Jan 18  Thu  Thomas Wagner (Helsinki)  Plasma Dynamics Group  
16:00  Identifying and Tracking Coronal Flux Ropes  
Google Meet  
Abstract: To understand solar eruptions and the destabilization mechanism of the corresponding flux ropes, modelling the magnetic field in the solar corona in a timedependent manner is commonly employed. However, identifying the field lines of solar flux ropes in simulation data is not trivial. We therefore developed a method for detecting and tracking flux ropes from modelling data. The extraction procedure uses a combination of some proxy map as input (for example the field line twist) and mathematical morphology algorithms, such as the morphological opening or the morphological gradient. The method is validated by applying it to timedependent magnetofrictional model (TMFM) simulations of active regions AR11176 and AR12473. With full access to the flux rope field lines, we investigate the eruptivity and propagation of the flux ropes through the modelling domain. Finally, the methodology is also wrapped into a graphical user interface (GUI) to further simplify its application. 



Jan 22  Mon  Dom Grainger  
13:00  
Hicks Seminar Room J11  


Jan 22  Mon  Dom Grainger (Sheffield)  
14:00  
Hicks Seminar Room J11  


Jan 24  Wed  Matteo Forconi (Rome)  Cosmology, Relativity and Gravitation  
15:00  JWST’s Revelations and the SuperLCDM’s Promise  
Hicks Seminar Room J11  
Abstract: The recent observations by the James Webb Space Telescope (JWST) of massive galaxies at high redshifts (z ∼ 10) significantly challenge the Lambda Cold Dark Matter (ΛCDM) cosmological model. These observations suggest a higher stellar mass density than previously predicted, and raise questions about galaxy formation and matter distribution in the early universe. To reconcile these findings with standard predictions, an investigation one can look into potential systematics. If systematic errors are ruled out, one might also wonder whether this new anomaly is somehow originated from the same underlying issue as the Hubble tension, suggesting the need for a beyondΛCDM phenomenological explanation. One potential avenue is exploring the Dark Energy Sector. Another challenge to the standard ΛCDM model arises from allowing nonGaussian fluctuations. Using the super sample signal, it is possible to promote the standard ΛCDM model to a more comprehensive SuperΛCDM model. This model allows to study nonGaussianity traces using only the power spectrum. The implications of this model extend to the field of neutrino physics, indicating that the traditional constraints on neutrino masses might need revision. 



Jan 30  Tue  Nirmal Kotal (Chennai Mathematical Institute )  
16:00  On Knutson Ideals and Polyomino  
Hicks Seminar Room J11  
Abstract: Consider a polynomial f with a squarefree leading term with respect to some monomial ordering. Consider the smallest set of ideals such that the principal ideal (f) is in the set; the colon ideal I:J is in the set for any ideal I in the set and any arbitrary ideal J; and if I and J are in the set, then the sum I+J and the intersection I∩J are in the set. ConcaVarbaro and Seccia extensively studied this class of ideals and called the members of the set as "Knutson ideals," associated with f, as they were first studied by A. Knutson. In this discussion, we will explore many algebraic features of these ideals, such as the Grobner basis, radicality, Fsplitting, etc. A polyomino is a set of unit squares on the plane that is made by joining the squares side by side. Qureshi associated an ideal generated by 2minors with polyomino. This presentation will explore the application of Knutson's methodology in the analysis of polyomino ideals. This is an ongoing joint project with Mitra Koley and Dharm Veer. 



Jan 31  Wed  Sebastian Schuster (Sheffield)  Cosmology, Relativity and Gravitation  
15:00  What's Physical? A SpaceTime Koan  
Hicks Seminar Room J11  
Abstract: Evaluating the physicality of a given spacetime can prove difficult. Often, this is relegated to easytocheck concepts: Absence of closed, timelike curves (vulgo: no time travel); validity of energy conditions (vulgo: mass/energy should be positive); geodesic completeness (vulgo: we shan't disappear); the related holefreeness (vulgo: again, we shan't disappear); and more. The problem is that these are not necessarily mutually compatible with each other. Worse, as in the case of energy conditions, not all such concepts are either easy to justify or even fulfilled in known, physical situations. This talk will serve two purposes. The first is to make everyone queasy about the pushmepullyou nature of physicality, as this allows us to critically examine which type of physicality may be more or less important in any given situation. Here, reverseengineered metrics like warp drives and tractor beams will be in the spotlight. The second is to hone in on one particularly befuddling concept: Time travel. Fascinating as it is, in general relativity the spacetime will either contain it or not. General relativity cannot explain why it might be there, or whether the confusion and contractions arising from it are due to the concept itself or from being in the wrong physical framework. Many arguments have to, at some point, wave their hands and allude to an unknown theory beyond it. To actually make this step beyond general relativity, I will present a very simple, quantum toy model of time travel with an emergent notion of time. While this first toy model will turn out to be not particularly illuminating, it still serves as a good starting point for more complicated toy models with richer structure. 



Feb 7  Wed  Luca Marchetti (New Brunswick)  Cosmology, Relativity and Gravitation  
16:00  Scalar cosmological perturbations from quantumgravitational entanglement  
Hicks Seminar Room J11  
Abstract: A major challenge at the interface between quantum gravity and cosmology is to understand how cosmological structures can emerge from physics at the Planck scale. In this talk, I will discuss the main challenges associated with the understanding of such an emergence process and provide a concrete example of how they can be addressed by extracting the physics of scalar and isotropic cosmological perturbations from full quantum gravity, as described by a causally complete BarrettCrane group field theory model. From the perspective of the underlying quantum gravity theory, cosmological perturbations will be associated with (relational) nearestneighbor twobody entanglement, providing crucial insights into the potentially purely quantumgravitational nature of cosmological perturbations. I will also show that at low energies the emergent relational dynamics of these perturbations are perfectly consistent with those of general relativity, while at transPlanckian scales quantum effects become important. Finally, I will comment on the implications of these quantum effects for the physics of the early universe and outline future research directions. 



