wolfgang m. wieland

Talks and Seminars

Simplicial Graviton from Selfdual Ashtekar Variables
Talk at Peyresq Physics, Peyresq (Thorame Haute, France),
13 June 2023.
Simplicial Graviton from Selfdual Ashtekar Variables
Seminar at Arnold Sommerfeld Center for Theoretical Physics (Oriti Group), LMU (Munich, Germany),
06 June 2023.
Boundary modes and quantum reference frames in linearized gravity
Talk at FAU2 Workshop, ECAP (Erlangen, Germany),
02 May 2023, slides.
Boundary modes and quantum reference frames in linearized gravity
Group Seminar at Qubits and Spacetime Unit (Philipp Höhn), OIST (Okinawa, Japan),
17 April 2023, talk available online.
Dissipation and Gravitational Subsystems
Group seminar during visit to Vidotto group at University of Western Ontario (London, Canada),
18 October 2022.
Time in Quantum Gravity
Talk at Time In Quantum Theory 2022, TU Wien (Vienna, Austria),
19 September 2022, programme.
Boundaries, dissipation and gravitational charge
Invited talk at 2nd Carroll Workshop, University of Mons (Mons, Belgium),
12 September 2022, slides.
Metriplectic geometry for gravitational subsystems
Presentation at Loops 2022, ENS (Lyon, France),
21 June 2022, slides.
General quantum formalisms for gravity
Panel discussion at Quantum Information Structure of Spacetime 2022, Western University (London, Ontario, Canada),
09 June 2022, talk available online.
Subsystems in gauge theory and gravity
Panel discussion (online) at Informational Architecture of Spacetime Workshop, Okinawa Institute for Science and Technology (Onna, Okinawa, Japan),
27 May 2022, slides.
Panel on Boundary Degrees of Freedom and Celestial Holography
Panel discussion at International Loop Gravity Seminar (ILQGS),
03 May 2022, slides.

How the Immirzi Parameter deforms the Boundary Charges on the Light Cone
talk at 56th recontres de Moriond, 30 January to 06 February 2022, La Thuile, Val d'Aosta, Italy,
06 February 2022, slides.
\(\boldsymbol{SL(2,\mathbb{R})}\) Holonomies on the Light Cone
talk at Faculty of Physics, University of Graz, visit to Prof. Reinhard Alkofer,
09 November 2021, slides (same topic as in Belgrade).
How the Immirzi Parameter deforms the \(\boldsymbol{SL(2,\mathbb{R})}\) boundary symmetries on the light cone
visit to Faculty of Physics, University of Belgrade, GPFSeminars 2021,
27 October 2021, slides.
\(\boldsymbol{SL(2,\mathbb{R})}\) Holonomies on the Light Cone
Talk at Sixteenth Marcel Grossmann Meeting (Online Meeting),
5 July 2021, video available online, slides.

This talk describes how the Barbero–Immirzi parameter, a couling constant akin to the theta parameter in QCD, deforms the SL(2,R) symmetries of the gravitational boundary data on a null surface. Our starting point is the definition of the action and its boundary terms. We introduce the covariant phase space and explain how the Holst term alters the symmetries on a null surface. We show that this alteration only affects the algebra of the edge modes, whereas the algebra of the radiative modes is unchanged. To compute the Poisson brackets explicitly, we work on an auxiliary phase space, where the SL(2,R) symmetries of the boundary fields are manifest. The physical phase space is obtained by imposing both first-class and second-class constraints. All gauge generators are at most quadratic in terms of the fundamental SL(2,R) variables. Finally, we discuss various strategies to quantise the system.

Panel Discussion on the Keys to the Future Developments of Quantum Gravity
Invited contribution for the Loop Quantum Gravity Summer School 2021 (Lyon, France),
23 June 2021, slides.

Barnich–Troessaert Bracket, edge modes, boundary symmetries and all that
Invited seminar at IPM – Institute for Research in Fundamental Sciences (Tehran, Iran),
15 June 2021, slides.

A summary will be given of the papers arXiv:2104.08377, 2104.05803 and 2012.01889. The main point of this seminar is to discuss how the ADM phase space for general relativity splits into edge modes and radiative modes and how these two different components can each be understood as genuine phase spaces for themselves. Each of these smaller phase spaces is equipped with a symplectic structure. The symplectic structure on the radiative phase space defines the familiar Poisson commutation relations for the asymptotic shear. Following the argument given in arXiv:2104.08377, it will be shown that the Poisson bracket for the edge modes (obtained by formally imposing second-class constraints on the ADM phase space and calculating the resulting Dirac bracket) is the Barnich–Troessaert bracket on a cross section of null infinity.

Null surfaces as open Hamiltonian systems
Invited talk given at International Loop Gravity Seminar (ILQGS),
10 April 2021, slides.

Null infinity from quasi-local phase space
Invited talk given at PI – Perimeter Institute (Waterloo ON, Canada),
18 March 2021, talk available at PIRSA.

I will consider the phase space at null-infinity from the \(r\rightarrow\infty\) limit of a quasi-local phase space for a finite box with a boundary that is null. This box will serve as a natural IR regulator. To remove the IR regulator, I will consider a double null foliation together with an adapted Newman–Penrose null tetrad. The limit to null infinity (on phase space) is obtained in the limit where the boundary is sent to infinity. I will introduce various charges and explain the role of the corresponding balance laws. The talk is based on the paper: arXiv:2012.01889.

Null surfaces as open Hamiltonian systems
Invited talk given at Kavli Institute for Theoretical Physics (Santa Barbara CA, U.S.A.),
04 February 2021, talk available online.
Observables vs. gauge symmetries: lessons from quasi-local holography
Talk given shortly after having joined IQOQI (Vienna, Austria),
16 October 2020, talk available online.