We study phenomenology of a light scalar dark matter (DM). In the model, there is an inert doublet scalar and a singlet Dirac fermion <math><mi>ψ</mi></math>, both charged under a global <math><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry. The mass of the lightest inert scalar <math><mi>H</mi></math> can be lighter than 10 GeV by imposing appropriate relations between three scalar quartic couplings. The lightest <math><msub><mi>Z</mi><mn>2</mn></msub></math> odd particle is stable and DM. In this paper, focusing on the parameter space where <math><mi>H</mi></math> is lighter than <math><mi>ψ</mi></math> and is DM, we discuss DM physics related to relic density, direct detection, indirect detection, collider searches, and other cosmological observations. We clarify differences from the case where <math><mrow><mi>ψ</mi></mrow></math> is instead DM, which has been focused on in previous works.

Japan

Ryo Higuchi

Germany

Syuhei Iguro

Spain

Shohei Okawa

Yuji Omura

Light mass window of inert doublet dark matter with lepton portal interaction

We discuss a model with a SU(2) L  doublet vector leptoquark (LQ), motivated by the recent experimental results relating to the lepton universality of   <math> <mover> <mi>B</mi> <mo>¯</mo> </mover> </math>  $$ \overline{B} $$  → D (*)   <math> <mi>τ</mi> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>τ</mi> </msub> </math>  $$ \tau {\overline{\nu}}_{\tau } $$ . We find that scalar operators predicted by the LQ are favored to explain the deviations, taking into account the recent LHCb result. We investigate the extensive phenomenology of the model and conclude that B  s  →   <math> <mi>τ</mi> <mover> <mi>τ</mi> <mo>¯</mo> </mover> </math>  $$ \tau \overline{\tau} $$ , B →   <math> <mi>Kτ</mi> <mover> <mi>τ</mi> <mo>¯</mo> </mover> </math>  $$ K\tau \overline{\tau} $$ , B  u  →   <math> <mi>τ</mi> <msub> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mi>τ</mi> </msub> </math>  $$ \tau {\overline{\nu}}_{\tau } $$  and high-p  T  di-τ lepton signatures at the LHC will probe the interesting parameter region in the near future.

A closer look at isodoublet vector leptoquark solution to the   <math> <msub> <mi>R</mi> <msup> <mi>D</mi> <mfenced> <mo>∗</mo> </mfenced> </msup> </msub> </math>  $$ {R}_{D^{\left(\ast \right)}} $$  anomaly

We investigate the di-Higgs production at the Large Hadron Collider in the two-Higgs doublet model (2HDM). In particular, we study the production of an extra neutral Higgs boson <math><mi>ϕ</mi></math> in association with the Standard Model (SM) Higgs boson <math><mi>h</mi></math> in the Higgs alignment limit. We analyze two scenarios where the additional Higgs <math><mi>ϕ</mi></math> is in a <math><mi>C</mi><mi>P</mi></math>-even or -odd state with a large top-Yukawa interaction. The leading contribution of this production comes from the top-quark loop-induced gluon-fusion channel <math><mi>g</mi><mi>g</mi><mo>→</mo><mi>h</mi><mi>ϕ</mi></math>. The measurement of the <math><mi>h</mi><mi>ϕ</mi></math> production can probe the quartic couplings in the Higgs potential as well as the top-Yukawa couplings. Imposing both theoretical constraints (from the perturbative unitarity and the vacuum stability bounds) and experimental bounds (from the SM Higgs and flavor physics measurements) on the 2HDM parameter space, we calculate the production cross section of <math><mi>g</mi><mi>g</mi><mo>→</mo><mi>h</mi><mi>ϕ</mi></math>. Furthermore, we scrutinize these processes in the parameter spaces where the CMS ditau and diphoton excesses around 100 GeV, and/or the muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> anomaly can be accommodated.