Feb 8  Thu  Balazs Asztalos  SP2RC/ESPOS seminar  
10:00  MHD Wave Propagation and Kelvin–Helmholtz Instability in Asymmetric Magnetic Slab Systems  


Feb 8  Thu  PGR Lean Study Group  
13:00  
Hicks Seminar Room J11  


Feb 8  Thu  Sarah Whitehouse (Sheffield)  Topology Seminar  
16:00  Homotopy theory of spectral sequences  
Hicks Seminar Room J11  
Abstract: For each r, maps which are quasiisomorphisms on the r page provide a class of weak equivalences on the category of spectral sequences. The talk will cover homotopy theory associated with this setting. We introduce the category of extended spectral sequences and show that this is bicomplete by analysis of a certain presheaf category modelled on discs. We endow the category of extended spectral sequences with various model category structures. One of these has the property that spectral sequences is a homotopically full subcategory and so, by results of Meier, exhibits the category of spectral sequences as a fibrant object in the BarwickKan model structure on relative categories. We also note how the presheaf approach provides some insight into the décalage functor on spectral sequences. This is joint work with Muriel Livernet. 



Feb 9  Fri  Matt Lennard & Jake Saunders (Sheffield)  
16:00  
Hicks Seminar Room J11  


Feb 12  Mon  Dom Grainger (University of Sheffield)  
15:00  
Hicks Seminar Room J11  


Feb 13  Tue  Luis Santiago Palacios (Bordeaux)  Number Theory seminar  
13:00  Geometry of the Bianchi eigenvariety at noncuspidal points  
Hicks Seminar Room J11 / Google Meet  
Abstract: An important tool to study automorphic representations in the framework of the Langlands program, is to produce $p$adic variation. Such variation is captured geometrically in the study of certain "moduli spaces" of padic automorphic forms, called eigenvarieties. In this talk, we first introduce Bianchi modular forms, that is, automorphic forms for $\mathrm{GL}_2$ over an imaginary quadratic field, and then discuss its contribution to the cohomology of the Bianchi threefold. After that, we present the Bianchi eigenvariety and state our result about its geometry at a special noncuspidal point. This is a joint work in progress with Daniel Barrera (Universidad de Santiago de Chile). 



Feb 13  Tue  Emmanouil Kalligeris (Sheffield)  Statistics Seminar  
15:00  A Twisted Markov Switching Mechanism for the Modelling of Incidence Rate Data  
Hicks Seminar Room J11  
Abstract: Various time series models have been used over the years to capture the dynamic behaviour of significant variables in various scientific fields such as epidemiology, seismology, meteorology, finance, etc. In this work, a conditional mean Markov regime switching model with covariates is proposed and studied for the analysis of incidence rate data. The components of the model are selected by both penalised likelihood techniques in conjunction with the Expectation Maximisation algorithm, with the aim of achieving a high level of robustness with respect to modelling the dynamic behaviour of epidemiological data. In addition to statistical inference, changepoint detection analysis is used to select the number of regimes, reducing the complexity associated with likelihood ratio tests. [Kalligeris EN, Karagrigoriou A, Parpoula C. (2023): On Stochastic Dynamic Modeling of Incidence Data. Int J Biostat, 10.1515/ijb20210134] 



Feb 14  Wed  Robin Stephenson (Sheffield)  Probability seminar  
16:00  Where do trees grow leaves?  
Hicks Seminar Room J11  
Abstract: We study a model of random binary trees grown ``by the leaves" in the style of Luczak and Winkler (2004). If $\tau_n$ is a uniform plane binary tree of size $n$, Luczak and Winkler, and later explicitly Caraceni and Stauffer, constructed a measure $\nu_{\tau_n}$ such that the tree obtained by adding a cherry on a leaf sampled according to $\nu_{\tau_n}$ is still uniformly distributed on the set of all plane binary trees with size $n+1$. It turns out that the measure $\nu_{\tau_n}$, which we call the leafgrowth measure, is noticeably different from the uniform measure on the leaves of the tree $\tau_n$. In fact we prove that as $n \to \infty$, with high probability it is almost entirely supported by a subset of only $n^{3 ( 2  \sqrt{3})+o(1)} \approx n^{0.8038...}$ leaves. In the continuous setting, we construct the scaling limit of this measure, which is a probability measure on the Brownian Continuum Random Tree supported by a fractal set of dimension $ 6 (2  \sqrt{3})$. We also compute the full (discrete) multifractal spectrum. This work is a first step towards understanding the diffusion limit of the discrete leafgrowth procedure. 



Feb 15  Thu  Cora Uhlemann (Newcastle)  Cosmology, Relativity and Gravitation  
11:00  Making dark matter waves  the cosmic web and wavelike dark matter  
Hicks Seminar Room J11  
Abstract: Despite the astonishing success of cosmological probes in constraining the LCDM model, the dark matter mass remains one of the least constrained physical parameters. Wavelike dark matter is an intriguing alternative to standard cold dark matter with key particle physics motivations (like the QCD axion or ultralight axionlike particles) and distinct astrophysical signatures. With a simple dynamical model for the evolution of the dark matter wavefunction, I will demonstrate how to predict the formation of destructive and constructive wave interference leading to topological defects and granules dressing the cosmic web of largescale structure. Our wavebased formalism is a versatile tool to describe the complex phasespace dynamics of cold dark matter in position space; and the fundamental description for wavelike dark matter such as ultralight particles, leading to exciting and varied probing mechanisms bridging cosmology and astroparticle physics. 



Feb 15  Thu  PGR Lean Study Group  
13:00  
Hicks Seminar Room J11  


Feb 20  Tue  Beth Romano (Kings College London)  Number Theory seminar  
13:00  Epipelagic representations in the local Langlands correspondence  
Hicks Seminar Room J11 / Google Meet  
Abstract: The local Langlands correspondence (LLC) is a kaleidoscope of conjectures relating local Galois theory, complex Lie theory, and representations of padic groups. The LLC is divided into two parts: first, there is the tame or depthzero part, where much is known and proofs tend to be uniform for all residue characteristics p. Then there is the positivedepth (or wild) part of the correspondence, where there is much that still needs to be explored. I will talk about recent results that build our understanding of this wild part of the LLC via epipelagic representations and their Langlands parameters. I will not assume background knowledge of the LLC, but will give an introduction to these ideas via examples. 



