We explore signatures of lepton number violation (LNV) from decays of the discovered Higgs (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi></math>) and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> bosons into a pair of right-handed neutrinos (RHNs). Due to the Majorana nature of RHNs, the final state can be the same-sign dilepton plus jets leading to two units of LNV. As a simple but plausible scenario, we investigate such a signal in models with a new <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mo stretchy="false">)</mo><mi>X</mi></msub></math> gauge symmetry, which naturally introduces three RHNs for gauge anomaly cancellation and is spontaneously broken down by a vacuum expectation value of an isospin singlet scalar field (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ϕ</mi></math>). In this scenario, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi></math> and the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> boson can decay into a pair of RHNs via the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>h</mi><mtext>−</mtext><mi>ϕ</mi></mrow></math> mixing and the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>Z</mi><mtext>−</mtext><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow></math> mixing with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> being a new massive gauge boson, respectively. Estimating the LNV signal and corresponding backgrounds for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mo>ℓ</mo><mo>±</mo></msup><msup><mo>ℓ</mo><mo>±</mo></msup><mn>4</mn><mi>j</mi></math> final states, we find bounds on the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>h</mi><mtext>−</mtext><mi>ϕ</mi></mrow></math> mixing and the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>Z</mi><mtext>−</mtext><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow></math> mixing as a function of a mass of RHNs at Higgs factories, e.g., at the High-Luminosity LHC with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>14</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>, future <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>−</mo></msup><msup><mi>e</mi><mo>+</mo></msup></math> colliders at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>250</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, muon colliders at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>125</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, as well as at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> factories, e.g., CEPC and Future Circular Collider (FCC-ee) at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>91.2</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>. We also discuss limits on the scalar mixing at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>−</mo></msup><msup><mi>μ</mi><mo>+</mo></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>+</mo></msup></math> collisions (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>μ</mi><mi>TRISTAN</mi></math>) with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>346</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><mn>775</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> and 2 TeV, respectively.

Japan

Arindam Das

China

Takaaki Nomura

Kei Yagyu

Lepton number violation from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Higgs</mi><mo>/</mo><mi>Z</mi></math> decays into a pair of right-handed neutrinos

We investigate the phenomenology of 2 Higgs doublet models (2HDMs) with a new U(1) gauge symmetry, U(1) , by which flavor changing neutral currents are forbidden at tree level. As an important consequence of the spontaneous breaking of both the U(1) and electroweak symmetries by electroweak vacuum expectation values, upper limits appear on masses of an additional gauge boson $\textit{Z′}$ and extra Higgs bosons which are less than the TeV scale. In addition, the standard model (SM) like Higgs boson $\textit{h}$ and a heavier Higgs boson $\textit{H}$ mainly decay into a pair of $\textit{Z′}$ which induces four lepton final states. These new decay modes cannot be suppressed by taking no $\textit{Z}$-$\textit{Z′}$ mixing and/or the Higgs alignment limit. We find that the minimum setup of these 2HDMs has been excluded by current data for four lepton searches at LHC. Such severe constraints can, however, be avoided by introducing a pair of vector-like fermions $\textit{χ}$ which are singlet under the SM symmetry but charged under U(1) , and can be a candidate of dark matter. Thanks to the existence of $\textit{χ}$, $\textit{Z′}$ can mainly decay into $$ \chi \overline{\chi} $$ instead of SM leptons. As benchmark models, we consider the U(1) and U(1) models realized by fixing specific U(1) charges, and find regions of parameter space allowed by theoretical and current experimental constraints. We clarify that $\textit{m}$ ∈ [160$\textit{,}$ 220] GeV and tan $\textit{β}$ ∈ [3$\textit{,}$ 4$\textit{.}$4] are allowed in the U(1) model, while $\textit{m}$ ∈ [160$\textit{,}$ 380] GeV and tan $\textit{β}$ ∈ [1$\textit{.}$6$\textit{,}$ 4$\textit{.}$4] are allowed in the U(1) model. In both the models, the $\textit{Z′}$ mass is constrained to be 100 GeV ≲ $$ {m}_{Z^{\prime }} $$ ≲ 110 GeV. Such a quite limited parameter space can further be explored at future collider experiments, e.g., High-Luminosity LHC and lepton colliders.

Yuanchao Lou

Hong Kong

Xinran Xu

Are 2HDMs with a gauged U(1) symmetry alive?

The extension of the Higgs sector with an additional complex triplet field is often considered for generating the neutrino mass by the Type-II seesaw mechanism. Such an extension generally predicts $\textit{ρ}$ ≠ 1, where $\textit{ρ}$ is the electroweak rho parameter at the tree level, so that the renormalization of the electroweak parameters is different from models like the standard model (SM) and two Higgs doublet models. In this paper, we present a full set of radiative corrections to decays of the 125 GeV Higgs boson ($\textit{h}$) in this model. One-loop contributions of the extra Higgs bosons as well as SM fermions and gauge bosons to the decay rates of $\textit{h}$ are calculated in the on-shell scheme. Gauge dependence appearing in the counter terms of mixing angles is eliminated by the pinch technique. Higher-order QCD corrections are also implemented. We find that the decay rates can significantly deviate from the predictions in the SM and other extensions such as the two Higgs doublet models and the singlet model. For example, the decay rates of $\textit{h}$ → $\textit{WW}$ and $\textit{h}$ → $\textit{ZZ}$ can be a few percent larger than the SM value under current experimental and theoretical constraints. In this case, deviations in $\textit{h}$ → $\textit{γγ}$ and Higgs self-coupling can reach about 20% and 100%, respectively. The pattern of the deviations is different from the other extended Higgs models. These characteristic predictions are expected to be detected at the High-Luminosity LHC or future Higgs factories.

