Heavy neutral leptons are introduced to explain the tiny neutrino masses via the seesaw mechanism. For proper small mixing parameter $$V_{\ell N},$$ the heavy neutral leptons become long-lived, which leads to the displaced vertex signature at colliders. In this paper, we consider the displaced heavy neutral lepton from the neutrinophilic Higgs doublet $$\Phi _\nu $$ decay. The new Higgs doublet with MeV scale VEV can naturally explain the tiny neutrino masses with TeV scale . Different from current experimental searches via the $$W^\pm \rightarrow \ell ^\pm N$$ decay, the branching ratios of new decays as $$H^\pm \rightarrow \ell ^\pm N$$ are not suppressed when $$|V_{\ell N}|\gtrsim 10^{-16}.$$ Therefore, a larger parameter space is expected to be detected at colliders. We then investigate the promising region at the 14 TeV HL-LHC and the 3 TeV CLIC. According to our simulation, the DV signature could probe $$|V_{\ell N}|^2\gtrsim 10^{-18}$$ with $$m_N<m_{H^+},$$ which covers the seesaw predicted value $$|V_{\ell N}|^2\sim m_\nu /m_N.$$ We could probe $$m_{H^+}\lesssim 1100$$ GeV at the 14 TeV HL-LHC and $$m_{H^+}\lesssim 1490$$ GeV at the 3 TeV CLIC.

