Programme
Timetable Abstracts Lunch Options Social Events Conference Poster
The conference will start on the morning of Monday 20th May, and close on the afternoon of Thursday 23rd May.
Abstracts
Invited Speakers
Clare Burrage
Searching for fifth forces with galactic and cosmological observationsFifth forces are motivated by theories of light scalar fields introduced to explain dark energy and in theories of modified gravity. I will discuss the constraints that can be placed on these models with observations on cosmological and galactic scales.
Ruth Durrer
Testing General Relativity with Cosmological Large Scale StructureGeneral Relativity (GR) is immensely successful. With the late discovery of gravitational waves from black hole and neutron star mergers, it has passed all the tests with flying colors. But so far, all observations have mainly tested the vacuum equations of GR. The most important non-vacuum case, cosmology, is in agreement with GR only after the introduction of two otherwise unknown components, 'Dark Matter' and 'Dark Energy' which amount to about 95% of the total energy budget of the present Universe. This lead people in the field to question the validity of GR for cosmology. Might it be that GR is flawed on large, cosmological scales? Or in the presence of matter in general? But how can we test Einstein's equation in the presence of matter? Can't we simply move any modification of the Einstein tensor to the right hand side and call it a 'dark matter/energy' component? In my talk I shall discuss possible ways (partially) out of this dilemma. How to test both, the left and the right hand side of Einstein's equations with cosmological observations.
Malcolm Fairbairn
Probes of the dark sector with Gravitational Waves and 21cmI will give a couple of examples of how gravitational waves and future 21cm observations might be able to place constraints on the dark sector.
Pablo Fosalba
Cosmology with EuclidJuan Garcia-Bellido
Cosmic Acceleration from First PrinciplesRuth Gregory
Slow Roll & Black HolesElisa Maggio
Testing the horizon of black holes with gravitational wavesGravitational waves open the possibility of investigating the nature of compact objects and probing the existence of horizons in black holes. This is particularly interesting given some quantum-gravity models that predict the presence of horizonless and singularity-free compact objects. Such exotic compact objects can emit a different gravitational wave signal relative to the black hole case. In this talk, I will discuss the imprints of horizonless compact objects in the inspiral and ringdown stages, focusing on the deviations from the black hole's tidal Love numbers and quasinormal mode spectrum.
Daan Meerburg
Cosmology from Non-Gaussian fieldsIn this talk I will discuss several challenges towards detecting primordial non-Gaussianties. With the CMB running out of modes, we have started focussing on large scale structure. Measurements of the 21cm brightness temperature allow us to observe almost our entire past light cone. Based on comoving volume arguments, the epoch starting during the dark ages and ending the epoch of reionzation (EoR) potentially contain a lot of modes. Besides being hard to detect, even at these high redshifts, when modes were more linear, I will argue both signal confusion and non-Gaussian covariance have to be considered. During the EoR, the tracer field is very non-Gaussian and standard summary statistics might no longer suffice. I will discuss how machine learning could help solving some of these challenges, while also benefiting efforts to understand astrophysical evolution during these epochs. Finally, ML applications in cosmology are rapidly developing. I will discuss an example of directly inferring primordial non-Gaussianity from a CMB map, but stress to apply common sense when analysing results.
Scott Melville
Cosmological Collider PhysicsThe early inflationary Universe is the ideal high-energy, high-curvature environment in which to search for new fundamental physics. The strong gravitational fields (rapid spacetime expansion) can create particles from the vacuum with masses far beyond the reach of terrestrial colliders. The goal of cosmological collider physics is to translate signals that could be measured by upcoming sky surveys (e.g. of primordial non-Gaussianity) into concrete properties of these particles produced during inflation and how their quantum fields interact with gravity. This talk will give an overview of the recent progress in this direction, and in particular how particle physics techniques from Minkowski spacetime are being applied in cosmological (quasi-de Sitter) spacetimes.
Eva-Maria Mueller
Primordial non-Gaussianities from eBOSS: lessons learned and challenges aheadMy talk will focus on the results of Mueller et al. 2021 "The clustering of galaxies in the completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Primordial non-Gaussianity in Fourier Space" (https://arxiv.org/abs/2106.13725).
