Lorentz Institute

Sept. 15, 2021, 3 p.m.
Casimir room (276), Oort building

A theory of Hybrid monodromy inflation with two fields

Morgane Konig

In this talk I will revisit the hybrid inflation theory first proposed by A.Linde. In his original paper, A.Linde considers an inflationary model involving two coupled massive scalar fields. This theory fails to predict a spectral index coherent with the Planck data. I will focus on a model developed by Stewart that allows for a viable spectral tilt that fits the current data. We will see that we can study this hybrid inflation as an effective field theory showing that its predictions agree with the Planck data. Furthermore, I will explore the quantum stability of this model and outline a possible mechanism realizing the scalars as compact axions dual to massive 4-forms.

Sept. 29, 2021, 3 p.m.
Casimir room (276), Oort building

Torsion-squared gravity, and its multiplier extensions

Will Baker

We review the recently suggested theory of torsion-squared plus curvature-squared invariants, which replaces the curvature scalar of Einstein and Hilbert. This theory is conformal around the flat, torsionless background, but is known to produce a viable cosmology when the torsion adopts a vacuum expectation value. While the linear theory has some attractive quantum properties, the nonlinear theory suffers from complexities which are furthermore suggested to condemn most other instances of Poincare gauge theory. We develop a general extension of Poincare gauge theory with sixty multiplier fields, of the kind employed already in teleparallel gravity. The potential of multipliers to passify the general dynamics is explored in the Hamiltonian picture. In the Lagrangian picture, the uniquely acceptable multiplier configuration is shown to support the Newtonian limit of the theory on the vacuum expectation value.

Oct. 13, 2021, 3 p.m.
Casimir room (276), Oort building

Primordial black holes in an early matter-dominated era and stochastic inflation

Julián Rey

We consider the possibility that the majority of dark matter in our Universe consists of black holes of primordial origin. We examine the effects of stochastic inflation and an early matter-dominated era on the abundance of these black holes. We show that the power spectrum of comoving curvature perturbations computed in stochastic inflation matches the result obtained by solving the Mukhanov-Sasaki equation at the linear level, even in the presence of an ultra-slow-roll phase. We also find a significant reduction in the required tuning of the parameters of the inflationary potential in the matter-dominated scenario, in contrast to the standard case of formation during radiation domination. We show that the stochastic background of primordial gravitational waves resulting from this mechanism could be detected by future space-based observatories.

Nov. 10, 2021, 3 p.m.
Casimir room (276), Oort building

Testing one-loop galaxy bias

Andrea Pezzotta

Observations of different types of galaxies, or clusters of galaxies, has led to realisation that these objects are biased tracers of the dark matter density field, and that a consistent theory of galaxy bias must be developed in order to fully exploit the cosmological constraining power of galaxy redshift surveys. From this point of view, perturbative approaches are a standard way of describing the galaxy density field as a function of the underlying matter distribution. In this talk we are going to present results from the testing of different modelling assumptions of one-loop galaxy bias, and their impact on the recovery of cosmological parameters. We investigate the relevance of allowing for either short range non-locality or scale-dependent stochasticity by fitting the real-space galaxy auto power spectrum and the combination between galaxy-galaxy and galaxy-matter power spectrum. From a comparison between the goodness-of-fit, unbiasedness of cosmological parameters, and merit of the model, we find that a simple four-parameter model (linear, quadratic, cubic non-local bias, and constant shot-noise) with fixed quadratic tidal bias provides a robust modelling choice for the auto power spectrum of the three galaxy samples, up to a maximum scale of 0.3 h/Mpc and for an effective volume of (6 Gpc/h)^3. On the contrary we find that the combined statistics seems to favour the presence of either higher derivatives or scale-dependent shot-noise, with the latter providing the most accurate and stable results.

Dec. 1, 2021, 3 p.m.
Casimir room (276), Oort building

Landau damping for gravitational waves

Flavio Bombacigno

We discuss the possibility that gravitational scalar waves could experience kinematic damping when propagating in a noncollisional gas of particles. In particular, by describing the medium at the equilibrium with a Jüttner–Maxwell distribution and under the hypothesis of homogeneity and isotropy, we analytically determine the damping rate of the signal. We find that Landau damping can take place only for subluminal phase velocities of the wave, when a characteristic relation between the effective mass of the scalar mode and the thermodynamic properties of the medium is satisfied. Then, we investigate by means of numerical techniques relativistic media in cosmological settings, showing how the interaction with gravitational scalar waves can lead to peculiar phenomenological marks in the power spectrum of the media.

Dec. 1, 2021, 3 p.m. CS Flavio Bombacigno (Universidad de Valencia & IFIC) Landau damping for gravitational waves

Dec. 8, 2021, 7 p.m. CE Michiel van den Broeke (Universiteit Utrecht) TBA

LS = Lorentz Seminar, Casimir room (276), Oort building
CE = Colloquium Ehrenfestii, De Sitter lecture room, Oort building
SBM = Soft & Biological Matter Seminar, Casimir room (276), Oort building
CS = Cosmology Seminar, Casimir room (276), Oort building
ST = String Theory Seminar, Casimir room (276), Oort building