30/09/2021 - 4pm, Anton Baleato Lizancos (UC Berkeley, USA), Fundamental Physics with CMB Lensing and Delensing
14/10/2021 - 4pm, Roman Konoplya (Silesian University, Opava, Czech Republic), Traversable wormholes in General Relativity without exotic matter
21/10/2021 - 4pm, Farbod Hassani (University of Oslo, Norway), TBA
28/10/2021 - 4pm, Stian Hartman (...), TBA
30/09/2021 -- Anton Baleato Lizancos (UC Berkeley, USA)
Time: 16:00
Place: online seminar
TITLE: Fundamental Physics with CMB Lensing and Delensing
ABSTRACT: Gravitational lensing of CMB photons by the matter distribution of the Universe can be both a blessing and nuisance. It's a blessing because of the way it can be harnessed to map the structures responsible for the deflections, and from this, constrain any physics affecting the growth of cosmic structure, such as the sum of the neutrino masses or dark matter. But lensing is also a nuisance because it generates B-mode polarization which obscures the highly-sought-after primordial signal associated with gravitational waves generated during cosmic inflation, our most accessible portal to physics near the GUT scale. In this talk, I will focus on key systematic effects that need to be controlled in order to harness the full potential of the Simons Observatory (SO), CMB-S4, and other upcoming experiments to make progress in these exciting areas. In the first part of my talk, I will briefly review the ways in which emission from galaxies and clusters can bias power spectra and cross-correlations of CMB lensing reconstructions, and describe our ongoing efforts to understand these biases analytically. Then, in the second part, I will explain how the lensing contamination to CMB B-modes can be removed — what is known as delensing — and discuss our recent findings regarding the performance of different delensing methods. I will also summarize preparatory work to delens SO data, and highlight biases to watch out for (and how to mitigate them) when the matter proxy used for delensing is either the cosmic infrared background or a lensing reconstruction derived from the CMB itself.
14/10/2021 -- Roman Konoplya (Silesian University, Opava, Czech Republic)
Time: 16:00
Place: Lecture Hall
TITLE: Traversable wormholes in General Relativity without exotic matter
ABSTRACT: I will start by briefly reviewing wormholes - exotic compact objects the interest to which has been recently largely revived. In [J. Blazquez-Salcedo, C. Knoll, E. Radu, Phys. Rev. Lett. 126 (2021) no.10, 101102] asymptotically flat traversable wormhole solutions were obtained in the Einstein-Dirac-Maxwell theory without using exotic matter. The normalizable numerical solutions found in this work above require a peculiar behavior at the throat: the mirror symmetry relatively the throat leads to the nonsmoothness of gravitational and matter fields. In particular, one must postulate the changing of the sign of the fermionic charge density at the throat requiring coexistence of particle and antiparticles without annihilation and posing a membrane of matter at the throat with specific properties. Apparently this kind of configurations could not exist in nature. We show that there are wormhole solutions, which are asymmetric relative to the throat and endowed by smooth gravitational and matter fields, being, thereby, free from all the above problems. This indicates that such wormhole configurations could also be supported in a realistic scenario.
21/10/2021 -- Farbod Hassani (University of Oslo, Norway)
Time: 16:00
Place: Lecture Hall
TITLE: TBA
ABSTRACT: TBA.