SciPost Submission Page
Gravitational waves from the early universe
by Rafael R. Lino dos Santos, Linda M. van Manen
This is not the latest submitted version.
Submission summary
| Authors (as registered SciPost users): | Rafael Robson Lino dos Santos · Linda van Manen |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2212.05594v1 (pdf) |
| Date submitted: | 2022-12-14 19:13 |
| Submitted by: | Lino dos Santos, Rafael Robson |
| Submitted to: | SciPost Physics Lecture Notes |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Phenomenological |
Abstract
These lecture notes are based on the course "Gravitational waves from the early universe" given at the 27th W.E. Heraeus "Saalburg" Summer School 2021 by Valerie Domcke. Ongoing and future collaborations will probe different frequency ranges of the gravitational wave spectrum, allowing for probing different stages of the early universe and Beyond Standard Model physics. Due to the very high energies involved, accelerators cannot probe them. Therefore, current knowledge about new physics is limited and relies on bounds from CMB observations and theoretical assumptions about these energy scales. While some models are in tension with CMB data, others are unconstrained in shorter wavelength scales. Nonetheless, each one of these models has a gravitational wave density spectrum that can be compared to data. These lecture notes review the formalism of gravitational waves in General Relativity and introduce stochastic gravitational waves, primordial sources, and detection efforts.
Current status:
Reports on this Submission
Strengths
1 - The article, based on lectures given by Valerie Domcke, covers topics of great current interest in gravitational wave cosmology.
2 - It combines relevant introductory material with both theoretical and observational expositions. It is useful to have a discussion of both GW sources and their detection in one place.
3 - It conveys the excitement of the field.
4 - The grammar and presentation are generally good.
Weaknesses
1 - The pedagogical approach is rather uneven. Some topics are covered almost from an undergraduate level, and others seem to be aimed at more advanced researchers. For example, in section 2.2, the discussion of gauge invariance is begun before introducing what a gauge transform is.
2 - There are quite a few inconsistencies of notation and signs of haste in the editing. For example, if c is kept explicitly, then it should appear in the retarded time formula around 3.4.
3 - Section 5 is too brief: it doesn't address much of the physics of the production of GWs, gives little more than formulae, and in places is confusing. What does it mean, for example, to say that "loops are more energetically favourable" on p30? The process of loop production conserves energy.
4 - Section introduces the Michelson interferometer, relevant for ground-based detectors, but only mentions the detectors more relevant for cosmology (PTA and LISA).
Report
I appreciate the Saalburg summer school's encouragement of participants to write up notes from the lectures they attend. It is a useful pedagogical exercise, and I hope that it has deepened the authors' interest in the field.
However, I don't think these notes are in a good enough shape to merit publication in SciPost. The notes should pay more attention to the order in which material is introduced, its level, its clarity, and its accuracy. In order to be a useful reference complementary to those already existing, I think they should include more explanation of early universe GW production, at a level that students could then go on to start reading the research literature. It would also be useful to have more discussion of relevant detectors like LISA and PTA.
Requested changes
I don't think the notes are sufficiently close to being publishable to make a detailed list of specific changes useful.