Seshadri Nadathur
DESI 2024: Cosmological results from Baryon Acoustic OscillationsI will present a summary of the measurements of Baryon Acoustic Oscillations in the data release 1 (DR1) of the Dark Energy Spectroscopic Instrument (DESI) and the cosmological constraints that can be derived from these. DESI BAO provide robust measurements of the transverse comoving distance and Hubble rate, relative to the sound horizon, using over 6 million extragalactic objects in seven redshift bins, over the redshift range 0.1<z<4.2, and increasing the previous largest such dataset by a factor of 3. Within a flat Lambda cold dark matter (LCDM) background model, these results are consistent with those from the CMB. In combination with external priors, we measure the Hubble constant H0 to 1% precision or better. We derive an upper limit on the sum of the neutrino masses of Mν < 0.072 eV (95% confidence) – I will explain how this limit depends on priors and assumptions about the background expansion. Most interestingly, we find tentative evidence for the dark energy equation of state varying with time from the combination of DESI BAO, CMB and type Ia supernovae – these joint constraints reject the cosmological constant LCDM model with significances of between 2.5 and 3.9 sigma, depending on the dataset used.
Johannes Noller
Testing cosmology with gravitational wavesThe gravitational waves we currently observe probe energy scales around 20 orders of magnitude larger than those corresponding to cosmology today. I will discuss challenges this implies for using gravitational wave observations to probe cosmological physics, but also how we can use techniques traditionally at home in particle physics to better understand how and when we can extrapolate and transport constraints across those scales. I will especially focus on showing how powerful constraints on (and novel insights into) the nature of dark energy can be obtained in this way. In doing so I will discuss bounds from a variety of systems, including gravitational wave dispersion, black hole ringdown and theoretical bounds from supermassive black hole mergers.
Fernando Quevedo
Quantum Transitions and the String LandscapeKai Schmitz
Evidence for a gravitational-wave background at nanohertz frequenciesPulsar timing arrays (PTAs) are gravitational-wave (GW) detectors of galactic dimensions that search for GWs with light-year wavelength washing through the Milky Way by monitoring arrays of pulsars, highly magnetized fast-spinning neutron stars that act like cosmic lighthouses, over time spans of years and decades. In this overview talk, I will review the 2023 results from PTA collaborations around the globe, which point to the existence of a GW background (GWB) hum permeating our Universe. Indeed, the tell-tale sign of a stochastic GWB signal is a characteristic cross-correlation pattern in the timing data for pairs of pulsars, the so-called Hellings-Downs curve, which is now seen for the first time at different levels of statistical significance in the latest PTA data sets. I will discuss the most likely explanation of this signal, namely, a cosmic population of inspiraling supermassive black-holes binaries at the centers of galaxies, but also highlight exotic sources powered by new particle physics in the early Universe, such as cosmic inflation, phase transitions, and cosmic strings. Finally, I will conclude with a brief outlook on the future of the field, in particular, upcoming measurements that may help in discriminating between a GWB signal of astrophysical origin and a GWB signal from the Big Bang.
Gianmassimo Tasinato
Primordial gravitational waves and their detection with gravitational wave experimentsMasahide Yamaguchi
Is the Coleman de Luccia action minimum?: AdS/CFT approachWe use the anti-de Sitter/conformal field theory (AdS/CFT) correspondence to find the least bounce action in an AdS false vacuum state, i.e., the most probable decay process of the metastable AdS vacuum within the Euclidean formalism by Callan and Coleman. It was shown that the O(4) symmetric bounce solution leads to the action minimum in the absence of gravity, but it is non-trivial in the presence of gravity. The AdS/CFT duality is used to evade the difficulties particular to a metastable gravitational system. To this end, we show that the Fubini bounce solution in CFT, corresponding to the Coleman de Luccia (CdL) bounce in AdS, gives the least action among all finite bounce solutions in a conformal scalar field theory. Thus, we prove that the CdL action is the least action among all possible large and thin-wall configurations under certain conditions.
Contributed Talks
Kymani Armstrong-Williams
The Double Copy: A Duality for Particles and GravityAn open problem in theoretical physics is to combine all four of the fundamental forces of nature into one single theory. Problematically, gravity has proven difficult to reconcile with the other forces. Recently, relationships between scattering amplitudes (the quantity related to the probability for an interaction to occur between two or more particles) in non-abelian gauge theories (such as the theory of quarks and gluons) and theories of quantum gravity have led to the discovery of a relation known as the double copy. First observed in string theory, the double copy relates scattering amplitudes in quantum gravity to their counterparts for those in non-abelian gauge theories. This property has been extended to relate solutions in classical electromagnetism with those in general relativity, via a theory known as the classical double copy. As a tool, the double copy has been invaluable for deriving results in gravity, that otherwise would be harder or impossible to do from first principles.
