## National Seminar Theoretical High Energy Physics November, 18th, 2022

We are delighted to announce that the National Seminar THEP will take place in person on

Friday November 18. The talks will be in room Z011 at CWI/Nikhef and the program will run from 10:30am to 3:30pm, followed by a “borrel”.

- Date:
Friday, 18 November 2022

- Speakers:
Ana Raclariu (UvA)

Thomas Gehrmann (UZH) (Nikhef colloquium)

Susanne Westhoff (RU)

Enis Belgacem (UU)

- Abstracts:
**Ana Raclariu (UvA) – From AdS to celestial holography**

Abstract:

The search for pragmatic observables of quantum gravity remains at the forefront of fundamental physics research. A large set of ideas collectively known as the gauge-gravity duality have proven fruitful in tackling this problem. While such a duality is believed to universally govern gravitational theories, its nature in theories of gravity that describe our universe to a good degree of approximation is still little understood.

In this talk I will discuss efforts in formulating a holographic correspondence for gravity in four-dimensional asymptotically flat spacetimes. The proposed dual theory lives on a two-dimensional celestial sphere at infinity and is constrained by a wide range of symmetries. I present recent evidence for this proposal by showing that it arises naturally in a flat space limit of AdS holography.**Thomas Gehrmann (University of Zurich) – Precision theory for high energy collider physics**

Abstract:

Benchmark cross sections are measured to high accuracy at the LHC. They provide in-depth information on the underlying particle dynamics, and they can be used for precision determinations of Standard Model parameters and in indirect searches for new physics effects. To match the quality of the experimental data, equally precise theory predictions are needed, which are obtained by going to high orders in perturbation theory. We describe techniques and recent results for precision calculations and discuss their impact for particle phenomenology.**Susanne Westhoff (RU) – New physics searches across the scales**

Abstract:

There is good reason to expect new fundamental physics at high energies. If new particles exist not too far above the energies at particle colliders, they can change the interactions of known particles through virtual effects. Effective field theories are a powerful tool to describe such changes in a general framework and to compare them to data. In this talk, I will show how to relate new physics effects in observables at different scales through a tower of effective field theories. Precise measurements at the LHC and at flavor experiments probe different directions in the large parameter space of effective interactions. In combination, they draw a fine-grained picture of how new physics at high energies may or may not look like.**Enis Belgacem (UU) – Spatial correlations of dark energy from inflationary quantum fluctuations**

Abstract:

I will describe a simple model where dark energy is a late-time consequence of the quantum fluctuations of a spectator scalar field, initially amplified by cosmic inflation. In such a scenario, the quantum origin of dark energy manifests in its fluctuations, with spatial correlations following a simple shape. The time evolution of correlators is conveniently studied within the stochastic formalism. After describing the methods and limitations of the stochastic formalism for the problem at hand, I will discuss the implications of dark energy fluctuations for the Hubble tension problem and for cosmological observables like luminosity distance correlators. The talk is mainly based on 2209.01601, 2111.04803 and 2209.00440. - Location:
Room Z011 at CWI/Nikhef

- Schedule:
The schedule is as follows:

10:00 Coffee/tea

10:30 Ana Raclariu (UvA)

11:15 Thomas Gehrmann (UZH) (Nikhef colloquium)

12:15 Lunch

14:00 Susanne Westhoff (RU)

14:45 Enis Belgacem (UU)

15:30 Borrel/drinks - Local organizers:
For questions or suggestions, please contact one of the organizers:

Wouter Waalewijn (NIKHEF)

tel: +31 (0)20 5255773

e-mail: wouterw@nikhef.nlMarieke Postma (Nikhef)

tel.: +31 (0)20 5925128

e-mail: mpostma@nikhef.nlTimothy Budd (RU)

tel.: +31(0)24 3616161

e-mail: T.Budd@science.ru.nl