UK Cosmo at Cambridge

Session

Scientific Talks

23 May 2023, 10:00

8. Dark Energy (and modified gravity) in two body problem: theoretical implications and observational constraints

23/05/2023, 10:00

General Theory of Relativity needs at least one modification - the Cosmological Constant. Yet there are possibilities for other modified theories of gravity to explain the accelerated expansion. In this talk I'm going to discuss the impact of Modified Gravity on the two-body problem. In particular, with the latest observational constraints from the galactic center and the S-stars, binary...

15. Radiation from Axion Strings with Adaptive Mesh Refinement

23/05/2023, 10:15

Axion strings are topological defects that arise in field theories with a spontaneously broken global symmetry, such as the Peccei-Quinn mechanism in QCD. Axion strings radiate axion particles, whose spectrum depends on the dynamics of the cosmological string network. The complex dynamics of the network make both analytic modelling and numerical simulation challenging, such that an accurate...

20. Growth of structure in regularised 4D Einstein-Gauss-Bonnet

23/05/2023, 10:30

Interest in modified gravity has been rekindled by cosmologists’ attempts to resolve cosmological tensions. For example, it has been suggested that parametrisations of modified structure growth can provide a better fit to large-scale structure data and can alleviate the S8 tension. In this era of precision cosmology we can successfully test these effects for modified gravity theories that so...

4. Cosmology and strong gravity with a subdominant scalar field

23/05/2023, 11:45

We discuss the cosmological evolution of a scalar field in theories motivated by beyond-GR compact object phenomenology, e.g. scalarization. Such theories predict strong-gravity deviations with respect to GR in the vicinity of very compact stars and black holes, but the asymptotic conditions are determined by cosmological arguments. We explore the stability of scalarization models on a...

14. The cosmological constant is probably still zero

23/05/2023, 12:00

We consider a wide class of four-dimensional effective field theories in which gravity is coupled to multiple four-forms and their dual scalar fields, with membrane sources charged under the corresponding three-form potentials. Four-form flux, quantised in units of the membrane charges, generically generates a landscape of vacua with a range of values for the cosmological constant that is...

19. Clockwork Cosmology

23/05/2023, 12:15

The clockwork mechanism has recently been proposed as a means to generate an exponentially suppressed coupling to matter from a fundamental theory of multiple interacting particles without any unnatural parameters. Applied in a gravitational setting within the framework of ghost-free multi-metric gravity, it provides us with a potential solution to the hierarchy problem, by generating a Planck...

6. How to find the Feynman Rules from any scalar-tensor theory and not collapse in the process

23/05/2023, 12:30

The ability to represent perturbative expansions of interacting quantum field theories in terms of simple diagrammatic rules has revolutionized calculations in particle physics. However, in the case of extended theories of gravity, deriving this set of rules requires linearization of gravity, perturbation of the scalar fields, and multiple field redefinitions, making this process very...

10. Spinning primordial black holes in a matter dominated universe

23/05/2023, 13:45

Interest in primordial black holes (PBHs) has spiked since the first detection of gravitational waves, and a few mass windows remain in which PBHs may still make up an appreciable part of dark matter. In a matter dominated universe, e.g. in the case of a first-order QCD phase transition, PBH production is enhanced and PBHs may have large dimensionless spins. We investigate the re-entry and...

13. Can primordial black holes form without fine-tuning?

23/05/2023, 14:00

Primordial black holes (PBHs) may form in the early universe, and could have relevance to cosmic evolution, particularly as a dark matter candidate. Forming PBHs requires increased power on small scales, corresponding to some kind of feature in the inflaton potential. I will present a study of the fine-tuning of PBH formation for four representative inflation models, discussing the different...

2. Primordial black holes and stochastic inflation beyond slow roll

23/05/2023, 14:15

Primordial Black Holes (PBHs) may form in the early universe, from the gravitational collapse of large density perturbations, generated by large quantum fluctuations during inflation. Since PBHs form from rare over-densities, their abundance is sensitive to the tail of the primordial probability distribution function (PDF) of the perturbations. It is therefore important to calculate the full...