China

Teppei Kitahara

Hantian Zhang

Chasing the two-Higgs doublet model in the di-Higgs boson production

We examine the sensitivity of the Large Hadron Collider (LHC) to light lepton portal dark matter with its mass below 10 GeV. The model features an extra doublet scalar field and singlet Dirac dark matter, which have Yukawa interactions with left-handed leptons. To correctly produce the dark matter abundance via the thermal freeze-out, a large mass splitting among the extra scalars is required, thus providing a light neutral scalar below   <math> <mi>O</mi> <mfenced> <mn>10</mn> </mfenced> <mi>GeV</mi> </math>  $$ \mathcal{O}(10)\textrm{GeV} $$  and heavy neutral and charged scalars at the electroweak scale. In this paper, we focus on the electroweak pair-production of the extra scalars with subsequent model-specific scalar decays and evaluate the current constraints with the LHC Run 2 data and the discovery potential at the High Luminosity LHC (HL-LHC). It turns out that a large part of the theoretically allowed parameter space can be tested at the HL-LHC by taking into account complementarity between slepton searches and mono-Z plus missing transverse energy search. We also discuss same-sign charged scalar production as a unique prediction of the model, and the implication of the collider searches in the thermal dark matter scenario.

Light lepton portal dark matter meets the LHC

Recently, the CMS collaboration has reported a di-tau excess with a local significance of 2.6–3.1 $$\sigma $$  <math> <mi>σ</mi> </math>   where the invariant mass is  $$m_{\tau \tau } =95$$  <math> <mrow> <msub> <mi>m</mi> <mrow> <mi>τ</mi> <mi>τ</mi> </mrow> </msub> <mo>=</mo> <mn>95</mn> </mrow> </math>  –100 GeV. This excess can be interpreted as a light scalar boson that couples to the third generation fermions, particularly top and  $$\tau $$  <math> <mi>τ</mi> </math>  . Based on the simplest model that can account for the CMS di-tau excess, we evaluate experimental sensitivities to the additional light resonance, using the results reported by the ATLAS collaboration. We see that a search for the top-quark associated production of the SM Higgs boson that decays into  $$\tau {\bar{\tau }}$$  <math> <mrow> <mi>τ</mi> <mover> <mrow> <mi>τ</mi> </mrow> <mrow> <mo>¯</mo> </mrow> </mover> </mrow> </math>   sets a strong model-independent limit. We also find that the CP-even scalar interpretation of the light resonance is excluded by the ATLAS results, while the CP-odd interpretation is not.

Scrutinizing the 95–100 GeV di-tau excess in the top associated process

We study a lepton portal dark matter model, motivated by the deviation of the <math><mi>W</mi></math> boson mass reported by the CDF collaboration. We introduce vectorlike leptons and a scalar dark matter (DM) that exclusively couples to the extra leptons and muon. The one-loop corrections induced by the new particles can shift the <math><mi>W</mi></math> boson mass. Besides, the discrepancy in the muon anomalous magnetic moment and the DM density can simultaneously be explained by this setup, if the vectorlike lepton is lighter than 200 GeV and nearly degenerate with the DM particle. We also see that the constraints on such a light extra lepton from the collider experiments can be evaded due to the existence of the DM particle.

South Korea

Junichiro Kawamura

<math><mi>W</mi></math> boson mass and muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> in a lepton portal dark matter model

We study lepton flavor violation (LFV) induced by one-loop box diagrams in Pati-Salam (PS) unification with vector-like families. The vector leptoquark (LQ) associated with the PS gauge symmetry breaking generally causes various LFV processes such as K  L  → μe and μ → e conversion at the tree-level, thereby driving its mass scale to be higher than PeV scale. The vector-like families are introduced to suppress such tree-level LFV processes, allowing the LQ to have TeV scale mass. In this paper, we point out that there are inevitable one-loop contributions to those LFV processes from the box diagrams mediated by both one LQ and one scalar field, even if the tree-level contributions are suppressed. We consider a concrete model for demonstration, and show that the vector-like fermion masses have an upper bound for a given LQ mass when the one-loop induced processes are consistent with the experimental limits. The vector-like fermion mass should be lighter than 3 TeV for 20 TeV LQ, if a combination of the couplings does not suppress K  L  → μe decay. Our findings would illustrate importance of the box diagrams involving both LQ and physical modes of symmetry breaking scalars in TeV scale vector LQ models.