Feb 21  Wed  João Paulo M Pitelli (Campinas State)  Cosmology, Relativity and Gravitation  
15:00  Thermal effects on a global monopole with Robin boundary conditions  
Hicks Seminar Room J11  
Abstract: The quantum theory of a scalar field propagating on a spacetime with a naked singularity is not determined until we specify a boundary condition at the boundary. When this choice is not unique, any physical observable will depend on the particular choice of boundary condition. In this work we illustrate this explicit dependence by analyzing the transition rate of an UnruhDeWitt detector coupled to a thermal state in the singular scenario of a global monopole. We show that the naked singularity manifests thermal effects with a nontrivial behavior with respect to the admissible boundary conditions. In particular, we show that the transition rate is finite at the singularity only for the Dirichlet boundary condition and that the divergence for the other possible (Robin) boundary conditions is consistent with the divergence of the thermal fluctuations. 



Feb 22  Thu  Joseph Grant  Topology Seminar  
16:00  Frobenius algebra objects in TemperleyLieb categories at roots of unity  
Hicks Seminar Room J11  
Abstract: Frobenius algebras appear in many parts of maths and have nice properties. One can define algebra objects in any monoidal category, and there is a standard definition of when such an algebra object is Frobenius. But this definition is not satisfied by something which we'd like to think of as an algebra object in TemperleyLieb categories at roots of unity. We will explore a more general definition of a Frobenius algebra object which covers this example, and will explore some of its properties. This is joint work with Mathew Pugh. 



Feb 22  Thu  Renato Miotto (Unicamp, Brazil)  Plasma Dynamics Group  
16:00  Bridging the gap between numerical simulations and experiments through computer vision and deep learning  
online / Google Meet  
Abstract: Several physics and engineering problems require knowledge of physical properties to be completely characterized. However, such properties cannot always be easily obtained experimentally, which means that numerical simulations are often necessary to study the problem in question. In the present work, we propose to leverage data from numerical simulations to extract relevant information from experimental visualizations of the flow field using deep learning. We uniquely treat the image semantic segmentation as an imagetoimage translation task that infers semantic labels of structures from the input images in a supervised way. The present methodology exploits the semantic proximity between images from the numerical and experimental domains to translate any properties of interest between them. Example applications are shown for a moving airfoil as well as for predicting forces on a sand dune. Extrapolation and interpolation for different flow regimes never seen by the neural network are discussed. 



Feb 26  Mon  Carina Dunlop (Surrey)  Mathematical Biology Seminar  
13:00  What do cells and tissues feel? The integration of cell contractility, growth and adhesion in mechanosensing  
Hicks Seminar Room J11  


Feb 27  Tue  Alexandros Groutides (Warwick)  Number Theory seminar  
13:00  On integral structures in smooth $\mathrm{GL}_2$representations and zeta integrals.  
Hicks Seminar Room J11 / Google Meet  
Abstract: We will discuss recent work on local integral structures in smooth ($\mathrm{GL}_2\times H$)representations, where $H$ is an unramified maximal torus of $\mathrm{GL}_2$. Inspired by work of LoefflerSkinnerZerbes, we will introduce certain unramified Hecke modules containing lattices with deep integral properties. We'll see how this approach recovers a GrossPrasad type multiplicity one result in this unramified setting and present an integral variant of it with applications to zeta integrals and automorphic modular forms. Finally, we will reformulate and answer a conjecture of Loeffler on integral unramified Hecke operators attached to the lattices mentioned above. 



Feb 27  Tue  Prof. Robin Henderson (Newcastle University)  Statistics Seminar  
15:00  Event History and Topological Data Analysis  
Hicks Seminar Room J11  
Abstract: Topological data analysis has become popular in recent years, though mainly outside the statistical literature. In this talk we review some of the elements of topological data analysis and we show links to event history and survival analysis. We argue that exploiting topological data as event history can be useful in the analysis of data in the form of images. We propose a version of the wellknown NelsonAalen cumulative hazard estimator for the comparison of topological features of random fields and for testing parametric assumptions. We suggest a Cox proportional hazards approach for the analysis of embedded metric trees. The NelsonAalen method is illustrated on globally distributed climate data and on neutral hydrogen distribution in the Milky Way. The Cox method is used to compare vascular patterns in fundus images of the eyes of healthy and diabetic retinopathy patients. 



Feb 28  Wed  Ozgur Bayindir (Queen Mary University of London)  Pure Maths Colloquium  
14:00  Algebraic Ktheory and chromatic redshift  
Hicks Seminar Room J11  
Abstract: I will begin with an introduction to algebraic Ktheory, ring spectra and the chromatic redshift conjecture. After this, I will talk about our new proof of the redshift conjecture for LubinTate spectra and our algebraic Ktheory computations. This work is partially joint with Christian Ausoni and Tasos Moulinos. 



Feb 29  Thu  Jack Romo (Leeds)  Topology Seminar  
16:00  $(\infty, 2)$Categories and their Homotopy Bicategories  
Hicks Seminar Room J11  
Abstract: Across the multitude of definitions for a higher category, a dividing line can be found between two major camps of model. On one side lives the ‘algebraic’ models where composition operations between morphisms are given, like Bénabou’s bicategories, tricategories following Gurski and the models of ncategory of Batanin and Leinster, Trimble and Penon. On the other end, one finds the ‘nonalgebraic’ models, where the space of possible composites is only guaranteed to be contractible. These include the models of Tamsamani and Paoli, along with quasicategories, Segal ncategories, complete nfold Segal spaces and more. The bridges between these models remain somewhat mysterious. Progress has been made in certain instances, as seen in the work of Tamsamani, Leinster, Lack and Paoli, Cottrell, Campbell, Nikolaus and others. Nonetheless, the correspondence remains incomplete; indeed, for instance, there is no fully verified means in the literature to take an `algebraic’ homotopy ncategory of any known model of $(\infty, n)$category for general n. In this talk, I will present my contributions to the problem of taking algebraic homotopy bicategories of nonalgebraic $(\infty, 2)$categories. This talk also serves as an introduction to the model of $(\infty, 2)$category I will be using, namely complete 2fold Segal spaces. If time permits, I will discuss how to compute the fundamental bigroupoid of a topological space with this construction. 



