# Upcoming seminars

*24th July 2018, 14:00 * **Renato Costa, ** Singularity free Universe in double field theory

*25th July 2018, 14:00 * **Oleg Teryaev, **Graviitational formfactors and pressure in elementary particles

*27th July 2018, 14:00 * **Richard Woodard, **A Nonlocal Metric Realization of MOND

*30th July 2018, 14:00 * **Shun-Pei Miao, **A Cosmological Coleman Weinberg Potentials and Inflation

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**24/07/2018 Renato Costa (University of Cape Town, South Africa)**

Place: TBA

The singularity problem is one of the hints that the \LambdaCDM models has to be extended at very high energies. We use the guiding principle of symmetries to extend the FLRW background to an explicitly T-dual one which is well described by double field theory (DFT). We show that, at the level of the background, one can have a singularity-free cosmology once the dual time coordinate introduced by DFT is inversely related to the standard time coordinate of general relativity. We also show that introducing matter in DFT cosmology naturally leads to the correct equation of state for the winding modes and to a more clear interpretation of the connection between the two time coordinates.

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**25/07/2018 Oleg Teryaev (Joint Institute for Nuclear Research, Dubna, Russia)**

Place: TBA

TBA

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**27/07/2018 Richard Woodard (University of Florida, USA)**

Place: TBA

MOND is a phenomenological model which modifies the extreme weak field regime of Newtonian gravity so as to explain galactic rotation curves without dark matter. If correct, it must be the non-relativistic, static limit of some relativistic modified gravity theory. I show how the only possible metric-based modification of gravity is nonlocal, and I construct the action using the Tully-Fisher relation and weak lensing. Then I explore the consequences of this model for cosmology. This talk is based on four arXiv papers: 1106.4984, 1405.0393,1608.07858 and 1804.01669.

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**30/07/2018 Shun-Pei Miao (National Cheng Kung University, Taiwan)**

Place: TBA

We consider an additional fine-tuning problem which afflicts scalar-driven models of inflation. The problem is that successful reheating requires the inflaton be coupled to ordinary matter, and quantum fluctuations of this matter induces Coleman-Weinberg potentials which are not Planck-suppressed. Unlike the flat space case, these potentials depend upon a still-unknown nonlocal functional of the metric which agrees with the Hubble parameter for de Sitter. Such a potential cannot be completely subtracted off by any local action. We numerically consider the effect of subtracting it off at the beginning of inflation in a simple model. For fermions the effect is to prevent inflation from ending unless the Yukawa coupling to the inflaton is so small as to endanger reheating. For gauge bosons the effect is to make inflation end almost instantly, again unless the gauge charge is unacceptably small.