arXiv subjects

Wei Chao

Publications and source records attributed to Wei Chao.

At least 37 records · Page 2Linked to original sources

arXiv2023

Direct detections of the Axion-like particle Revisited

Axion-like particles (ALPs) are promising dark matter candidates. Their signals in direct detection experiments arise from the well-known inverse Primakoff effect or the inverse Compton scattering of the ALPs with the electron. In this paper, we revisit the direct detection of ALP by carefully considering the interference between the inverse Primakoff amplitude and the inverse Compton amplitude in the scattering process $a+e \to e+γ$ for the first time. It shows that the contribution of the interference term turns to be dominated in the scattering for a large ALP energy. Given the new analytical formula, signals or constraints of ALP couplings in various projected experiments are investigated. Our results show that these experiments may put strong constraints on ALP couplings for relatively heavy ALP. We further study projected constraints on the ALP from the JUNO experiment, which shows competitive constraints on ALP couplings using a ten-year exposure.

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arXiv2023

Majorana Majoron and the Baryon Asymmetry of the Universe

The spontaneous breaking of the global lepton number, an accidental symmetry in the Standard Model of particle physics, results in a massless goldstone boson, the Majoron, which can be taken as a cold dark matter candidate with properties similar to these of the axion. In this letter, we propose a novel mass generation mechanism for the Majoron via radiative corrections induced by the interaction of a tiny lepton-number-violating (LNV) Majorana mass term of right-handed neutrinos in the canonical seesaw mechanism. We show that this LNV Majorana mass term not only generates the mass of the Majoron but also leads to a non-zero initial velocity of the Majoron, which subsequently impacts on the relic abundance of the Majoron generated in the early universe via the misalignment mechanism. With the assistance of the Weinberg operator, the same initial velocity may also generate the lepton asymmetry, which is subsequently transported into the baryon asymmetry of the universe (BAU) via the weak sphaleron process. As a result, the neutrino masses, dark matter and the BAU can be addressed in this concise theoretical framework.

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arXiv2023

Axion effects on gamma-ray spectral irregularities with AGN redshift uncertainty

We investigate the photon-axionlike particle (ALP) oscillation effects on TeV gamma-ray spectral irregularities from the uncertain redshift active galactic nuclei (AGN) VER J0521+211. The gamma-ray spectra are measured by Fermi-LAT and VERITAS with the three flux states in 2013 and 2014. We set the combined constraints on the ALP parameter ($m_a, g_{aγ}$) space with these states and test the extragalactic background light (EBL) absorption effect on ALP constraints with the redshift limit scenarios $z_0\sim\mathcal{O}(0.1-0.3)$. The 99% $\rm C.L.$ photon-ALP combined constraints set by VER J0521+211 are roughly at $g_{aγ} \gtrsim 2.0\times 10^{-11} \rm \, GeV^{-1}$ for $1.0\times10^{-9} \, {\rm eV} \lesssim m_a \lesssim 1.0\times10^{-7} \, {\rm eV}$. We find no clear connection between the redshift limit scenarios and the photon-ALP constraints. Both the underestimated and overestimated redshifts can affect the constraint results.

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arXiv2022

Axion-like Dark Matter from the Type-II Seesaw Mechanism

Although axion-like particles (ALPs) are popular dark matter candidates, their mass generation mechanisms as well as cosmic thermal evolutions are still unclear. In this letter, we propose a new mass generation mechanism of ALP during the electroweak phase transition in the presence of the type-II seesaw mechanism. As ALP gets mass uniquely at the electroweak scale, there is a cutoff scale on the ALP oscillation temperature irrelevant to the specific mass of ALP, which is a distinctive feature of this scenario. The ALP couples to the active neutrinos, leaving the matter effect of neutrino oscillations in a dense ALP environment as a smoking gun. As a by-product, the recent $W$-boson mass anomaly observed by the CDF collaboration is also quoted by the TeV-scale type-II seesaw. We explain three kinds of new physics phenomena are with one stroke.

