arXiv subjects

Kwei-Chou Yang

Publications and source records attributed to Kwei-Chou Yang.

At least 19 recordsLinked to original sources

arXiv2025

Nearly Degenerate Majorana Dark Matter and Its Self-Interactions in a Gauged $U(1)_{L_\mu - L_\tau}$ Model

We propose a model of nearly degenerate Majorana dark matter (DM) in a gauged $U(1)_{L_\mu - L_\tau}$ extension of the Standard Model. Spontaneous symmetry breaking generates a dominant Majorana mass via a strong Yukawa coupling, splitting the dark fermion into two nearly degenerate states. The lighter state ($\chi_-$) is the DM candidate, with an allowed mass of $\sim 10$ GeV to several hundred GeV. Crucially, within the $10 \sim 75$ GeV mass range and a scalar mediator at the tens of MeV scale, this strong coupling dictates the thermal relic abundance and induces significant elastic self-interactions. These self-interactions naturally resolve small-scale structure anomalies, such as the core-cusp problem, while satisfying massive cluster constraints. Furthermore, we place stringent joint constraints on the scalar mass and the Higgs mixing angle $\alpha$ using the latest LZ 2025 direct detection data. The model's gauge boson $Z^\prime$ maintains early-Universe thermal equilibrium and accommodates the muon anomalous magnetic moment $(g-2)_\mu$, remaining consistent with updated cosmological and experimental bounds.

hep-ph↗

arXiv2024

Self-Interacting Forbidden Dark Matter under a Cannibally Co-Decaying Phase

In a usual dark matter (DM) model without a huge mass difference between the DM and lighter mediator, using the coupling strength suitable for having the correct relic density, the resulting self-interaction becomes several orders of magnitude smaller than that required to interpret the small scale structures. We present a framework that can offer a solution for this point. We consider a model that contains the vector DM and a heavier but unstable Higgs-like scalar in the hidden sector. When the temperature drops below $\sim m_{\rm DM}$, the hidden sector, which is thermally decoupled from the visible sector, enters a cannibal phase, during which the DM density is depleted with the out-of-equilibrium decay of the scalar. The favored parameter region, giving the correct relic density and the proper size of self-interactions, shows the scalar-to-DM mass ratio $\in [1.1,1.33]$ and the scalar mass $\in[9,114]\,{\rm MeV}$. A sizable parameter space still survives the most current constraints and can be further probed by the near future NA62 beam dump experiment.

hep-ph↗

arXiv2022

Freeze-out Forbidden Dark Matter in the Hidden Sector in the Mass Range from sub-GeV to TeV

Kinematically forbidden channels can set the freeze-out dark matter (DM) relic abundance. These channels are described by DM annihilations into heavier states, which vanish at zero temperature limit, but occur at finite temperatures in the early Universe. For the case that the final state of the forbidden channel is scalar mediators that couple to Standard Model (SM) matter through mixing with the SM Higgs, the signals from DM-nucleon interactions and from mediator-related missing energy or displaced vertices could be detected by direct detections and particle physics experiments, respectively. We thus present a study on the simplest secluded vector dark matter model that can exhibit this scenario in the mass range from sub-GeV to TeV. The dark matter resides in the hidden sector, which is in thermal equilibrium with the SM before freeze-out. During freeze-out, the depletion of its density results from its annihilation into two heavier but metastable scalars, where the coupling can be determined by having the correct relic density and constrained by the perturbative unitarity bound. However, much of the allowed parameter space is insensitive to the mixing angle between the hidden scalar and SM Higgs. We find that a more significant mass splitting between DM and the mediator can be allowed only in the sub-GeV region. Moreover, the mass splitting in the TeV region is required to be within the percent level. This model of the forbidden DM interacting with SM particles through the scalar portal is testable in experiments.

hep-ph↗

arXiv2022

Thermodynamic Evolution of Secluded Vector Dark Matter: Conventional WIMPs and Nonconventional WIMPs