Importance of vector leptoquark-scalar box diagrams in Pati-Salam unification with vector-like families

In this paper, we show an explicit way to realize a TeV-scale vector leptoquark from the Pati-Salam unification with extra vectorlike families. The leptoquark mass is constrained to be heavier than PeV scale by the measurement of a flavor violating kaon decay, <math><msub><mi>K</mi><mi>L</mi></msub><mo>→</mo><mi>μ</mi><mi>e</mi></math>, in conventional models. This strong constraint can be avoided by introducing vectorlike families consistently with the quark and lepton masses and Cabbibo-Kobayashi-Maskawa and Pontecorvo-Maki-Nakagawa-Sakata matrices. In this model, the vector leptoquark can be sufficiently light to explain the recent <math><mi>b</mi><mo>→</mo><mi>s</mi><mi>μ</mi><mi>μ</mi></math> anomaly, while the <math><mi>b</mi><mo>→</mo><mi>c</mi><mi>τ</mi><mi>ν</mi></math> anomaly is difficult to be explained due to the strong constraints from the <math><msup><mi>Z</mi><mo>′</mo></msup></math> boson and vectorlike quark searches at the LHC. When the <math><mi>b</mi><mo>→</mo><mi>s</mi><mi>μ</mi><mi>μ</mi></math> anomaly is explained, we show that <math><mrow><mi>O</mi><mrow><mtext> </mtext><mo>(</mo><mn>0.2</mn><mo>)</mo></mrow><mo>%</mo></mrow></math> tuning is required in the fermion matrix, the future experiments in <math><mi>μ</mi><mo>→</mo><mi>e</mi><mi>γ</mi></math> and <math><mrow><mi>μ</mi><mtext>−</mtext><mi>e</mi></mrow></math> conversions will cover most available parameter space, and sizable neutral meson mixings, induced by the extra Higgs doublets, are unavoidable.

Canada

TeV-scale vector leptoquark from Pati-Salam unification with vectorlike families

In this paper, we focus on the supersymmetric model with left-right (LR) symmetry, that is especially proposed in our previous work [1]. In this model, there are four Higgs doublets in order to realize the Standard Model (SM) fermion masses and the Cabibbo-Kobayashi-Maskawa matrix. The heavy Higgs doublets unavoidably have flavor changing couplings to the SM fermions and induce flavor-changing neutral currents at tree level. We study broader parameter space than the previous work with including the renormalization group corrections to the Yukawa couplings between the LR breaking scale,   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (1013) GeV, and the supersymmetry breaking scales,   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (100) TeV. The CP violating observable in K–  <math> <mover> <mi>K</mi> <mo>¯</mo> </mover> </math>  $$ \overline{K} $$  mixing, ϵ  K , strongly constrains the model, so that heavy Higgs mass should be heavier than   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (100) TeV. We study the lepton flavor violating (LFV) processes setting heavy Higgs masses to be 170 TeV. The branching ratios of μ → 3e and the μ–e conversion can be larger than 10 −16 that could be covered by the future experiments. We also study the degree of fine-tuning in the parameter region that predicts testable LFV processes.

Yoshihiro Shigekami

Higgs flavor phenomenology in a supersymmetric left-right model with parity

We explore a novel possibility that dark matter has a light mass below 1 GeV in a lepton portal dark matter model. There are Yukawa couplings involving dark matter, left-handed leptons and an extra scalar doublet in the model. In the light mass region, dark matter is thermally produced via its annihilation into neutrinos. In order to obtain the correct relic abundance and avoid collider bounds, a neutral scalar is required to be light while charged scalars need to be heavier than the electroweak scale. Such a mass spectrum is realized by adjusting quartic couplings in the scalar potential or introducing an extra singlet scalar. It turns out that the mass region of 10 MeV–10 GeV is almost free from experimental and observational constraints. We also point out that searches for extra neutrino flux from galactic dark matter annihilations with neutrino telescopes are the best way to test our model.