Zakaria Belkhadria
Scalarized Black Hole Solutions in Modified TheoriesThis presentation delves into the study of 'hairy' black holes within the framework of Einstein scalar Maxwell gravity and Einstein scalar Gauss-Bonnet theories, with a focus on revealing new scalarized black hole solutions. We revisit established scalarization phenomena and venture into new solution territories, particularly highlighting the blend of linear and non-linear scalarization in Einstein Scalar Maxwell gravity. Our goal also includes the identification of new scalarized black hole solutions in Gauss-Bonnet theory with a Maxwell field, while outlining their observational significance. Our approach leverages numerical techniques to scrutinize asymptotically flat, spontaneous, and non-linear scalarized black holes in the Einstein-Maxwell-Scalar model, with a keen emphasis on the horizon radii and scalar field intensities. We culminate with an analysis of how scalarization sources shape the horizon area. Our research enhances the comprehension of black hole scalarization and paves the way for continued investigation in this exciting field.
Sebastian Bocquet
Cosmology from the Abundance of SPT Clusters with DES and HST Weak LensingThe abundance of massive halos (and of the galaxy clusters they host) has long been recognized as a promising probe of the large-scale structure of the universe. Over the past decade, tremendous progress was made, notably thanks to the availability of high-resolution surveys of the cosmic microwave background (CMB) and of the X-ray sky, of high-quality measurements of gravitational lensing, and of advanced numerical simulations. The sample of galaxy clusters selected by the South Pole Telescope (SPT) in the CMB now exceeds a thousand objects. The Dark Energy Survey (DES) allows for measurements of gravitational lensing for almost 700 sample clusters with exquisit control over systematic uncertainties. We supplement this dataset with 39 lensing measurements of high-redshift clusters with the Hubble Space Telescope (HST). The joint analysis of the cluster abundance and weak-lensing mass calibration provides tight cosmological constraints that are competitive with other major probes. In my talk, I will review the SPT cluster cosmology and mass calibration program. I will focus on the latest SPT + DES Y3 + HST analysis and present the resulting cosmological constraints. I will highlight upcoming opportunities for multi-observatory, multi-wavelength studies of clusters and the large-scale structure.
Molly Burkmar
Non-Singular Cosmology from Non-Linear Dark EnergyThe Standard Model of Cosmology provides a successful framework for the history of our Universe, however there are problems which require addressing. A key problem is that singularities arise at high energies, and their current interpretation is that they represent points where General Relativity (GR) breaks down. Therefore, it is worth considering an alternative to the 'Big Bang' as the origin story of the Universe. Bouncing and emergent cosmologies provide a way to evade this singularity and can be produced by a dynamic dark energy within GR , however dark matter and radiation need to be included in the set-up to be able to describe a realistic scenario. In this talk, I will first present the dynamics of non-singular models produced by a dark energy which evolves between two cosmological constants, showing the effect of including non-interacting dark matter and radiation, and explain the caveats to these models. I will then present the dynamics when a non-gravitational interaction term is included between the dark components. In general all models are non-singular: flat and open models are past asymptotic to a de Sitter state, whilst for a subset of closed models this de Sitter state is a transition phase through a bounce.
Ryan Camilleri
Investigating beyond ΛCDM using the state-of-art supernova sample from the Dark Energy SurveyType Ia Supernovae act as standard candles which provide a fundamental way to probe the expansion history of the Universe. While the standard cosmological model fits current data well, uncertainty remains. This uncertainty has led to a wealth of exotic cosmological models being proposed. In my work, I constrain a variety non-standard models using the DES 5-year sample - the largest single sample of SNe Ia to date. In this talk, I will present these results. I will also discuss cosmological assumptions that appear in the main DES supernova cosmology analyses, evaluate their impact, and provide guidance on when the DES Hubble diagram can be used to test non-standard models.
