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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)
Abstract:
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.