Gravitational wave cosmology

Gravitational waves are a new window to hear the universe. Image credit: LIGO/T. Pyle.

Gravitational waves are the new window to observe the universe. They are clean source of information, as they barely interact with matter. LIGO detected gravitational waves coming from the merger of binary black holes and binary neutron stars but these are not the only detectable sources of gravitational waves.

Gravitational waves may have also been generated from quantum fluctuations during inflation, cosmic strings and phase transitions in the early universe, when the energy scale was extremely high. Now, due to the large number of unresolved sources in our universe, these signals will appear as a Stochastic Gravitational Wave Background (see this review on the cosmological sources). I am interested in exploring cosmological sources of the gravitational wave background and the information that can be extracted about the history of our universe. In particular, I have explored the generation of induced1 gravitational waves in a general cosmological background in this article) for the first time in an analytical way. The induced gravitational waves are an essential contribution to the stochastic gravitational wave background as they carry information about the primordial fluctuations and may be linked to the primordial black hole scenario (check this review on primordial black holes). I have also proposed to use the induced gravitational waves as a probe of the thermal history of the universe here.

Interestingly, gravitational waves generated out of quantum fluctuations during inflation also leave an imprint in the Cosmic Microwave Background as B-mode2 polarization of the radiation we receive (check my works on inflation and CMB here). I also study technical aspects of the theoretical formulation of gravitational waves in cosmology.


  1. Since gravity is a non-linear theory, matter fluctuations can source gravitational waves at second order in perturbation theory. ^
  2. B-mode refers to the curl like pattern that only gravitational waves (and lensing) leaves in the CMB. ^
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Guillem Domènech
Researcher in gravity and cosmology

I am an Emmy Noether Research Group Leader at the Insitute for Theoretical Physics at the Leibniz University Hannover. My research focuses in various aspects of cosmology, gravity and particle physics.

Posts

Illustration of the early universe in the context of the primordial black hole scenario and induced gravitational waves. Figure made by …

Publications

The primordial spectrum of fluctuations may present a large peak as a result of enhancing features during inflation. This may include, …

The primordial fluctuations on large scales are adiabatic, but on smaller scales this need not be the case. Here we derive the general …

A bulk acoustic wave cavity as high frequency gravitational wave antenna has recently detected two rare events at $5.5$MHz. Assuming …

Oscillations in the frequency profile of the scalar-induced contribution to the stochastic gravitational wave background are a …

We provide a review on the state-of-the-art of gravitational waves induced by primordial fluctuations, so-called induced gravitational …

Primordial black holes (PBHs) from the early Universe have been connected with the nature of dark matter and can significantly affect …

In view of growing interest in long range scalar forces in the early universe to generate primordial black holes, we study in detail …

We investigate in detail the spectrum of gravitational waves induced by a peaked primordial curvature power spectrum generated in …

Gravitational waves (GWs) induced by scalar curvature fluctuations are an important source of the cosmological GW background and a …

We calculate the gravitational waves (GWs) induced by the density fluctuations due to inhomogeneous distribution of primordial black …

Recently, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) claimed the detection of a stochastic …

The scalar perturbation induced gravitational waves are a probe of the primordial density perturbation spectrum on small scales. In …

Gravitational waves are inevitably produced by second order terms in cosmological perturbation theory. Most notably, the so-called …

The combination of non-minimal couplings to gravity with the post-inflationary kinetic-dominated era typically appearing in …

In view of growing interest in tensor modes and their possible detection, we clarify the definition of tensor modes up to 2nd order in …

Talks

Outreach talk for the European Researcher’s Night 2021, venetonight at Padova.