Masashi Aiko

Shinya Kanemura

Mariko Kikuchi

Kodai Sakurai

Sora Taniguchi

Radiative corrections to decays of the 125 GeV Higgs boson in the complex Higgs triplet model

We investigate the implications of spontaneous <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> violation in the general two Higgs doublet model, which leads to a nondecoupling structure of the Higgs sector. All the masses of the Higgs bosons are purely determined by the vacuum expectation value of the Higgs fields, and are thus constrained to be smaller than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mn>500</mn><mo stretchy="false">)</mo><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> by the perturbative unitarity bound. Such a nondecoupling nature predicts sizable deviations from the Standard Model expectations in the observables of the discovered Higgs boson (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi></math>). We find that the magnitude of deviations in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mrow><mi>h</mi><mo stretchy="false">→</mo><mi>γ</mi><mi>γ</mi></mrow></msub></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mrow><mi>h</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>γ</mi></mrow></msub></math>) are larger than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><mn>10</mn><mo>%</mo><mo stretchy="false">(</mo><mn>4</mn><mo>%</mo><mo stretchy="false">)</mo></math> in the Higgs alignment limit. Moreover, we show that a robust correlation emerges between the deviations in the one-loop corrected <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mi>h</mi><mi>h</mi></math> coupling and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="script">B</mi><mrow><mi>h</mi><mo stretchy="false">→</mo><mi>γ</mi><mi>γ</mi></mrow></msub></math> to be, e.g., 200% (50%) and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>−</mo><mn>10.3</mn><mo>%</mo></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>−</mo><mn>10.8</mn><mo>%</mo></math>), respectively, under the constraints from theoretical bounds and current experimental data. Using a few benchmark points, we highlight that flavor-violating decays of the additional Higgs bosons can be sizable due to the constrained structure of the Yukawa interactions.

India

Tanmoy Mondal

Probing spontaneous <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> violation through precision Higgs observables

We discuss triple <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> boson signatures via the decay chain of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mo stretchy="false">→</mo><msup><mi>Z</mi><mo>′</mo></msup><mi>ϕ</mi><mo stretchy="false">→</mo><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup></math>, with a new light scalar <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ϕ</mi></math>, at future <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> factories such as the Circular Electron-Positron Collider and Future Circular Collider. These new bosons <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ϕ</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> naturally appear in models with a new <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> gauge symmetry which is spontaneously broken and introduced in various new physics scenarios. The branching ratio of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mo stretchy="false">→</mo><msup><mi>Z</mi><mo>′</mo></msup><mi>ϕ</mi><mo stretchy="false">→</mo><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup></math> can be larger than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>12</mn></mrow></msup></math>, which gives <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>O</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> events at Tera-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> experiments, when a product of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mi>X</mi></msub></math> (new gauge coupling) and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ζ</mi></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mo>−</mo><msup><mi>Z</mi><mo>′</mo></msup></math> mixing) is larger than around <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>6</mn></mrow></msup></math>. We find that the search for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mo stretchy="false">→</mo><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup></math> can significantly improve the current bound on a kinetic mixing parameter <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi></math> in the dark photon case, where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>e</mi><mi>ε</mi><mo>≳</mo><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup><mo stretchy="false">)</mo></math> with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mi>X</mi></msub><mo>=</mo><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math> can be explored at Tera-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> experiments. We also show that a sufficiently large number of events with multilepton plus hadronic jets can be obtained in benchmark points, which cannot be realized by the usual decay of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> in the standard model.

Triple <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow></math> signatures at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> factories

We investigate multi-lepton jet events from the decay of the 125 GeV Higgs boson ($\textit{h}$) into quadruple new gauge bosons ($\textit{Z}$′) at the LHC. Such an exotic decay is realized via the process of $\textit{h → ϕϕ → Z}$′$\textit{Z}$′$\textit{Z}$′$\textit{Z}$′ with new scalar boson $\textit{ϕ}$ in models with an additional U(1) gauge symmetry. Charged leptons coming from the $\textit{Z}$′ decay tend to be observed as lepton-jets rather than isolated leptons when the masses of $\textit{Z}$′ and $\textit{ϕ}$ are smaller than $$ \mathcal{O} $$ (10) GeV, because of the highly-boosted effects. Performing the signal and background analyses, we find that the branching ratio of $\textit{h}$ → 4$\textit{Z}$′ is maximally constrained to be smaller than of order 10 (10 ) by using the muonic-lepton jets assuming the integrated luminosity of 140 fb (3000 fb ) at LHC. For lighter $\textit{Z}$′ ($\textit{<}$ 2$\textit{m}$ ), we can use the electronic-lepton jets instead of the muon-jets, by which the upper limit on the branching ratio is obtained to be of order 10 –10 . These bounds can be converted into the constraint on model parameters such as a mixing angle between $\textit{h}$ and $\textit{ϕ}$. It is shown that stronger bounds on the mixing angle are obtained in the dark photon case as compared with the previous constraints given by flavor experiments and the Higgs decay $\textit{h → Z}$′$\textit{Z}$′ in the mass range of $$ {m}_{Z^{\prime }} $$ ≲ 10 GeV.

