Seminars this week

Cosmology, Relativity and Gravitation

Laura Iacconi (Queen Mary)

Mapping inflationary loop corrections to boundary terms

Wed, 12 March at 15:00
Hicks Seminar Room J11

Abstract

Both single- and multi-field models of inflation might lead to enhanced scalar fluctuations on scales much smaller than those seeding the large-scale structure formation. In these scenarios, it is possible that the spike of power at high wavenumber might induce large corrections to the scalar power spectrum, e.g. in the form of loop corrections, potentially endangering the perturbativity of the underlying models. In this talk we discuss recent developments in the calculation of the 1-loop correction to a large-scale adiabatic mode. We demonstrate that non-volume-suppressed corrections only contribute at the boundaries of the momentum integral. To achieve this we employ expansion methods, such as the $\delta N$ formalism, as well as more general expansions that do not rely on assumption of validity of the separate universe picture.

SP2RC/ESPOS seminar

Yara De Leo (INAF – Catania Astrophysical Observatory, Italy)

Two Distinct Eruptive Events Observed by Metis on October 28, 2021

Thu, 13 March at 10:00
Zoom

Abstract

On October 28, 2021 the first X-class solar flare of Solar Cycle 25 occurred in active region NOAA AR 12887 with a peak at 15:35 UT. It produced the rare event of ground-level enhancement of the solar relativistic proton flux and a global extreme ultraviolet wave, along with a fast halo coronal mass ejection (CME) as seen from Earth’s perspective. A few hours before the flare, a slower CME had erupted from a quiet Sun region just behind the northwestern solar limb. Solar Orbiter was almost aligned with the Sun-Earth line and, during a synoptic campaign, its coronagraph Metis detected the two CME events in both Visible Light (VL) and UltraViolet (UV) channels. The earlier CME took place in the north-west (NW) sector of Metis field of view, while several bright features of the flare-related event appeared mostly to the south-east (SE). The NW and SE events have two distinct origins, but were both characterized by a very bright emission in HI Ly-alpha visible in the UV images of Metis up to 8 solar radii. This work is a follow-up study of two out of the six events analyzed by Russano et al. 2024 (A&A, 683, A191), aimed at investigating the evolution of these two almost co-temporal CMEs but originating in such distinct source regions. To that end, we extensively inspect data sets from numerous remote-sensing instruments observing the Sun in several spatial and spectral regimes. We characterize several aspects of these CMEs, including their three-dimensional properties, kinematics, mass, and temporal evolution of those quantities. Results of this work point to notable differences between these two events showing significant UV emission in the corona.

Topology Seminar

Daniel Luckhardt (Sheffield)

The Giry monad revisited

Thu, 13 March at 16:00
Hicks Seminar Room J11

Abstract

For over 40 years the Giry monad has been an object of intense investigations plagued by difficulties. Typically---as already done by Giry—the monad is restricted to specific classes of topological spaces to achieve tractability. In this talk we will return to a $\sigma$-algebra as the only structure and carefully analyse, how the monad can be restricted, while still covering all cases relevant for real-world application. Again---as for Giry---limit preservation properties will serve as a touchstone. Unlike Giry we obtain also result on weak pullback preservation. Moreover the journey will lead us ward the boundaries of ZCF and beyond.

Maths Knowledge Exchange Hub Triage Workshops

Office for National Statistics

Reliable confidence intervals for proportions in the UK Annual Population Survey

Fri, 14 March at 10:00
https://tinyurl.com/5n8yc8y9

Abstract

The ONS compiles the Annual Population Survey (APS) based on surveying households across the UK. It provides quarterly snapshots for key labour market statistics such as official employment figures, job characteristics and work-related education. Government departments, public bodies and charities use this survey extensively for policy making and research. There is increasing user demand for data disaggregated by demography and geography, and this exacerbates difficulties in calculating uncertainties for estimates due to small subpopulation sample sizes. Improvements to the estimates and their uncertainties can therefore have significant public impact. We are specifically interested in validating methodology for computing confidence intervals (CIs) for small and large proportions in the APS. For simple random samples (SRS), several well-established methods are available, such as the Wald, Wilson or Clopper-Pearson CIs. However, for surveys such as the APS with complex sample designs including, for example, stratification, clustering or longitudinal elements, this is still an area of active research. A common strategy consists in adapting the SRS approaches by introducing an effective sample size which incorporates the impact of the sample design on precision. Unfortunately, the literature disagrees on how to estimate the effective sample size, and the optimal approach may depend on the specific survey design. We therefore aim to develop a CI method appropriate for the APS and validate its performance. This could be approached through simulated samples based on suitably simplified versions of the APS sample design. Further aspects requiring more research concern CIs for sample subgroups and accounting for a calibration stage within survey weighting.

Number Theory seminar

Elena Collacciani (Padova)

Tue, 18 March at 14:00
Hicks Seminar Room J11 / Google Meet

Category theory reading seminar

Enriched duality in double categories 4

Tue, 18 March at 14:00
**F35**

Cosmology, Relativity and Gravitation

Jens Chluba (Manchester)

CMB spectral distortion science beyond the monopole

Wed, 19 March at 15:00
Hicks Seminar Room J11

Abstract

CMB spectral distortions have now been recognized as an important new probe in cosmology. However, most of the science has focused on CMB monopole distortions. In my talk, I will give a brief update on the status of CMB spectral distortions and then explain how it has now become possible to compute the full spectro-spatial evolution of the CMB including distortions. Anisotropic distortion signals do not require an absolute calibration and can be constrained with Planck, Litebird, CMB-S4 and the SKA, opening yet another way to study the primordial universe.

Topology Seminar

Andrew Fisher (Sheffield)

Thu, 20 March at 16:00
Hicks Seminar Room J11