Jan 24  Wed  Matteo Forconi (Rome)  Cosmology, Relativity and Gravitation  
15:00  JWST’s Revelations and the SuperLCDM’s Promise  
Hicks Seminar Room J11  
Abstract: The recent observations by the James Webb Space Telescope (JWST) of massive galaxies at high redshifts (z ∼ 10) significantly challenge the Lambda Cold Dark Matter (ΛCDM) cosmological model. These observations suggest a higher stellar mass density than previously predicted, and raise questions about galaxy formation and matter distribution in the early universe. To reconcile these findings with standard predictions, an investigation one can look into potential systematics. If systematic errors are ruled out, one might also wonder whether this new anomaly is somehow originated from the same underlying issue as the Hubble tension, suggesting the need for a beyondΛCDM phenomenological explanation. One potential avenue is exploring the Dark Energy Sector. Another challenge to the standard ΛCDM model arises from allowing nonGaussian fluctuations. Using the super sample signal, it is possible to promote the standard ΛCDM model to a more comprehensive SuperΛCDM model. This model allows to study nonGaussianity traces using only the power spectrum. The implications of this model extend to the field of neutrino physics, indicating that the traditional constraints on neutrino masses might need revision. 



Jan 31  Wed  Sebastian Schuster (Sheffield)  Cosmology, Relativity and Gravitation  
15:00  What's Physical? A SpaceTime Koan  
Hicks Seminar Room J11  
Abstract: Evaluating the physicality of a given spacetime can prove difficult. Often, this is relegated to easytocheck concepts: Absence of closed, timelike curves (vulgo: no time travel); validity of energy conditions (vulgo: mass/energy should be positive); geodesic completeness (vulgo: we shan't disappear); the related holefreeness (vulgo: again, we shan't disappear); and more. The problem is that these are not necessarily mutually compatible with each other. Worse, as in the case of energy conditions, not all such concepts are either easy to justify or even fulfilled in known, physical situations. This talk will serve two purposes. The first is to make everyone queasy about the pushmepullyou nature of physicality, as this allows us to critically examine which type of physicality may be more or less important in any given situation. Here, reverseengineered metrics like warp drives and tractor beams will be in the spotlight. The second is to hone in on one particularly befuddling concept: Time travel. Fascinating as it is, in general relativity the spacetime will either contain it or not. General relativity cannot explain why it might be there, or whether the confusion and contractions arising from it are due to the concept itself or from being in the wrong physical framework. Many arguments have to, at some point, wave their hands and allude to an unknown theory beyond it. To actually make this step beyond general relativity, I will present a very simple, quantum toy model of time travel with an emergent notion of time. While this first toy model will turn out to be not particularly illuminating, it still serves as a good starting point for more complicated toy models with richer structure. 



Feb 7  Wed  Luca Marchetti (New Brunswick)  Cosmology, Relativity and Gravitation  
16:00  Scalar cosmological perturbations from quantumgravitational entanglement  
Hicks Seminar Room J11  
Abstract: A major challenge at the interface between quantum gravity and cosmology is to understand how cosmological structures can emerge from physics at the Planck scale. In this talk, I will discuss the main challenges associated with the understanding of such an emergence process and provide a concrete example of how they can be addressed by extracting the physics of scalar and isotropic cosmological perturbations from full quantum gravity, as described by a causally complete BarrettCrane group field theory model. From the perspective of the underlying quantum gravity theory, cosmological perturbations will be associated with (relational) nearestneighbor twobody entanglement, providing crucial insights into the potentially purely quantumgravitational nature of cosmological perturbations. I will also show that at low energies the emergent relational dynamics of these perturbations are perfectly consistent with those of general relativity, while at transPlanckian scales quantum effects become important. Finally, I will comment on the implications of these quantum effects for the physics of the early universe and outline future research directions. 



Feb 15  Thu  Cora Uhlemann (Newcastle)  Cosmology, Relativity and Gravitation  
11:00  Making dark matter waves  the cosmic web and wavelike dark matter  
Hicks Seminar Room J11  
Abstract: Despite the astonishing success of cosmological probes in constraining the LCDM model, the dark matter mass remains one of the least constrained physical parameters. Wavelike dark matter is an intriguing alternative to standard cold dark matter with key particle physics motivations (like the QCD axion or ultralight axionlike particles) and distinct astrophysical signatures. With a simple dynamical model for the evolution of the dark matter wavefunction, I will demonstrate how to predict the formation of destructive and constructive wave interference leading to topological defects and granules dressing the cosmic web of largescale structure. Our wavebased formalism is a versatile tool to describe the complex phasespace dynamics of cold dark matter in position space; and the fundamental description for wavelike dark matter such as ultralight particles, leading to exciting and varied probing mechanisms bridging cosmology and astroparticle physics. 



Feb 21  Wed  João Paulo M Pitelli (Campinas State)  Cosmology, Relativity and Gravitation  
15:00  Thermal effects on a global monopole with Robin boundary conditions  
Hicks Seminar Room J11  
Abstract: The quantum theory of a scalar field propagating on a spacetime with a naked singularity is not determined until we specify a boundary condition at the boundary. When this choice is not unique, any physical observable will depend on the particular choice of boundary condition. In this work we illustrate this explicit dependence by analyzing the transition rate of an UnruhDeWitt detector coupled to a thermal state in the singular scenario of a global monopole. We show that the naked singularity manifests thermal effects with a nontrivial behavior with respect to the admissible boundary conditions. In particular, we show that the transition rate is finite at the singularity only for the Dirichlet boundary condition and that the divergence for the other possible (Robin) boundary conditions is consistent with the divergence of the thermal fluctuations. 



Mar 6  Wed  William Giare (Sheffield)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Mar 8  Fri  Stefano Gariazzo (IFT Madrid)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Mar 13  Wed  Eemeli Tomberg (Lancaster)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Mar 20  Wed  Aindriú Conroy (Charles U Prague)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Apr 17  Wed  Adrià Gómez Valent (Barcelona)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Apr 24  Wed  Elsa Teixeira (Montpellier)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


Apr 26  Fri  Thomas Montandon (Montpellier)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


May 1  Wed  Suddhasattwa Brahma (Edinburgh)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


May 8  Wed  Gabriele Barca (Rome/Sheffield)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  


May 22  Wed  Eleonora Di Valentino (Sheffield)  Cosmology, Relativity and Gravitation  
15:00  
Hicks Seminar Room J11  