Mar 4  Mon  Michael Clerx (Nottingham)  Mathematical Biology Seminar  
13:00  Estimating parameters for biological timeseries models: lessons learned from a deep dive into ion channel modelling  
Hicks Seminar Room J11  


Mar 4  Mon  Lea Bottini  The Sheffield Geometry and Physics Seminar  
14:00  Gapped phases and phase transitions from the SymTFT  
Hicks Seminar Room J11  
Abstract: In this talk, I will introduce the concept of Symmetry Topological Field Theory (SymTFT); this is a (d+1)dimensional topological theory associated to a ddimensional theory T, which neatly encodes its symmetry properties and has emerged as a key tool to study generalized symmetries. In particular, I will show how the SymTFT can be used to determine gapped infrared phases of 2d theories that have a symmetry S described in general by a fusion category. This approach gives concrete computational tools to extract information on the gapped phase, such as the symmetry breaking pattern, the number of vacua, and the action of the symmetry on such vacua. Moreover, I will introduce a generalization of the usual SymTFT framework that allows us to characterize phase transitions between such gapped phases. The SymTFT also manifestly encodes the order parameters for the phases, thus providing a generalized version of the Landau paradigm for symmetries that go beyond the standard grouplike case. 



Mar 4  Mon  Franco Rota  The Sheffield Geometry and Physics Seminar  
15:00  Nondegeneracy invariants of Enriques surfaces  
Hicks Seminar Room J11  
Abstract: Every Enriques surface Y has an elliptic pencil, and every elliptic pencil on Y has two multiple fibers, whose reduced support is called a halffiber. The nondegeneracy invariant of an Enriques surface is defined to be the maximum number of halffibers meeting each other at exactly one point. This invariants influences the projective geometry of Y, as well as the structure of its derived category. In collaboration with R. Moschetti and L. Schaffler, we study techniques to compute nondegeneracy. These mix computer algebra and classical geometric methods. I'll illustrate our results in a few examples and I'll outline future directions. 



Mar 5  Tue  Lewis M Combes  Number Theory seminar  
13:00  Period polynomials of level 1 Bianchi modular forms  
Hicks Seminar Room J11 / Google Meet  
Abstract: The period polynomial of a classical modular form encodes important arithmetic information about the form itself, being made out of critical Lvalues and connecting to congruences via Haberland's formula. In this talk, we report on work to generalise these connections to the setting of Bianchi modular formsthose over an imaginary quadratic field. We demonstrate explicit congruences between various types of Bianchi modular form, and show how to detect them using a pairing on period polynomials. 



Mar 6  Wed  Simon Willerton (Sheffield)  Pure Maths Colloquium  
14:00  Instantaneous dimension of metric spaces via spread and magnitude  
Hicks Seminar Room J11  
Abstract: Some spaces seem to have different dimensions at different scales. A long thin strip might appear onedimensional at a distance, then twodimensional when zoomed in on, but when zoomed in on even closer it is seen to be made of a finite array of points, so at that scale it seems zerodimensional. I will present a way of quantifying this phenomenon using a couple of measures of the size of metric spaces, namely magnitude and spread. I will show lots of examples for finite metric spaces. 



Mar 6  Wed  William Giare (Sheffield)  Cosmology, Relativity and Gravitation  
15:00  Do we need to rethink inflation?  
Hicks Seminar Room J11  
Abstract: I will discuss some arguments that have led me to question whether we need to reassess our understanding of cosmic inflation. Largescale CMB temperature and polarization measurements from the Planck satellite and the BICEP/Keck collaboration have established stringent constraints on the amplitude of primordial gravitational waves (r < 0.036) and the spectral index of scalar modes (ns = 0.9649 ± 0.0044). In contrast, smallscale CMB data from the Atacama Cosmology Telescope yield divergent predictions, pointing towards a scaleinvariant spectrum (ns = 1.008 ± 0.015). This leads to an overall disagreement regarding the inflationary potential as inferred by CMB experiments probing different angular scales in the sky. The wellknown Hubble tension further compounds the challenge. Solutions involving new physics at early times may reshape the predictions for inflation based on largescale measurements to align with trends observed in smallscale data. As a result, with inflation, we find ourselves between the known and the unknown. 



Mar 7  Thu  Ryan Campbell (Queen's University Belfast, United Kingdo)  SP2RC/ESPOS seminar  
10:00  DKIST's view of quiet photospheric magnetism and application of neural networks to the characterisation of Stokes profiles  
Abstract: A new era of solar physics commences with observations of the quiet Sun using the 4metre Daniel K. Inouye Solar Telescope/Visible Spectropolarimeter (DKIST/ViSP). We present fullStokes observations taken during DKIST’s cycle 1, in the Fe I 630.1/630.2 nm lines, allowing us to examine smallscale magnetism in the photosphere. We use the Stokes Inversion based on Response functions (SIR) code to invert the Fe I line pair. We reveal the existence of a serpentine magnetic element for the first time. A statistical analysis is undertaken, comparing inversions of DKIST data with Hinode data. A novel machine learning technique is used to characterise and contrast the shapes of circular polarisation signals found in the groundbased and spacebased data, and synthetic observations produced from MANCHA simulations are used to aid our understanding of the differences between datasets. 



Mar 7  Thu  Nadia Mazza (Lancaster)  Topology Seminar  
16:00  Endotrivial modules for finite groups of Lie type  
Hicks Seminar Room J11  
Abstract: Let G be a finite group and k a field of positive characteristic p diving the order of G. An endotrivial kGmodule is a finitely generated kGmodule which is "invertible" in some suitable sense. Since the late 70s, these modules have been intensely studied in modular representation theory. In this talk, we review the essential background on endotrivial modules, and present some results about endotrivial modules for finite groups of Lie type, obtained jointly with Carlson, Grodal and Nakano. 



Mar 8  Fri  Fabrizio del Monte (Sheffield)  
11:00  


Mar 8  Fri  Stefano Gariazzo (IFT Madrid)  Cosmology, Relativity and Gravitation  
15:00  Relic neutrinos: decoupling and direct detection perspectives  
Hicks Seminar Room J11  
Abstract: A background radiation of relic neutrinos, originated during the early phases of the Universe expansion, is predicted by the standard cosmological model, but has never been confirmed by a direct measurement. In this seminar, I will review some of the theoretical and phenomenological aspects of relic neutrino decoupling, present indirect evidence of their existence and discuss proposed techniques and ongoing experimental efforts for attempting the first direct detection of the neutrino background. 



