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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.**

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