China

Fa-Xin Yang

Feng-Lan Shao

Zhi-Long Han

Yi Jin

Honglei Li

Displaced heavy neutral lepton from new Higgs doublet

The new gauge boson <math altimg='si1.svg'><msup><mrow><mi>Z</mi></mrow><mrow><mo>&#8242;</mo></mrow></msup></math> in <math altimg='si2.svg'><mi>U</mi><msub><mrow><mo stretchy='false'>(</mo><mn>1</mn><mo stretchy='false'>)</mo></mrow><mrow><mi>B</mi><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></mrow></msub></math> is widely considered as the mediator of dark matter. In this paper, we propose the inelastic Dirac dark matter in <math altimg='si2.svg'><mi>U</mi><msub><mrow><mo stretchy='false'>(</mo><mn>1</mn><mo stretchy='false'>)</mo></mrow><mrow><mi>B</mi><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></mrow></msub></math>. The dark sector contains two Dirac fermions <math altimg='si26.svg'><msub><mrow><mover accent='true'><mrow><mi>&#967;</mi></mrow><mrow><mo stretchy='false'>&#732;</mo></mrow></mover></mrow><mrow><mn>1</mn></mrow></msub></math> and <math altimg='si27.svg'><msub><mrow><mover accent='true'><mrow><mi>&#967;</mi></mrow><mrow><mo stretchy='false'>&#732;</mo></mrow></mover></mrow><mrow><mn>2</mn></mrow></msub></math> with <math altimg='si2.svg'><mi>U</mi><msub><mrow><mo stretchy='false'>(</mo><mn>1</mn><mo stretchy='false'>)</mo></mrow><mrow><mi>B</mi><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></mrow></msub></math> charge 0 and &#8722;1, respectively. A <math altimg='si5.svg'><msub><mrow><mi>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math> symmetry is also introduced to ensure the stability of dark matter. The mass term <math altimg='si25.svg'><mi>&#948;</mi><mi>m</mi><msub><mrow><mover accent='true'><mrow><mover accent='true'><mrow><mi>&#967;</mi></mrow><mrow><mo stretchy='false'>&#732;</mo></mrow></mover></mrow><mrow><mo stretchy='false'>&#175;</mo></mrow></mover></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mover accent='true'><mrow><mi>&#967;</mi></mrow><mrow><mo stretchy='false'>&#732;</mo></mrow></mover></mrow><mrow><mn>2</mn></mrow></msub></math> induces the mixing of dark fermion. Then the lightest dark fermion <math altimg='si7.svg'><msub><mrow><mi>&#967;</mi></mrow><mrow><mn>1</mn></mrow></msub></math> becomes the dark matter candidate, whose coupling to <math altimg='si1.svg'><msup><mrow><mi>Z</mi></mrow><mrow><mo>&#8242;</mo></mrow></msup></math> is suppressed by the mixing angle <italic>&#952;</italic>. Instead of freezing-out via pair annihilation as <math altimg='si8.svg'><msub><mrow><mi>&#967;</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mover accent='true'><mrow><mi>&#967;</mi></mrow><mrow><mo stretchy='false'>&#175;</mo></mrow></mover></mrow><mrow><mn>1</mn></mrow></msub><mo stretchy='false'>&#8594;</mo><mi>f</mi><mover accent='true'><mrow><mi>f</mi></mrow><mrow><mo stretchy='false'>&#175;</mo></mrow></mover></math>, we show that the observed relic abundance can be obtained through the processes as coannihilation <math altimg='si9.svg'><msub><mrow><mi>&#967;</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>&#967;</mi></mrow><mrow><mn>2</mn></mrow></msub><mo stretchy='false'>&#8594;</mo><mi>f</mi><mover accent='true'><mrow><mi>f</mi></mrow><mrow><mo stretchy='false'>&#175;</mo></mrow></mover></math> and conversion <math altimg='si10.svg'><msub><mrow><mi>&#967;</mi></mrow><mrow><mi>i</mi></mrow></msub><msub><mrow><mi>&#967;</mi></mrow><mrow><mn>2</mn></mrow></msub><mo stretchy='false'>&#8594;</mo><msub><mrow><mi>&#967;</mi></mrow><mrow><mi>j</mi></mrow></msub><msub><mrow><mi>&#967;</mi></mrow><mrow><mn>1</mn></mrow></msub></math>. We then explore the feasible parameter space of inelastic Dirac dark matter in <math altimg='si2.svg'><mi>U</mi><msub><mrow><mo stretchy='false'>(</mo><mn>1</mn><mo stretchy='false'>)</mo></mrow><mrow><mi>B</mi><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></mrow></msub></math>. Under various experimental constraints, the inelastic Dirac dark matter prefers the region with <math altimg='si11.svg'><mn>3</mn><mo>&#215;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>6</mn></mrow></msup><mo>&#8818;</mo><msup><mrow><mi>g</mi></mrow><mrow><mo>&#8242;</mo></mrow></msup><mo>&#8818;</mo><mn>2</mn><mo>&#215;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>4</mn></mrow></msup></math> and <math altimg='si12.svg'><mn>0.02</mn><mspace width='0.25em' /><mtext>GeV</mtext><mo>&#8818;</mo><msub><mrow><mi>m</mi></mrow><mrow><msup><mrow><mi>Z</mi></mrow><mrow><mo>&#8242;</mo></mrow></msup></mrow></msub><mo>&#8818;</mo><mn>10</mn></math> GeV, which is within the reach of future Belle II, FASER and SHiP.

Jing-Jing Zhang

Ang Liu

Inelastic Dirac dark matter in <italic>U</italic>(1) <inf><italic>B</italic>&#8722;<italic>L</italic></inf>

In this paper, we investigate the common parameter space of dark matter and leptogenesis in the U(1) B−L  symmetry. This model involves a complex scalar ϕ, sterile neutrinos N, and Majorana dark matter χ, where only dark matter χ is charged under the Z 2 symmetry. Masses of N and χ are generated via the Yukawa interactions to ϕ after breaking of the U(1) B−L  symmetry. TeV scale sterile neutrinos N are responsible for the generation of baryon asymmetry through the resonance leptogenesis mechanism. The new particles in the U(1) B−L  have a significant impact on the dilution of N, thus on leptogenesis. Meanwhile, the annihilation processes of dark matter χ are almost identical to that of N, which indicates that both leptogenesis and dark matter are closely related to satisfying the observed results simultaneously. Under various theoretical and experimental constraints, the viable common parameter space of dark matter and leptogenesis is obtained for both global and local U(1) B−L  symmetry.