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arXiv2022

$\mathbf{{N}_{eff}}$ from Excited DM state

For a cold dark matter (DM) originating from the co-annihilation processes, there will be excited state(s) in the dark sector, that may decay or annihilate away shortly after their freeze-out. In this paper we investigate the impact of the decay of these excited states on the effective number of neutrino species, $N_{\rm eff}^{}$, which is an important cosmological parameter and will be tested by the future CMB-S4 project. We work in the framework of pseudo-Dirac DM mode via the Higgs portal. The relic density and the direct detection signal of the DM are calculated, which gives the available parameter space. Impacts of the excited state (the heavy component of the pseudo-Dirac fermion) on the decoupling of active neutrinos are investigated by solving Boltzmann equations of photon and neutrinos with collision term induced by the decay of the excited state. The numerical result shows that $|N_{\rm eff}^{}|$ can be of the order $10^{-4}$, which depends on the mass and lifetime of excited DM state.

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arXiv2021

Pseudo-Dirac Sterile Neutrino Dark Matter

Sterile neutrino is a promising dark matter (DM) candidate. However the parameter space of this scenario has almost been ruled out by the X-ray observation results whenever the sterile neutrino is solely produced by the Dodelson-Widrow (DW) mechanism in the early Universe. In this letter we propose an extension to the minimal sterile neutrino DM model by introducing the pseudo-Dirac sterile neutrino, which implies the existence of two nearly degenerate Majorana states $\hat N_{1,2}^{}$, and a permutation symmetry. The heavy state $\hat N_1$ is produced via the DW mechanism, and the light state $\hat N_2$, which serves as the DM, is produced from the decay of $\hat N_1$ in the early Universe. The X-ray constraint is avoided by the permutation symmetry, which forbidden the two-body decay of the DM into active neutrinos and photon. A promising signal of this scenario is the effective number of neutrino species, which will be precisely measured in future experiments, such as CMB stage IV. We further study the impact of this model on the cosmological parameters. The Markov Chain Monte Carlo analysis for the Planck + BAO+R19 data gives $H_0=69.2_{-0.59}^{+0.58}$, which may relieve the Hubble tension.

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arXiv2021

First Order Color Symmetry Breaking and Restoration Triggered by Electroweak Symmetry Non-restoration

In this paper we propose a new approach for the spontaneous breaking and restoration of the $SU(3)_C$ color symmetry in the framework of electroweak symmetry non-restoration (EWSNR) at high temperature, which provides an alternative approach for the Baryogenesis. Due to the exotic high vacuum expectation value (VEV) of the SM Higgs doublet in EWSNR, the color symmetry can be spontaneous broken succeeding the electroweak phase transition whenever there is a negative quartic coupling between the SM Higgs and a scalar color triplet. The color symmetry is then restored at low temperature as the VEV of SM Higgs evolving to small value. We show that the phase transitions related to color breaking and restoration can be first order, and the stochastic gravitational wave (GW) signals are smoking-gun of these processes. We demonstrate the possibility of detecting these GW signals in future GW experiments such as DECIGO and BBO.

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arXiv2021

A new Direct Detection Strategy for the Cosmic Neutrino Background

The direct detection of cosmic neutrino background (CNB) has been a longstanding challenge in particle physics, due to its low number density and tiny neutrino masses. In this work, we consider the spectrum of the CNB boosted by cosmic rays via the neutrino self-interaction, and calculate the event rate of the boosted CNB-plasmon scattering in term of the dielectric response, which accounts for in-medium screening effect of a condensed matter target. This can be taken as the new direct detection strategy for the CNB in complementary to the traditional one, which captures the CNB on a $β$-unstable nucleus. Our result shows that one can either see the event of the CNB for the exposure of per kg$\cdot$year, or puts a strong constraint on the neutrino self-interaction. We further explore the background induced by the sub-MeV dark matter and the boosted super-light dark matter.

