2018 seminars

2018 seminars

Click on the talk title to download the presentation (if available).


  • 28.03.2018 Jacopo Fumagalli (NIKHEF Amsterdam)
    Unitarity and predictiveness of Higgs inflationary models.
    Abstract: In this talk I consider different types of single field inflationary models such as Higgs inflation-type (old and new proposal) and Cosmological Attractors. I will discuss the relationship between their unitarity and renormalizability properties and the quest for predictiveness. In the pursuit of consistently connecting low and high energy physics (described in terms of Standard model and inflationary parameters respectively), various aspects have to be carefully taken into account. Thus, the naïve “tree level picture” might change once quantum as well as UV corrections are considered. I will show under which circumstances a model has robust predictions or it loose its predictive power respectively. Finally, I will critically comment on the assumptions about the unknown UV completion on which the results rely.
  • 11.04.2018 Francesc Ferrer (Washington U., St. Louis)
    Cosmology of axionic string-wall networks.
    Abstract: A network of strings and domain walls can arise from a sequence of phase transitions in the early universe. Such hybrid configurations are expected, for example, in scenarios where the Peccei-Quinn symmetry is broken after inflation. We will review the evolution of these systems, that generically provide a contribution to the axion dark matter abundance. Long-lived networks can generate a new dark matter component that could be unveiled by gravitational wave detectors.
  • 25.04.2018 Tommi Tenkanen (Queen Mary University of London)
    Primordial Black Holes as Dark Matter.
    Abstract: I present some recent cosmological and astrophysical constraints on the fraction of dark matter (DM) in primordial black holes (PBHs). I consider a variety of production mechanisms and mass functions for PBHs and discuss whether they can constitute the observed DM abundance or not. I also discuss how one can constrain the physics of the early Universe with the constraints on PBHs, presenting, among other things, constraints on the running of the inflaton spectral index which are comparable to those from the Planck satellite.
  • 23.05.2018 Javier Rubio (U. Heidelberg, ITP)
    Higgs-Dilaton Cosmology: An inflation–dark-energy connection.
    Abstract: Inflation and dark energy share many essential properties. I will describe how these two eras can be easily unified into a common framework based on scale invariance. In particular, I will present a scale-invariant extension of the Standard Model non-minimally coupled to gravity containing just an additional degree of freedom on top of the Standard Model particle content. This model has some interesting features such as i) the existence of a conserved current that effectively forbids the generation of isocurvature perturbations ii) an alpha-attractor solution for the spectral tilt and the tensor-to-scalar ratio, iii) the absence of fifth-force effects and iv) a set measurable consistency relations between the inflationary observables and the dark-energy equation-of-state parameter that can be tested with future cosmological observations.
  • 06.06.2018 Neil Barrie (IPMU)
    Pendulum Leptogenesis.
    Abstract: We propose a new non-thermal Leptogenesis mechanism that takes place during the reheating epoch, utilising the Ratchet mechanism. The interplay between the oscillation of the inflaton during reheating and a scalar lepton leads to a dynamical system that emulates the well-known forced pendulum. This is found to produce driven motion in the phase of the scalar lepton which leads to the generation of a non-zero lepton number density that is later redistributed to baryon number via sphaleron processes. This model successfully reproduces the observed baryon asymmetry, while simultaneously providing an origin for neutrino masses via the seesaw mechanism.
  • 18.07.2018 Asuka Ito (Kobe U.)
    A strategy for detecting the bispectrum of stochastic gravitational waves.
    Abstract: The bispectrum of primordial gravitational waves is one of the keys to probe the early universe and the beyond standard model.In this talk, I give a method for detecting bispectra of stochastic gravitational waves. Generally, bispectra form a momentum triangle because of homogeneity of the universe. I show that an optimal filter function enables us to extract a specific configuration of the momentum triangle from the correlation of the signals. Applying this method to the pulsar timing array gravitational wave detector, as an concrete example, I argue about the dependance of positions of three pulsars to the sensitivity, which is called the overlap reduction function in the case of power spectra.


  • 29.08.2018 Toyokazu Sekiguchi (University of Tokyo)
    Simulation of the axion electrodynamics and some cosmological applications.
    Abstract: In this talk, I will describe a novel simulation method for the axion electrodynamics. We extend the classical Yee’s algorithm to incorporate the axion. This allows efficient mixing of the dynamics of the axion and electromagnetic fields in addition to accurate conservation of the constraint equations. We then present two cosmological applications of our simulation method. One is suppression of the abundance of the QCD axion via couplings to a hidden photon. The other is the late-time axion magnetogenesis in the presence of magnetic mixing between the SM electromagnetic and a hidden photon fields.
  • 12.09.2018 Eleonora Villa (CTP Warsaw)
    Relativistic perturbation theory in ΛCDM and beyond: Effects on cosmological dynamics and observations.
    Abstract: We present results from the relativistic treatment of cosmological perturbation theory in two contexts. From the theoretical side, we study relativistic corrections to the Newtonian evolution of cosmological perturbations up to second order for a CDM universe with a cosmological constant. We use coordinate systems that extend the Eulerian and Lagrangian pictures to General Relativity. Our novel expressions for all the metric perturbations, matter density and velocity extend previous results in the literature.
    From the observational side, we study the impact of a relativistic derivation of galaxy number counts for future galaxy surveys, considering the ΛCDM model and two extensions: massive neutrinos and modifications of General Relativity. Our study focuses on the biases on the constraints and on the estimation of the cosmological parameters. Our findings show the importance of including lensing in galaxy clustering analyses for testing General Relativity.
  • 10.10.2018 Andi Hektor (KBFI, Tallinn)
    Speculations of new physics on the EDGES 21cm anomaly.
    Abstract: The EDGES experiment has published the first positive results of the measurement of the global cosmological 21cm signal from the young Universe. The surprise was a two times lower baryonic temperature or, alternatively, an enhanced radio background compared to the one predicted by the standard cosmology. As the new physics alone can explain the drop in the temperature or the extra radio background, it has triggered a wave of explanations involving new physics or doubts about the signal extraction. In general, any hypothetical tiny signal of new physics can be more visible in the less complex cosmological and astrophysical environment of the cosmic dawn. For example, an energetic signal from the annihilation or decay of dark matter particle contrasts out more easily. As the baryonic content of the Universe has its coldest moment at the end of cosmic dark ages and just before the first stars start to form (at the redshifts ~20) it allows to search many interesting signals of new physics: milli-charged dark matter, various exotic remnants (axion miniclusters, cosmic defects, primordial black holes), charged exotic particles, earlier shorter epochs of dark energy domination etc. During the upcoming next years, the field will be under very exciting and intensive development. A number of experiments will test the results of EDGES: PRIZM, SARAS2, LEDA, SCI-HI, HYPERION, CPT etc. If the EDGES results will be proven our understanding of the Universe needs some serious revisions. The talk is based on the recent papers: 1805.09319, 1805.06513, 1803.09697, 1803.03245 and the discussions at the workshop, https://indico.cern.ch/event/730318.