Séminaire

The Present and Future of CMB Polarization Observations

One of the big goals of today’s CMB experiments is to look for the faint signature of primordial gravitational waves in the B-mode polarization. Finding it would give us a unique window into the physics of the very early Universe and the Inflationary epoch.

Higgs inflation and the Palatini formulation of General Relativity

The Standard Model Higgs can be the inflaton, providing an attractively economical scenario. The core idea is simple, but there are complications both on the side of quantum corrections and gravity. I will discuss possibilities and problems due to such complications. In particular I will cover how the predictions of Higgs inflation depend on what is the correct formulation of general relativity: metric, Palatini or something else.

Searches for High-Energy Neutrinos from the Cygnus Bubble, Galactic Plane, and AGNs with Multi-Messenger Observations

High-energy neutrino and γ-ray emission are expected from the Galactic plane, produced by interactions between cosmic rays and the interstellar medium or radiation fields. Recent LHAASO observations have detected diffuse γ-rays from the Galactic plane and an ultrahigh-energy γ-ray bubble (Cygnus Bubble) up to PeV energies, suggesting the possibility of neutrino emission. Using 7 years of publicly available IceCube track data with the full detector, we conducted searches for neutrino signals correlated with LHAASO diffuse Galactic γ-ray emission and Cygnus Bubble using a template method.

Modeling particle transport and acceleration with stochastic differential equations

Understanding the complex transport of particles in turbulent plasmas is of great relevance in various fields. In astrophysics, the diffusive transport of high-energy particles is often described in an ensemble-averaged way, employing a transport equation that describes the time evolution of the particles distribution function in space and momentum. The standard transport equation can also be re-written into a set of stochastic differential equation.

Beyond the Limits of Quintessence

Current cosmological data seem to point beyond the limits of quintessence for the behavior of dark energy accelerating the universe. This requires challenging physics such as modified gravity, interactions, or altered vacuum, in analogy with how non-Gaussianity in inflation requires physics beyond standard dynamics. We explore some possibilities.

Some "background checks" for Warm Inflation

Warm Inflation is a variant inflationary scenario where the inflaton field continuously dissipates its energy to a subdominant radiation bath during inflation. Among the many advantages that WI has over its more standard counterpart, which we will refer to as Cold Inflation, is that WI smoothly transits to a radiation dominated Universe post inflation without invoking the need of a reheating phase, dynamics of which is still quite unknown. The dissipation effects effective during Warm Inflation makes the dynamics of the inflation quite intricate. Even the simple graceful exit in Cold Inflation turns out to be not so simple in Warm Inflation. In this talk, we will do the background analysis of Warm Inflation and shed light on how Warm Inflation ends or gracefully exits. These graceful exit criteria also constrain the form of the potential and the dissipative coefficients that one may choose for their Warm Inflationary model. Moreover, it indicates whether Warm Inflation can at all exit to a radiation dominated epoch or not.

Evolution of the Comptonizing medium of the black-hole candidate Swift J1727.8–1613 along the accretion state transition using NICER

Evidence for a strong connection between the X-ray corona and the radio jet in black hole X-ray binaries has grown significantly. During state transitions, the inferred corona size correlates with both the jet’s flux and its synchrotron spectrum properties, offering insights into jet acceleration mechanisms. We investigate the properties of the Comptonizing medium in Swift J1727.8-1613 using the time-dependent Comptonization model vkompth, with NICER observations of type-C QPOs in the hard and hard-intermediate states.
Séminaire