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arXiv2021

Loop effect with vector mediator in the coherent neutrino-nucleus scattering

The observation of the coherent elastic neutrino-nucleus scattering (CE$ν$NS) provides us opportunities to explore a wide class of new physics. In the Standard Model (SM), the CE$ν$NS process arises from the vector and axial-vector neutral currents through the exchange of $Z$ boson and the axial-vector current contribution turns out to be subdominant. It is thus natural to consider the extra contributions to CE$ν$NS from more generic new physics beyond the SM with (axial-)vector interactions associated with a new vector mediator $Z'$. Besides the ordinary CE$ν$NS, the active neutrinos can convert into a new exotic fermion $χ$ through the process $νN\to χN$ mediated by $Z'$ without violating the coherence. It would be interesting to consider the implication of this conversion for the new fermion sector beyond the SM. We consider the framework of a simplified neutrino model in which a new Dirac fermion $χ$ interacts with active neutrinos and a leptophobic vector mediator $Z'$. We evaluate both the tree-level and loop-level contributions to the CE$ν$NS and in particular the loop diagrams produce active neutrino elastic scattering process $νN\to νN$ with the fermion $χ$ inside the loops. When the interaction between $Z'$ and the SM quarks is vector type and axial-vector type, the CE$ν$NS processes are respectively dominated by the tree-level and loop-level contributions. We investigate the constraints on the model parameters by fitting to the COHERENT data, assuming a wide range of $m_χ$. The parameter space with $m_χ$ larger than the maximal energy of incoming neutrinos can be constrained by including the loop-level contribution. More importantly, the inclusion of loop diagrams can place constraint on axial-vector interaction whose tree-level process is absent in the coherent neutrino-nucleus scattering.

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arXiv2021

Direct detection of Sub-GeV Dark Matter via 3-body Inelastic Scattering Process

Direct detection of Sub-GeV dark matter (DM) is challenging because the recoil energy of the nuclei or electron from the elastic scattering of a sub-GeV DM off the target can hardly reach the detector threshold. In this paper, we present a new direct detection strategy for sub-GeV DM via the three-body inelastic scattering process, $χ+ χ+ {\rm SM} \to η+ {\rm SM}$, where $χ$ is DM candidate and $η$ is either a DM composite state or any dark radiation. This process is common for a large class of DM models without presuming particular thermal history in the early Universe. The typical signature from this process is almost a monoenergetic pulse signal where the recoil energy comes from either the binding energy or the consumed DM particle. We show that detectable DM mass range can be effectively enlarged compared to the elastic scattering process.

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arXiv2021

Connecting Primordial Black Hole to boosted sub-GeV Dark Matter through neutrino

The explorations of alternative dark matter (DM) candidates beyond WIMP motivated primordial black holes (PBHs) or sub-GeV DM particle in the Milky Way. Neutrinos from PBH evaporation at the present times play as a novel medium boosting sub-GeV DM and leaving signatures in the terrestrial experiments. We explore the boosted DM by the neutrino flux from PBH evaporation (PBH$ν$BDM) so as to connect the macroscopic PBHs to sub-GeV DM particle. We consider this PBH$ν$BDM scenario to interpret the XENON1T keV excess. The projected bounds on the sub-GeV DM-electron scattering cross section and the fraction of DM composed of PBHs $f_{\rm PBH}$ are imposed for future experiments.

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arXiv2021

Dark matter, $Z^{\prime}$, vector-like quark at the LHC and $b\to s μμ$ anomaly

Combining the $b\to sμ^+μ^-$ anomaly and dark matter observables, we study the capability of LHC to test dark matter, $Z^{\prime}$, and vector-like quark. We focus on a local $U(1)_{L_μ-L_τ}$ model with a vector-like $SU(2)_L$ doublet quark $Q$ and a complex singlet scalar whose lightest component $X_I$ is a candidate of dark matter. After imposing relevant constraints, we find that the $b\to sμ^+μ^-$ anomaly and the relic abundance of dark matter favor $m_{X_I}< 350$ GeV and $m_{Z^{\prime}}< 450$ GeV for $m_Q<$ 2 TeV and $m_{X_R}<$ 2 TeV (the heavy partner of $m_{X_I}$). The current searches for jets and missing transverse momentum at the LHC sizably reduce the mass ranges of the vector-like quark, and $m_Q$ is required to be larger than 1.7 TeV. Finally, we discuss the possibility of probing these new particles at the high luminosity LHC via the QCD process $pp \to D\bar{D}$ or $pp \to U\bar{U}$ followed by the decay $D\to s (b) Z'X_I$ or $U \to u (c) Z' X_I$ and then $Z'\toμ^+μ^-$. Taking a benchmark point of $m_Q$=1.93 TeV, $m_{Z^\prime}=170$ GeV, and $m_{X_I}=$ 145 GeV, we perform a detailed Monte Carlo simulation, and find that such benchmark point can be accessible at the 14 TeV LHC with an integrated luminosity 3000 fb$^{-1}$.