Priyesh Chakraborty
de Sitter as an Axion DetectorAxions, scalar fields with compact field spaces, are some of the most well-motivated candidates for physics beyond the Standard Model. In this talk, I will explain how inflationary correlations are uniquely sensitive to the topology of a scalar's field space, and can thus be used to distinguish axions from other light scalar fields even if they share the exact same action. As a proof of concept, I will show that axions can have a qualitatively distinct impact on a heavy field's cosmological collider signal. The talk will be based on arxiv: 2311.09219 and arxiv: 2310.01494.
Daniel del Corral Martínez
Self-resonance during preheating in alpha-attractor modelsThe purpose of this talk is to explain the amplification of curvature perturbations at small scales due to the effect of self-resonance. By making a series expansion of the inflationary potential and solving perturbatively for the inflaton field, we transform the Mukhanov-Sasaki equation into a Hill equation and give expressions for the Floquet exponents for a potential with both cubic and quartic terms in its expansion. We then compare with full numerical computations and propose some applications.
Steve Cunnington
Launching the ultra-large-scale era with radio intensity mappingMeasuring fluctuations spanning "ultra-large" scales (≳100Mpc/h) in cosmic large-scale structure is a route to access more linear modes as well as probe primordial non-Gaussianity and relativistic effects. Wide-sky surveys with radio telescopes such as the Square Kilometre Array Observatory (SKAO) have the potential to lead the way in probing the largest scales in the late Universe. This will be achieved by surveying diffuse 21cm emission from extragalactic neutral hydrogen (HI), a technique known as HI intensity mapping. This will be a primary aim for the future SKAO once constructed. However, the 64-dish precursor, MeerKAT, is already providing surveys that will grow into competitive spectroscopic volumes (∼10,000 square degrees, 0.4 < z < 1.45) over the next few years. I will present the first detection of cosmological signal using HI intensity mapping with a multi-dish array. This detection using MeerKAT validates the "single-dish" intensity mapping technique, which the full SKAO will rely on to probe ultra-large scales. I will also present encouraging results that demonstrate growing confidence in handling systematics, often associated with a novel technique of this kind. These results mark important milestones in the roadmap for the cosmology science case with the full SKAO.
Konstantinos Dimopoulos
How an oscillating inflaton produces enhanced gravitational radiationTwo classes of inflationary models are presented, which lead to a stiff period after inflation that boosts the signal of primordial gravitational waves (GWs). In both families of models studied, we consider an oscillating scalar condensate, which when far away from the minimum it is overdamped by a warped kinetic term, a la α-attractors. This leads to successful inflation. Carefully avoiding the danger of the oscillating condensate becoming fragmented by resonant effects, we study when a boosted GW spectrum is obtained, that overlaps with future observations without generating too much GW radiation to de-stabilise Big Bang Nucleosynthesis. Our mechanism ends up with a characteristic GW spectrum, which if observed, can lead to the determination of the inflation energy scale, the reheating temperature and the steepness of the scalar potential around its minimum.
Carlos Duaso Pueyo
A Cosmological Bootstrap for Resonant Non-GaussianityThe cosmological bootstrap is an approach to directly fix inflationary primordial correlators from symmetries and first principles, bypassing the usual in-in computation. Approximate scale invariance has always been an important ingredient of the bootstrap, but now we have shown that it is possible to relax this restriction if one retains a discrete scaling subgroup. As a result, we have found an infinite class of solutions to the weaker bootstrap constraints and have shown that they reproduce and extend resonant non-Gaussianity, which arises in well-motivated models such as axion monodromy inflation. On the practical side, these templates will be useful for the search of oscillatory features in the inflationary dynamics. On the conceptual side, we hope that our work opens the path towards extending the cosmological bootstrap to more general theories of inflation.
Steffen Gielen
Unitary unimodular gravity and singularity resolutionOne might hope that gravitational singularities in cosmology and black holes are resolved in a quantum theory of gravity, but there is no consensus on how exactly this happens and what assumptions such a mechanism would rely on. Here I will discuss the close connection between unitarity of quantum evolution in a preferred time coordinate (the one used in unimodular gravity) and an apparently generic mechanism of resolving cosmological singularities. I will also show prospects on extending the arguments to black holes.
