Title: Gravitational Waves from the Fifth Dimension

Speaker: David Mateos
Universitat de Barcelona & ICREA

Abstract:
The experimental revolution unleashed by the discovery of gravitational
waves will gradually unfold over the coming decades. Maximizing the
discovery potential requires a theoretical understanding of out-of
equilibrium quantum matter coupled to dynamical classical gravity.
This regime is extremely challenging to address with conventional
methods. Holography, a theoretical framework originating from string
theory, maps this problem to the dynamics of classical gravity in five
dimensions. I will discuss the insights that holography can offer into
the gravitational waves produced during phase transitions in the Early
Universe and in neutron star mergers. These gravitational waves may
provide invaluable information about physics beyond the Standard
Model in the former case, and about the phase diagram of Quantum
Chromodynamics in the latter.

Speaker: Polina Petriakova

Title: QFT and stochastic formalism in cosmology

Abstract: I would like to discuss recent results in well-known (and not
so much) techniques to calculate correlation functions in the
long-wavelength approximation in de Sitter space and beyond. The main
focus of my talk is the connection of the stochastic formalism to
(non-)perturbative QFT’s results in curved spacetime.

The talk is based on:
1. A. Kamenshchik and P. Petriakova, IR finite correlation functions in
de Sitter space, a smooth massless limit, and an autonomous equation,
arXiv:[2410.16226] [hep-th]; accepted in JHEP.
2. A. Kamenshchik and P. Petriakova, From the Fokker-Planck equation to
perturbative QFT’s results in de Sitter space, arXiv: [2504.XXXXX].

TITLE: Simulating high-energy particle collisions

SPEAKER: Mikel Mendizabal Morentin (DESY)

ABSTRACT:
High-energy proton-proton collisions allow us to probe the fundamental particles and interactions
described by the Standard Model — and to search for phenomena beyond it. To interpret these
collisions and test our theoretical predictions, simulations play a crucial role. At the Large Hadron
Collider (LHC), they are indispensable tools used in a wide range of tasks, from signal and
background estimation to detector alignment and data correction.
However, simulating such collisions is highly non-trivial. Each event involves a variety of complex
processes, including the structure of the proton, partonic interactions, particle radiation, and the
subsequent hadronisation of outgoing particles. In this talk, I will introduce the basic concepts
behind proton-proton collision simulations, with a particular focus on parton showers. I will also
present the Parton Branching method, an event generator that incorporates transverse
momentum-dependent (TMD) physics, along with novel ideas aimed at increasing the precision of
parton showers.

The Quantum Way of Doing Computations,
Simulations and Measurements

Rainer Blatt

Institute for Experimental Physics,
University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
Rainer.Blatt@uibk.ac.at, http://www.quantumoptics.at

Institute for Quantum Optics and Quantum Information,
Austrian Academy of Sciences, Otto-Hittmair-Platz 1, A-6020 Innsbruck, Austria
Rainer.Blatt@oeaw.ac.at, http://www.iqoqi.at

Alpine Quantum Technologies (AQT) GmbH,
Technikerstrasse 17, A-6020 Innsbruck, Austria
http://www.aqt.eu

In this presentation, we review the fundamental functional principles of quantum information
processing and provide an update on the status of the Innsbruck trapped-ion quantum computer
[1]. Using strings of trapped ions, we implement a quantum information processor to carry out
quantum operations. We present an overview of the available quantum toolbox and discuss the
scalability of this approach. The quantum computing methodology is exemplified through analog
and digital quantum simulations [2,3]. By utilizing the quantum toolbox for entanglement-
enhanced Ramsey interferometry, we determine optimal parameters for quantum metrology [4].
To protect against the impact of noise, quantum computers encode logical quantum information
redundantly across multiple qubits using error-correcting codes. We highlight the implementation
of a fault-tolerant universal set of gates on two logical qubits within the trapped-ion quantum
computer [5]. With Alpine Quantum Technologies, a commercially available NISQ-type quantum
processor has been developed and is already accessible for industrial applications.

[1] I. Pogorelov et al., PRX Quantum 2, 020343 (2021)
[2] C. Kokail et al., Nature 569, 355–360 (2019)
[3] M. K. Joshi et al., Science 376, 720 (2022)
[4] C. D. Marciniak et al., Nature 603, 604 (2022)
[5] L. Postler et al., Nature 605, 675 (2022)

TITLE: ” The Fate of Magnetic Monopoles in the Early Universe “

SPEAKER: Maximilian Bachmaier (Univ. of Muenchen, Germany)

ABSTRACT:                                    
The standard model of particle physics is a good approximation for lowerenergy scales. In the early hot universe, however, it is assumed that there was a so-calledgrand unified theory, which unifies the three fundamental forces of particle physics: theelectromagnetic, the weak, and the strong force. However, all attempts to unify thesethree forces lead to a possible overabundance of ‘t Hooft-Polyakov magnetic monopoles.But why magnetic monopoles haven’t been observed so far? In my presentation, I willdiscuss the so-called magnetic monopole problem and present two solutions for this inmore detail. First, I will present our numerical study on monopole interactions with domainwalls in an SU(2) gauge theory. We observe that the collision leads to the erasure of themagnetic monopoles and thus may solve the monopole problem (Dvali, Liu, and Vachaspati1997). Second, I will present monopoles connected by cosmic strings (Langacker, Pi 1980),particularly focusing on the “slingshot effect” that describes monopoles traversing theboundary between Coulomb and confining phases. This passage causes the gauge field tobe confined in a cosmic string connected to the domain wall separating the two phases.These two phenomena, relevant in the early universe, could leave observable imprints suchas gravitational radiation.

