masters.

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Abstract not available

• Speaker: Samuel Brookes, University of Cambridge
• Wednesday 21 May 2025, 14:30-15:00
• Venue: Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.
• Series: Theory - Chemistry Research Interest Group; organiser: Lisa Masters.

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In this talk, we consider large Boltzmann stable planar maps with index (1,2). In recent joint work with Nicolas Curien and Grégory Miermont, we established that this model converges, in the scaling limit, to a random compact metric space that we construct explicitly. The goal of this presentation is to outline the main steps of our proof. We will also discuss various properties of the scaling limit, including its topology and geodesic structure.

• Speaker: Armand Riera (Paris)
• Tuesday 04 March 2025, 14:00-15:00
• Venue: MR12.
• Series: Probability; organiser: ww295.

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Schramm and Sheffield introduced the notion of height gap for the continuum Gaussian free field (GFF) in dimension 2. It turns out that this height gap has a natural interpretation through clusters of Brownian loops arising in Brownian loop soups representations of the GFF . By considering different intensity parameters 0

• Speaker: Titus Lupu (Paris)
• Tuesday 18 February 2025, 14:00-15:00
• Venue: MR12.
• Series: Probability; organiser: ww295.

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The Weddell Gyre mediates carbon exchange between the abyssal ocean and atmosphere, which is critical to global climate. This region also features large and highly variable freshwater fluxes due to seasonal sea ice, net precipitation, and glacial melt; however, the impact of these freshwater fluxes on the regional carbon cycle has not been fully explored. Using a novel budget analysis of dissolved inorganic carbon (DIC) mass in the Biogeochemical Southern Ocean State Estimate and revisiting hydrographic analysis from the ANDREX cruises, we highlight two freshwater-driven transports. Where freshwater with minimal DIC enters the ocean, it displaces DIC -rich seawater outwards, driving a lateral transport of 75±5 Tg DIC /year. Additionally, sea ice export requires a compensating import of seawater, which carries 48±11 Tg DIC /year into the gyre. Though often overlooked, these freshwater displacement effects are of leading order in the Weddell Gyre carbon budget in the state estimate and in regrouped box-inversion estimates. Implications for evaluating basin-scale carbon transports are considered. [Time permitting, I’ll also share some results on the role of heat addition in driving circulation change and warming patterns in the Indian sector of the Southern Ocean.]

• Speaker: Benjamin Taylor, Scripps Institution of Oceanography
• Wednesday 26 February 2025, 15:30-16:30
• Venue: BAS Seminar Room 1.
• Series: British Antarctic Survey - Polar Oceans seminar series; organiser: Dr Birgit Rogalla.

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The SPECULOOS project is dedicated to the discovery of transiting exoplanets around ultracool dwarfs using high-precision ground-based observations. To enhance sensitivity to these cool stars, we have implemented SPIRIT , a new infrared detector utilizing CMOS technology instead of traditional CCDs. In this talk, I will present my work on developing the data pipeline for SPIRIT and optimizing its performance for detecting exoplanet transits. I will also highlight the discovery of TOI -2407b, a Neptune-like planet observed with this system.

• Speaker: Clàudia Janó Muñoz (University of Cambridge)
• Tuesday 25 February 2025, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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Abstract not available

• Speaker: Víctor Navarro-Fernández, Imperial College London
• Monday 17 March 2025, 14:00-15:00
• Venue: MR13.
• Series: Partial Differential Equations seminar; organiser: Amelie Justine Loher.

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Obtaining accurate predictions of thermodynamic properties, especially free energies which define the state of a system, is one of the key goals in atomistic simulations. This can enable a direct understanding of atomic-scale processes and provide a direct link to experiment. Achieving this requires converged statistical sampling from accurate wavefunction based potential energy surfaces, which is a formidable challenge due to the very high computational cost of such methods. Here, we leverage advances in machine learning potentials to efficiently obtain converged thermodynamic properties at increasing levels of theory. To showcase the potential of this approach, I will use the ion pairing of CaCO3 as a benchmark system, since it presents a significant challenge from both electronic structure and sampling perspectives. I will show that a machine learning framework based on second order Møller-Plesset Perturbation Theory delivers excellent agreement with experiment for the ion-pair association free energy—a challenging property for first principles atomistic simulations. Furthermore I will show that classical force fields get the right answer for the wrong reasons. Finally, I will discuss steps towards developing CCSD accuracy machine learning models, the ‘gold-standard’ of quantum chemical methods.

• Speaker: Niamh O'Neill, University of Cambridge
• Wednesday 26 February 2025, 15:00-15:30
• Venue: Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.
• Series: Theory - Chemistry Research Interest Group; organiser: Lisa Masters.

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=== Hybrid talk ===

Join Zoom Meeting https://cam-ac-uk.zoom.us/j/87143365195?pwd=SELTNkOcfVrIE1IppYCsbooOVqenzI.1

Meeting ID: 871 4336 5195

Passcode: 541180

NOTE UNUSUAL DAY

• Speaker: Francisco Ferreira Ruiz (Royal Holloway, University of London)
• Wednesday 12 March 2025, 17:00-18:00
• Venue: MR14 Centre for Mathematical Sciences.
• Series: Formalisation of mathematics with interactive theorem provers ; organiser: Anand Rao Tadipatri.

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Elliptic curves are one of the simplest non-trivial objects in algebraic geometry, which are pervasive in modern number theory, but also see applications in point counting algorithms and public key cryptography. Due to their geometric nature, formalising a working definition typically requires a lot of technical machinery, let alone any non-trivial results. Yet, the Lean community has managed to formalise two of the most fundamental theorems in the theory of elliptic curves, with scope for many more projects. In this talk, I will explain these theorems, and how we inadvertently discovered new proofs in our formalisation attempts.

Slides: https://multramate.github.io/talks/afoec/main.pdf

• Speaker: David Angdinata (University College London)
• Thursday 13 February 2025, 17:00-18:00
• Venue: MR14 Centre for Mathematical Sciences.
• Series: Formalisation of mathematics with interactive theorem provers ; organiser: Anand Rao Tadipatri.

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Gravitational wave radiation is only unambiguously defined at future null infinity – the location in spacetime where light rays arrive and where global properties of spacetimes can be measured. Reaching future null infinity is thus very important for extracting correct waveforms. A convenient way to include it in numerical relativity simulations is via hyperboloidal foliations. I will focus on conformal compactification as method to implement free hyperboloidal evolution, in the BSSN / conformal Z4 formulations. After illustrating its advantages, I will report on some ongoing applications in spherical symmetry: an extension to include the Maxwell equations, scattering simulations on a given background, and wave equation(s) evolved on some FLRW -type spacetimes with time-dependent scale factor. I will conclude giving an update on ongoing work in 3D evolutions.

• Speaker: Alex Vañó-Viñuales (IST Lisbon)
• Friday 21 February 2025, 13:00-14:00
• Venue: Potter room.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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