Challenges of the Standard Cosmological Model
Round 1
Reviewer 1 Report
In this manuscript, the author briefly explained some problems of current cosmological observations. The explanations are clear and easy to understand. I recommend that this review paper be published in its present form.
Author Response
I would like to thank the referee for taking the time to read the paper. I have extensively revised the English language and I hope now it is now in a better shape.
Reviewer 2 Report
The work is a review of the current state of tensions in cosmolgy. After a brief overview of the standard LCDM model, the author briefly introduces the current state of crisis of the model and focuses on the well known tensions on H0 and s8 parameters, also providing complementary discussions on AL anomalies and the curvature of the universe.
The review attempts to condense a lot of information and is definitely aimed at a reader already familiar with the topic. In fact, the review has no didactic tone whatsoever and no equations are included to guide the reader to further understanding. For a reader already expert in the field, however, it is a good summary of the current state of the art. I find the work well-written and well-structured, aligning with the various works already written by the same author on the topic. I believe that the article can be published in the Universe journal after the author addressed the following suggestions:
1- the introduction lacks references in its many statements. Although some reviews are cited at the end of the section, I feel that at least the basic bibliography should be provided in the text.
2- The introduction mentions the SNOWMASS call. It would be interesting to specify (in the text or as a footnote) what this call is and why it is important to mention it so directly. Indeed, the explanation of community activity it may be of interest to understand the work behind this line of research but it may also be jarring if it is not stressed why it is so important to mention it. Also, note that there are acronyms (i.e LoIs, SH0ES etc) that are not explained. Finally, I find it weird to refer directly to the reader with "you can also find" and "I encurage you" instead of using passive forms or referring to a general reader.
3- It is necessary to check whether the increasing numbering of the references is respected. I have noticed that some are out of place.
4- In section 2, the author refers to the use of Bayesian analyses for the estimation of cosmological parameters. Actually various statistics are used to do this, and the simplest form of the MCMC method is widely used. This should be mentioned and perhaps the codes most commonly used by the scientific community should be cited.
5- The discussion in section 2.2 should be concluded with a comment on the effective validity of the solutions mentioned for solving the problem of H0 estimates.
6- universe should always be written with the use of lower or upper case, as chosen by the author.
7- In 2.2.1, the author mentions analyses done "without performing a model comparison and without any consideration regarding the goodness of the fit". It would be helpful to mention by which criterion the goodness of the model was ruled.
8- the author discusses the model-dependence of BAO estimation, which is an interesting and legitimate topic especially when analysing alternative models to the LCDM. At the same time, it is worth mentioning that there is a treatment of BAO that makes them less model-dependent, called angular 2-point BAO correlation function, and these data are also implemented in Montepython code (see 1804.07261). These estimates have larger error bars due to non-use of the radial component of the estimate, but are still valid even for alternative model constraints.
9- Section 3.2 deals with the internal inconsistency of data at low and high Planck multipoles. It is necessary in this section to improve the bibliography, especially by providing citations where it is stated that the data prefer Alens>1 or Alens=1. Furthermore, it is worth mentioning that several people in the Planck collaboration traces this inconsistency to statistical fluctuation and that the scientific community does not unanimously perceive this anomaly as a real physical problem.
10-Also in Sec. 3.3 I note a reference gap, e.g. where Omegak constraints are provided.
11-In recent years, the debate on the curvature of the universe has led many to question whether and how the choice of data type affects the parameter constraint, and to wonder how data should be chosen and safely combined for analysis in order to obtain physically meaningful results. It would be interesting for the discussion of the article to mention this awareness.
12- In sec. 3.4 the compatibility between different experiments is discussed, citing how assuming inflationary parameters such as spectral index running and running of the running can influence these results. These parameters are not introduced at all and I suggest to revisit this part.
Author Response
I would like to thank the referee for taking the time to read the paper. Below my detailed answer to their comments. 1- the introduction lacks references in its many statements. Although some reviews are cited at the end of the section, I feel that at least the basic bibliography should be provided in the text. I added a few references in the introduction.2- The introduction mentions the SNOWMASS call. It would be interesting to specify (in the text or as a footnote) what this call is and why it is important to mention it so directly. Indeed, the explanation of community activity it may be of interest to understand the work behind this line of research but it may also be jarring if it is not stressed why it is so important to mention it. Also, note that there are acronyms (i.e LoIs, SH0ES etc) that are not explained. Finally, I find it weird to refer directly to the reader with "you can also find" and "I encurage you" instead of using passive forms or referring to a general reader. I added a footnote explaining what Snowmass is and its importance, and I modified the direct references to the reader (that were actually weird!).
3- It is necessary to check whether the increasing numbering of the references is respected. I have noticed that some are out of place. I fixed the references.
4- In section 2, the author refers to the use of Bayesian analyses for the estimation of cosmological parameters. Actually various statistics are used to do this, and the simplest form of the MCMC method is widely used. This should be mentioned and perhaps the codes most commonly used by the scientific community should be cited. I added the references to the most common MCMC codes used for the data analysis.
5- The discussion in section 2.2 should be concluded with a comment on the effective validity of the solutions mentioned for solving the problem of H0 estimates. I added a comment about the validity at the end of the section.
6- universe should always be written with the use of lower or upper case, as chosen by the author. I corrected Universe with a capital letter in everywhere.
7- In 2.2.1, the author mentions analyses done "without performing a model comparison and without any consideration regarding the goodness of the fit". It would be helpful to mention by which criterion the goodness of the model was ruled. I added the definition of tension that is used to classify the goodness of the model.
8- the author discusses the model-dependence of BAO estimation, which is an interesting and legitimate topic especially when analysing alternative models to the LCDM. At the same time, it is worth mentioning that there is a treatment of BAO that makes them less model-dependent, called angular 2-point BAO correlation function, and these data are also implemented in Montepython code (see 1804.07261). These estimates have larger error bars due to non-use of the radial component of the estimate, but are still valid even for alternative model constraints. I added a footnote for the angular 2-point BAO correlation function including the references.
9- Section 3.2 deals with the internal inconsistency of data at low and high Planck multipoles. It is necessary in this section to improve the bibliography, especially by providing citations where it is stated that the data prefer Alens>1 or Alens=1. Furthermore, it is worth mentioning that several people in the Planck collaboration traces this inconsistency to statistical fluctuation and that the scientific community does not unanimously perceive this anomaly as a real physical problem. I added a comment explaining that the official position of the Planck collaboration is to consider Alens a statistical fluctuation, and the consequences that this produces on the reliability of the results.
10-Also in Sec. 3.3 I note a reference gap, e.g. where Omegak constraints are provided. I added a reference to the Efstathiou and Gratton paper, but I am not sure what else is missing. I hope that is enough.
11-In recent years, the debate on the curvature of the universe has led many to question whether and how the choice of data type affects the parameter constraint, and to wonder how data should be chosen and safely combined for analysis in order to obtain physically meaningful results. It would be interesting for the discussion of the article to mention this awareness. I added a comment about this at the end of the section with related reference.
12- In sec. 3.4 the compatibility between different experiments is discussed, citing how assuming inflationary parameters such as spectral index running and running of the running can influence these results. These parameters are not introduced at all and I suggest to revisit this part. I added the definition of the inflationary parameters. I also would like to point out that I extensively revised the English language of the paper as requested by the second referee. I would like to thank the reviewer once again for the useful comments that improved the quality of the manuscript and I hope the paper is now ready for publication. Sincerely, Eleonora Di Valentino
