Gravitational-Wave Primordial Cosmology

17 mai 2021, 14:00 → 19 mai 2021, 18:30 Europe/Paris

This virtual workshop gathers a group of international experts on gravitational-wave primordial cosmology. It will take place on zoom, over three half-days on May 17th-19th, from 2pm to 6.30pm CEST.

The main goal of the workshop is to critically review recent progress about the potential of gravitational waves to probe inflation on small scales, but related aspects like preheating, primordial black holes, phase transitions and the thermal history of the universe will also be discussed. A particular focus will be given to the observability of the various properties of the stochastic gravitational wave background, including its spectral shape and polarisation, and their implications for the inflationary mechanism and field content. Cross-correlations with other observables will also be discussed, together with methods of data analysis and prospect for detection.

But this workshop will not be limited to a review of recent progress. It also aims at collectively identifying important open questions and assessing the potential of discovery of gravitational wave astronomy for primordial cosmology. For this, in addition to invited presentations, lasting 30 minutes each, time will be left for informal discussions, and the workshop will end with a summary of the important issues to address in this field.

There is no registration fee, but registration through indico is compulsory.

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Speakers include:

• Matteo Braglia
• Chiara Caprini
• Sébastien Clesse
• Ema Dimastrogiovanni
• Guilhem Domenech
• Matteo Fasiello
• Daniel Figueroa
• Ryusuke Jinno
• Azadeh Maleknejad
• Subodh Patil
• Shi Pi
• Mauro Pieroni
• Antonio Riotto
• Lorenzo Sorbo
• Spyros Sypsas
• Gianmassimo Tasinato
• Caner Ünal
• Lukas Witkowski

Organisers: Sébastien Renaux-Petel, Jacopo Fumagalli, Sebastian Garcia-Saenz, Sadra Jazayeri, Lucas Pinol, Lukas Witkowski

This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme under grant agreement No 758792, project GEODESI.

 

lundi 17 mai

1 Welcome

Orateur: Sébastien Renaux-Petel (IAP-CNRS)

Welcome.mp4

2 Cosmology with LISA

Orateur: Chiara Caprini

Caprini.mp4

Caprini.pdf

3 Measuring the net circular polarization of the stochastic gravitational wave background with interferometers

Orateur: Lorenzo Sorbo

Sorbo.mp4

Sorbo.pdf

4 Stochastic Gravitational Wave Backgrounds (SGWB) characterization with LISA

In this talk I will discuss Stochastic Gravitational Wave Backgrounds (SGWB) characterization with LISA. After a general introduction on SGWB detection, I will explain the peculiar features of LISA with a focus on the response function and on the noise spectrum. The core of my talk will be the presentation of two different methods for model independent SGWB frequency reconstruction:
- The so-called ``binning method'' (1906.09244, 2009.11845) based on the idea of approximating the signal with a piecewise-defined function where each sub-function is a power law.
- A more recent method (2004.01135) based on principal components analysis.
The problem of component separation to disentangle a cosmological SGWB from astrophysical foregrounds is addressed in both cases.

Orateur: Mauro Pieroni

Pieroni.mp4

Pieroni.pdf

5 Open discussion

Mo-open-discussion-1.mp4

16:10 Break

6 Gauge Fields in Inflation, Origin of Matter, and Gravitational Waves

Modern cosmology inevitably involves particle physics beyond the Standard Model to explain long-standing puzzles: the origin of matter asymmetry, nature of dark matter and cosmic inflation. In this talk, I will explain that gauge fields in inflation can possibly solve and relate these seemingly unrelated mysteries of modern cosmology. As a smoking gun, this setup has robust observable signatures for the gravitational background to be probed by future CMB missions and laser interferometer detectors.

Orateur: Azadeh Maleknejad

Maleknejad.mp4

Maleknejad.pdf

7 Probing the Early Universe Particle Content with Primordial Messengers

Some of our best ideas on early universe physics are about to be put to the test by an unprecedented array of cosmological probes. The data these will collect span a vast range of scales, from the CMB to large scale structure, from pulsar timing arrays all the way to laser interferometers. This combined wealth of new information holds the potential to transform not just our understanding of cosmology, but also particle physics. Probing the earliest accessible epoch, the accelerated expansion known as inflation, is absolutely crucial: inflation can provide a cosmological portal to otherwise inaccessible energy scales. This is the “cosmological collider” idea. The spectacular success of the inflationary paradigm in explaining the origin of cosmic structure demands that we tackle a number of compelling questions still in need of an answer:
- what is the energy scale of inflation?
- what fields were active during inflation?
In this talk I will review recent progress on the inflationary field content focussing on an effective theory approach. I will also highlight key observables, starting with primordial gravitational waves, and discuss the prospect for detection.

Orateur: Matteo Fasiello

Fasiello.mp4

Fasiello.pdf

8 Testing inflation with small-scale anisotropies

Inflation predicts a stochastic background of gravitational waves. In this talk I will discuss how anisotropies in the gravitational wave energy density can be a powerful tool in characterizing the inflationary GW background and potentially distinguishing it from backgrounds due to other sources.

