Meeting of the UK Cosmology Community at Newcastle University from Monday, May 16 to Tuesday, May 17 – in celebration of the 150th anniversary of the College of Physical Science in Newcastle – read more about the history of physics and cosmology at Newcastle!

**Location:** Newcastle University, Herschel Building (see the virtual look around) – read more about the history behind the Herschel Building. For travel advice, see the Visiting page.

**Organisers:** Kate Brown (she/her), Alex Gough (they/them), Ian Moss (he/him), Cora Uhlemann (she/her, email me for questions)

**Code of Conduct: **All meeting participants must adhere to the UK Cosmology Code of Conduct and sign their agreement during on site registration.

**Monday**, May 16, 2022

*12.00 – 13.30 Registration & Lunch in the Herschel Building Penthouse (top floor)*

Room: Herschel Building, Lecture Theatre 3 (see link for room layout to help plan your talk)

**13.30 – 13.35 Welcome **

**13.35 – 14.35 Invited Plenary Talk** **(50+10 min), chair: Ian Moss**

- ‘Direct Detection of Dark Energy; The XENON1T Experiment’ by Prof. Anne Christine Davis (DAMTP, Cambridge)

A*bstract:*Most of the efforts in searching for dark energy (DE) have focused on its gravitational signatures, and in particular on constraining its equation of state. However, non-gravitational interactions between DE and visible matter are somewhat inevitable, and might lead to the possibility of “direct detection of dark energy” (analogous to direct detection of dark matter). Such interactions need to be appropriately screened on local scales. We discuss our recent work where we argued that it is possible to detect (screened) DE in underground experiments nominally devoted to the direct detection of dark matter. Our results raise the tantalizing possibility that the 3.3σ electron recoil excess seen by the XENON1T experiment in 2020 may be the first direct detection of DE, and open new unforeseen vistas for the scientific scope of direct detection dark matter experiments.

**14.35 – 14.55 Lightning Talks (4, 4+1 min each), chair: Ian Moss**

- ‘Quintessential inflation in Palatini modified gravity’ by Samuel Sánchez López (Lancaster)
~~‘Multi-field alpha-attractor inflation: turning trajectories and geometry’ by Laura Iacconi (Portsmouth)~~- ‘Gravitational wave production in non-local Starobinsky model’ by Dr Anna Tokareva (Imperial College London)
- ‘Ending inflation with a bang: Higgs vacuum decay in R^2 gravity’ by Andreas Mantziris (Imperial College London)
- ‘Boostless Cosmological Collider Bootstrap’ by Dr Dong-Gang Wang (Cambridge)

**14.55 – 15.25 Long Talk** **(25+5 min), chair: Ian Moss**

- ‘From the tabletop to the Big Bang: quantum simulators of false vacuum decay’ by Dr Alex Jenkins (University College London)
*Abstract:*False vacuum decay (FVD) plays a vital role in many models of the early Universe, with important implications for inflation, the multiverse, and gravitational waves. However, it is also a very challenging process to model theoretically, with existing approaches relying on numerous assumptions that have yet to be empirically tested. An exciting route forward is to use laboratory experiments which undergo transitions analogous to FVD, allowing nature to simulate all of the non-perturbative quantum effects for us. In this talk, I will discuss ongoing work to develop such analogue FVD experiments within the Quantum Simulators for Fundamental Physics (QSimFP) consortium. In particular, I will present numerical lattice simulations of ultracold atom systems undergoing FVD, and discuss outstanding challenges in using upcoming experimental data to understand the early Universe

*15.25 – 15.30 Conference Picture*

*15.30 – 16.00 Coffee*

**16.00 – 17.30 Long Talks (3, 25+5 min each), chair: Gerasimos Rigopoulos**

- ‘On Graviton non-Gaussianities in the Effective Field Theory of Inflation’ by Ayngaran Thavanesan (Cambridge)

Abstract: In cosmology we measure correlation functions (cosmological correlators) which we can trace back to the boundary at the end of inflation. In the spirit of the S-matrix in flat space and holography in AdS, the cosmological bootstrap allows us to compute these boundary observables by sidestepping cumbersome Lagrangians, and instead using dS isometries and fundamental principles with no explicit reference to time evolution, i.e. “bootstrapping time”. Recently, progress has been made on bootstrapping correlators in the case where dS boosts are broken, to make more phenomenologically relevant observational predictions. In this talk I will explain how we can use locality and unitarity to bootstrap the graviton three-point function within the Effective Field Theory of Inflation (EFToI). I will first present the full class of operators that contribute to the on-shell two- and three-point functions of gravitons, and show how our analysis also captures graviton bispectra with a perturbative correction to the graviton two-point function. - ‘Gravitational Collapse of Quantum Fields’ by Benjamin Berczi (Nottingham)

