Primordial Black Hole Messenger of Dark Universe

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is a compact and comprehensive review on the primordial black hole in understanding the physics beyond the Standard Model of the elementary particles and the dark matter. 

I have, however, some requests.

The author says about the importance of the gravitational wave but details are not given. I would like to know how the primordial gravitational waves were created by the primordial black holes and how they carry any information of the physics beyond the Standard Model. 

The author mainly considered the inflation generated by the axion field. The nature of the axion distinguished from other fields or particles is that it is a pseudo scalar with odd parity. Therefore the condensation of the axion field strongly violates the parity symmetry and therefore the condensation in the present universe conflicts with the observation although it may condense in the early universe like the inflation era. Therefore there should be traces of the violation in the large scale structure and gravitational wave. Therefore I would be happy if the author could mention the effects. 

Comments on the Quality of English Language

For example, "comma"s are missing in many places, which made me understand the sentences.

Author Response

Comments 1: 

The author says about the importance of the gravitational wave but details are not given. I would like to know how the primordial gravitational waves were created by the primordial black holes and how they carry any information of the physics beyond the Standard Model. 

Response:  I am grateful to the reviewer for mentioning this important point. Indeed, PBH formation and evolution are inevitably accompanied by gravitational perturbations, being the source of gravitational wave signals and various forms of gravitational wave background. This point is mentioned in the text (page 3 lines 54-57) and References [38-46] to the current discussions of this topic are added to the Bibliography in the revised version.

Comments 2: The author mainly considered the inflation generated by the axion field. The nature of the axion distinguished from other fields or particles is that it is a pseudo scalar with odd parity. Therefore the condensation of the axion field strongly violates the parity symmetry and therefore the condensation in the present universe conflicts with the observation although it may condense in the early universe like the inflation era. Therefore there should be traces of the violation in the large scale structure and gravitational wave. Therefore I would be happy if the author could mention the effects. 

Response 2: I thank the reviewer for drawing attention to necessity to clarify these points. In the considered scenarios inflation is not driven by axion field, which is a spectator at the inflationary stage, driven by specific inflaton field. The considered scenarios involve pseudo-Nambu-Goldstone nature of the ALP field and have no relation with the pseudoscalar nature of axion. These points are mentioned and clarified in the text (page 4 between lines 114 and 115 and page 5 lines 126-127).

However, if the first phase transition takes place in the early Universe after reheating, axion can play the role of a CP violating phase before ALP field oscillations start. Space distribution of such phase reflects the pattern of axion string network and its contribution to baryosynthesis can lead to strong inhomogeneity of baryon excess, making possible formation of antimatter domains in baryon asymmetrical Universe. This comment with the corresponding references is added to the text (page 8 line 244) and Bibliography (references [101, 102].

Following Editor's recommemdations the repeating rate and self-citations are reduced in the revised version. The corresponding corrected sentences are marked blue in the text. The comments by other reviewers are also taken into account and the corresponding corrections and insertions are marked red. All the noticed misprints are corrected.

 

Reviewer 2 Report

Comments and Suggestions for Authors

This is a timely work devoted on essential topics of modern theoretical physics. The approach is concise, to the point and includes many mainstream aspects of PBHs as DM candidates and their allignment with beyond SM physics. I recommend that this article is accepted for publication. 

Author Response

Comments: This is a timely work devoted on essential topics of modern theoretical physics. The approach is concise, to the point and includes many mainstream aspects of PBHs as DM candidates and their allignment with beyond SM physics. I recommend that this article is accepted for publication. 

Response: I can only thank the reviewer for kind evaluation of my work. Following Editor's recommemdations the repeating rate and self-citations are reduced in the revised version, as well as the comments by other reviewers are taken into account

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript reviews primordial black hole mechanisms and consequences for cosmology and astrophysics in the viewpoint of particle physics motivated models. This review is interesting, well described, capturing all the relevant information either of the basics, and some of its models. The manuscript alludes to the existence of modified gravity models that also tackle the issue of primordial black holes, and to several other reviews so to complement the present work.

 

I have only two comments for minor revisions:

- Perhaps, some references (or reviews) on the modified gravity approach to this topic would allow for a reader to access additional information;

- A revision on the writting, since there are many typos (commas instead of ending points, capital letters when there should be non-capital, two ending points instead of just one). This would allow for a softer reading of the work.

 

After implementing these minor revisions, I recommend the work for publication.

Author Response

Comments 1. Perhaps, some references (or reviews) on the modified gravity approach to this topic would allow for a reader to access additional information;

Response: I am grateful to the reviewer for this comment. Discussion on page 3 lines 81-83 and the corresponding references 59-70 are added to the Bibliography of the revised version and marked red. 

Comments 2: A revision on the writting, since there are many typos (commas instead of ending points, capital letters when there should be non-capital, two ending points instead of just one). This would allow for a softer reading of the work.

Response: I thank the reviewer for attention to this points. All the noticed misprints are corrected in the revised version.

Following Editor's recommemdations the repeating rate and self-citations are reduced in the revised version. The corresponding corrected sentences are marked blue in the text. The comments by other reviewers are also taken into account and the corresponding corrections and insertions are marked red.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I am satisfied by the revisions and I may recommend this paper for publication.