Jinmian Li

Multi-lepton jets from quadruple $\textit{Z}$′ via the Higgs decay at LHC

We discuss multi-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> signatures coming from decays of Higgs bosons in models with a spontaneously broken <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msup><mo stretchy="false">)</mo><mo>′</mo></msup></math> symmetry, which can be observed as “lepton jets” or multilepton final states depending on the mass range of new bosons. We consider anomaly-free <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msup><mo stretchy="false">)</mo><mo>′</mo></msup></math> models without introducing new fermions except for right-handed neutrinos, in which the Higgs sector is composed of an isospin doublet and a singlet fields with zero and nonzero <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msup><mo stretchy="false">)</mo><mo>′</mo></msup></math> charges, respectively. The multi-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> signatures can then be obtained via the decays of the discovered (extra) Higgs boson <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ϕ</mi></math>), i.e., <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ϕ</mi><mo stretchy="false">→</mo><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup></math>, and/or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mo stretchy="false">→</mo><mi>ϕ</mi><mi>ϕ</mi><mo stretchy="false">→</mo><mn>4</mn><msup><mi>Z</mi><mo>′</mo></msup></math> as far as kinematically allowed. We give the upper limit on the branching ratios of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi></math> into <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup><msup><mi>Z</mi><mo>′</mo></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4</mn><msup><mi>Z</mi><mo>′</mo></msup></math> from the current experimental data in each model. We also show the deviation in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>h</mi><mi>h</mi><mi>h</mi></math> coupling from the standard model prediction at one-loop level, and find that its amount is typically smaller than 1%.

Multi-<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> signatures of spontaneously broken local <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msup><mo stretchy="false">)</mo><mo>′</mo></msup></math> symmetry

In models with non-minimal Higgs sectors, enforcing (near) Higgs alignment, necessary to prevent significant deviations in the Higgs boson coupling from the standard model prediction, causes a serious fine-tuning problem. We demonstrate that the Higgs alignment is naturally deduced from the multicritical point principle (MPP) in the general two Higgs doublet model while keeping non-zero CP-violating phases. Furthermore, we discuss the possibility of realizing the Yukawa alignment from the MPP, which is necessary to prevent flavor-changing neutral currents mediated by Higgs bosons at tree level, and find that it seems difficult to realize it by the MPP due to the non-diagonal structure of the CKM matrix.

Taiwan

Hikaru Kawai

South Korea

Kiyoharu Kawana

Kin-ya Oda

Higgs alignment from multicritical-point principle in two Higgs doublet models

We propose a new renormalization scheme in the two Higgs doublet models with a softly-broken <math><msub><mrow><mi>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math> symmetry and CP-conservation in the Higgs sector. In this scheme, counterterms for mixing angles of the Higgs bosons are determined by using the decay rates of the discovered Higgs boson h, i.e., <math><mi>h</mi><mo>→</mo><msup><mrow><mi>τ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup></math> and <math><mi>h</mi><mo>→</mo><mi>Z</mi><msup><mrow><mi>Z</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>→</mo><mi>Z</mi><msup><mrow><mi>ℓ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>ℓ</mi></mrow><mrow><mo>−</mo></mrow></msup></math> at next leading order (NLO) instead of using the renormalized two-point functions which are adopted in the previous scheme. We require that the decay rates at NLO are determined to be the corresponding predictions at NLO in the Standard Model (SM) times square of the scaling factor which describes the deviation of h couplings at tree level from the SM value. The mixing angles then maintain the meaning of the “alignmentness”, i.e., how the properties of h are close to the SM predictions, while they lose such meaning in the previous scheme. We compare the predictions of the decay rates at NLO given in the new scheme and those in the previous scheme.

New renormalization scheme in the two Higgs doublet models

We discuss the Higgs phenomenology in models with a new <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>X</mi></mrow></msub></math> gauge symmetry including the <math><mi>U</mi><msub><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> scenario, where three right-handed neutrinos are inevitably introduced due to the gauge anomaly cancellations. We find that the decay branching ratio of the discovered Higgs boson into a pair of new massive gauge bosons (<math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math>) can significantly be enhanced in the Dirac neutrino case as compared with the Majorana case for a fixed value of the new gauge coupling and the mass of <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> under constraints from current experimental data. Because of such an enhancement, the Dirac case can indirectly be discriminated from the Majorana case via the Higgs decay.