A gravitational wave background from a first order phase transition at the electroweak scale may be observable with future detectors such as LISA. While the Standard Model does not predict a first order phase transition, these occur in many BSM scenarios, including various dark matter models. Therefore, detecting a stochastic gravitational wave background could point to new physics, while a null detection could constrain or even exclude many BSM models. However, recovering the physical parameters of an underlying phase transition from a possible signal at LISA is not straightforward, partly due to other possible sources of a stochastic gravitational wave background, such as a population of white dwarf binaries. In this talk I will present our recent advances in reconstructing the phase transition parameters - and therefore the underlying physical model - from realistic mock LISA data using parameterised templates as an approximation to a more complete physical model, which greatly speeds up the process. I will also discuss how we hope to make our mock LISA data more realistic in the future.

Dark matter with self-interactions might solve well-standing issues of small scale structure and/or shed light on the origin of the observed supermassive black holes. I will entertain the possibility that asymmetric dark matter that possesses self-interactions might form its own compact objects. These objects could be detected via production of gravitational waves from mergers. In addition, under certain conditions they might produce a very distinctive γ-ray outburst that can be a smoking gun signature for the identification of such "dark stars".

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Cette présentation passera en revue les grands instruments et mesures de politiques publiques permettant de décarboner nos économies : normes, taxes, quotas, subventions, etc. L’objectif sera de souligner leurs forces, leurs faiblesses et la bonne façon de les utiliser. Cette déclinaison s’appuiera sur des cas concrets dans les différents secteurs émissifs (bâtiment, transport, agriculture et alimentation, industrie), afin d’illustrer la diversité et la complémentarité de ces instruments.

Light-front (LF) form of quantum field theory has a few serious conceptual advantages, but also some puzzling features. In my talk, I shall suggest potential solutions to some of the LF "failures". First, presence of the vacuum "bubbles" in the Hamiltonian LF perturbation theory will be clarified. The resulting vacuum amplitudes are non-vanishing despite the notorious "triviality" of the LF vacuum and agree with the results of Feynman perturbation theory evaluated in terms of the LF variables. Next, I will show that some apparent consistency problems of the LF theory can be solved if mathematically adequate treatment is adopted. Contradictions related to the LF restriction of the two-point function are removed if the scalar field contains regularization terms in the plane-wave factors. As a consequence, the correct equal-LF time commutators are reproduced from the Pauli-Jordan function, and the sign function present in them is naturally replaced by a function suppressed for large x^- - values. The value of the two-point function at coinciding points is also correctly obtained in the Hamiltonian (”on shell”) formulation. Then a novel look at the LF zero modes will be described, based on a consistent quantization of two-dimensional massless LF fields. Finally, the operator solution of the Thirring-Wess model in the light-front formulation will be presented.

Since direct detection experiments over the last few decades have been unsuccessful in finding dark matter consistent with a WIMP undergoing thermal freeze-out, we should re-examine whether this is indeed the right way to think about dark matter. One can make two possible departures from this paradigm — either by changing the mechanism that determines the DM density or by changing the nature of DM as an elementary particle. Often, when we move away from the WIMP paradigm, the direct detection cross section is too small to be observable and possibly production at colliders becomes our first line of attack. We will examine the generic signatures of both these possibilities at the LHC.

It is well understood the light element lithium in stars generally gets destroyed. Thus, stars are known as lithium sinks. Contrary to this general understanding a few stars show large amount of lithium. In some rare cases this amount exceeds the present interstellar value of A(Li)= 3.2 dex by about a factor of 10. This has been a nagging problem in stellar astrophysics for more than 4 decades since its first discovery in early 1980s. In this discuss the problem and observational efforts leading to evidence of large lithoum origin in red giants.

In 2015 the LIGO collaboration announced the first direct detection of gravitational waves from the coalesce of two intermediate mass black holes, ushering in a new era in direct observations of extreme gravitational environments. Since then, laser interferometers have detected 100s more binary systems. The next gravitational frontier is to use observations of pulsars to form what is effectively a galactic sized gravitational wave detector. These pulsar timing arrays (PTAs) have been in operation for nearly two decades in North America, Europe, and Australia. I will discuss the basic physics behind PTAs and some of the key details of their data analysis. If there is time, I will discuss ways in which we can use PTAs to detect physics beyond the standard model.