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Flavoured $(g-2)_μ$ with Dark Lepton Seasoning
by Harun Acaroğlu, Prateek Agrawal, Monika Blanke
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Submission summary
| Authors (as registered SciPost users): | Harun Acaroğlu |
| Submission information | |
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| Preprint Link: | https://arxiv.org/abs/2212.08142v2 (pdf) |
| Date submitted: | 2023-06-15 12:51 |
| Submitted by: | Acaroğlu, Harun |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Phenomenological |
Abstract
As a joint explanation for the dark matter (DM) problem and the muon $(g-2)$ anomaly, we propose a simplified model of lepton-flavoured complex scalar DM with couplings to both the left- and right-handed leptons of the Standard Model (SM). Both interactions are governed by the same new flavour-violating coupling matrix $\lambda$, however we allow for a relative scaling of the coupling strength. The SM is further extended by two fermion representations, transforming as an $SU(2)_L$ doublet and singlet, respectively, and mediating these interactions. The fermions additionally couple to the SM Higgs doublet via a new Yukawa coupling. To study the model's phenomenology we first investigate constraints from collider searches, flavour experiments, precision tests of the SM, the DM relic density, and direct as well as indirect detection experiments individually. We then perform a combined analysis by demanding that all mentioned constraints are satisfied simultaneously. We use the results of this combined analysis and examine if the model is capable of accommodating the $(g-2)_\mu$ anomaly within its viable parameter space without introducing fine-tuned lepton masses. For all benchmark scenarios we consider, we find that the central value of $\Delta a_\mu^\text{exp}$ can be reached without generating too large corrections to the lepton masses. We hence conclude that this model qualifies as a viable and attractive lepton-flavoured DM model that at the same time solves the $(g-2)_\mu$ anomaly.
Current status:
Reports on this Submission
Report #4 by Anonymous (Referee 5) on 2023-9-5 (Invited Report)
- Cite as: Anonymous, Report on arXiv:2212.08142v2, delivered 2023-09-05, doi: 10.21468/SciPost.Report.7767
Report
The authors of manuscript 2212.08142 explore a model extending the Standard Model by scalar and vector-like fermion to address the dark matter and the muon $(g-2)$ problem within a unified framework. The study involves a detailed investigation, restricted by choice of parameter space, of phenomenology while investigating constraints from collider searches, flavor experiments, indirect and direct detection analysis, etc. For the paper to be suitable for publication, the authors should consider incorporating the following points.
1. Update the reference with new results for muon $g-2$.
2. The model consists of three copies of scalar fields, a vector-like doublet, and a singlet. With these new fields, there should be more terms in the Lagrangian in Eq.~(2.1); it should be clearly stated how these terms are forbidden in Sec.~(2.1). Moreover, the authors consider three complex scalar fields; would it not be minimal to just one scalar field?
3. In Eq.(2.11), the mass for the scalar fields should have additional term proportional $\lambda_{H\phi}$.
4. Numerous assumptions are made regarding the choice of the masses. How does the analysis vary for different choices? For instance, does the model allow fermionic DM if $m_{\psi_0}$ becomes the lightest particle? If so, the authors should briefly comment on how this can be accomplished without delving into a detailed study.
5. On page 8, in the first paragraph of sec~3.1, line 8, the authors mention that $3\ell$+MET is strongly constrained due to lepton flavor violation (LFV). Expanding this discussion by including specific examples on LFV observables would be good.
6. In sec.~(3.2), how are signal cross-sections being compared with the experimental upper limit? More detail on signal and background estimates would further enhance this section. In addition, in Fig.~(3.3) (d), why does the limit around $m_{\psi_2} = 400$ GeV gets weaker?
7. In sec.~(4.2), the authors have tuned the nonchiral part of LFV to zero without any proper explanation.
8. In equation.~(6.3) the coannihilation channels does not suffers much suppression when the $m_\psi$ is close to $m_\phi$. It would be good to comment on this and mention why these corners of the parameter are not included. Moreover, below Eq.(6.3), the authors argued that DM annihilation via SM Higgs can be neglected. However, the authors state that they have chosen $\lambda_{H\phi}$ such that the tree-level and one-loop contribution cancel in Direct detection. If so, why is DM annihilation via $\lambda_{H\phi}$ not considered?
9. DM with large Yukawa couplings with $Z_2$ odd fermion can also drive its bare mass squared term to negative
values via RGE, potentially breaking the discrete symmetry responsible for stabilizing DM. Authors should check if their parameter space leads to such issues or not.
10. On page 37 sec~(9.2), the authors mention ``one needs small Yukawa couplings $y_\psi \lesssim 10^{-1}$ in order to stay within the $2\sigma$ band ..". However, it is unclear how small this coupling can be. Perhaps the plot would have been more clearer if the $y_\psi$ was in log scale.
11. Incorporating $(g-2)_\mu$ within the model while maintaining perturbative couplings should give an upper limit on the new physics scale. What is the range of the masses and couplings that one can have in this model while incorporating DM and $(g-2)_\mu$? Comments on this matter greatly enhance the paper.
Report #2 by Anonymous (Referee 6) on 2023-8-28 (Invited Report)
- Cite as: Anonymous, Report on arXiv:2212.08142v2, delivered 2023-08-28, doi: 10.21468/SciPost.Report.7735
Report
In this manuscript, the authors perform a comprehensive analysis of a specific model with new scalars and heavy leptons that simultaneously explains the current observation of the muon (g-2) and provides for a viable dark matter candidate. The work is an extension of an earlier project; the difference is an extension of the particle content and less assumptions on the flavor structure of the introduced couplings.
The paper addresses two important open questions in particle physics and is thus in general of relevance. However, the model has 26 parameters, so that many assumptions need to be made to make a phenomenological statement. Moreover, the considered observables and their interpretation are standard and do not suggest new search directions. In this sense, I find the information gain compared to previous work rather modest.
The presentation in the manuscript is very clear and the analysis of the various observables is conducted in a solid, careful way. I would like to invite the authors to consider the following questions and comments:
1) The Lagrangian in (2.1) assumes, as far as I can see, a Z2 symmetry in the dark sector, which is motivated later in the text with the stability of the DM candidate. It would be good to make this statement already around (2.1); otherwise the Lagrangian would allow for additional interaction terms.
2) What is the motivation for assuming the hierarchy in (2.12)?
3) Among the collider observables considered in Sec. 3, I would expect that effects of virtual dark sector particles on Higgs and electroweak observables play a significant role in setting bounds on the model parameters. See e.g. https://arxiv.org/abs/1810.10993 or https://arxiv.org/abs/1708.01614. Later in the text, the authors mention that electroweak precision observables should be negligible in this respect. I would appreciate a quantitative discussion of this point.
4) For heavy leptons with couplings to both left- and right-handed SM leptons, I would expect loop corrections to the SM lepton masses that do not scale with the bare mass. With a general flavor structure, these contributions could be undesirably large and require fine-tuning with the bare mass to obtain the observed masses. Also here, I would appreciate a discussion of this issue.
5) To determine the relic abundance from dark matter freeze-out, the authors consider two specific scenarios. What is the motivation for precisely these benchmarks?
6) In the QDF scenario, the dark scalars are nearly degenerate in mass. Are loop contributions to the mass splitting relevant in the parameter space that produces the right relic abundance? Since the (co-)annihilation rate is exponentially sensitive to the mass splitting if several annihilation processes contribute to setting the relic abundance, I would expect that even a small change in the mass splitting could have a remarkable effect.