Organisation des séminaires et calendrier

In this talk we will explore different topological charges of supergravity theories supported by a non-trivial U-duality bundle. In case these charges would be conserved, they would lead to global symmetries, which we believe to be absent in any consistent theory of quantum gravity. With the UV completions of string and M-theory at hand we explore, which kind of UV objects are necessary to break all global symmetries in the IR supergravity theory. This leads to interesting string backgrounds including higher-dimensional superconformal field theories, twisted compactifications, and non-geometric defects.

Gravitational waves, scattering amplitudes and BMS

Carlo Heissenberg (IPhT)

Scattering amplitudes offer a new strategy to calculate gravitational observables that reorganizes more traditional general relativity calculations in terms of gauge invariant, on-shell ingredients. The link between amplitudes and gravitational waves has led to several new results over the past few years and has stimulated a fruitful dialog with complementary approaches. Additional insight comes from universal constraints that govern the emission of low-frequency gravitational waves, soft theorems. The latter are closely related to the structure of infrared divergences, memory effects and symmetries that emerge at null infinity in asymptotically flat spacetimes.

The aim of this lecture series is to provide an introduction to these topics and to illustrate some of the key connections that link them together.

Topics:

• gravitational observables in the post-Minkowskian regime from scattering amplitudes
• eikonal phase and deflection angle in hyperbolic two-body encounters
• asymptotic symmetries of asymptotically flat spacetimes, BMS group
• memory effect and soft graviton theorem
• soft limit of the energy emission spectrum, static angular momentum loss
• gravitational waveforms beyond the soft limit
• radiated energy and angular momentum

Course website: https://courses.ipht.fr/?q=en/node/323

Livestream on youtube.com/IPhT-TV: no subscription required

Videoconference: subscribe to the course newsletter to receive links

Speaker: Jacopos de Nardis (Université de Cergy)

I will present how ensembles of tensor networks provide incredibly valuable insights into quantum dynamics, quantum scrambling, and entanglement transitions, while remaining effectively “classical” from a complexity perspective. In particular, I will demonstrate how random tensor networks can be employed to study the anticoncentration of wave functions under generic chaotic circuits, and how ensembles of matrix product states, obtained by truncating the dynamics of hybrid quantum circuits, can be used to detect and understand entanglement transitions.

Gravitational waves, scattering amplitudes and BMS

Carlo Heissenberg (IPhT)

Scattering amplitudes offer a new strategy to calculate gravitational observables that reorganizes more traditional general relativity calculations in terms of gauge invariant, on-shell ingredients. The link between amplitudes and gravitational waves has led to several new results over the past few years and has stimulated a fruitful dialog with complementary approaches. Additional insight comes from universal constraints that govern the emission of low-frequency gravitational waves, soft theorems. The latter are closely related to the structure of infrared divergences, memory effects and symmetries that emerge at null infinity in asymptotically flat spacetimes.

The aim of this lecture series is to provide an introduction to these topics and to illustrate some of the key connections that link them together.

Topics:

• gravitational observables in the post-Minkowskian regime from scattering amplitudes
• eikonal phase and deflection angle in hyperbolic two-body encounters
• asymptotic symmetries of asymptotically flat spacetimes, BMS group
• memory effect and soft graviton theorem
• soft limit of the energy emission spectrum, static angular momentum loss
• gravitational waveforms beyond the soft limit
• radiated energy and angular momentum

Course website: https://courses.ipht.fr/?q=en/node/323

Livestream on youtube.com/IPhT-TV: no subscription required

Videoconference: subscribe to the course newsletter to receive links

I will start describing how the Veneziano 4-point amplitude and its generalisation to N-point, called Dual Resonance Model (DRM), were constructed using the properties of S-matrix theory. This procedure is opposite to the usual one where one constructs the S-matrix starting from a Lagrangian. In this case the S-matrix was constructed without knowing the corresponding Lagrangian. Then I will discuss how the amplitude was rewritten in terms of an infinite set of harmonic oscillators that allowed to determine the spectrum of physical states and their scattering amplitudes. Absence of negative norm states, required by unitarity, restrict the intercept of the Regge trajectory to be equal to 1. Already in 1970 Nambu, Nielsen and Susskind proposed that the underlying theory was a string theory, but it took few more years, by quantising the Nambu-Goto action in the light-cone gauge, to show that the spectrum of physical states coincided with the spectrum extracted from the DRM with $\alpha_0=1$. Later it was shown that also the scattering amplitudes at tree and multiloop level were the same. I will conclude discussing the attempt of writing the scattering amplitude for pions that brought instead to the superstring. A string theory for pions is still absent. In modern language this will require to construct a string extension of the non-linear sigma-model, but all attempts in this direction generated scattering amplitudes with negative norm states violating unitarity.

Gravitational waves, scattering amplitudes and BMS

Carlo Heissenberg (IPhT)

Scattering amplitudes offer a new strategy to calculate gravitational observables that reorganizes more traditional general relativity calculations in terms of gauge invariant, on-shell ingredients. The link between amplitudes and gravitational waves has led to several new results over the past few years and has stimulated a fruitful dialog with complementary approaches. Additional insight comes from universal constraints that govern the emission of low-frequency gravitational waves, soft theorems. The latter are closely related to the structure of infrared divergences, memory effects and symmetries that emerge at null infinity in asymptotically flat spacetimes.

The aim of this lecture series is to provide an introduction to these topics and to illustrate some of the key connections that link them together.

Topics:
– gravitational observables in the post-Minkowskian regime from scattering amplitudes
– eikonal phase and deflection angle in hyperbolic two-body encounters
– asymptotic symmetries of asymptotically flat spacetimes, BMS group
– memory effect and soft graviton theorem
– soft limit of the energy emission spectrum, static angular momentum loss
– gravitational waveforms beyond the soft limit
– radiated energy and angular momentum

Course website: https://courses.ipht.fr/?q=en/node/323

Livestream on youtube.com/IPhT-TV: no subscription required

Videoconference: subscribe to the course newsletter to receive links

Scattering amplitudes offer a new strategy to calculate gravitational observables that reorganizes more traditional general relativity calculations in terms of gauge invariant, on-shell ingredients. The link between amplitudes and gravitational waves has led to several new results over the past few years and has stimulated a fruitful dialog with complementary approaches. Additional insight comes from universal constraints that govern the emission of low-frequency gravitational waves, soft theorems. The latter are closely related to the structure of infrared divergences, memory effects and symmetries that emerge at null infinity in asymptotically flat spacetimes.

The aim of this lecture series is to provide an introduction to these topics and to illustrate some of the key connections that link them together.

Topics:

• gravitational observables in the post-Minkowskian regime from scattering amplitudes
• eikonal phase and deflection angle in hyperbolic two-body encounters
• asymptotic symmetries of asymptotically flat spacetimes, BMS group
• memory effect and soft graviton theorem
• soft limit of the energy emission spectrum, static angular momentum loss
• gravitational waveforms beyond the soft limit
• radiated energy and angular momentum

Course website: https://courses.ipht.fr/?q=en/node/323

Livestream on youtube.com/IPhT-TV: no subscription required

Videoconference: subscribe to the course newsletter to receive links

TBA