Mar 8  Fri  Andrew Neate (Sheffield)  
16:00  
Hicks Seminar Room J11  


Mar 11  Mon  Alex Fletcher (Sheffield)  Mathematical Biology Seminar  
13:00  
Hicks J11  


Mar 12  Tue  Andrea Dotto (Cambridge)  Number Theory seminar  
13:00  Some consequences of mod p multiplicity one for Shimura curves  
Hicks Seminar Room J11 / Google Meet  
Abstract: The multiplicity of Hecke eigenspaces in the mod p cohomology of Shimura curves is a classical invariant, which has been computed in significant generality when the group is split at p. This talk will focus on the complementary case of nonsplit quaternion algebras, and will describe a new multiplicity one result, as well as some of its consequences regarding the structure of completed cohomology. I will also discuss applications towards the categorical mod p Langlands correspondence for the nonsplit inner form of GL_2(Q_p). Part of the talk will comprise a joint work in progress with Bao Le Hung. 



Mar 13  Wed  Evgeny Shinder (Sheffield)  Pure Maths Colloquium  
14:00  Gromov's cancellation question in birational algebraic geometry  
Hicks Seminar Room J11  
Abstract: I explain some cancellation and noncancellation phenomena in algebraic geometry and relate them to the structure of the Grothendieck ring of varieties and to the groups of birational selfmaps of algebraic varieties, in particular the Cremona groups. 



Mar 13  Wed  Eemeli Tomberg (Lancaster)  Cosmology, Relativity and Gravitation  
15:00  Primordial black holes and stochastic inflation  
Hicks Seminar Room J11  
Abstract: Quantum fluctuations from cosmic inflation give rise to the macroscopic structures of the universe. The strongest fluctuations collapse into primordial black holes, a dark matter candidate and a possible source of gravitational waves. Stochastic inflation is a tool to compute the fluctuation statistics nonperturbatively, needed for accurate black hole predictions. I discuss recent progress in these computations, their numerical implementation and analytical approximations, and the implications for black hole abundance in singlefield models of inflation. 



Mar 14  Thu  Giannis Dakanalis (National Observatory of Athens)  Plasma Dynamics Group  
16:00  Swirling motions in the lower solar atmosphere: detection, statistics and profile analysis from multiwavelength observations  
LT6 (Hicks Building)  
Abstract: Ubiquitous vortical motions in the solar atmosphere have been recently revealed by high resolution observations from both spaceborne and groundbased observatories in quiet, as well as, in active regions. In chromospheric observations obtained in spectral lines, such as the Halpha and Ca II IR, they manifest themselves as swirling dark spiral and circularshaped patches known as “chromospheric swirls”. Their suggested contribution to the channeling of energy, mass and momentum from the subphotospheric to the higher layers of the solar atmosphere places them amongst potential candidates for atmospheric heating. In this context, their detection and statistical information concerning their population and several significant physical parameters and properties are of vital importance. To overcome the drawbacks of the detection methods based on visual inspection or on the Local Correlation Tracking (LCT) techniques, we have developed a novel automated detection method, which is purely based on their morphological characteristics. We will be presenting a brief description of the algorithm and the results from its application on high resolution observations obtained with the CRisp Imaging SpectroPolarimeter (CRISP) of the Swedish 1m Solar Telescope (SST) in three chromospheric spectral lines, namely, the Halpha, Ca II IR and Ca II K lines. The results include several statistical parameters such as their number, spatial distribution and temporal evolution, as well as significant physical parameters, such as radii and lifetimes. Specifically, for the estimation of the mean lifetime, apart from the usual approaches, the statistical method of survival analysis was implemented. This approach, which estimates more accurately the mean lifetime of a population, although common in several other scientific fields, is scarcely used in solar physics/astrophysics. We will finally be focusing on cospatially detected swirling structures in all three chromospheric lines and the profile analysis performed to derive significant physical parameters, such as lineofsight velocities, FWHM and equivalent widths. 



Mar 15  Fri  Noemi Zsamberger (Sheffield)  SP2RC/ESPOS seminar  
13:00  Nonparallel wave propagation in an asymmetric magnetic slab  
Google meet link: https://meet.google.com/ciqzovurzm  
Abstract: Interactions between the highly dynamic atmosphere of our Sun and the magnetic fields permeating its atmosphere give rise to a wide variety of magnetohydrodynamic (MHD) wave phenomena. Combining observations of MHD waves with an applied mathematical description of the waveguides has allowed researchers to determine elusive physical quantities of the solar atmosphere using the methods of solar magnetoseismolgy. The ‘classical’ models utilised in this discipline describe straight, symmetrical MHD waveguides (slabs or flux tubes). A recent direction of research has focused on wave propagation in asymmetric slab waveguides, where the direction of propagation was strictly parallel to the magnetic field lines within the slab. Here, some further results are presented in the case when a magnetic slab is embedded in a nonmagnetic, asymmetric environment, and the direction of propagation is allowed to deviate from the internal magnetic field lines of the slab. We describe this nonparallel wave propagation in various analytical approximations relevant to solar atmospheric waveguides (thin and wide slabs, lowbeta plasmas) and present numerical solutions to the full dispersion relation to expand on our findings. 



Mar 18  Mon  Philip Pearce (UCL)  Mathematical Biology Seminar  
13:00  Some consequences of phenotypic heterogeneity in living active matter  
Hicks Seminar Room J11  


Mar 18  Mon  Qaasim Shafi (Birmingham)  The Sheffield Geometry and Physics Seminar  
14:00  Refined curve counts on surfaces with descendants  
Hicks Seminar Room J11  
Abstract: An old theorem of Mikhalkin says that the number of rational plane curves of degree d through 3d1 points is equal to a count of tropical curves, combinatorial objects which are more amenable to computations. One can try to generalise this result in two directions, either by allowing for higher genus curves or allowing for different conditions than solely passing through points. I’ll discuss a generalisation which does both, using intersection theory on the moduli space of curves and integrable hierarchies, as well as ongoing work connecting this thread to quantum scattering diagrams coming from log CalabiYau surfaces. This is joint work with Patrick KennedyHunt and Ajith Urundolil Kumaran. 