Orateur: Ema Dimastrogiovanni

Dimastrogiovanni.mp4

Dimastrogiovanni.pdf

9 Open discussion

Mo-open-discussion-2.mp4

mardi 18 mai

10 Probing gravitational waves using spectral distortions

CMB anisotropies probe primordial gravitational wave backgrounds of frequencies between 10^{-18} and 10^{-15} Hz. Pulsar timing arrays begin to be sensitive to backgrounds starting in the nano-hertz regime, seemingly leaving an approximately six decade gap in frequency coverage. This talk will discuss how spectral distortions of the CMB covers this gap in a meaningful way, and discuss various phenomenological consequences for a variety of beyond the standard model scenarios, including low scale (dark sector) phase transitions, cosmic strings and ultra-light axions.

Orateur: Subodh Patil

Patil.mp4

Patil.pdf

11 Features in the stochastic gravitational wave background from two-field inflationary models.

Orateur: Matteo Braglia

Braglia.mp4

Braglia.pdf

12 Oscillations in the stochastic gravitational wave background from small-scale features

Orateur: Lukas Witkowski

Witkowski.mp4

Witkowski.pdf

13 Observing primordial GWs from excited states

Orateur: Spyros Sypsas

Sypsas.mp4

Sypsas.pdf

14 Open discussion

Tu-open-discussion-1.mp4

16:00 Break

15 Probing the Physics of Inflation with Gravitational Wave Experiments

Orateur: Gianmassimo Tasinato

Tasinato.mp4

Tasinato.pdf

16 Imprints of Primordial Non-Gaussianity on Gravitational Wave Spectrum

I will talk about the imprints of small, mild and large primordial local NG in density perturbations on the induced GW spectrum.

Orateur: Caner Ünal

Unal.mp4

Unal.pdf

17 Are induced GWs gauge dependent?

Orateur: Guillem Domènech

Domenech.mp4

Domenech.pdf

18 Open discussion

Tu-open-discussion-2.mp4

mercredi 19 mai

19 NANOGrav 12.5-yr result and induced gravitational waves

I will briefly review the properties of SGWB induced by the scalar perturbation, as well as its connection to the primordial black holes (PBHs). NANOGrav reported the discovery of a common-spectrum process of the time residuals in their 12.5-yr data set of pulsar timing array, which might be the first detection of nano-hertz SGWB. Based on the recent developments on the spectral shape of SGWB, I will show that this signal could be connected to the planet-mass PBH candidates found by OGLE recently, if there is a dust-like stage prior to the radiation dominated era.

Orateur: Shi Pi

Pi.mp4

Pi.pdf

20 Primordial Nano Black Holes

Orateur: Antonio Riotto

Riotto.mp4

Riotto.pdf

21 Primordial Black Holes: gravitational-wave signatures and possible contribution to the dark matter

The detection of gravitational-waves from binary black hole mergers has rekindled the idea that primordial black holes may have formed in the early Universe. I will review some recent developments in the field of primordial black holes: formation mechanisms, mass function, astrophysical limits, possible contribution to the Dark Matter and links to the Baryogenesis. I will particularly focus on their gravitational-wave signatures: merging rates, explanation of recent LIGO/Virgo events (GW190521, GW190815, GW190425), subsolar black hole searches, stochastic gravitational-wave backgrounds and continuous waves or high-frequency GW detectors as a probe of planetary-mass primordial black holes.

Orateur: Sebastien Clesse

Clesse.mp4

Clesse.pdf

22 Open discussion

We-open-discussion.mp4

16:00 Break

23 Deformation of the gravitational wave spectrum by density perturbations

In recent years, the possibility of having large density perturbations at high wavenumbers has been actively studied, especially in the study of primordial black holes (PBHs). In this presentation, we point out that such density perturbations affect any pre-existing gravitational wave (GW) spectrum through CMB-like effects. Since GWs produced in the early universe propagate through the density perturbations before reaching the observer, GWs coming from each direction experience different evolution depending on the density perturbations. As a result, the observed (directionally averaged) GWs generally have a deformed spectrum compared to the original one. Therefore, by carefully comparing the observed spectrum with the theoretical GW spectrum at the time of production, we may be able to indirectly observe density perturbations at high wevenumbers. In this presentation, we explain how this effect shows up and estimate the maximum expected impact on the GW spectrum, taking into account the latest bound on density perturbations from PBH searches.

Orateur: Jinno Ryusuke

Jinno.mp4

Jinno.pdf

24 Probing the 'primordial dark ages’ with gravitational waves. Implications for reheating.

Orateur: Daniel Figueroa

Figueroa.mp4

Figueroa.pdf

25 Guided discussion

Dimastrogiovanni.pdf

Figueroa.pdf

Guided-discussion.mp4

Introduction-Renaux-Petel.pdf

Wands.pdf