Common origin of dark matter and leptogenesis in U(1) B−L

Heavy neutral leptons N are the most appealing candidates to generate tiny neutrino masses. We studied the signature of heavy neutral leptons in gauged   $ U(1)_{L_\mu-L_\tau} $   at a muon collider. Charged under the   $ U(1)_{L_\mu-L_\tau} $   symmetry, the heavy neutral leptons can be pair produced via the new gauge boson   $ U(1)_{L_\mu-L_\tau} $   at the muon collider as   $ U(1)_{L_\mu-L_\tau} $   and   $ U(1)_{L_\mu-L_\tau} $  . We then performed a detailed analysis on the lepton number violation signature   $ U(1)_{L_\mu-L_\tau} $   and   $ U(1)_{L_\mu-L_\tau} $   at the 3 TeV muon collider, where the hadronic decays of W boson are treated as fat-jets J. These lepton number violation signatures have quite clean backgrounds at the muon collider. Our simulation shows that a wide range of viable parameter space is within the reach of the 3 TeV muon collider. For instance, with new gauge coupling   $ U(1)_{L_\mu-L_\tau} $   and an integrated luminosity of 1000 fb  $ U(1)_{L_\mu-L_\tau} $  , the   $ U(1)_{L_\mu-L_\tau} $   signal could probe   $ U(1)_{L_\mu-L_\tau} $   TeV. Meanwhile, if the gauge boson mass satisfies   $ U(1)_{L_\mu-L_\tau} $  , the   $ U(1)_{L_\mu-L_\tau} $   signature would be more promising than the   $ U(1)_{L_\mu-L_\tau} $   signature.

Ru-Yi He

Jia-Qi Huang

Jin-Yuan Xu

Heavy neutral leptons in gauged (1) At Muon Collider  

We study the production of light nuclei in the coalescence mechanism of Au-Au collisions at midrapidity at   $ \sqrt{s_{NN}}=3 $  GeV. We derive analytic formulas of the momentum distributions of two bodies, three bodies, and four nucleons coalescing into light nuclei and naturally explain the transverse momentum spectra of the deuteron (d), triton (t), helium-3 ($^{3}$He), and helium-4 ($^{4}$He). We reproduce data on the yield rapidity densities, yield ratios, and averaged transverse momenta of d, t, $^{3}$He, and $^{4}$He and provide the proportions of contributions from different coalescence sources for t, $^{3}$He, and $^{4}$He in their production. We find that besides nucleon coalescence, nucleon+nucleus coalescence and nucleus+nucleus coalescence may play requisite roles in light nucleus production in Au-Au collisions at   $ \sqrt{s_{NN}}=3 $   GeV.

Rui-Qin Wang

Ji-Peng Lv

Yan-Hao Li

Jun Song

Different coalescence sources of light nucleus production in Au-Au collisions at GeV  

In this paper, we study the feeble sterile neutrino portal dark matter under the <math><msub><mi>Z</mi><mn>3</mn></msub></math> symmetry. The dark sector consists of one fermion singlet <math><mi>χ</mi></math> and one scalar singlet <math><mi>χ</mi></math>, which transform as <math><mi>χ</mi><mo>→</mo><msup><mi>e</mi><mrow><mi>i</mi><mn>2</mn><mi>π</mi><mo>/</mo><mn>3</mn></mrow></msup><mi>χ</mi><mo>,</mo><mi>ϕ</mi><mo>→</mo><msup><mi>e</mi><mrow><mi>i</mi><mn>2</mn><mi>π</mi><mo>/</mo><mn>3</mn></mrow></msup><mi>ϕ</mi></math> under the <math><msub><mi>Z</mi><mn>3</mn></msub></math> symmetry. Regarding fermion singlet <math><mi>χ</mi></math> as the dark matter candidate, the new interaction terms <math><msub><mi>y</mi><mi>χ</mi></msub><mi>ϕ</mi><mover><msup><mi>χ</mi><mi>c</mi></msup><mo>¯</mo></mover><mi>χ</mi></math> and <math><mi>μ</mi><msup><mi>ϕ</mi><mn>3</mn></msup><mo>/</mo><mn>2</mn></math> could induce various new production channels. For instance, when <math><msub><mi>m</mi><mi>ϕ</mi></msub><mo>&gt;</mo><mn>2</mn><msub><mi>m</mi><mi>χ</mi></msub></math>, the pair decay <math><mi>ϕ</mi><mo>→</mo><mi>χ</mi><mi>χ</mi></math> could be the dominant channel, rather than the delayed decay <math><mi>ϕ</mi><mo>→</mo><mi>χ</mi><mi>ν</mi></math>. Another appealing scenario is when the dark sector is initially produced through the scattering process as <math><mi>N</mi><mi>N</mi><mo>→</mo><mi>χ</mi><mi>χ</mi><mo>,</mo><mi>N</mi><mi>N</mi><mo>→</mo><mi>ϕ</mi><mi>ϕ</mi><mo>,</mo><mi>h</mi><mi>ν</mi><mo>→</mo><mi>χ</mi><mi>ϕ</mi></math>, then the semiproduction processes <math><mi>N</mi><mi>χ</mi><mo>→</mo><mi>ϕ</mi><mi>ϕ</mi><mo>,</mo><mi>N</mi><mi>ϕ</mi><mo>→</mo><mi>ϕ</mi><mi>χ</mi><mo>,</mo><mi>N</mi><mi>χ</mi><mo>→</mo><mi>χ</mi><mi>χ</mi></math> could lead to the exponential growth of dark sector abundances. The phenomenology of the sterile neutrino and the cosmological impact of the dark scalar are also considered in the <math><msub><mi>Z</mi><mn>3</mn></msub></math> symmetric model.

