Seminars this semester


   Series:


May 20 Wed Kieran Finn (University of Manchester)
15:00 https://app.vscene.net/r/KjKhl4yTE4 Frame Covariance in Quantum Gravity
 
  Abstract:
The laws of physics should not depend on how we choose to describe them. However, this is exactly what happens in the standard formulation of quantum field theories. The effective action receives different quantum corrections depending on how we parametrise our fields and even Feynman diagrams can yield results that depend on the definition of the fields we choose to work with. In this talk I will rectify these problems by introducing the notion of frame covariance, in which the quantum fields are treated as coordinates on a manifold, known as the field space. Field redefinitions are then simply diffeomorphisms of this manifold and thus we can impose reparametrisation invariance using well-known techniques from differential geometry. This talk is based on arXiv:1910.06661.
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May 27 Wed Philippe Brax (Universite Paris-Saclay)
15:00 https://app.vscene.net/r/KjKhl4yTE4 Charged Dark matter and H0 tension
 
  Abstract:
I will describe recent models of non-linear electrodynamics with charged dark matter and their cosmological consequences. In particular, I will emphasize the inhomogeneous nature of the resulting cosmology. This follows from the screening of the extra U(1) in a way akin to the K-mouflage mechanism of modified gravity. I will eventually argue that this may have some applications to the local dynamics vs large scale structure of the Universe and the H0 tension.
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Jun 3 Wed Visakan Balakumar (University of Sheffield)
00:00 https://app.vscene.net/r/KjKhl4yTE4 Hadamard renormalisation for a charged scalar field
 
  Abstract:
The Hadamard renormalisation method provides a powerful and axiomatic approach to renormalising the stress-energy tensor in the study of quantum fields in curved spacetime. This procedure has been developed by Decanini and Folacci for massive neutral scalar fields in a general spacetime of arbitrary dimension. Motivated by the study of superradiant scattering in Reissner–Nordström black holes, we extend their work to include charged scalar fields in spacetimes with a classical, background gauge field and explicitly demonstrate the Hadamard renormalisation procedure in four dimensions.
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Jun 17 Wed Hal Haggard (Bard College)
15:00 https://app.vscene.net/r/KjKhl4yTE4 The Black Hole Spin Puzzle, Black Hole Entropy, and Gravitational Wave Observations
 
  Abstract:
Black hole entropy is a robust prediction of quantum gravity with no observational test to date. This entropy can be used to determine the probability distribution of the spin of black holes at equilibrium in the microcanonical ensemble. This ensemble, relevant for black holes formed in the early universe, predicts the existence of a population of black holes with zero spin. Observations of such a population at LIGO, Virgo, and future gravitational wave observatories would elucidate the statistical nature of black hole entropy and the origin of stellar mass black holes.
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Jun 24 Wed Ippocratis Saltas (CEICO)
15:00 https://app.vscene.net/r/KjKhl4yTE4 New tests of gravity at large and small scales in the Universe
 
  Abstract:
In this talk, I will explain the implications of the recent measurement of the gravitational waves’ speed for large and small scales in the Universe. I will pay special focus on how the physics of stellar structure, and in particular helioseismology, can provide us with tight constraints on the residual scalar-gravity interactions.
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Jul 1 Wed Nelson Nunes (University of Lisbon)
15:00 https://app.vscene.net/r/KjKhl4yTE4 Disformal couplings with a LambdaCDM background
 
  Abstract:
The discovery of the accelerated expansion of the Universe is now very well established and the LambdaCDM paradigm is the strongest candidate to explain it. Nonetheless, there are tensions between the relatively high level of clustering found in cosmic microwave background experiments and the smaller one obtained from large-scale observations in the late Universe. A way to alleviate this issue is to consider a scalar field dark energy component conformally coupled to dark matter maintaining a LambdaCDM background cosmology. In this presentation we extend these studies to allow in addition disformal couplings which we explore by performing a dynamical system analysis.
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Jul 8 Wed Robert Brandenberger (McGill University)
15:00 https://app.vscene.net/r/KjKhl4yTE4 Is Inflationary Cosmology Consistent with Fundamental Physics?
 
  Abstract:
The inflationary scenario is currently the paradigm of early universe cosmology. However, an embedding of inflation into a fundamental theory is missing. I will first show that there are alternative early universe scenarios which are consistent with current observations. Hence, we do not require inflation to explain the data. Then I will discuss recent challenges which indicate that standard inflation is NOT consistent with fundamental physics. Specifically, I will discuss the "Swampland Criteria" and the "Trans-Planckian Censorship Conjecture".
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