A*bstract:*The behaviour of quantum fields around black holes has been in the forefront of research for almost half a century, since the discovery of Hawking radiation in 1974. However, we still know remarkably little about the details of the evaporation of black holes beyond first order approximations. In this talk, I will introduce our formalism using which a fully quantum mechanical field can be simulated to collapse into a black hole. Initial results of the quantum effects around the formed black hole will be presented, in addition to the verification of Choptuik scaling in critical collapse of semiclassical black holes. - ‘Scalar perturbations in cosmological scenarios with a modified Friedmann equation’ by Lisa Mickel (Sheffield)
*Abstract:*When applying quantum gravity theories to cosmology, one often obtains an effective Friedman equation that captures dominant quantum gravity corrections, such as the replacement of the Big Bang singularity by a bounce. We study what statements can be made for the evolution of cosmological perturbations from a modified Friedmann equation alone, using the separate universe framework. In particular, we focus on the curvature perturbation on uniform density hypersurfaces and the comoving curvature perturbation, which are commonly used to characterise scalar perturbations in cosmology. We ask whether general relativistic conservation laws of these quantities hold also for a modified Friedmann equation, and show that while they remain valid for a certain type of modification, this is generally not the case.

**from 19.15 Conference Dinner** (information circulated via email)

**Tuesday**, May 17, 2022

Room: Herschel Building, Lecture Theatre 3 (see link for room layout to help plan your talk)

**09.00 – 10.00 Invited Plenary Talk** **(50+10 min), chair: Cora Uhlemann**

- ‘Dissecting the cosmic web with caustics’ by Dr Job Feldbrugge (Higgs Centre, Edinburgh)

A*bstract:*The cosmic web is the largest geometric structure in our universe, consisting of an intricate network of empty voids bounded by thin walls, elongated filaments, and dense clusters. Given the array of upcoming cosmological redshift surveys, new analytic tools are needed to study the formation of the various structures, quantify the geometry and topology, and isolate the elements of the cosmic web. New techniques might, for example, help to understand the link between the properties of galaxies and their placement in the large-scale structure. In this talk, I will present my recent developments in the study of the caustic skeleton of the cosmic web. By tracing the phase-space structure of the dark matter sheet, I identify the relevant caustics and illustrate their role in the cosmic web. I quantify the topology of the phase-space structure using persistent homology. Finally, I will present a non-linear extension of constrained Gaussian random field theory. When combined with caustic skeleton theory, this extension allows us to create a specialized set of initial conditions dissecting the elements of the cosmic web. These initial conditions will help cosmologists to systematically study the properties and interplay of the elements of the cosmic web, and their influence on the embedded galaxies.

**10.00 -10.30 Lightning Talks (6, 4+1 min each), chair: Cora Uhlemann**

- ‘The halo bispectrum as a sensitive probe of massive neutrinos and baryon physics’ by Dr Victoria Yankelevich (Liverpool John Moores University)
- ‘Minkowski Functionals in Joint Galaxy Clustering & Weak Lensing Analysis’ by Nisha Grewal (Edinburgh)
- ‘Nonlinear Horndeski Analysis with HiCOLA’ by Ashim Sen Gupta (Queen Mary University London)
- ‘Using SELCIE to investigate screened scalar field models sourced by complex systems’ by Chad Briddon (Nottingham)
- ‘Statistical cosmology from the weak lensing of gravitational waves’ by Charlie Mpetha (Edinburgh)
- ‘Evolution of Voids using wave mechanics’ by Aoibhinn Gallagher (Maynooth University)

*10.30 – 11.00 Coffee*

**11.00 – 12.30 Long Talks (3**, **25+5 min each), chair: Danielle Leonard**

- ‘Searching for the fundamental nature of dark matter in the cosmic large-scale structure’ by Dr Keir Rogers (University of Toronto)
*Abstract:*The fundamental nature of dark matter so far eludes direct detection experiments, but it has left its imprint in the large-scale structure (LSS) of the Universe. Extracting this information requires accurate modelling of structure formation and careful handling of astrophysical uncertainties. I will present new bounds using the LSS on two compelling dark matter scenarios that are otherwise beyond the reach of direct detection. Ultra-light axion dark matter, particles with very low mass and astrophysically-sized wavelengths, is produced in high-energy models like string theory (“axiverse”). I will rule out axions that are proposed to resolve the so-called cold dark matter “small-scale crisis” (mass ~ 10^-22 eV) using the Lyman-alpha forest, but demonstrate how a mixed axion dark matter model (as produced in the string axiverse) could resolve the S_8 tension (mass ~ 10^-25 eV) using Planck, ACT and SPT CMB data and BOSS galaxy multipoles. Further, I will set the strongest limits to-date on the dark matter — proton cross section for dark matter particles lighter than a proton (mass < GeV). The LSS model involves one-loop perturbation theory, a non-cold dark matter halo model and, to capture the smallest scales, a machine learning model called an “emulator”, trained using hydrodynamical simulations and an active learning technique called Bayesian optimisation. - ‘Tachyonic instability priors for dark energy’ by Rafaela Gsooner (Portsmouth)
*Abstract:*Theoretical priors are an essential ingredient for the efficient computation of cosmological dark energy constraints by excluding unviable parameter space a priori. Perhaps the most straightforward example of such priors in the context of dynamical dark energy theories are the stability criteria associated with requiring the absence of ghost, gradient and tachyonic instabilities. The latter is the least well explored of these and, in contrast to its siblings, not as clear cut. In this talk, we investigate the role of the tachyonic instability criterion in the setting of Horndeski gravity theories and answer the question if an equally informative prior can be put in place. - ‘Do anthropic arguments really work?’ by Dr Daniele Sorini (Edinburgh)

