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| Feb 12 |
Wed |
Lei Zu (NCBJ Warsaw) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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Probing Dark Matter Non-gravitational Interactions with Weak Lensing Surveys
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F20 |
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Abstract:
Modern cosmological surveys, with their unprecedented precision, have established weak lensing as a powerful probe of the matter distribution in the universe, enabling us to test the nature of dark matter (DM) interactions. The talk will briefly introduce this topic and present our recent investigation of weak lensing constraints on DM interactions with baryons and neutrinos. We utilize cosmological N-body simulations to model the nonlinear evolution of structure formation on weak lensing scales (k ~ 0.1–1 h/Mpc). To efficiently explore the parameter space of cosmological models, we have developed a novel numerical method that facilitates the use of simulation results. Our analysis of DES Year 3 data reveals significant constraints on DM-proton scattering, improving upon previous constraints from cosmic microwave background (CMB) data by up to a factor of five. Furthermore, our analysis of cosmic shear data reveals an intriguing ~3σ hint of a non-vanishing DM-neutrino interaction, which strengthens similar previous findings in high-multipole CMB and Lyman-α forest data. We also discuss how this interaction could simultaneously ameliorate the persisting S8 tension.
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| Feb 19 |
Wed |
Adam Smith (Sheffield) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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Axion-dilaton interactions in the dark sector
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Hicks Seminar Room J11 |
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Abstract:
Axion-dilaton models provide a well-motivated, minimal class of models for which kinetic interactions between multiple scalar fields and their predictions can be explored, in particular in late time cosmology. I will review this class of models and present the formalism we developed for studying kinetic interactions between rapidly oscillating axion fields and their dilaton partners on cosmological scales.
I will then show how this formalism can be used to study two cases of phenomenological interest. Firstly, the cosmological implications of prescribing an axion and a dilaton field to describe dark matter and dark energy, respectively, along with the predicted interactions with other cosmological species. Secondly, the implications of allowing an axion field to couple to multiple species of matter and how this can be used to build early dark energy theories compatible with novel multi-field screening mechanisms.
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| Feb 26 |
Wed |
Jacob Thompson (Sheffield) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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Quantum corrected anti-de Sitter spacetime: backreaction from the RSET (and a little bit of RKT)
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Hicks Seminar Room J11 |
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Abstract:
The question on a lot of theoretical physicists’ minds at the moment is, when is the next coffee break? And to a lesser extent, how do we connect quantum mechanics with general relativity and have a fully self-consistent theory of quantum gravity? Quantum field theory on curved spacetimes, a semi-classical theory, is one such approach. This describes how quantum fields (modelled by a renormalised stress-energy tensor) behave on classical curved backgrounds.
In this talk I will outline how this approach works and what role backreaction - required for a fully self-consistent theory - plays. I will also describe an approximation to full semi-classical gravity, quantum corrections, and present some results on three- and four-dimensional anti-de Sitter spacetime for the massless, conformally coupled scalar field. I will additionally show some preliminary results for a relativistic kinetic theory (RKT) approach where matter is modelled as a classical gas of particles, and how we have used this as an approximation to the RSET on the RHS of the semi-classical Einstein equations.
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| Mar 5 |
Wed |
Benito Juárez Aubry (York) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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Advances and challenges in semiclassical gravity
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Hicks Seminar Room J11 |
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Abstract:
Semiclassical gravity offers a description of the semiclassical regime of quantum gravity, in which quantum matter sources the Einstein field equation through the expectation value of the matter fields' stress-energy tensor, while the quantum fields propagate in the spacetime they curve. In this talk, I will briefly review the status of this theory, including some challenges and advances. Amongst the advances, I will discuss what we understand in terms of exact solutions to the theory. I will also discuss the role of strong cosmic censorship in semiclassical gravity and how it prevents information loss in black hole evaporation. Finally I will discuss some conceptual difficulties and tensions and propose new avenues to explore to get a better grasp of these problems.
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| Mar 12 |
Wed |
Laura Iacconi (Queen Mary) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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Mapping inflationary loop corrections to boundary terms
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Hicks Seminar Room J11 |
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Abstract:
Both single- and multi-field models of inflation might lead to enhanced scalar fluctuations on scales much smaller than those seeding the large-scale structure formation. In these scenarios, it is possible that the spike of power at high wavenumber might induce large corrections to the scalar power spectrum, e.g. in the form of loop corrections, potentially endangering the perturbativity of the underlying models. In this talk we discuss recent developments in the calculation of the 1-loop correction to a large-scale adiabatic mode. We demonstrate that non-volume-suppressed corrections only contribute at the boundaries of the momentum integral. To achieve this we employ expansion methods, such as the $\delta N$ formalism, as well as more general expansions that do not rely on assumption of validity of the separate universe picture.
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| Mar 19 |
Wed |
Jens Chluba (Manchester) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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CMB spectral distortion science beyond the monopole
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Hicks Seminar Room J11 |
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Abstract:
CMB spectral distortions have now been recognized as an important new probe in cosmology. However, most of the science has focused on CMB monopole distortions. In my talk, I will give a brief update on the status of CMB spectral distortions and then explain how it has now become possible to compute the full spectro-spatial evolution of the CMB including distortions. Anisotropic distortion signals do not require an absolute calibration and can be constrained with Planck, Litebird, CMB-S4 and the SKA, opening yet another way to study the primordial universe.
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| Mar 26 |
Wed |
Julio Arrechea (SISSA) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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Hicks Seminar Room J11 |
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| Apr 2 |
Wed |
Silvia Schiattarella (Nottingham) |
Cosmology, Relativity and Gravitation |
| 15:00 |
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Hicks Seminar Room J11 |
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| Apr 30 |
Wed |
Hanyu Cheng (Sheffield & Shanghai Jiao Tong) |
Cosmology, Relativity and Gravitation |
| 15:15 |
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Hicks Seminar Room J11 |
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| May 7 |
Wed |
Sofie Ried (Sheffield) |
Cosmology, Relativity and Gravitation |
| 15:15 |
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Hicks Seminar Room J11 |
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