Mar 19  Tue  Yoon Jae Nho  The Sheffield Geometry and Physics Seminar  
10:00  Spectral networks and Floer theory  
Hicks Seminar Room J11  
Abstract: In this talk, I will give a brief introduction to the theory of spectral networks on a marked Riemann surface. I will describe how the GMN nonabelianization map can be understood in terms of Lagrangian Floer theory of the spectral curve in the cotangent bundle of the Riemann surface, for the quadratic differentials case. If time permits, I will describe one way to generalize this to the higher rank situation. 



Mar 19  Tue  Jake Saunders (Booking room for online talk at Southampton PGR Seminar)  
12:00  
Hicks Seminar Room J11  


Mar 20  Wed  Emine Yildirim (University of Leeds)  Pure Maths Colloquium  
14:00  Why the Return to Pictures in Algebra?  
Hicks Seminar Room J11  
Abstract: In ancient Greece, geometry was about points, lines, circles, and communicated through pictures. The 17th Century marked a transformative shift, connecting geometry with algebra, and lead to working with equations over visual representations. Algebraic geometry emerged as a magical blend of geometric intuition and algebraic methods. Commutative algebra, mainly the study of polynomial rings and their ideals, dominated the field for an extensive period. Then with the emergence of noncommutative algebras, such as matrix algebras, our unstoppable geometric intuition hit an immovable wall. The solution? A return to pictures as representations. In this expository talk, I will introduce a visual perspective on algebras, exploring path algebras and their captivating connections to different fields. 



Mar 20  Wed  Aindriú Conroy (Charles U Prague)  Cosmology, Relativity and Gravitation  
15:00  UnruhDeWitt Particle Detectors in Bouncing Cosmologies  
Hicks Seminar Room J11  
Abstract: There is no welldefined notion of a particle in quantum field theory in curved spacetime due to the lack of global symmetries. The standard procedure in quantum field theory is to treat fields rather than particles as the fundamental object of interest. Nevertheless, in a seminal 1976 paper by W. G. Unruh, an operational meaning was given to the particle concept by examining the absorption and emission of field quanta by a twolevel atom. This is the socalled UnruhDeWitt detector and, in this operational sense, we say a particle is what a particle detector detects! In this talk, we begin by formulating an analytic model of a nonsingular bouncing cosmology, the bounce phase of which receives a correction inspired by loop quantum cosmology. We then study the semiclassical particle production associated with spacetime within the UnruhDeWitt particle detector framework, analysing the rate of particle detection with the aim of (a) understanding quantum effects at early times; (b) identify relics of prebounce physics; and (c) highlighting signatures of nonsingular theories. 



Mar 21  Thu  Július Koza (Astronomical Institute, Slovak Academy of Sciences, Slovakia)  SP2RC/ESPOS seminar  
10:00  Datadriven model of temporal evolution of the solar Mg II h and k profiles over the solar cycle  
Zoom  
Abstract: The solar radiation in the cores of the Mg II h & k spectral lines strongly correlates with solar magnetic activity and global variations of magnetic fields with the solar cycle. This work provides a datadriven model of temporal evolution of the solar fulldisk Mg II h & k profiles over the solar cycle. Based on selected 76 IRIS nearUV fullSun mosaics covering almost the full solar cycle 24, we find the parameters of doubleGaussian fits of the diskaveraged Mg II h & k profiles and a model of their temporal evolution parameterized by the Bremen composite Mg II index. The Markov Chain Monte Carlo algorithm implemented in the IDL toolkit SoBAT is used in modeling and predicting temporal evolution of the Mg II h & k peaktocenter intensity ratio and the Bremen Mg II index. The relevant fulldisk Mg II h & k calibrated profiles with uncertainties and spectral irradiances are provided as an online machinereadable table. To facilitate utilization of the model corresponding routines, written in IDL, are made publicly available at GitHub. Coauthors: Stanislav Gunár (The Czech Academy of Sciences, Czech Republic), Pavol Schwartz (Slovak Academy of Sciences, Slovakia), Petr Heinzel (The Czech Academy of Sciences, Czech Republic; University of Wrocław, Poland), Wenjuan Liu (The Czech Academy of Sciences, Czech Republic) Web announcement: https://espos.stream/2024/03/21/Koza/ Zoom link: https://zoom.us/j/165498165 (Meeting ID: 165 498 165) 



Mar 21  Thu  Andy Baker (Glasgow)  Topology Seminar  
16:00  Endotrivial modules for the quaternion group and iterated Jokers in chromatic homotopy theory  
Hicks Seminar Room J11  
Abstract: The Joker is a famous very singular example of an endotrivial module over the 8dimension subHopf algebra of the mod 2 Steenrod algebra generated by $\operatorname{Sq}^1$ and $\operatorname{Sq}^2$. It is known that this can be realised as the cohomology of two distinct SpanierWhitehead dual spectra. Similarly, the double and iterated double are also realisable, but then the process stops. 



Apr 4  Thu  Daniel NóbregaSiverio (Instituto de Astrofísica de Canarias —IAC, Spain)  SP2RC/ESPOS seminar  
10:00  Deciphering solar coronal heating: Energizing smallscale loops through surface convection  
Zoom  
Abstract: The solar atmosphere is filled with clusters of hot smallscale loops commonly known as Coronal Bright Points (CBPs). These ubiquitous structures stand out in the Sun by their strong Xray and/or extremeultraviolet (EUV) emission for hours to days, which makes them a crucial piece when solving the solar coronal heating puzzle. Here we present a novel 3D numerical model using the Bifrost code that explains the sustained CBP heating for several hours. We find that stochastic photospheric convective motions alone significantly stress the CBP magnetic field topology, leading to important Joule and viscous heating concentrated around the CBP’s inner spine at a few megameters above the solar surface. We validate our model by comparing simultaneous CBP observations from SDO and SST with observable diagnostics calculated from the numerical results for EUV wavelengths as well as for the Halpha line using the Multi3D synthesis code. Coauthors: Fernando MorenoInsertis, Klaus Galsgaard, Kilian Krikova, Luc Rouppe van der Voort, Reetika Joshi, and Maria Madjarska Web announcement: https://espos.stream/2024/04/04/NobregaSiverio/ Zoom link: https://zoom.us/j/165498165 (Meeting ID: 165 498 165) 



