Current and future constraints on cosmology and modified gravitational wave friction from binary black holes

Gravitational wave (GW) standard sirens are well-established probes with which one can measure cosmological parameters, and are complementary to other probes like the cosmic microwave background or supernovae standard candles. I will focus on dark GW sirens, specifically binary black holes (BBHs) for which there is only GW data. Relying on the assumption of a source mass model for the BBH distribution, we consider four models that are representative of the BBH population observed so far.

On Adiabatic Renormalization with a Physically Motivated Infrared Cut-Off

Within the framework of the inflationary paradigm, it is well-known that correlation functions (or in general bi-linear observables) of quantum fields on a curved background suffer from divergences. In general, the presence of ultraviolet (UV) divergences due to fluctuations on arbitrary short scales is a common aspect of quantum field theory.

Ghosts without Runaway

I will discuss our recent work Phys.Rev.Lett. 128 (2022) 4, 041301 in which we present a simple class of mechanical models where a canonical degree freedom interacts with another one with a negative kinetic term, i.e., with a ghost. We prove analytically that the classical motion of the system is completely stable for all initial conditions, notwithstanding that the conserved Hamiltonian is unbounded from below and above. Numerical computations fully supported this.

Light Dark Matter: Collective Effects in the Lab and in Stars

Light dark matter candidates, such as axions and hidden photons, call for new ideas in direct detection. I discuss the recently proposed strategy of searching for e.g. axions using tunable cryogenic plasmas. The plasma haloscope enables resonant conversion by matching the axion mass to a plasma frequency, therefore converting axions to plasmons. Metamaterials are promising candidates, as the plasma frequency can be tuned. Besides axions, other dark matter candidates, such as hidden photons and scalars, can be successfully targeted with a plasma haloscope.

Solar mass black holes from neutron stars and bosonic dark matter

Black holes with masses ~1 Msun cannot be produced via stellar evolution. A popular scenario of their formation involves transmutation of neutron stars - by accumulation of dark matter triggering gravitational collapse in the star centers. We show that this scenario can be realized in the models of bosonic dark matter despite the apparently contradicting requirements on the interactions of dark matter particles: on the one hand, they should couple to neutrons strongly enough to be captured inside the neutron stars, on the other, their loop-induced self-interactions impede collapse.

Geometrical aspects of stochastic inflation: a path (integral) to the discretisation ambiguity and its resolution

Langevin equation, Markovian process, multiplicative noise, Fokker-Planck equation, Schwinger-Keldysh formalism and much more... During this seminar, almost organised as a lecture, you will embark on a journey into the world of stochastic processes, with focus on their applications in the early Universe in the context of so-called stochastic inflation. We will begin by discussing how stochasticity emerges from the coarse-graining procedure, necessary to describe the effective dynamics of the largest cosmological scales that are affected by the quantum nature of the small-scale fluctuations.

Baryonic effects in the Effective Field Theory of Large-Scale Structure and an analytic recipe for lensing in CMB-S4

Upcoming Large-Scale Structure surveys will likely become the next leading sources of cosmological information, making it crucial to have a precise understanding of the influence of baryons on cosmological observables. The Effective Field Theory of Large-Scale Structure (EFTofLSS) provides a consistent way to predict the clustering of dark matter and baryons on large scales, where their leading corrections in perturbation theory are given by a simple and calculable functional form even after the onset of baryonic processes.


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