The secluded dark matter resides within a hidden sector and self-annihilates into lighter mediators which subsequently decay to the Standard Model (SM) particles. Depending on the coupling strength of the mediator to the SM, the hidden sector can be kinetically decoupled from the SM bath when the temperature drops below the mediator's mass, and the dark matter annihilation cross section at freeze-out is thus possible to be boosted above the conventional value of weak interacting massive particles. We present a comprehensive study on thermodynamic evolution of the hidden sector from the first principle, using the simplest secluded vector dark matter model. Motivated by the observation of Galactic center gamma-ray excess, we take two mass sets $\sim{\cal O}(80\, \text{GeV})$ for the dark matter and mediator as examples to illustrate the thermodynamics. The coupled Boltzmann moment equations for number densities and temperature evolutions of the hidden sector are numerically solved. The formalism can be easily extended to a general secluded dark matter model. We show that a long-lived mediator can result in a boosted dark matter annihilation cross section to account for the relic abundance. We further show the parameter space which provides a good fit to the Galactic center excess data and is compatible with the current bounds and LUX-ZEPLIN projected sensitivity. We find that the future observations of dwarf spheroidal galaxies offer promising reach to probe the most relic allowed parameter space relevant to the boosted dark matter annihilation cross section.

hep-ph↗

arXiv2021

Diffusion of Cosmic Antiprotons Generated throughout the Dark Matter Halo -- A Semi-Analytical Solution for a Linear Galactic Wind Model

The public GALPROP code gives a fully numerical solution for the spectrum of cosmic rays propagating through a linear Galactic wind directed outwards from the Galactic plane in the framework of a cylindrical diffusion model. Alternatively, for the linear Galactic wind case, we present a semi-analytical solution of the two-zone cylindrical model which describes the spectrum of cosmic-ray antiprotons produced from the primary sources throughout the dark matter halo. While the secondary antiprotons can be generated by, e.g., the GALPROP WebRun, consistently using this semi-analytical solution for the primary ones would be helpful to build a suited dark matter (DM) model, which may be sophisticated, and then to perform a statistical analysis when confronting with data. As an example, using the obtained formula, we study the possible DM signal, through the channel $\text{DM DM} \to {\bar b}b$, and its constraint from the measurement of the AMS-02 antiproton-to-proton ratio. The indication of the DM signal is discussed. The advantage of the semi-analytical approach and its comparison with the GALPROP model are presented.

astro-ph.HE↗

arXiv2020

A Potentially Detectable Gamma-Ray Line in the Fermi Galactic Center Excess -- In Light of One-Step Cascade Annihilations of Secluded (Vector) Dark Matter via the Higgs Portal

We show the presence of a potentially detectable gamma-ray line in the Fermi Galactic center excess in light of the secluded (vector) dark matter (DM) model in which the hidden scalar, nearly degenerate with DM in mass, mediates the interaction of the secluded DM with the Standard Model (SM) due to its mixing with the SM Higgs. We find that the parameter region $m_X\in[60, 132]$ GeV can provide a good fit to the Fermi Galactic center gamma-ray excess spectrum, appearing a prominent gamma-ray line with the energy $\in [30, 66]$ GeV. The best fit gives $m_X\simeq m_S \simeq 86$ GeV with a $p$-value$\, =0.42$, so that the resultant gamma-ray line, arising from the decay of the scalar mediator into $γγ$, peaks at 43 GeV. We derive constraints on the annihilation cross section from the Fermi-LAT gamma-ray line search, gamma-ray observations of the Fermi-LAT dwarf spheroidal galaxies, and Planck cosmic microwave background measurement. For the secluded vector DM model, the parameter space constrained by the current XENON1T and future LUX-ZEPLIN is shown. Finally, for the mixing angle between the Higgs sectors, we discuss its lower bound, which is required by the big bang nucleosynthesis constraint and relevant to the hidden sector decoupling temperature.

hep-ph↗

arXiv2018

Hidden Higgs Portal Vector Dark Matter for the Galactic Center Gamma-Ray Excess from the Two-Step Cascade Annihilation, and Muon g-2

