SciPost Submission Page
A Final Word on FCNC-Baryogenesis from Heavy Higgs Bosons
by Wei-Shu Hou, Tanmoy Modak and Tilman Plehn
This is not the current version.
|As Contributors:||Tanmoy Modak · Tilman Plehn|
|Date submitted:||2020-12-16 10:39|
|Submitted by:||Modak, Tanmoy|
|Submitted to:||SciPost Physics|
Electroweak baryogenesis in a two-Higgs doublet model is a well-motivated and testable scenario for physics beyond the Standard Model. An attractive way of providing $CP$ violation is through flavor-changing Higgs couplings, where linking top and charm quarks is hardly constrained by flavor and $CP$-violation constraints. We show how this scenario can be conclusively tested by searching for heavy charged and neutral Higgs bosons at the LHC. While the charged Higgs signature requires a dedicated analysis, the neutral Higgs signature will be covered by a general search for same-sign top pairs.
Submission & Refereeing History
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Anonymous Report 3 on 2021-2-3 (Invited Report)
I believe that the paper "A Final Word on FCNC-Baryogenesis from Heavy Higgs Bosons" by Wei-Shu Hou, Tanmoy Modak and Tilman Plehn has enough novelty to be published in SciPost Physics.
1. The model and parameter space are clearly formulated.
2. It was shown the LHC can probe almost entire parameter space responsible for EWBG within the framework of two Higgs doublet model
3. The the complicated 2HD model parameter space relevant to EWBG was elegantly expressed in terms of two variables -- |\rho| and |c_\gamma| and results a very clearly presented in this pane
4. The phenomenological analysis are done at a good quality level
using Madgraph-PYTHIA-Delphes chain including jet matching
To conclude -- the paper well written and contain new results of a good quality
There are only few points which should be clarified before I could recommend the paper for the publication:
1. Author have taken almost all relevant backgrounds
for "b W^+W^+W^-" 3lepton signature, except "t t-bar" one:
naively this background would lead only two di-lepton signature,
however the third lepton could come from as "fake" one
or from b-quark decay: the probability for this lepton is very low
- 0.1% - 0.01%, but as we know the tt-bar cross section is huge.
So this background can be easily the leading one for the
"b W^+W^+W^-" signature. It should bec checked or at least roughly estimated.
2. I believe that title of the paper is too ambitious -- the paper is well addressing problem of probing of the parameter space only within the framework of 2HDM at the LHC, within the framework of more general/different model the limits in |\rho| and |c_\gamma|
would be not necessarily correct or relevant.
I think this should be clearly stressed in the conclusions and
possibly in the title.
I believe the paper deserve the publication in journal upon addressing problem mentioned above (and formulated in short below)
1. Authors should estimate the contribution
of ttbar background to 3lepton signature from "bH^+"
(see details above)
2. Authors should clearly states the validity of their results
withih the prameter space of different models and possibly change the ttile which is more relevant to 2HDM
Anonymous Report 2 on 2021-1-17 (Invited Report)
The present study investigates LHC constraints on the baryogenesis-motivated parameter region of a type-III two-Higgs-doublet model, where the necessary CP violation arises through a complex flavour-changing Higgs-top-charm coupling rho_tc. It is a follow-up on a series of papers by one of the authors on this model, including Ref. 25, which studied the aspect of electroweak baryogenesis, and a recent PRL article (Ref. 28), where the collider signatures in presence of non-zero rho_tc were elaborated.
Indeed, while not explicetly focussing on the baryogenesis-motivated parameter region, Ref. 28 already presents the most important constrains from searches for heavy charged and neutral Higgs states. In particular the it is already pointed out that the ttW control region (CRW) of the CMS 4top analysis with 137/fb excludes rho_tc >~0.4. A follow-up paper on the short PRL article with the technical details of the collider analyses would in principle be interesting, if done properly. The present manuscript attempts this for the specific case of small rho_tt but sizeable rho_tc, but unfortunately falls short of the necessary details and scrutiny.
* Introduction and section 2:
- As also critisized by the first referee, the model is not motivated well in the paper, nor is the considered parameter space. The reader is left to search the previous literature for details. The relevant references are mentioned throughout the text, but no consistent overview of the previous literature leading up to this work is given. The couplings lambda_ii and rho_ij are introduced completely ad hoc in the introduction; while some explanation comes in section 2, one has to make an effort to piece things together while reading.
- Refs [3-5] are an extremely selective list of theorists' fits of the Higgs couplings. There exists a vast literature on this subject, most of which is ignored here. Moreover, and perhaps more importantly, dedicated measurements of the Higgs couplings have been published directly by ATLAS and CMS.
- Eq. (1) is duplicated in eq. (8).
