Seminar on Early Universe and Gravitation

Time: Monday 14:00-16:00
Location:1st floor at the 4th Bldg of Science faculty

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Seminar archive


2017/12/18 (月)

Speaker: Shun-Pei Miao (National Cheng Kung Univ.) [from 1:30 PM]
Title: Deducing Cosmological Observables from the S-matrix
We study one loop quantum gravitational corrections to the long range force induced by the exchange of a massless scalar between two massive scalars. The various diagrams contributing to the flat space S-matrix are evaluated in a general covariant gauge and we show that dependence on the gauge parameters cancels at a point considerably before forming the full S-matrix, which is unobservable in cosmology. It is possible to interpret our computation as a solution to the effective field equations --- which could be done even in cosmology --- but taking account of quantum gravitational corrections from the source and from the observer.

2018/1/15 (月)

Speaker: Teruaki Suyama (RESCEU)

2018/1/22 (月)

Speaker: Eugeny Babichev (Laboratoire de Physique Théorique d'Orsay)
Title: Caustic free completion of k-essence
Both k-essence and the pressureless perfect fluid develop caustic
singularities at finite time. We explore the connection between the two
and show that they belong to the same class of models, which admits the
caustic free completion by means of the canonical complex scalar field.
Specifically, the free massive/self-interacting complex scalar
reproduces dynamics of pressureless perfect fluid/shift-symmetric
k-essence under certain initial conditions in the limit of large
mass/sharp self-interacting potential. We elucidate a mechanism of
resolving caustic singularities in the complete picture.

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