Sterile neutrino portal dark matter from semiproduction

Provided the dark sector consisted of a dark scalar <math><mi>ϕ</mi></math> and a dark fermion <math><mi>χ</mi></math> under an exact <math><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry, the sterile neutrino <math><mi>N</mi></math> can act as the messenger between the dark sector and standard model via the Yukawa coupling <math><msub><mi>λ</mi><mrow><mi>d</mi><mi>s</mi></mrow></msub><mover><mi>χ</mi><mo>¯</mo></mover><mi>ϕ</mi><mi>N</mi></math>. In this paper, we focus on the specific scenario <math><msub><mi>m</mi><mi>N</mi></msub><mo>&gt;</mo><msub><mi>m</mi><mi>ϕ</mi></msub><mo>+</mo><msub><mi>m</mi><mi>χ</mi></msub></math> with <math><mi>χ</mi></math> being a feebly interacting massive particle (FIMP) dark matter. The decay width of dark scalar <math><mi>ϕ</mi></math> is doubly suppressed by the smallness of Yukawa coupling <math><msub><mi>λ</mi><mrow><mi>d</mi><mi>s</mi></mrow></msub></math> and mixing angle <math><mi>θ</mi></math>. The delayed decay <math><mi>ϕ</mi><mo>→</mo><mi>χ</mi><mi>ν</mi></math> will have a great impact on cosmological observables such as the big bang nucleosynthesis, the cosmic microwave background anisotropy power spectra, the effective number of relativistic neutrino species <math><msub><mi>N</mi><mi>eff</mi></msub></math> and the energetic neutrino flux. Meanwhile, the sterile neutrino can generate displaced vertex signature at colliders when <math><msub><mi>m</mi><mi>N</mi></msub><mo>&lt;</mo><msub><mi>m</mi><mi>W</mi></msub></math>. The dark scalar <math><mi>ϕ</mi></math> will also induce measurable Higgs invisible decay for relatively large quartic coupling. A comprehensive analysis of constraints from cosmology and collider is performed in this paper. We find that almost the whole parameter space with <math><msub><mi>m</mi><mi>N</mi></msub><mo>&lt;</mo><msub><mi>m</mi><mi>W</mi></msub></math> is under the reach of future experiments.

Constraints on sterile neutrino portal dark matter from cosmology and collider

In this paper, we propose the sterile neutrino portal dark matter in  $$\nu $$  <math> <mi>ν</mi> </math>  THDM. This model can naturally generate tiny neutrino mass with the neutrinophilic scalar doublet  $$\Phi _{\nu }$$  <math> <msub> <mi>Φ</mi> <mi>ν</mi> </msub> </math>   and sterile neutrinos N around TeV scale. Charged under a  $$Z_2$$  <math> <msub> <mi>Z</mi> <mn>2</mn> </msub> </math>   symmetry, one Dirac fermion singlet  $$\chi $$  <math> <mi>χ</mi> </math>   and one scalar singlet  $$\phi $$  <math> <mi>ϕ</mi> </math>   are further introduced in the dark sector. The sterile neutrinos N are the mediators between the DM and SM. Depending on the coupling strength, the DM can be either WIMP or FIMP. For the WIMP scenario, pair annihilation of DM into NN is the key channel to satisfy various bounds, which could be tested at indirect detection experiments. For the FIMP scenario, besides the direct production of DM from freeze-in mechanism, contributions from late decay of NLOP is also important. When sterile neutrinos are heavier than the dark sector, NLOP is long-lived due to tiny mixing angle between sterile and light neutrinos. Constrains from free-streaming length, CMB, BBN and neutrino experiments are considered.

