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Calendar of Physics Talks Vienna
| Asymptotic symmetries at Spatial Infinity |
| Speaker: | Sharad Mishra (BITS Pilani Goa Campus) |
| Abstract: | We describe asymptotic symmetries at spatial infinity of asymptotically flat spacetimes within the context of a generalization of the Beig-Schmidt-Ashtekar-Romano-framework. We demonstrate that it is possible to relax certain smoothness requirements of the asymptotic transformations considered previously, without violating asymptotic flatness. This leads to an enhancement of the asymptotic symmetry group that includes logarithmic supertranslations at spatial infinity. Our results compliment several recent results which confirm the existence of logarithmic supertranslations at spatial infinity in the Hamiltonian formalism. |
| Date: | Wed, 17.09.2025 |
| Time: | 14:00 |
| Duration: | 60 min |
| Location: | FH HS 1, TU Wien, Wiedner Hauptstr. 8, Freihaus, red area, 1st and 2nd floor |
| Contact: | Daniel Grumiller |
| Boundedness and Decay of Waves on Decelerated FLRW Spacetimes |
| Speaker: | Mahdi Haghshenas (Imperial College London) |
| Abstract: | The standard cosmological models of a homogeneous and isotropic universe in general relativity are described by the Friedmann--Lemaître--Robertson--Walker (FLRW) spacetimes. A natural step toward understanding the dynamics of wave-type equations---including the Einstein equations---near these backgrounds is to study the scalar wave equation on FLRW spacetimes and establish robust energy estimates.
In this talk, after outlining the stability problem for FLRW spacetimes, we consider the wave equation---as a proxy for the Einstein equations---on decelerated FLRW spacetimes with R^3 spatial sections. We demonstrate how dispersion and expansion affect the long-time behaviour of waves. In particular, we present uniform energy bounds and integrated local energy decay estimates across the full decelerated expansion range. Moreover, we describe a hierarchy of r^p-weighted energy estimates, in the |
| Date: | Wed, 17.09.2025 |
| Time: | 14:15 |
| Duration: | 60 min |
| Location: | VERA Seminar Room (Viktor-Franz-Hess Lecture Hall), Waehringer Straße 17, Hoftrakt |
| Contact: | D. Fajman |
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