- It is not clear what are the actual constraints on rho_tt, and what are the consequences for this study if both rho_tt and rho_tc are relevant.
* Section 3
- "For b-tagging as well as c-jet and light-jet rejection, we rely on Delphes" is too vague. The standard ATLAS card can change over time, so details on the assumed reconstruction efficiencies must be given, and not only for (b)jets but also for lepton ID. The same is true for extra jets: details on the matching and merging parameters are necessary.
- Cross sections in Table 2: while it can be justified to compute sub-leading contributions at lower order, this needs to be justified and explained properly. "for simplicity" is not good enough.
- How many events were actually generated?
- Run 3 and HL-LHC reach: to what extent are the efficiencies of the standard ATLAS Delphes card appropriate for HL-LHC simulation?
- What about pile-up?
* Section 4
- Same concerns as above for standard CMS Delphes card and details on the event generation.
- The CMS 4 top analysis has been reinterpreted with MadAnalysis5 in Phys.Lett.B 784 (2018) 223 [1805.10835]. There, a specific Delphes card was developed to reproduce well the CMS results. This was for 35/fb of integrated luminosity, but an update of the recast code (and appropriately tuned Delphes card) are available also for the 137/fb version, see https://madanalysis.irmp.ucl.ac.be/wiki/PublicAnalysisDatabase
While these recast codes consider only the signal regions of the CMS analysis but not the control regions, the fact that a specific tuning was necessary raises severe doubts about the validity of using the standard CMS Delphes card in the present work. How has this been validated? Details on this must be explained and the accuracy of the reinterpretation demonstrated.
- The same-sign top search is a crucial for this work. Why is it relegated to the appendix? Again, relevant details are not explained.
- Given the very strong conclusions about ruling out the model under investigation, the impact of the uncertainties mentioned in the last paragraph before the conclusions should be quantified.
In conclusion, while the study is interesting in principle, much more detail (and care) is needed to make the paper suitable for publication. I actually have more comments on the paper, but given the shortcomings listed above I refrain from going into finer details in this iteration.
* General remark: for the sake of reproducibility, the MadGraph model (UFO) file, all the Monte Carlo settings for the event generation (i.e. the MG5, Pythia, Delphes cards) and the analysis codes should be made public on an appropriate versioned and citable open-access repository, for example Zenodo. Ideally, this would be supplemented moreover with the numerical results (event counts) of the simulations.
Anonymous Report 1 on 2021-1-15 (Invited Report)
The authors study the possibility of BG in a general THDM. They conclude that
with future LHC Run 3 or HL-LHC searches this scenario can fully be tested.
I cannot recommend the paper for publication, since there are several open and
unresolved issues. These are the following:
# model definition:
The potential is defined in eq. (4) and the couplings to fermions in eq. (6).
It remains unclear what are the input parameters of the model.
The various choices of the rho matrices have to be deduced from information
scattered over the article. The choide of the elements of the rho matrices
appears fully ad-hoc to satisfy experimental constraints. Is there any
underlying model that would produce such a extremely weird pattern that the
# checks on the model parameters:
There is hardly any information on the checks performed. The authors mention
in passing perturbativity, positivity, unitarity, and electroweak precision
data. It remains completely unclear what the effects of these are on the model
as such and on the particular parameter choices the authors make. Completely
absent seem to be checks for the properties of the SM-like Higgs boson at 125 GeV,
as well as checks for the BSM Higgs searches for the additional Higgs bosons
(except the particular channels the authors are analysing later).
# Fig. 1:
What is the point in showing it for MH+- = 300 GeV and 500 GeV? The only
difference seems to come from Bs-Bsbar mixing. What are the other relevant
parameters here? How do they influence the excluded regions? Furthermore, it
appears that the searches for t -> ch can rule out the scenario under
investigation in the (near?) future. The authors do not comment on this.
# "usual" BSM Higgs production and decay modes:
The authors are investigating solely the channels they are interested
in. However, there should be some "usual" channels, such as gb -> tH+-,
H+- -> tb, which may be suppressed (because of the weird and unmotivated
choice of rho^U,D), but via CKM mixing they should still play a significant
role. The authors do not comment on this.
# Calculation of signal and background:
Some channels are calculated at NLO, others at LO, which in particular seems
to include the signal channels. Why? I do not see any motivation for this from
the physics point of view.
# Fig. 4:
It seems that what the authors label "CRW" alone is already excluding a lot of
the allowed parameter space, so this should be looked at first, since it is an
existing limit. Also this channel, which is not in the main focus of the
authors, seems to be able to rule out their scenario with future LHC
runs. Again this is not discussed.
I do not include several smaller issues that I have, e.g. concerning
citations, since the above issues are far more relevant.
But looking at Ref.  I wonder whether the authors really read their
article before submitting it.