Rafaela Gsponer
Early Dark Energy in the light of large scale structure dataEarly dark energy (EDE) is a dark-energy-like component active in the early stages of the universe and is one of many proposed ways of resolving the Hubble tension. Up to now, it is not agreed upon if EDE can solve the Hubble tension whilst fitting the cosmic microwave background and large-scale structure simultaneously or not. In this talk, I will review the status of EDE, describing the challenges that this model has to overcome. I will discuss my recent work on using an effective field theory-based approach for the full shape analysis of the galaxy power spectrum and how including higher redshift large-scale structure data, as eBOSS and DESI, can constrain the validity of EDE as a solution to the Hubble tension.
Charlie Hoy
Revisiting the cosmic string origin of GW190521For the first time we analyse gravitational-wave strain data using waveforms constructed from strong gravity simulations of cosmic string loops collapsing to Schwarzschild black holes; a previously unconsidered source. Since the expected signal is dominated by a black-hole ringdown, it can mimic the observed gravitational waves from high-mass binary black hole mergers at current detector sensitivities. By analysing GW190521, a short duration gravitational-wave event observed in the third LIGO-Virgo-KAGRA observing run, we show that a direct detection of collapsing cosmic strings with gravitational-waves may be possible with greater sensitivity; we show that describing GW190521 as a collapsing cosmic string loop is favoured over previous cosmic string analyses by an approximate log Bayes factor of 22. Future gravitational-wave detectors that target lower frequencies will help distinguish between high mass binary black holes and collapsing cosmic strings, highlighting the potential for discovering signatures of new physics.
Joseph Jackson
The separate-universe approach and sudden transitions during inflationThe separate-universe approach gives an intuitive way to understand the evolution of cosmological perturbations in the long-wavelength limit. It uses solutions of the spatially-homogeneous equations of motion to model the evolution of the inhomogeneous universe on large scales. We show that the separate-universe approach fails on a finite range of super-Hubble scales at a sudden transition from slow roll to ultra-slow roll during inflation in the very early universe. Such transitions are a feature of inflation models giving a large enhancement in the primordial power spectrum on small scales, necessary to produce primordial black holes after inflation. We show that the separate-universe approach still works in a piece-wise fashion, before and after the transition, but spatial gradients on finite scales require a discontinuity in the homogeneous solution at the transition. We discuss the implications for the δN formalism and stochastic inflation, which employ the separate-universe approximation.
Alex Jenkins
Cold-atom analogues for vacuum decayFalse vacuum decay plays a vital role in many models of the early Universe. However, we lack a satisfying theoretical understanding of this process, with existing approaches working only in imaginary (Euclidean) time, and relying on crucial assumptions that have yet to be empirically tested. An exciting route forward is to use cold-atom systems which undergo first-order phase transitions that are analogous to vacuum decay. In this talk, I will present recent theoretical work to understand this analogy using semiclassical lattice simulations, and will discuss possibilities and challenges for realising these analogues in the laboratory.
Konstantin Leyde
Galaxy reconstruction for gravitational wave cosmologyCompact binary coalescences that are observed through gravitational waves (GWs) provide an independent method to constrain the current expansion rate of the Universe, the Hubble constant, H0. In addition to the information on the luminosity distance that is directly provided from the GW, redshift information is also needed for the H0 measurement. All GW events observed thus far (with the exception of the binary neutron star merger GW170817) do not have electromagnetic counterparts, and other methods are needed to provide this redshift information. One method uses galaxy catalogs, attributing a probability to each galaxy in the catalog of having hosted the GW event. From this, one can use the redshift of the galaxies to calculate H0 for each GW event and then combine the result in a hierarchical way to measure H0 from all GW sources. However, currently publicly available galaxy catalogs are incomplete at the distances of most GW events and hence provide little information on the redshift. In this talk, I will describe a Bayesian approach on how to complete these galaxy catalogs, consistent with the dark matter density being described by a Gaussian random field. We validate our method with the Millennium simulations and show that we can accurately recover the number of galaxies in each 3D pixel. I will summarize important parameters that, in addition to the power spectrum that describes the dark matter density, strongly impact the final reconstructed catalog and that we have to marginalize over. Finally, I will identify current computational limitations to this approach.