                       
DATE: MONDAY, MAY 14th, 2025
TIME: 11:40 am

LOCATION: Theoretical Physics Seminar Room

TITLE:   An effective Hubble constant in f(R) modified gravity

SPEAKER: Tiziano Schiavone, Institute of Space Sciences (ICE-CSIC) Bellaterra

ABSTRACT:  The precise determination of the current expansion rate of the Universe, the Hubble constant  ($H_0$), remains a central challenge in cosmology. To address the persistent $H_0$ tension and reconcile the  discrepant values inferred from observations at different redshifts z, we investigate $𝑓(𝑅)$ modified gravity theories 
in the Jordan frame. In this context, an additional degree of freedom arises from a scalar field non-minimally coupled  to gravity, naturally inducing a redshift-dependent effective Hubble constant, $H_0^{EFF}(z)$. We reconstruct the  scalar field potential to ensure that $H_0^{EFF}$ decreases with z, potentially resolving the mismatch between  early- and late-time measurements. More broadly, $H_0^{EFF}(z)$ offers a diagnostic tool, especially in  redshift-binned analyses, for testing cosmological models.
                                   

                       
DATE: FRIDAY, MAY 16th, 2025
TIME: 11:40 am

LOCATION: Theoretical Physics Seminar Room

Observing Dark Matter Decays to Gravitons via Graviton-Photon Conversion
https://arxiv.org/pdf/2503.19019

TITLE: All black holes of type D: their metric forms and physical properties

SPEAKER: Jiri Podolsky (Charles University, Prague).

ABSTRACT: We will review some new results concerning the large class of interesting type D solutions
to the Einstein-Maxwell field equations with an aligned electromagnetic field. These represent black holes
with rotation, NUT parameter, electric and magnetic charges, acceleration, and any value of cosmological
constant. In particular, we will present their original Plebanski-Demianski form, and its more recent
Griffiths-Podolsky-Vratny, and As- torino representations. We will discuss their mutual relations, with the
emphasis on the elusive family of accelerating (purely) NUT black holes. Usefulness of these new metric
forms will be demonstrated on studies of singularities, horizons, conformal diagrams, ergoregions, rotating
strings causing the acceleration, their possible twist, and thermody- namic characteristic of these black hole
spacetimes.

DATE: WEDNESDAY, May 28th, 2025

TIME: 11:40 am

LOCATION: Theoretical Physics Seminar Room

Giuseppe Vitagliano (Atominstitut, Vienna):
Many-body entanglement quantification with collective measurements”

I will present some recent results on entanglement detection and
quantification with collective measurements in many-body ensembles.
First I will give an introduction into entanglement and the idea of
‘spin squeezing’, which was introduced in the context of metrology,
and explain the relation between the two concepts. I will show how the
original spin squeezing approach can be generalized in several
respects and how it allows to quantify multipartite entanglement in
different types of experimentally-controlled many-body systems, such
as cold atomic clouds or solid-state magnetic materials. These
entanglement witnesses are based on variances of collective operators,
which can be extracted from simple averaged two-body correlation
functions, which is the reason why they find widespread application in
many-body systems, where higher-order correlation functions of more
complex measurements are generally very challenging. In particular I
will present particular examples of criteria that have been recently
applied to quantify entanglement in experiments with cold or ultracold
atomic gases. In the final part, I will focus on the quantification of
entanglement by means of entanglement monotones with similar methods,
and I will show the results of applying this method to many-spin
systems at equilibrium as well as with experimental data of a
spin-squeezed Bose-Einstein condensates of ∼500 atoms.

We would like to inform you that a meeting of the EHU Quantum Center (EHU QC) 
will be held on Wednesday, June 25th, at 12:00 – 13:00, in Room 1.A1 of the 
Science and Technology Building at the Leioa Campus. The purpose of this 
meeting is to provide updates on current initiatives and to foster discussion among 
all members.

The agenda will include the following items:

1. Progress Report on the María Goyri Building Project.
2. Review of Ongoing Actions and Initiatives of the EHU Quantum Center.
3. Open Session for Questions and Answers.

We look forward to seeing you all there.

TITLE: Electromagnetic self-force in Kerr spacetime for bound
and unbound trajectories

SPEAKER: Ethan James German (Univ. of Sheffield, UK)

ABSTRACT: In this talk, I will describe new results for the self-force acting on a
charged particle moving along bound or scattering trajectories in the equatorial plane
of a spinning black hole. The self-force is calculated in the frequency domain by using
the method of extended homogenous solutions. The self force is applied to calculate
observables such as the periastron advance for bound orbits, and the deflection angle
shift for scattering trajectories, using the method of osculating geodesics. We compare
these results with a Keplerian approximation derived from the Abraham-Lorentz Force.
Finally, I will compare and contrast the electromagnetic results with those from
gravitational self-force analyses.

DATE: FRIDAY, June 27th, 2025

TIME: 11:40 am

LOCATION: Theoretical Physics Seminar Room