Sterile neutrino portal dark matter in  $$\nu $$  <math> <mi>ν</mi> </math>  THDM

With the kinetic freeze-out nucleons and antinucleons obtained from the quark combination model, we study the production of light nuclei and antinuclei in the (anti-)nucleon coalescence mechanism in relativistic heavy ion collisions. We derive analytic formulas of the momentum distributions of different light nuclei and apply them to compute transverse momentum <math><mo>(</mo><msub><mi>p</mi><mi>T</mi></msub><mo>)</mo></math> spectra of (anti-)deuterons <math><mo>(</mo><mi>d</mi></math>, <math><mover><mi>d</mi><mo>¯</mo></mover><mo>)</mo></math> and (anti-)tritons <math><mo>(</mo><mi>t</mi><mo>,</mo></math> <math><mover><mi>t</mi><mo>¯</mo></mover><mo>)</mo></math> in Au-Au collisions at <math><mrow><msqrt><msub><mi>s</mi><mi>NN</mi></msub></msqrt><mo>=</mo><mn>7.7</mn><mo>,</mo><mo> </mo><mn>11.5</mn><mo>,</mo><mo> </mo><mn>19.6</mn><mo>,</mo><mo> </mo><mn>27</mn><mo>,</mo><mo> </mo><mn>39</mn><mo>,</mo><mo> </mo><mn>54.4</mn><mo> </mo><mi>GeV</mi></mrow></math>. We find that the experimental data available for these <math><msub><mi>p</mi><mi>T</mi></msub></math> spectra can be well reproduced. We further study the yields and yield ratios of different light (anti-)nuclei and naturally explain their interesting behaviors as a function of the collision energy. We especially point out that the multiparticle yield ratio <math><mrow><mi>t</mi><mi>p</mi><mo>/</mo><msup><mi>d</mi><mn>2</mn></msup></mrow></math> should be carefully corrected from hyperon weak decays for protons to probe the production characteristics of light nuclei. All of our results show that the coalescence mechanism for (anti-)nucleons plays a dominant role for the production of light nuclei and antinuclei at the BNL Relativistic Heavy Ion Collider beam energy scan energies.

Xiang-Yu Zhao

Yan-Ting Feng

Production characteristics of light (anti-)nuclei from (anti-)nucleon coalescence in heavy ion collisions at energies employed at the RHIC beam energy scan

We study the momentum dependence of the production of light nuclei in high-energy collisions in the nucleon coalescence mechanism. We derive formulas of the momentum distributions of deuterons <math><mi>d</mi></math> and helions <math><mmultiscripts><mi>He</mi><mprescripts></mprescripts><none></none><mn>3</mn></mmultiscripts></math>. We obtain the analytic expressions of the coalescence factor <math><msub><mi>B</mi><mi>A</mi></msub></math> (<math><msub><mi>B</mi><mn>2</mn></msub></math> for <math><mi>d</mi></math> and <math><msub><mi>B</mi><mn>3</mn></msub></math> for <math><mmultiscripts><mi>He</mi><mprescripts></mprescripts><none></none><mn>3</mn></mmultiscripts></math>) as functions of the collision system size and the momentum. We apply the deduced results to <math><mi>p</mi><mo>−</mo><mi>p</mi></math>, <math><mi>p</mi></math>-Pb and Pb-Pb collisions to explain naturally the interesting behavior of <math><msub><mi>B</mi><mi>A</mi></msub></math> observed in experiments at the CERN Large Hadron Collider.

Momentum dependence of light nuclei production in <math><mi>p</mi><mo>−</mo><mi>p</mi></math>, <math><mi>p</mi><mtext>−</mtext><mi>Pb</mi></math>, and Pb-Pb collisions at energies available at the CERN Large Hadron Collider