Searching for Pairs of Higgs Bosons in the LHC Run 2 Dataset
Round 1
Reviewer 1 Report
Let me start by apologizing for the delay in submitting this review.
In summary, this paper is a very useful review of dihiggs at LHC and I think it will be a useful resource for people in the field. I think the paper should be accepted, but I have a few suggestions for the authors that I will list below that can clarify a few points.
But first: there is something wrong with the pdf file that I have read: something is missing in a lot of places – empty space instead of whatever is missing (in some places it is HH, W or Z that is missing). I suspect that there are some author defined LaTeX commands that have not been translated in the conversion to pdf, but I can't be sure, so this must be checked. I attach a pdf file where I have marked in red the places I found, but there may be others that I have missed. In addition, there is a misprint on p 13: "seraches" should be "searches".
But now to the more interesting points I would like to raise:
1. p 2, lines 64-65:
"These measurements imply that..." regarding the metastability of the Universe. This is true if the SM is true, but given the theme of the paper, looking for deviations from the SM, I think it should be pointed out that this result holds for the SM only.
2. p 3-4, around and after eq (5):
It is explained that SMEFT has a Higgs doublet while HEFT has only the Higgs boson field. I think it would be worthwhile to mention that SMEFT is formulated in an SU(2)xU(1) invariant way, and then the potential has to be minimised, while HEFT is U(1) invariant and the EW symmetry has already been broken. (It's obvious, but for a reader not familiar with these theories it may be nice.)
3. p 5, top of page:
The deviation in the top Yukawa is called \kappa. Maybe call it \kappa_t instead?
4. p 5, line 128:
"distributions as function of m are shown..." Should this be m_{HH}?
5. p 6, line 157:
Why is the diagram with the chromomagnetic operator not simulated yet? Would it make a difference?
6. p 6 and forward:
It would be nice to write down which operators in SMEFT and HEFT that the various couplings/Wilson coefficients correspond to, and the same for the chromomagnetic operator mentioned above.
7. p 6-7:
Another point is that some of the SMEFT operators contain derivatives, e.g. Q_{\phi D} and Q_\{phi \box} in the Warsaw basis. This would give momentum dependence in the Feynman rules and therefore not just an overall change in coupling strength. Is this important and can it change the kinematical distributions?
8. p 6-7, line 163 and below:
It is pointed out that in SMEFT, kappa and c_2 are related, which is not the case in HEFT. Does that mean that SMEFT is missing something that can be described in HEFT? Or is it a redundancy in HEFT? Are there UV complete models that can be described by HEFT but not by SMEFT? This may be a bit too theoretical for this paper, but perhaps something can be commented.
9. p 7, caption of Table 2:
Wilson coefficients in HEFT or SMEFT?
10. p 25, second bullet point:
"which allowed" should be "which would allow"
Comments for author File: 
Comments.pdf
Author Response
Let me start by apologizing for the delay in submitting this review.
In summary, this paper is a very useful review of dihiggs at LHC and I think it will be a useful resource for people in the field. I think the paper should be accepted, but I have a few suggestions for the authors that I will list below that can clarify a few points.
>> Thanks.
But first: there is something wrong with the pdf file that I have read: something is missing in a lot of places – empty space instead of whatever is missing (in some places it is HH, W or Z that is missing). I suspect that there are some author defined LaTeX commands that have not been translated in the conversion to pdf, but I can't be sure, so this must be checked. I attach a pdf file where I have marked in red the places I found, but there may be others that I have missed. In addition, there is a misprint on p 13: "seraches" should be "searches".
>> Indeed, there seems to be something wrong with the compilation by the journal -- apologies for that. We have tried to make it as package-independent as possible for the re-submission.
But now to the more interesting points I would like to raise:
- p 2, lines 64-65:
"These measurements imply that..." regarding the metastability of the Universe. This is true if the SM is true, but given the theme of the paper, looking for deviations from the SM, I think it should be pointed out that this result holds for the SM only.
>> Added “These measurements thus imply that, in the SM,...”
- p 3-4, around and after eq (5):
It is explained that SMEFT has a Higgs doublet while HEFT has only the Higgs boson field. I think it would be worthwhile to mention that SMEFT is formulated in an SU(2)xU(1) invariant way, and then the potential has to be minimised, while HEFT is U(1) invariant and the EW symmetry has already been broken. (It's obvious, but for a reader not familiar with these theories it may be nice.)
