Την Τετάρτη 21 Ιανουαρίου στις 11:00 (προσοχή στην ασυνήθιστη ώρα) ο Gerben Oling (University of Edinburgh) θα δώσει ένα διαδικτυακό σεμινάριο.

Η ομιλία θα αναμεταδοθεί μέσω Zoom στον ακόλουθο σύνδεσμο:
https://authgr.zoom.us/j/98918046175?pwd=K1mxaaGGabhebBpq3tAbmVnX4Es9c0.1

Meeting ID: 989 1804 6175
Passcode: 009243

Ακολουθούν ο τίτλος και η περίληψη της ομιλίας.

Τίτλος: A boundary energy-momentum tensor from gravity near null infinity

Περίληψη: I will discuss how solving the Einstein equations in a radial expansion around null infinity in terms of arbitrary boundary metric data can be used to derive a boundary energy-momentum tensor whose diffeomorphism Ward identities generalize the usual Bondi loss equations. Generalizing holography from AdS/CFT to spacetimes with vanishing cosmological constant has been a long-standing goal. The limit of vanishing AdS curvature radius can be interpreted as an ultra-local or Carrollian limit on the boundary, which is related to the (conformal) Carrollian structure at null infinity. However, a straightforward application of such Carrollian limits to standard Lorentzian field theories often gives clearly unsatisfactory results. Motivated by this, we can turn to the bulk for hints on how such putative dual Carroll theories should be more appropriately constructed. In this talk, I will describe some of the recent work on extracting an energy-momentum-news complex from the dynamics of Einstein gravity near asymptotic null infinity in three and four bulk dimensions. In analogy with standard holographic renormalization in AdS/CFT, this is achieved by radially solving the Einstein equations near null infinity for general boundary data and introducing appropriate counterterms for the resulting on-shell action, and variations then define currents and their corresponding Ward identities.