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10:00 to 11:00 |
Masahide Yamaguchi (Tokyo Institute of Technology, Japan) |
Quantum Tunnelling in the Universe |
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11:00 to 11:20 |
Discussion |
Discussion |
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11:20 to 11:30 |
Break |
Break |
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11:30 to 12:00 |
Teruaki Suyama (Tokyo Institute of Technology, Japan) |
Formation of Primordial Black Holes in the Early Universe Computations of the primordial black hole (PBH) mass function discussed in the literature have conceptual issues. They stem from that the mass function is a differential quantity and the standard criterion of the PBH formation from the seed primordial fluctuations cannot be directly applied to the computation of the differential quantities. We propose a new criterion of the PBH formation which is an addition of one extra condition to the existing one. By doing this, we derive a formal expression of the PBH mass function without introducing any ambiguous interpretations which exist in the previous studies. Once the underlying primordial fluctuations are specified, the PBH mass function can be in principle determined by the new formula.
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12:00 to 12:30 |
Katy Clough (University of Oxford, UK) |
Initial Conditions for Inflation Inflation solves a number of problems in early universe cosmology but potentially introduces some new ones regarding how it was able to get started in the first place. In this talk I will explain these issues in the context of single field slow roll inflationary models, and discuss how they might restrict the phase space of initial conditions and early universe models that we consider valid. I will describe work I have done using numerical relativity to investigate the problem in the non-linear regime.
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12:30 to 12:50 |
Discussion |
Discussion |
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12:50 to 14:00 |
Break |
Lunch |
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14:00 to 15:00 |
Patrick Peter (IAP, France) |
The Bouncing Scenario Although inflation is widely accepted as the paradigmatic description of the very early moments of the Universe, alternatives are still possible, in particular in view of the fact that the standard scenario leaves undiscussed the issue of the beginning of times, i.e. the primordial singularity. Resolving it results in a bouncing scenario, that may or may not include a phase of accelerated expansion. In the latter case, a purely bouncing scenario ensues which can account for most of the currently known properties of the observable Universe. After motivating alternatives to inflation, I will show how one can build a working bouncing model and how it might solve the usual standard issues related with the horizon and spatial curvature (the flatness problem). Finally, I’ll discuss some yet-unsolved questions such as isotropization and perturbations through the bounce.
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15:00 to 15:20 |
Discussion |
Discussion |
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15:20 to 15:30 |
Break |
Break |
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15:30 to 16:00 |
Jerome Quintin (Max Planck Institute for Gravitational Physics, Germany) |
Limiting Curvature in the Very Early Universe Finding effective theories of modified gravity that can resolve the Big Bang singularity and avoid other physical pathologies such as ghost and gradient instabilities has turned out to be a rather difficult task. The concept of limiting curvature, where one bounds a finite number of curvature-invariant functions thanks to constraint equations, is a promising avenue in that direction, but its implementation has only led to mixed results. Cuscuton gravity, which can be defined as a special subclass of k-essence theory for instance, is a minimal modification of gravity since it does not introduce any new degree of freedom on a cosmological background. Importantly, it naturally incorporates the idea of limiting extrinsic curvature as we will present. Accordingly, we show how models of cuscuton gravity and even extended cuscuton models (as a subclass of Horndeski theory) possess non-singular cosmological solutions and how those are perfectly stable. It is also shown how limiting extrinsic curvature can be generalized, which clarifies the relation with other modified gravity theories (such as mimetic gravity) and allows one to build models in which anisotropies are also bounded in the very early universe.
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16:00 to 16:15 |
Discussion |
Discussion |
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