>> We agree with the suggestion and added
“ and the theory is formulated in a $SU(2)\times U(1)$ invariant way where the electroweak symmetry is broken by the scalar potential minimization.” when SMEFT is mentioned and
“In this case the theory is invariant under $U(1)$ and the electroweak symmetry is assumed to have been already broken.” when HEFT is described
- p 5, top of page:
The deviation in the top Yukawa is called \kappa. Maybe call it \kappa_t instead?
>> this is another misprint
- p 5, line 128:
"distributions as function of m are shown..." Should this be m_{HH}?
>> yes, again, a problem with the compilation
- p 6, line 157:
Why is the diagram with the chromomagnetic operator not simulated yet? Would it make a difference?
>> This diagram appears only at higher order in the HEFT expansion. This is therefore not included in the existing NLO MC, that simulates an HEFT. For SMEFT, the operator is present but only in the LO SMEFT MC that is not used by the reviewed analyses, and there is no study that we can cite to quantify the impact in a SMEFT scenario. We edited the sentence to clarify that this is not simulated in the NLO MC.
- p 6 and forward:
It would be nice to write down which operators in SMEFT and HEFT that the various couplings/Wilson coefficients correspond to, and the same for the chromomagnetic operator mentioned above.
>> We have added in the text the correspondence for the HEFT, since there is a simple 1-to-1 mapping. For SMEFT, we believe that it would be quite confusing, since this needs to define a basis and spell out for every interaction the specific combination of couplings, and we would prefer to maintain the text as it is for simplicity.
- p 6-7:
Another point is that some of the SMEFT operators contain derivatives, e.g. Q_{\phi D} and Q_\{phi \box} in the Warsaw basis. This would give momentum dependence in the Feynman rules and therefore not just an overall change in coupling strength. Is this important and can it change the kinematical distributions?
>> We agree that this is a possible effect of such operators, although it has not been studied how large would be this impact on the distributions in comparison to the interference with SM diagrams involving the ttH and HHH vertices. In general, HH production in SMEFT is thus far less studied in comparison to HEFT, and we do not have reference studies that we could quote to address this aspect.
- p 6-7, line 163 and below:
It is pointed out that in SMEFT, kappa and c_2 are related, which is not the case in HEFT. Does that mean that SMEFT is missing something that can be described in HEFT? Or is it a redundancy in HEFT? Are there UV complete models that can be described by HEFT but not by SMEFT? This may be a bit too theoretical for this paper, but perhaps something can be commented.
>> see answer to question #6
- p 7, caption of Table 2:
Wilson coefficients in HEFT or SMEFT?
>> Those are the HEFT coefficients, we updated the caption accordingly
- p 25, second bullet point:
"which allowed" should be "which would allow"
>> Done.
Reviewer 2 Report
The write up is a concise review of the physics and the search results of the diHiggs with Run 2 data at the LHC. However, numerous corrections are needed to make it legible. There are missing symbols in many places. Please check PDF version before submitting.
In the text, m is used for both Higgs mass or HH mass. Please distinguish them by giving subscripts.
L13: empty parentheses
L31: empty parentheses
L38: to study (the Higgs boson ?) as a
L46: capitalize start of sentence
L49: remove "a"
L60: fix empty parentheses
L77: study of ......
L79: decay to ....
L98: For the ..... case
L113: effects in ......
Fig. 3. Figure is for sqrt(s)=14 TeV do you have one for 13 TeV?
L180: missing symbols in parentheses
L188: for ....
L207: bbbar is missing
L217: are .... and
L221:,227: missing symbols at the start of the bullets
L243: symbol missing in parentheses
L251: study of ....
L253: such as ...
L267 of ...
L268: and ...
L276: change m to m_HH
L290: bbbar missing after "big three"
L295: symbols missing in subsection heading
L300: in the .... channel
L306: symbols missing
L307: seraches -> searches
L329: m->m_4b
L341: 3 and 4 -> 3-jet and 4-jet
L344: missing symbols
L346: in -> is
L347: m->m_HH
L351: missing symbols
L352: m->m_HH?
L364: missing symbols
L373: : missing symbols
L381: missing symbols
L406: missing symbols
L409: missing symbols
L410: all ... decays
L416, 420, 427: missing symbols
Fig. 20 There wasn't description in the main text.
Author Response
The write up is a concise review of the physics and the search results of the diHiggs with Run 2 data at the LHC. However, numerous corrections are needed to make it legible. There are missing symbols in many places. Please check PDF version before submitting.