Ameek Malhotra
Measuring kinematic anisotropies with pulsar timing arraysRecent Pulsar Timing Array (PTA) collaborations show strong evidence for a stochastic gravitational wave background (SGWB) of unknown origin with the characteristic Hellings-Downs inter-pulsar correlations. In case the observed SGWB is of early-universe origin, our relative motion with respect to the SGWB rest frame is a guaranteed source of anisotropy, leading to order 10-3 energy density fluctuations of the SGWB. These kinematic anisotropies are likely to be larger than the intrinsic anisotropies, akin to the cosmic microwave background (CMB) dipole anisotropy. We assess the sensitivity of current PTA data to the kinematic dipole anisotropy and also provide forecasts with which the magnitude and direction of the kinematic dipole may be measured in the future with an SKA-like experiment. We also discuss how the spectral shape of the SGWB and the location of pulsar observed affects the prospects of detecting the kinematic dipole with PTA. A detection of this anisotropy may provide clues to the origin of the SGWB and possibly shed light on the discrepancy in the magnitude of the kinematic dipole as measured by CMB and LSS observations.
Swagat Saurav Mishra
Towards the origin of matter in the universe: Inflaton fragmentation, Oscillon formation and decayThe transition epoch between the end of inflation and the beginning of thermal radiation domination, known as 'reheating', remains as one of the fundamental open problems in Cosmology. During the earliest stages of reheating, the oscillating inflaton condensate is supposed to decay non-perturbatively (via parametric resonance) into other lighter bosonic degrees of freedom that are coupled to the inflaton. This period is termed as 'preheating'. However, if the external couplings of the inflaton are weak enough, then the homogeneous inflaton condensate might get fragmented by strong attractive self-interactions to form quasi-stable solitonic objects, known as 'oscillons'. The speaker will discuss the possibility of oscillon formation during the preheating phase of asymptotically flat inflationary potentials that are favoured by CMB observations. A detailed numerical analysis was performed to study the post-inflationary dynamics of asymptotically flat potentials using the publicly available lattice simulation code 'CosmoLattice' for the relevant parameter range. Oscillons were found to be present for the entirety of the runtime of our simulations, comprising more than 40% of the total energy density. The speaker will also provide a discussion on the formation and decay of oscillons in presence of an external coupling. The talk will conclude with an emphasis upon the novel possibility that primordial matter in the universe could have originated from the decay of these solitonic objects.
Emanuele Panella
Can a stochastic cosmology mimic Lambda and CDM?A key prediction of consistent theories of classical gravity coupled to quantum matter is that the metric has to evolve stochastically. Motivated by these considerations, we study a stochastic Einstein-de Sitter Universe, in order to explore whether a random source in Einstein's equations can reproduce the phenomenology of Λ. We find two interesting effects. At early times, we argue that violation of the Hamiltonian constraint of GR manifests itself as phantom extra matter, possibly playing the role of cold dark matter in structure formation. At late times, instead, we show that diffusion away from Friedmann equations mimics qualitatively the redshift-luminosity distance curves of ΛCDM universes with non-zero cosmological constant. To test the latter observation quantitatively, we conclude by placing bounds on the diffusion coefficient using supernovae data from the Pantheon+ and SH0ES datasets. In particular, we show that, in this simple toy model, the hypothesis of an effective cosmological constant coming entirely from stochasticity in the evolution of the scale factor is strongly disfavoured with respect to ΛCDM models. The tension can be relaxed by introducing a non-zero Λ in the equations of motion directly, representing either a bare cosmological constant or an effective one arising from unrelated phenomena.
Raphael Picard
Induced gravitational waves: the effect of first order tensor perturbationsGravitational waves provide a new observational tool to study the universe. Second-order cosmological perturbation theory allows to study gravitational waves sourced by terms quadratic in first order quantities. For example, so-called scalar induced gravitational waves are sourced by first order scalar fluctuations and have been studied extensively. In this presentation I discuss the implications and possibilities of including tensor fluctuations at first order in the source term. I will show how the first order tensor fluctuations change the spectral energy density of the induced waves, particularly on small scales, and will discuss implications for their detectability and observational constraints for models of inflation.
Agustín Silva
Emergence of inflaton potential from asymptotically safe gravityAsymptotic safety is a powerful mechanism for obtaining a consistent and predictive quantum field theory beyond the realm of perturbation theory. It hinges on an interacting fixed point of the Wilsonian renormalization group flow, which controls the microscopic dynamics. Connecting the fixed point to observations requires constructing the set of effective actions compatible with this microscopic dynamics. Technically, this information is stored in the UV-critical surface of the fixed point. In this talk, I will describe a novel approach for extracting this information based on analytical and pseudo-spectral methods. I will illustrate the methods at the level of a four-dimensional scalar-tensor theory. As a result of applying these techniques, I will show how single-field inflationary models, compatible with observations, naturally emerge from a gravitational UV fixed point. The talk is based on arXiv:2403.08541.