Apr 15  Mon  Francesca Scarabel (Leeds)  Mathematical Biology Seminar  
13:00  Structured population models  
Hicks Seminar Room J11  


Apr 15  Mon  Johannes Walcher (Heidelberg)  The Sheffield Geometry and Physics Seminar  
14:00  Exponential networks for linear partitions  
Hicks Seminar Room J11  
Abstract: Previous work has given proof and evidence that BPS states in local CalabiYau 3folds can be described and counted by exponential networks on the punctured plane, with the help of a suitable nonabelianization map to the mirror curve. This provides an appealing elementary depiction of moduli of special Lagrangian submanifolds, but so far only a handful of examples have been successfully worked out in detail. In this talk, I will present an explicit correspondence between torus fixed points of the Hilbert scheme of points on C^2\subset C^3 and anomaly free exponential networks attached to the quadratically framed pair of pants. This description realizes an interesting, and seemingly novel, "age decomposition'' of linear partitions. We also provide further details about the networks' perspective on the full Dbrane moduli space.(Joint work with Sibasish Banerjee, Mauricion Romo, Raphael Senghaas) 



Apr 16  Tue  Dominic Grainger and Dr Ben Wigley (Sheffield)  Statistics Seminar  
15:00  Dominic: The Efficient Modelling of Individual Animal Movement in Continuous Time; Ben: Stressing over shape: A Procrustean investigation of dental fluctuating asymmetry.  
Hicks Seminar Room J11  


Apr 17  Wed  Tony Samuel (University of Birmingham)  Pure Maths Colloquium  
14:00  Complexity and geometry of aperiodic systems  
Hicks Seminar Room J11  
Abstract: Aperiodic sequences and sequence spaces form prototypical mathematical models of quasicrystals. The most quintessential examples include subshifts of Sturmian words and substitutions, which are ubiquitous objects in ergodic theory and aperiodic order. Two of the most striking features these shift spaces have, are that they have zero topological entropy and are uniquely ergodic. Random substitutions are a generalisation of deterministic substitutions, and in stark contrast to their deterministic counterparts, subshifts of random substitutions often have positive topological entropy and exhibit uncountably many ergodic measures. Moreover, they have been shown to provide mathematical models for physical quasicrystals with defects. We will begin by talking about subshifts generated by Sturmian words and ways to measure their complexity beyond topological entropy, and show how this measure of complexity can be used to build a classification via Jarník sets. We will then build a bridge between these subshifts and subshifts of random substitutions. We will conclude with some recent dynamical results on subshifts of random substitutions and ways to visualise these subshifts. Namely, we will present a method to build a new class of Rauzy fractals. 



Apr 18  Thu  Briony Eldridge (Southampton)  Topology Seminar  
16:00  Loop Spaces of Polyhedral Products Associated with Substitution Complexes  
Hicks Seminar Room J11  
Abstract: Polyhedral products are a topological space formed by gluing together ingredient spaces in a manner governed by a simplicial complex. They appear in many areas of study, including toric topology, combinatorics, commutative algebra, complex geometry and geometric group theory. A fundamental problem is to determine how operations on simplicial complexes change the topology of the polyhedral product. In this talk, we consider the substitution complex operation. We obtain a description of the loop space associated with some substitution complexes, and use this to build a new family of simplicial complexes such that the homotopy type of the loop space of the moment angle complex is a product of spheres and loops on spheres. 



Apr 18  Thu  José Juan González Avilés (Universidad Nacional Autónoma de México)  Plasma Dynamics Group  
16:00  Global MHD simulations of solar wind streams in the inner heliosphere using sunRunner3D  
online / Google Meet  
Abstract: Understanding the largescale threedimensional structure of the inner heliosphere, while important in its own right, is crucial for space weather applications, such as forecasting the time of arrival and propagation of coronal mass ejections (CMEs). This study uses sunRunner3D (SR3D), a 3D MHD model, to simulate solar wind (SW) streams and generate background states. SR3D employs the boundary conditions generated by CORHEL and the PLUTO code to compute the plasma properties of the SW with the magnetohydrodynamic (MHD) approximation up to 1.1 AU in the inner heliosphere. We demonstrate that SR3D reproduces global features of Corotating Interaction Regions (CIRs) observed by Earthbased spacecraft (OMNI) and STEREOA for a set of Carrington rotations that cover a period that lays in the late declining phase of solar cycle 24. Additionally, we demonstrate that the model solutions are valid in the corotating and inertial frames of references. Moreover, a comparison between SR3D simulations and insitu measurements shows reasonable agreement with the observations, and our results are comparable to those achieved by Predictive Science Inc.'s MAS code and SWASTiSW framework. 



Apr 19  Fri  Adrià Gómez Valent (Barcelona)  Cosmology, Relativity and Gravitation  
14:00  Is there still room for lowz solutions to the Hubble tension?  
Hicks Seminar Room J11  
Abstract: The ∼5\sigma mismatch between the value of the Hubble parameter measured by SH0ES and the one inferred from the inverse distance ladder (IDL) constitutes the biggest tension afflicting the standard model of cosmology, which could be pointing to the need of physics beyond LCDM. In this talk I will review the background history required to solve the H0 tension if we consider standard prerecombination physics, paying special attention to the role played by the data on baryon acoustic oscillations (BAO) employed to build the IDL. I will show that the anisotropic BAO data favor an ultralatetime (phantomlike) enhancement of H(z) at z<0.2, accompanied by a transition in the absolute magnitude of supernovae of Type Ia M(z) in the same redshift range. The effective dark energy (DE) density must be smaller than in the standard model at higher redshifts. Instead, when angular BAO data (claimed to be less subject to model dependencies) is employed in the analysis, the increase of H(z) must start at much higher redshifts, typically in the range z= 0.50.8. In this case, M(z) could experience also a transition (although much smoother) and the effective DE density becomes negative at z\sim 2. Both scenarios require a violation of the weak energy condition, but leave an imprint on completely different redshift ranges and might also have a different impact on the perturbed observables. They allow for the effective crossing of the phantom divide. I will put the accent on the utmost importance of the choice of the BAO data set in the study of the possible solutions to the H0 tension. 