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arXiv2020

Filtered pseudo-scalar dark matter and gravitational waves from first order phase transition

If dark matter (DM) acquires mass during a first order phase transition, there will be a filtering-out effect when DM enters the expanding bubble. In this paper we study the filtering-out effect for a pseudo-scalar DM, whose mass may partially come from a first order phase transition in the hidden sector. We calculate the ratio of DM that may enter the bubble for various bubble wall velocities as well as various status of DM (in the thermal equilibrium, or out of the thermal equilibrium) at the time of phase transition, which results in small penetration rate that may affect the final relic abundance of the DM. We further study the stochastic gravitational wave signals emitted by the hidden sector phase transition at the space-based interferometer experiments as the smoking-gun of this model.

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arXiv2020

Probing Bottom-flavored Scalar Dark Matters at Loop Level

In this paper we consider loop corrections to the spin-independent WIMP-nucleon scattering cross section in bottom-quark flavored scalar-type dark matter models. We focus on two scenarios: (a) a complex scalar dark matter with a scalar particle as the mediator; and (b) a real scalar dark matter with a vector boson as the mediator. In both scenarios, the direct detection cross sections are either spin-dependent or kinematically forbidden at the tree-level. Corrections induced by the WIMP-gluon effective operator, scalar-type WIMP-quark effective operator, and the twist-2 effective operator are calculated. Numerical results show that loop induced spin-independent WIMP-nucleon scattering cross sections are quite considerable in both scenarios.

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arXiv2020

Neutrino oscillation in dark matter with $L_μ-L_τ$

In this paper, we study the phenomenology of a Dirac dark matter in the $L_μ-L_τ$ model and investigate the neutrino oscillation in the dark halo. Since dark matter couples to the muon neutrino and the tau neutrino with opposite sign couplings, it contributes effective potentials, $\pm A_χ$, to the evolution equation of the neutrino flavor transition amplitude, which can be significant for high energy neutrino oscillations in a dense dark matter environment. We discuss neutrino masses, lepton mixing angles, Dirac CP phase, and neutrino oscillation probabilities in the dark halo using full numerical calculations. Results show that neutrinos can endure very different matter effects. When the potential $A_χ$ becomes ultra-large, three neutrino flavors decouple from each other.

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arXiv2020

Neutrino Portal via Loops

One loop correction to the dark matter (DM) annihilation cross section is usually assumed to be sub-dominate in calculating the DM relic density. In this paper, we propose a scenario where DM freezes out mainly via loops in the neutrino portal. For a scalar DM annihilating into neutrino via a triangle diagram, or a Majorana DM annihilating into neutrino via a box diagram, the observed DM relic density can be generated if the mediator is Majorana fermion. We further work out the neutrino Debye mass and neutrino oscillation probabilities in the dark halo. Numerical results show that impactions of DM to these physical observables are negligible on the Earth, however the analytical results can be applied to evaluate neutrino properties in a dense DM environment.

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arXiv2020

Pseudo-Dirac Dark Matter in XENON1T

The XENON1T dark matter experiment recently reported 0.65 ton-year exposure measurement on electron recoils , which shows an excess in $2\sim 3$ KeV recoils above the detector background. In this paper we present a Pseudo-Dirac dark matter scenario to explain the excess via inelastic dark matter-electron scattering. With a KeV scale mass splitting between the two components of the Pseudo-Dirac dark matter, the slightly excited component can down-scatter on electrons. The desired dark matter masses are about 10 GeV with a 4 KeV mass-splitting and unity coupling to electrons, which generate the observed XENON1T recoil events, give the appropriate dark matter relic abundance and satisfy collider search limits.

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arXiv2019

CP violation in the top-assisted electroweak baryogenesis

The origin of the baryon asymmetry of the universe (BAU) is a longstanding problem in the high energy physics. The electroweak baryogenesis mechanism, which generates the BAU during the first order electroweak phase transition, provides a testable solution to this problem. In this paper we revisit the top-assisted electroweak baryogenesis model, which extends the standard model (SM) with only one scalar singlet. Constraints on the new CP-violating coupling as well as the mixing between the SM Higgs and the new scalar singlet are derived by considering the latest result of ACME and oblique observables. Furthermore, we derive constraints on these two parameters arising from the data of Higgs measurement at the LHC as well as the four top-quark production at the LHC.

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