Enrico Specogna
Breaking Planck's Lensing Anomaly: A Parametric ApproachParametrising the growth of large scale structure is a powerful tool; it allows us to detect deviations from the Standard Model of cosmology - SM in a general way, without making limiting assumptions about their fundamental nature. We present a series of analyses carried on two such parametrisations: the growth index - 'γ', a modification of the growth of linear perturbations in the SM, and the 'μ0−Σ0' framework, a modification of the Poisson and lensing equations from General Relativity - GR. Planck's 2018 analysis has shown a 2σ evidence of Modified Gravity - MG (i.e., non-zero μ0 and Σ0), while other CMB experiments such as ACT and SPT showed consistency with GR. We asked if this evidence for MG could stand the test of alternative approaches to analyse Planck's data. We did not find this to be the case; the usage of the HiLLiPoP likelihood on Planck's data does not reveal any deviation from the SM, suggesting that Planck's lensing anomaly could plausibly explain its MG detection.
Eemeli Tomberg
Compaction function profiles from stochastic inflationPrimordial black holes can arise from quantum fluctuations produced during cosmic inflation. Stochastic inflation is a method to compute the fluctuation statistics non-perturbatively, including non-Gaussianities. I discuss recent progress in the numerical implementation of the method, allowing us to compute the radial dependence of the fluctuations' compaction function in random patches of space. These compaction function profiles are needed for accurate black hole predictions. Using example models of ultra-slow-roll inflation, I discuss the spiky, stochastic nature of the profiles, their dependence on the curvature power spectrum, and the implications for the abundance and mass distribution of primordial black holes.
Chen Yuan
Probing Primordial Black Holes through Gravitational WavesA subsolar gravitational wave (GW) event was reported recently in the second part of the third observation run by the LIGO-Virgo-KAGRA collaboration. This event denoted SSM200308, was found to have mass components in the sub-solar mass range. We explore the possibility that primordial black holes (PBHs), resulting from the collapse of Gaussian perturbations, could explain the SSM200308 event. By performing Bayesian parameter estimation, we found that the PBH merger rate can fit the data if PBHs constitute a few thousandth of the dark matter. However, we further investigated the GWs associated with PBHs. We found that, although the GW background from binary PBHs is consistent with current observational constraints, the scalar- induced GWs accompanied by the formation of these PBHs would contradict the pulsar timing array constraints, rendering PBHs generated from the collapse of Gaussian perturbations may not explain the origin of SSM200308.
Where to get lunch
University Cafes
Portland Cafe, Ground floor, Portland Building
The Hub, Dennis Sciama Building, PO1 3FX. (Hot food and sandwiches)
Nearby Cafes and Sandwich Shops
Cafe In The Park, Victoria Park, PO1 3HJ (Sandwiches and cakes)
John Pounds Centre Cafe, Queen Street, PO1 3HN (Sandwiches and light meals)
Subway, Queen Street, PO1 3HY (Subs)
Pret A Manger, Gunwharf Quays PO1 3TZ (Sandwiches, salads)
Cornish Bakery, Gunwharf Quays PO1 3TG (Pastries)
Caffe Nero, Gunwharf Quays, PO1 3BF (Coffee, pastries, sandwiches)
Convenience Stores
Tesco Express, Gunwharf Quays, PO1 3SF
Co-op, Queen Street, PO1 3HY
Informal Welcome
Gather at the Brewhouse Southsea for informal drinks between 6pm and 8pm on Sunday 19th May.
Fun Quiz Night
Networking event at The Old Customs House, 7pm. Early Career Researchers are especially encouraged to attend.
Conference Dinner
The conference dinner will be held at The Cosy Club on Wednesday 22nd May. Drinks (prosecco or pink lemonade) will be served at 7pm for dinner at 7:30pm. The menu is available here. Please note that sides cost extra and there is a supplement for steak, which must be paid for at the time of ordering. Wine and lemonade will be provided, but any additional drinks will need to be paid for.
Poster
Download a poster for the conference here.
Social Events