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 Thursday, 04 April 2024

    Video-Recording for any system with MP4-support

   - Video.mp4  (ca. 542 Mb)

 15:15 – 16:35


"From graviton scattering to black-hole quantum amplitudes in general relativity"


                                                   Henrik Johansson

                                                                 (Uppsala and Nordita)




Since the discovery of gravitational waves from coalescing black holes,

It has become crucial to better understand gravitational two-body dynamics

and associated gravitational radiation. The gravitational force is often

viewed as inherently different from the other fundamental forces: general

relativity being a classical theory well-suited for describing macroscopic

physics but failing when quantum effects become important at small scales.

Yet, general relativity shares much common ground with modern particle

physics: it is the theory of a spin-2 field in much the same way that

Maxwell's Electromagnetism is a theory of a spin-1 field, both propagating

at the speed of light. Both can be quantized in similar ways, resulting in

photons and gravitons as the force carrier particles. In this quantum

framework, Feynman rules can be constructed, and gedanken quantum

experiments can be set up for the scattering of gravitons. On the other

hand, general relativity is often treated as a different beast because of

its ability to bend spacetime and form black holes. Black holes are still

poorly understood objects, yet general relativity predicts them to be

simple, characterized only by their mass, angular momentum and charge!

Naively, this makes them remarkably similar to elementary particles,

which, unlike black holes, have no internal structure.


In this talk I will treat general relativity akin to a quantum field

theory, and introduce some modern methods and perspectives that allow

for the computation of graviton scattering amplitudes with striking ease.

It relies on recent advances where the mathematical structure of scattering

amplitudes are found to be almost identical for gravity and the

better-understood strong force, the latter being mediated by spin-1 particles

called gluons. I will discuss some recent applications to analytical studies of

gravitational two-body dynamics and gravitational radiation.

Interestingly, modeling the black holes as elementary particles and

computing their quantum amplitudes works surprisingly well.

I will discuss the simplest amplitudes for both Schwarzschild and

Kerr black holes.


About the Speaker:


Henrik Johansson received his PhD in 2009 from UCLA and held postdoc

positions at CEA Saclay until 2012 and at CERN until 2014, when he took up

a Senior Lecturer position jointly at Nordita and Uppsala University.

He is a Wallenberg academy fellow since 2013 and a recipient of a Knut and

Alice Wallenberg Foundation grant in 2018.  Henrik's field of research is

high-energy physics with special emphasis on quantum corrections to

scattering processes in gravity and gauge theories. He is well known

for his pioneering work (with Z. Bern and JJM. Carrasco) on formulating

quantum calculation in gravity as a double copy of calculations in

gauge theory.


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