Apr 22  Mon  TBC  Mathematical Biology Seminar  
13:00  
Hicks F41  


Apr 22  Mon  Cheuk Yu Mak (Southampton)  The Sheffield Geometry and Physics Seminar  
14:00  Loop group action on symplectic cohomology  
Hicks Seminar Room J11  
Abstract: For a compact Lie group G, its massless Coulomb branch algebra is the Gequivariant BorelMoore homology of its based loop space. This algebra is the same as the algebra of regular functions on the BFM space. In this talk, we will explain how this algebra acts on the equivariant symplectic cohomology of Hamiltonian Gmanifolds when the symplectic manifolds are open and convex. This is a generalization of the closed case where symplectic cohomology is replaced with quantum cohomology. Following Teleman, we also explain how it relates to the Coulomb branch algebra of cotangenttype representations. This is joint work with Eduardo González and Dan Pomerleano. 



Apr 22  Mon  Cyril Closset (Birmingham)  The Sheffield Geometry and Physics Seminar  
15:00  
Hicks Seminar Room J11  


Apr 24  Wed  Catherine Meusburger (University of Erlangen)  Pure Maths Colloquium  
14:00  DijkgraafWitten theory with defects  
Hicks Seminar Room J11  
Abstract: We use 3d defect TQFTs to give a gauge theoretical formulation of (untwisted) DijkgraafWitten TQFT with defects. This leads to a simple description in terms of embedding quivers, groupoids and their representations. Defect DijkgraafWitten TQFTs is then formulated in terms of spans of groupoids and representations of spans. This is work in progress with João FaríaMartins, University of Leeds. 



Apr 24  Wed  Elsa Teixeira (Montpellier)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Apr 26  Fri  Thomas Montandon (Montpellier)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Apr 29  Mon  Enrico Dell'Arra (Sheffield)  Mathematical Biology Seminar  
13:00  
Hicks J11  


Apr 29  Mon  Sukjoo Lee (Edinburgh)  The Sheffield Geometry and Physics Seminar  
14:00  
Hicks Seminar Room J11  


Apr 29  Mon  Dylan Butson (Oxford)  The Sheffield Geometry and Physics Seminar  
15:00  
Hicks Seminar Room J11  


Apr 30  Tue  Bence Hevesi (Kings College London)  Number Theory seminar  
13:00  
Hicks Seminar Room J11 / Google Meet  


May 1  Wed  David Corfield (University of Kent)  Pure Maths Colloquium  
14:00  
Hicks Seminar Room J11  


May 2  Thu  Ehud Meir (Aberdeen)  Topology Seminar  
16:00  
Hicks Seminar Room J11  


May 7  Tue  Jay Taylor (Manchester)  Number Theory seminar  
13:00  
Hicks Seminar Room J11 / Google Meet  


May 8  Wed  Rohini Ramadas (University of Warwick)  Pure Maths Colloquium  
14:00  
Hicks Seminar Room J11  


May 8  Wed  Gabriele Barca (Rome/Sheffield)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


May 8  Wed  Alessandro Chiarini (OIST, Okinawa, Japan)  Fluid Dynamics Seminar  
16:00  Finitesize inertial spherical particles in homogeneous isotropic turbulence  
Diamond LT2  
Abstract: We use direct numerical simulations to study the fluidsolid interaction of nondilute suspensions of spherical particles in homogeneous isotropic turbulence. I will discuss how finitesize inertial spherical particles modulate turbulence, and how they preferentially accumulate in specific regions of the flow. In particular, we observe that particles of different size and density modulate the flow in a different way. For small and heavy particles, the classical energy cascade is inhibited, and the energy transfer across scales is essentially driven by the fluidsolid interaction. We also find that particles of different size and density have a different level of clustering. I will discuss their collective motion and preferential location in relation with properties of the carrier flow. 



May 9  Thu  Georg Struth (Sheffield)  Topology Seminar  
16:00  Singleset Cubical Categories and Their Formalisation with a Proof Assistant  
Hicks Seminar Room J11  
Abstract: Cubical sets and cubical categories are widely used in mathematics and computer science, from homotopy theory to homotopy type theory, higherdimensional automata and, last but not least, higherdimensional rewriting, where our own interest in these structures lies. To formalise cubical categories with the Isabelle/HOL proof assistant along the path of least resistance, we take a singleset approach to categories, which leads to new axioms for cubical categories. Taming the large number of initial candidate axioms has relied essentially on Isabelle's proof automation. Yet we justify their correctness relative to the standard axiomatisation by Al Agl, Brown and Steiner via categorical equivalence proofs outside of Isabelle. In combination, these results present a case study in experimental mathematics with a proof assistant. In this talk I will focus on the formalisation experience  lights and shadows  and conclude with some general remarks about formalised mathematics. This is joint work with Philippe Malbos and Tanguy Massacrier (Université Claude Bernard Lyon 1). 



May 13  Mon  TBC  Mathematical Biology Seminar  
13:00  
Hicks J11  


May 15  Wed  Álvaro Álvarez Domínguez (Madrid)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


May 20  Mon  Juan Morales (Glasgow)  Mathematical Biology Seminar  
13:00  
Hicks Seminar Room J11  


May 20  Mon  Phillip Engel (Bonn)  The Sheffield Geometry and Physics Seminar  
14:00  
Hicks Seminar Room J11  


May 20  Mon  Matteo Sacchi (Oxford)  The Sheffield Geometry and Physics Seminar  
15:00  
Hicks Seminar Room J11  


May 21  Tue  Owen Patashnick (Kings College London)  Number Theory seminar  
13:00  
Hicks Seminar Room J11 / Google Meet  


May 23  Thu  Nika Shakiba (British Columbia)  Mathematical Biology Seminar  
11:00  TBC  
Hicks Seminar Room J11  


May 29  Wed  Lucia MenendezPidal (Madrid)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  