In the text, m is used for both Higgs mass or HH mass. Please distinguish them by giving subscripts.
>> Most of your comments are due to a compilation error on the journal’s part. We have simplified the macros used to hopefully avoid this issue going forward.
L13: empty parentheses
>> Done.
L31: empty parentheses
>> Done.
L38: to study (the Higgs boson ?) as a
>> Done.
L46: capitalize start of sentence
>> missing “HH”
L49: remove "a"
>> Done.
L60: fix empty parentheses
>> Done.
L77: study of ......
>> missing “HH”
L79: decay to ....
>> missing “HH”
L98: For the ..... case
>> missing “HH”
L113: effects in ......
>> missing “HH”
Fig. 3. Figure is for sqrt(s)=14 TeV do you have one for 13 TeV?
>> No, this is the benchmark energy for the LHC
L180: missing symbols in parentheses
>> Fixed
L188: for ....
>> missing “HH”
L207: bbbar is missing
>> Fixed
L217: are .... and
>> “ttbar and Z plus b jets” - fixed
L221:,227: missing symbols at the start of the bullets
>> Fixed
L243: symbol missing in parentheses
>> Fixed
L251: study of ....
>> missing “HH”
L253: such as …
>> bbbb
L267 of ...
>> bbyy, bbtautau, bbbb
L268: and …
>> above
L276: change m to m_HH
>> missing “HH”
L290: bbbar missing after "big three"
>> Fixed
L295: symbols missing in subsection heading
>> Fixed
L300: in the .... channel
>> Fixed
L306: symbols missing
>> Fixed
L307: seraches -> searches
>> Done
L329: m->m_4b
>> missing “HH”
L341: 3 and 4 -> 3-jet and 4-jet
>> missing “3b and 4b”
L344: missing symbols
>> FIxed
L346: in -> is
>> FIxed
L347: m->m_HH
>> missing “HH”
L351: missing symbols
>> Fixed
L352: m->m_HH?
>> missing “HH”
L364: missing symbols
>> Fixed
L373: : missing symbols
>> Fixed
L381: missing symbols
>> Fixed
L406: missing symbols
>> Fixed
L409: missing symbols
>> Fixed
L410: all ... decays
>> missing “HH”
L416, 420, 427: missing symbols
>> FIxed
Fig. 20 There wasn't description in the main text.
>> Added, thanks.
Reviewer 3 Report
In the pdf draft that I received, several symbols were missing. The problem is so severe that some sentences are unclear. I suspect that you forgot to upload some tex file containing symbol definitions, is that the case? Anyway, this is absolutely mandatory to fix in your resubmission.
Apart from that, the article is interesting and competently written. Some minor comments:
Equation 3: why don't you plug the precise value of m that you provide one line later, and the precise value of v that is determined by the SM parameters, and provide the precise value of lambda predicted by the SM +- its uncertainty propagated from m and v? This number is not often found in the literature, so you would do a service to the reader.
Table 1: "FTapprox" appears here but it is not explained. I suggest to mention it somewhere in the text, or in the caption.
Bibliography: for many technical reports, in particular the TDRs, your bibliography style is not providing the full reference but only authors, title and year.
Author Response
In the pdf draft that I received, several symbols were missing. The problem is so severe that some sentences are unclear. I suspect that you forgot to upload some tex file containing symbol definitions, is that the case? Anyway, this is absolutely mandatory to fix in your resubmission.
>> We think the hepnames package was not available during the compilation, so we have simplified the definitions used.
Apart from that, the article is interesting and competently written. Some minor comments:
Equation 3: why don't you plug the precise value of m that you provide one line later, and the precise value of v that is determined by the SM parameters, and provide the precise value of lambda predicted by the SM +- its uncertainty propagated from m and v? This number is not often found in the literature, so you would do a service to the reader.
>> The precise value doesn’t add anything in the context of current HH studies, where we present results in terms of lambda/lambda_SM, so we prefer not to add this calculation.
Table 1: "FTapprox" appears here but it is not explained. I suggest to mention it somewhere in the text, or in the caption.
>> Added to the caption
Bibliography: for many technical reports, in particular the TDRs, your bibliography style is not providing the full reference but only authors, title and year.
>> We have fixed the display of TDRs and other publications. Now the draft reports the full reference, including the document number
Round 2
Reviewer 2 Report
Dear authors,
The revised manuscript addresses the corrections.