11. Multi-field inflation with large scalar fluctuations: non-Gaussianity and perturbativity

23/05/2023, 14:30

Recently multi-field inflation models that can produce large scalar fluctuations on small scales have drawn a lot of attention, primarily because they could lead to primordial black hole production and generation of large second-order gravitational waves. In this talk, we focus on models where the scalar fields responsible for inflation live on a hyperbolic field space, and present new results...

3. Quantum field theory in curved spacetime and the CMB hemispherical power asymmetry

23/05/2023, 14:45

Before we ask what is the theory of quantum gravity, it is a legitimate quest to formulate a robust quantum field theory in curved spacetime (QFTCS). Several conceptual conundrums have been issues of concern over several decades because no S-matrix formulation is yet found in QFTCS. We argue that the institutional thinking of fixing the spacetime geometry, observers, and light cones and then...

16. Unimodular Hartle-Hawking wave packets and their probability interpretation

23/05/2023, 15:00

We re-examine the Hartle-Hawking wave function from the point of view of a quantum theory which starts from the connection representation and allows for off-shell non-constancy of $\Lambda$ (as in unimodular theory), with a concomitant dual relational time variable. By translating its structures to the metric representation we find a non-trivial inner product rendering wave packets of...

21. Impact of a quantum gravity bounce on cosmological perturbations

23/05/2023, 15:15

In this talk we will explore a phenomenological avenue to connect quantum gravity to cosmological perturbations. Namely, we will discuss the impact of a modified Friedmann equation on the evolution of gauge invariant perturbation variables. Such Friedmann equations may arise from quantum gravitational theories such as Loop Quantum Cosmology (LQC) or Group Field Theory (GFT) and in these cases...

18. New Insight on Neutrino Dark Matter Interactions from Small-Scale CMB Observations

23/05/2023, 16:00

In this talk, I will discuss the possibility of using cosmological observations to constrain models that involve interactions between neutrinos and dark matter. I will show that small-scale measurements of the cosmic microwave background with a few per cent accuracy are critical to uncover unique signatures from tiny couplings that would require a much higher sensitivity at lower multipoles,...

1. Modelling of Astrophysical Systematics for Cosmology with LSST

23/05/2023, 16:15

LSST will provide an unprecedented wealth of astronomical data, with which we will be able to tightly constrain the values of the cosmological parameters, notably those which describe the poorly understood dark energy component. As weak lensing and galaxy clustering measurements provide a way to infer key cosmological quantities such as the dark matter distribution, the evolution of cosmic...

12. The Wide–Angle Power Spectrum

23/05/2023, 16:30

We examine the computation of wide-angle corrections to the galaxy power spectrum including redshift-space distortions and relativistic Doppler corrections, and also including multiple tracers with differing clustering, magnification and evolution biases. We show that the inclusion of the relativistic Doppler contribution, as well as radial derivative terms, are crucial for a consistent...

9. The observed number counts in luminosity distance space

23/05/2023, 16:45

Next generation surveys will provide us with an unprecedented number of detections of supernovae Type Ia and gravitational wave merger events. Cross-correlations of such objects offer novel and powerful insights into the large-scale distribution of matter in the universe. Both of these sources carry information on their luminosity distance, but remain uninformative about their redshifts; hence...

5. The angular power spectrum of gravitational-wave transient sources as a probe of the large-scale structure

23/05/2023, 17:00

We present a new, simulation-based inference method to compute the angular power spectrum of the distribution of foreground gravitational-wave transient events. As a first application of this method, we use the binary black hole mergers observed during the LIGO, Virgo, and KAGRA third observation run to test the spatial distribution of these sources. We find no evidence for anisotropy in their...

7. Dictionary Learning: A Novel Approach to Detecting Binary Black Holes in the Presence of Galactic Noise with LISA

23/05/2023, 17:15

The noise produced by the inspiral of millions of white dwarf binaries in the Milky Way may pose a threat to one of the main goals of the space-based LISA mission: the detection of massive black hole binary mergers. We present a novel study for reconstruction of merger waveforms in the presence of Galactic confusion noise using dictionary learning. We discuss the limitations of untangling...