Την Τετάρτη 10 Δεκεμβρίου στις 12:00 μ.μ. ο Βασίλειος Λέτσιος (University of Mons) θα δώσει δια ζώσης ομιλία στην αίθουσα σεμιναρίων του Εργαστηρίου Θεωρητικής Φυσικής του ΑΠΘ (4ος όροφος, αίθουσα 23).
Η ομιλία θα αναμεταδοθεί μέσω Zoom στον ακόλουθο σύνδεσμο:
https://authgr.zoom.us/j/93272907791?pwd=W1iPYUl6SNKWmvVL7AdhGpyJr1e3vH.1
Meeting ID: 932 7290 7791
Passcode: 272270
Ακολουθούν ο τίτλος και η περίληψη της ομιλίας.
Τίτλος: Features of Gravitini and Supersymmetry on de Sitter spacetime
Περίληψη: It is commonly believed that a unitary supersymmetric quantum field theory (QFT) involving graviton and gravitino fields on fixed 4-dimensional de Sitter spacetime (dS4) cannot exist due to known challenges associated with supersymmetry (SUSY) on spaces with positive cosmological constant. In this talk, we contradict this expectation by presenting a new unitary supersymmetric QFT on dS4 background: the free supersymmetric theory of the chiral graviton and chiral gravitino fields. The theory overcomes the known obstacles to unitary global SUSY on de Sitter because the commutator between two SUSY transformations closes on the conformal algebra so(4,2) rather than the de Sitter algebra so(4,1). Crucially, the
so(4,2) symmetry is realised through unconventional conformal-like transformations. Along the way, we will discuss curious features of the free gravitino QFT on dS4: canonical quantisation with the use of a real action functional forces the field to be chiral, if one insists on the positivity of the norm in the QFT Fock space. As a complementary approach, we will compute the Euclidean 1-loop path integral of the gravitino on Euclidean dS4, and show that group-theoretic characters associated with the UIRs of so(4,1) appear. This indicates that the tension between chirality and unitarity seems to be absent in the Euclidean picture.
Extra pedagogical information for students:
De Sitter spacetime (dS4 ) is the maximally symmetric solution of vacuum Einstein equations with positive cosmological constant and describes a spacetime that expands in an accelerating manner, like the one we might be living in. Elementary particles on dS4 are identified with unitary irreducible representations (UIRs) of the dS algebra so(4,1), generalising Wigner’s classification for Minkowski spacetime. However, there is a big gap in the literature concerning higher-spin fermionic particles on de Sitter, unlike their more well-studied bosonic counterparts. For pedagogical reasons, the talk is split into two parts, with the second part building on the first. The first part will introduce the gravitino (massless spin-3/2) particle on dS4. By studying its mode solutions, we will clarify that it corresponds to a direct sum of UIRs (helicities: +3/2 and -3/2) of so(4,1) despite having a purely imaginary (!) mass parameter – as one would expect from Minkowskian intuition, where the gravitino has a zero mass. The second and main part of the talk is described by the abstract.
