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Overview

Theo Murphy meeting organised by Dr Steffen Gielen and Dr Jean-Luc Lehners.

Quantum theory describes the behaviour of matter, but was it in fact also instrumental in explaining the structure of space and time? This meeting will discuss how the quantum properties of spacetime can change our understanding of the foundations of cosmology, and how their impact could be tested observationally in the near future.

Attending this event

This meeting is intended for researchers in relevant fields. This will be a residential meeting held at Sedgebrook Hall, Northampton, NN6 8BD.

  • Free to attend
  • Limited places, advance registration essential

  • This is an in-person meeting only

  • Meals during the meeting can be paid for through Eventbrite (lunches on both days of the meeting and dinner on the first night)
  • Participants will need to book their own accommodation with Sedgebrook Hall.

Enquiries: contact the Scientific Programmes team

Image credit: NASA/ESA and Jean-Luc Lehners.

Organisers

Schedule

09:05-09:30
Title of the talk will be available soon.

Abstract

Abstract of the talk will be available soon.

09:30-09:45
Discussion
09:45-10:15
Primordial black holes as a probe of quantum gravity and higher dimensions

Abstract

Primordial black holes (PBHs) may have formed in the early universe and provide an important link between microphysics and macrophysics. In the macroscopic context, it has been proposed that PBHs larger than 1015g could explain various cosmological conundra: the existence of dark matter, the cosmic photon-to-baryon ratio, unexplained microlensing events, some of the LIGO/Virgo/KAGRA gravitational wave events, the puzzling early formation of certain cosmic structures, and the existence of supermassive black holes in galactic nuclei. Since PBHs form from quantum fluctuations in the early universe, this provides an indirect probe of quantum spacetime. In the microscopic context, the existence of Hawking radiation provides a direct probe of quantum spacetime and offers a unification of relativity theory, quantum mechanics and thermodynamics. However, only PBHs could be small enough for such radiation to be detectable and only those smaller than 1015g would have evaporated completely by now. Finally, black holes of 10-5g may provide a probe of higher dimensions, a possible link between elementary particles and black holes, and quantum gravity itself.

Speakers

10:20-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Gravitational signatures of warped throats

Abstract

Warped compactifications provide a rich arena to explore phenomenological and cosmological questions such as the hierarchy problem, cosmological inflation, dark energy and dark matter. In this talk, Dr Ivonne Zavala Carrasco will discuss gravitational signatures arising from compactifying type IIB string theory on a compact space containing a warped  throat. She will focus on the gravitational sector of the resulting 4d EFT, with its tower of Kaluza-Klein (KK) gravitons. By assuming that we live on a (3+1)-dimensional brane within the throat, the author will discuss how the Newtonian potential is modified, and how these modifications can be tested by gravitational experiments. She will then discuss  how the extra massive KK gravitons in warped throats affect gravitational wave signals and its possible tests at current and future gravitational wave experiments.

Speakers

11:30-11:45
Discussion
11:45-12:15
Non-equilibrium quantum dynamics in cosmology

Abstract

Dr Brahma will discuss inflation as an open quantum system and derive quantum corrections to cosmological observables, such as the power spectrum, showing explicitly why it is important to go beyond standard (Wilsonian) effective field theory. He will highlight deep insights this approach provides regarding quantum entanglement in the early universe and emphasize the features which apply to other gravitational systems.

Speakers

12:15-12:30
Discussion
12:20-13:20
Lunch

13:30-14:00
Quantum gravity here and now, and at the end of the world

Abstract

Professor João Magueijo will review a recent approach to connecting quantum gravity and the real world by deconstantizing the constants of nature, and using their conjugate as a time variable. This is nothing but a generalization of unimodular gravity. The wave functions are then packets of plane waves moving in a space that generalizes the Chern-Simons functional. For appropriate states they link up with classical cosmology in the appropriate limit. There are however deviations, namely during the matter to Lambda transition, raising the possibility that quantum gravity could be in action here and now. At the other extreme Professor Magueijo will show how this approach can be used to resolve the cosmological singularity, and perhaps more.

Speakers

14:00-14:15
Discussion
14:15-14:45
Tensions in cosmology and implications for the standard model

Abstract

The scenario that has been selected as the standard cosmological model is Lambda Cold Dark Matter (ΛCDM), which provides a remarkable fit to the bulk of available cosmological data. However, discrepancies among key cosmological parameters of the model have emerged with different statistical significance. While some portion of these discrepancies may be due to systematic errors, their persistence across probes can indicate a failure of the canonical ΛCDM model. Dr Di Valentino will review these tensions, showing some interesting extended cosmological scenarios that can alleviate them.

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Cosmological implications of the Swampland Program and the Dark Dimension

Abstract

Consistency with quantum gravity can have significant consequences on low energy physics. Not every effective field can be consistently coupled to quantum gravity unless it satisfies some additional consistency constraints, dubbed swampland constraints. In this talk Dr Irene Valenzuela will review the most important swampland conjectures and their implications for cosmology. The best understood constraints imply that theories with very small gauge couplings or parametrically large scalar field variations are inconsistent with quantum gravity. The author will also describe recent progress regarding whether accelerating cosmologies at parametrically large time can be embedded in string theory. Furthermore, she will describe a scenario motivated by the swampland program in which the smallness of the cosmological constant emerges from living near a boundary of the quantum gravity field space. A universal feature of this scenario is that there is a light infinite tower of states which is correlated to the value of the vacuum energy. Dr Valenzuela will show how experimental constraints force this tower to correspond to a KK tower (of mass of order neutrino scale) of a single extra mesoscopic dimension of order 10^{-6) m, which we denote as the dark dimension.

Speakers

16:00-16:15
Discussion
16:15-17:00
Panel discussion/Overview
09:00-09:30
Dr Xingang Chen, Harvard University, USA

Abstract

Abstract of the talk will be available soon.

Speakers

09:30-09:45
Discussion
09:45-10:15
Probing the origin of spacetime by heavy particles

Abstract

Abstract of the talk will be available soon.

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Title of the talk will be available soon.

Abstract

Abstract of the talk will be available soon. 

11:30-11:45
Discussion
11:45-12:15
Quantum origin of spacetime in the era of gravitational astronomy

Abstract

Professor Mairi Sakellariadou will briefly introduce approaches to quantum gravity and summarise some of their phenomenological and observational implications. She will then employ currently available observational data, with emphasis in gravitational waves, in order to test theories aiming at explaining the origin of spacetime.

Speakers

12:15-12:30
Discussion
13:30-14:00
Emergent cosmology from quantum gravity condensates

Abstract

In the group field theory (GFT) framework for quantum gravity, effective cosmological dynamics emerge as the hydrodynamics of simple condensates of quanta of geometry. The quantum equations of motion for these GFT condensate states are given in relational terms with respect to the matter field (here assumed to be a scalar field), and these imply dynamics for the volume of the universe that correspond to modified Friedmann equations, with quantum gravity modifications, in a specific regime of the theory corresponding to a Gross–Pitaevskii approximation where interactions are subdominant. The classical Friedmann equations of general relativity are recovered in a suitable semi-classical limit, while the quantum geometries associated with these GFT condensate states are non-singular: a bounce generically occurs in the Planck regime. For some choices of condensate states, these modified Friedmann equations are very similar to those of loop quantum cosmology.

Speakers

14:00-14:15
Discussion
14:15-14:45
Title of the talk will be available soon.

Abstract

Abstract of the talk will be available soon.

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Title of the talk will be available soon.
16:00-16:15
Discussion
16:15-17:00
Panel discussion/overview

Abstract