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SUMMARY:Ilkka Mäkinen (University of Warsaw)
DTSTART;VALUE=DATE-TIME:20200430T183000Z
DTEND;VALUE=DATE-TIME:20200430T193000Z
DTSTAMP;VALUE=DATE-TIME:20230208T080853Z
UID:PIQuantumGravity/1
DESCRIPTION:Title: Quantum-reduced loop gravity from the perspective of full LQG
\nby Ilkka Mäkinen (University of Warsaw) as part of PI Quantum Gravity\n
\n\nAbstract\nQuantum-reduced loop gravity is a model of loop quantum grav
ity\, whose characteristic feature is the considerable simplicity of its k
inematical structure in comparison with that of full loop quantum gravity.
The model therefore provides an accessible testing ground for probing the
physical implications of loop quantum gravity. In my talk I will give a b
rief introduction to quantum-reduced loop gravity\, and examine the relati
on between the quantum-reduced model and full loop quantum gravity. In par
ticular\, I will focus on clarifying how the operators of the quantum redu
ced model are related to those of the full theory. I will show that despit
e their simplicity\, the operators of the quantum-reduced model are simply
the operators of the full theory acting on states in the Hilbert space of
the quantum-reduced model. In order to pass from the full theory operator
s to the "reduced" operators\, one only has to keep in mind that the state
s of the quantum-reduced model are labeled with large spins\, and discard
terms which are of lower than leading order in j.\n
LOCATION:https://researchseminars.org/talk/PIQuantumGravity/1/
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BEGIN:VEVENT
SUMMARY:Simone Speziale (Aix Marseille University)
DTSTART;VALUE=DATE-TIME:20200514T190000Z
DTEND;VALUE=DATE-TIME:20200514T203000Z
DTSTAMP;VALUE=DATE-TIME:20230208T080853Z
UID:PIQuantumGravity/2
DESCRIPTION:Title: Asymptotics of the EPRL model on arbitrary vertices\nby Simon
e Speziale (Aix Marseille University) as part of PI Quantum Gravity\n\n\nA
bstract\nWe introduce a new technique to study the critical point equation
s of the eprl model. We show that it correctly reproduces the 4-simplex as
ymptotics\, and how to apply it to an arbitrary vertex. We find that for g
eneral vertices\, the asymptotics can be linked to a Regge action for poly
topes\, but contain also more general geometries\, called conformal twiste
d geometries. We present explicit examples including the hypercube\, and d
iscuss implications.\n
LOCATION:https://researchseminars.org/talk/PIQuantumGravity/2/
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BEGIN:VEVENT
SUMMARY:Thomas Mertens (Universiteit Gent)
DTSTART;VALUE=DATE-TIME:20200521T183000Z
DTEND;VALUE=DATE-TIME:20200521T193000Z
DTSTAMP;VALUE=DATE-TIME:20230208T080853Z
UID:PIQuantumGravity/3
DESCRIPTION:Title: Bulk observables in JT gravity\nby Thomas Mertens (Universite
it Gent) as part of PI Quantum Gravity\n\n\nAbstract\nUsing a definition o
f bulk diff-invariant observables\, we go into the bulk of 2d Jackiw-Teite
lboim gravity. By mapping the computation to a Schwarzian path integral\,
we study exact bulk correlation functions and discuss their physical impli
cations. We describe how the black hole thermal atmosphere gets modified b
y quantum gravitational corrections. Finally\, we will discuss how higher
topological effects further modify the spectral density and detector respo
nse in the Unruh heat bath.\n
LOCATION:https://researchseminars.org/talk/PIQuantumGravity/3/
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SUMMARY:Yannick Herfray (Université Libre de Bruxelles)
DTSTART;VALUE=DATE-TIME:20200528T183000Z
DTEND;VALUE=DATE-TIME:20200528T193000Z
DTSTAMP;VALUE=DATE-TIME:20230208T080853Z
UID:PIQuantumGravity/4
DESCRIPTION:Title: Conformal Geometry of Null Infinity\, including gravitational wav
es\nby Yannick Herfray (Université Libre de Bruxelles) as part of PI
Quantum Gravity\n\n\nAbstract\nSince the seminal work of Penrose\, it has
been understood that conformal compactifications (or "asymptotic simplicit
y") is the geometrical framework underlying Bondi-Sachs' description of as
ymptotically flat space-times as an asymptotic expansion. From this point
of view the asymptotic boundary\, a.k.a "null-infinity"\, naturally is a c
onformal null (i.e degenerate) manifold. In particular\, "Weyl rescaling"
of null-infinity should be understood as gauge transformations. As far as
gravitational waves are concerned\, it has been well advertised by Ashteka
r that if one work with a fixed representative for the conformal metric\,
gravitational radiations can be neatly parametrized as a choice of "equiva
lence class of metric-compatible connections". This nice intrinsic descrip
tion however amounts to working in a fixed gauge and\, what is more\, the
presence of equivalence class tend to make this point of view tedious to w
ork with.\n\nI will review these well-known facts and show how modern meth
ods in conformal geometry (namely tractor calculus) can be adapted to the
degenerate conformal geometry of null-infinity to encode the presence of g
ravitational waves in a completely geometrical (gauge invariant) way: Asht
ekar's (equivalence class of) connections are proved to be in 1-1 correspo
ndence with choices of (genuine) tractor connection\, gravitational radiat
ion is invariantly described by the tractor curvature and the degeneracy o
f gravity vacua correspond to the degeneracy of flat tractor connections.
The whole construction is fully geometrical and manifestly conformally inv
ariant."\n
LOCATION:https://researchseminars.org/talk/PIQuantumGravity/4/
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