We have built a lepton-specific next-to-minimal two-Higgs-doublet-portal vector dark matter model. The vector dark matter in the hidden sector does not directly couple to the visible sector, but instead annihilates into the hidden Higgs bosons which decay through a small coupling into the CP-odd Higgs bosons. In this model, the Galactic center gamma-ray excess is mainly due to the 2-step cascade annihilation with $τ$'s in the final state. The obtained mass of the CP-odd Higgs $A$ in the Galactic center excess fit can explain the muon $g-2$ anomaly at the 2$σ$ level without violating the stringent constraints from the lepton universality and $τ$ decays. We show three different freeze-out types of the dark matter relic, called (i) the conventional WIMP dark matter, (ii) the unconventional WIMP dark matter and (iii) the cannibally co-decaying dark matter, depending on the magnitudes of the mixing angles between the hidden Higgs and visible two-Higgs doublets. The dark matter in the hidden sector is secluded from detections in the direct searches or colliders, while the dark matter annihilation signals are not suppressed in a general hidden sector dark matter model. We discuss the constraints from observations of the dwarf spheroidal galaxies and the Fermi-LAT projected sensitivity.

hep-ph↗

arXiv2018

Search for Scalar Dark Matter via Pseudoscalar Portal Interactions: In Light of the Galactic Center Gamma-Ray Excess

In light of the observed Galactic center gamma-ray excess, we investigate a simplified model, for which the scalar dark matter interacts with quarks through a pseudoscalar mediator. The viable regions of the parameter space, that can also account for the relic density and evade the current searches, are identified, if the low-velocity dark matter annihilates through an $s$-channel off-shell mediator mostly into $\bar{b} b$, and/or annihilates directly into two ${\it hidden}$ on-shell mediators, which subsequently decay into the quark pairs. These two kinds of annihilations are $s$ wave. The projected monojet limit set by the high luminosity LHC sensitivity could constrain the favored parameter space, where the mediator's mass is larger than the dark matter mass by a factor of 2. We show that the projected sensitivity of 15-year Fermi-LAT observations of dwarf spheroidal galaxies can provide a stringent constraint on the most parameter space allowed in this model. If the on-shell mediator channel contributes to the dark matter annihilation cross sections over 50$\%$, this model with a lighter mediator can be probed in the projected PICO-500L experiment.

hep-ph↗

arXiv2017

Light-Cone Distribution Amplitudes of Light $J^{PC}=2^{--}$ Tensor Mesons in QCD

We present a study for two-quark light-cone distribution amplitudes for the $1^3D_2$ light tensor meson states with quantum number $J^{PC}=2^{--}$. Because of the G-parity, the chiral-even two-quark light-cone distribution amplitudes of this tensor meson are antisymmetric under the interchange of momentum fractions of the quark and antiquark in the SU(3) limit, while the chiral-odd ones are symmetric. The asymptotic leading-twist LCDAs with the strange quark mass correction are shown. We estimate the relevant parameters, the decay constants $f_T$ and $f_T^\perp$, and first Gegenbauer moment $a_1^\perp$, by using the QCD sum rule method. These parameters play a central role in the investigation of $B$ meson decaying into the $2^{--}$ tensor mesons.

hep-ph↗

arXiv2016

Fermionic Dark Matter through a Light Pseudoscalar Portal: Hints from the DAMA Results

We study the fermionic dark matter (DM) particle interacting with Standard Model quarks via a light pseudoscalar mediator. We consider separately the scenarios for which the DM-pseudoscalar coupling is $CP$ conserving or $CP$ violating. We show that taking a contact interaction is not suitable, even when the mediator has a mass of the same order of magnitude as the typical momentum transfer at the direct-detection experiments, such that the allowed DAMA region is excluded or considerably modified by the correct relic density requirement. The DAMA result seems to indicate that the $CP$-violating interaction is dominant at direct searches. We find that, if the proton-to-neutron effective coupling ratio is $-60\sim -40$, the exclusion limits set by SuperCDMS, XENON100, and LUX are highly suppressed, and the DAMA signal can thus be easily reconciled with these null measurements. For this model, the allowed region determined by the DAMA signal and correct relic density can successfully satisfy the conditions required by the thermal equilibrium, big bang nucleosynthesis, and DM self-interactions. The results of future measurements on flavor physics will provide important constraints on the related models. Precise measurements performed by COUPP, PICASSO, SIMPLE and KIMS should be able to test this model in the near future.

