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Stellar magnetic fields are key ingredients in the formation and evolution of stars and planets. Surface magnetic fields impact the characterization of stars and exoplanets, introducing spurious signals in radial velocity curves, and are at the origin of activity phenomena that impact habitability. Understanding the processes at the origin of magnetic field generation in stars is crucial to study the stellar and planetary evolution and to detect and characterize new habitable worlds, at the era of new high-resolution spectrometers, providing unprecedented sensitivity. In this talk, I present the latest efforts aimed at modeling the spectra of magnetic low-mass stars and investigating the link between large-scale and small-scale magnetic field structures observed with the high-resolution near-infrared spectra produced by some of the most advanced instruments, such as SPIRou, or WINERED.

The minimal two-triplet extension of the Standard Model demanding custodial symmetry gives rise to a new model, the extended Georgi-Machacek (eGM) model, not the well-known Georgi-Machacek (GM) model. Via computing one-loop corrections to all 2 to 2 scattering amplitudes in the eGM model, we place NLO unitarity bounds on the quartic couplings. On top of that, we derive stringent conditions on the quartic couplings ensuring there exists no field direction that leads to an unbounded potential. Finally, we perform a global fit for the eGM model using HEPfit to these theoretical bounds together with the latest Run II LHC data on Higgs signal strengths. We delineate the allowed ranges for the heavy Higgs boson masses and their mass differences. We further re-analyse the parameter space of the well known GM model by including NLO unitarity bounds for the first time. The global fit for GM model, with these improved theoretical and latest experimental constraints significantly refines the allowed ranges of the quartic couplings and heavy Higgs masses present in the literature.

In this talk, we will explore entangled relativity, a general theory of relativity that offers a more parsimonious approach compared to general relativity when integrated within a quantum field theory framework. Requiring only two universal dimensionful parameters instead of three, entangled relativity retains the key components of general relativity, including a four-dimensional spacetime manifold, a metric tensor representing the mechanical properties of space, inertia, and gravitation, and matter fields generating curvature. The term « entangled » does not directly refer to quantum entanglement but rather emphasizes that matter fields and gravity are intrinsically intertwined and cannot be treated separately at the level of the formulation of the theory. Entangled relativity converges toward, or reduces to, general relativity and standard quantum field theory in most cases but predicts a variable quantum of action (ħ) in response to gravitational phenomena, particularly in dense environments like neutron stars or the early universe. After presenting and explaining the theory, I will present a few predictions that may become observable in the foreseeable future, and which do not depend on any theoretical parameter.

TBA

The origin of the prompt emission in gamma-ray bursts (GRBs) remains highly debated despite decades of research. The GRB jet is initially optically thick and the trapped radiation is released when the jet transitions to the optically thin regime at the photospheric radius. Due to the high radiation pressure close to the central engine, shocks that occur before this transition are radiation mediated. In this seminar, I give an introduction to the theory of radiation-mediated shocks (RMSs) in the context of GRBs. I show that such shocks are expected in GRB jets and that the energized radiation downstream of the shock exhibits several promising features with regard to the observations. However, these shocks are computationally challenging to model from first principles. With this motivation, we have developed an approximate simulation code that is both quick and accurate. The simulation code is unique in its ability to fit an RMS model to the observational data.

Linear-perturbation theory has proven to be an extremely powerful tool to compare inflationary models with observational data. Recently, the newcoming high-precision observations call for predictions beyond linear perturbations. Such effects are known to be relevant for example in the production of primordial black holes or scalar-induced gravitational waves.

The separate-universe approach proposes to capture some of these non-linearities. It describes the universe as a set of causally disconnected homogeneous and isotropic patches (FLRW). In this talk, I will show that by allowing the patches to exhibit constant curvature, the separate-universe approach can be extended to non-slow-roll models. I will discuss the case of ultra-slow roll where this new approach allows to correctly predict the power spectrum of scalar perturbations together with non-Gaussianities.

Electrospheres are environments with the same origin as pulsars: a highly magnetized rotating neutron star. In pulsars, a cascade of electron-positron pair creation enriches the plasma. The plasma surrounding an electrosphere consists solely of particles that have escaped from the surface of the neutron star. Most of the 300 million presumed neutron stars in the Galaxy are not pulsars, but are surrounded by an electrosphere. Electrospheres are therefore fairly common objects, despite their low luminosity, which has so far prevented direct observation.

Electrospheres whose magnetic axis is aligned with the rotation axis have been well described for decades. The case of a magnetic axis oblique to the axis of rotation has resisted much theoretical research. We aimed at studying the physics of aligned and oblique electrospheres using a dedicated numerical simulation code which would enable ab initio simulations with realistic neutron star parameters. This code has recently been completed. Several numerical simulations have been carried out.

In this seminar, we briefly introduce the numerical simulation code and show the results of a parametric study. Many oblique electrospheres have the a structure analogous to those of the aligned electrospheres already known, but others have more specific properties. Some of them can enrich the interstellar medium with a plasma of ions and electrons.