A*bstract:*The anthropic explanation for the peculiarly small observed value of the cosmological constant argues that this value promotes the formation of stars, planets, and ultimately of observers such as ourselves. I will show that the analytic model of cosmic star formation by Sorini & Peacock (2021) predicts that although the observed value of the cosmological constant maximises the overall efficiency of star formation in the universe, the probability of generating observers peaks at ∼400−500 times larger values. These preliminary results suggest that an immediate connection between star formation efficiency and observers’ generation is not straightforward, and highlight the subtleties involved with the application of anthropic reasoning.

**12:30 – 12:35 Closing Remarks**

*12.35 – 13.30 Lunch in the Herschel Building Penthouse (top floor)*

## Participants

Santiago | Agüí Salcedo | University of Cambridge |

Emma | Albertini | Imperial College |

Theo | Anton | Queen Mary University of London |

David | Benisty | University of Cambridge |

Benjamin | Berczi | University of Nottingham |

Jonathan | Betts | The University of Sheffield |

Chad | Briddon | University of Nottingham |

Lucy | Brissenden | Lancaster University |

Kate | Brown | Newcastle University |

Molly | Burkmar | University of Portsmouth |

Archie | Cable | Imperial College London |

Andrea | Calcinari | University of Sheffield |

Francesca | Caloro | Newcastle University |

Pedro | Carrilho | University of Edinburgh |

Calvin | Chen | Imperial College London |

Timothy | Clifton | Queen Mary University of London |

Ed | Copeland | University of Nottingham |

Carolina | Cuesta-Lazaro | Durham University |

Richard | Daniel | University of Sheffield |

Matthew | Davies | Queen Mary University of London |

Anne | Davis | Cambridge Univeristy |

Mariaveronica | De Angelis | University of Sheffield |

Job | Feldbrugge | University of Edinburgh |

Aoibhinn | Gallagher | Maynooth University |

Steffen | Gielen | University of Sheffield |

Harry | Goodhew | University of Cambridge |

Alex | Gough | Newcastle University |

Oliver | Gould | University of Nottingham |

Beth | Gould | Newcastle University |

Nisha | Grewal | University of Edinburgh |

Rafaela | Gsooner | University of Portsmouth |

Joachim | Harnois-Deraps | Newcastle University |

Alex | Jenkins | University College London |

Chakkrit | Kaeonikhom | University of Portsmouth |

Danielle | Leonard | Newcastle University |

Gary | Liu | Newcastle University |

Hayley | Macpherson | University of Cambridge |

Andreas | Mantziris | Imperial College London |

Alessandro | Maraio | University of Edinburgh |

Bradley | March | The University of Nottingham |

Aoibheann | Margalit | Imperial College London |

Paul | McFadden | Newcastle University |

Giorgio | Mentasti | Imperial College London |

Lisa | Mickel | University of Sheffield |

Swagat Saurav | Mishra | University of Nottingham |

Ian | Moss | Newcastle University |

Charlie | Mpetha | University of Edinburgh |

Arad | Nasiri | Imperial College London |

Pritha | Paul | Queen Mary University of London |

Gaspard | Poulot | University of Sheffield |

Alkistis | Pourtsidou | University of Edinburgh |

Lizzy | Ratcliffe | Newcastle University |

Gerasimos | Rigopoulos | Newcastle University |

Mark | Roberts | |

Mathew | Robertson | University of Sussex |

Keir | Rogers | University of Toronto |

Samuel | Sánchez López | Lancaster University |

Niko | Sarcevic | Newcastle University |

David | Seery | University of Sussex |

Ashim | Sen Gupta | Queen Mary University of London |

Sergio | Sevillano | University of Nottingham |

Sergi | Sirera Lahoz | University of Portsmouth |

Daniele | Sorini | University of Edinburgh |

Alex | Soto | Newcastle University |

Theo | Steele | University of Cambridge |

Elsa | Teixeira | University of Sheffield |

Ayngaran | Thavanesan | University of Cambridge |

Anna | Tokareva | Imperial College London |

Maria | Tsedrik | University of Edinburgh |

Cora | Uhlemann | Newcastle University |

Carsten | van de Bruck | University of Sheffield |

Dong-Gang | Wang | University of Cambridge |

Ashley | Wilkins | Newcastle University |

Victoria | Yankelevich | Liverpool John Moores University |

Houri | Ziaeepour | Franche Comte University & University College London MSSL |