hep-ph↗

arXiv2016

$B \to J/ψK$ Decays in QCD Factorization

The hadronic decays $B\to J/ψK(K^*)$ are interesting because experimentally they are the only color-suppressed modes which have been measured, and theoretically they are calculable by QCD factorization even the emitted meson $Jψ$ is heavy. We analyze the decay $B\to JψK$ within the framework of QCD factorization in the heavy quark limit. We show explicitly the scale and $γ_5$-scheme independence of decay amplitudes and infrared safety of nonfactorizable corrections at twist-2 order. Leading-twist contributions from the light-cone distribution amplitudes (LCDAs) of the mesons are too small to accommodate the data; the nonfactorizable corrections to naive factorization are small and not significant. We study the twist-3 effects due to the kaon and find that the coefficient $a_2(JψK)$ is largely enhanced by the nonfactorizable spectator interactions arising from the twist-3 kaon LCDA $ϕ^K_σ$, which are formally power-suppressed but chirally, logarithmically and kinematically enhanced. Therefore, factorization breaks down at twist-3 order. Higher-twist effects of $Jψ$ are briefly discussed. Our result also resolves the long-standing sign ambiguity of $a_2(JψK)$, which turns out to be positive for its real part.

hep-ph↗

arXiv2016

Comment on "Dark Matter with Pseudoscalar-Mediated Interactions Explains the DAMA Signal and the Galactic Center Excess"

Arina et al. have proposed the Dirac fermionic dark matter with pseudoscalar-mediated interactions to explain the Galactic Center excess, correct relic density and DAMA signal. They have assumed that contact interactions remain roughly valid in calculating scattering rates at the direct detection even when the mediator mass is the same order as the typical momentum transfer. We show that such a replacement is not suitable. Adopting the full form of interactions, we show that the gamma-ray excess allowed parameters are completely outside of the DAMA iodine 3$σ$ region, even for heavy-flavor-universal couplings, for which $m_{DM} \sim 40$ GeV in the gamma-ray excess fit. As for Higgs-like couplings, the two regions overlap for $m_a\lesssim$ 15 MeV, where long-range interactions, instead of contact interactions, occur at the DAMA.

hep-ph↗

arXiv2013

Dark Matter Mass Constrained by the Relic Abundance, Direct Detections, and Colliders

We take into account a generic form of a Dirac fermionic dark matter (DM), which communicates with the Standard Model quarks via a scalar mediator, in a model-independent way. Four special interaction scenarios are investigated, where one is parity conserving and the other three are parity violating. Three of them result in the $v$ suppressed DM-nucleon cross sections, where $v \sim 10^{-3} c$ is the velocity of the DM in the laboratory frame. We constrain the masses of the dark matter and mediator as well as the couplings from the thermal relic abundance, and the recent results of the XENON100 direct detection and collider experiments involving the two channels: (i) monojet plus large missing transverse energy, and (ii) dijet. The current monojet constraint is not stronger than that from the requirement of the correct relic density and the null result by the XENON100 direct detection. We find that the dijet resonance measurements can exclude a large part of the parameter space $(m_χ, m_Y)$, where the couplings for the mediator coupled to the dark matter and to the quarks are small and have roughly the same magnitude. The constraint from indirect detections and diphoton resonance searches is also briefly discussed.

hep-ph↗

arXiv2013

Revisiting charmless hadronic B decays to scalar mesons

Hadronic charmless B decays to scalar mesons are studied within the framework of QCD factorization (QCDF). Considering two different scenarios for scalar mesons above 1 GeV, we find that the data favor the scenario in which the scalars $a_0(1450)$ and $K_0^*(1430)$ are the lowest lying $q\bar q$ bound states. This in turn implies a preferred four-quark nature for light scalars below 1 GeV. Assuming $K_0^*(1430)$ being a lowest lying $q\bar s$ state, we show that the data of $B\to K_0^*(1430)η^{(')}$ and $B\to K_0^*(1430)(ρ,ω,ϕ)$ can be accommodated in QCDF without introducing power corrections induced from penguin annihilation, while the predicted $B^-\to \ov K_0^{*0}(1430)π^-$ and $\ov B^0\to K_0^{*-}(1430)π^+$ are too small compared to experiment. In principle, the data of $K_0^*(1430)π$ modes can be explained if penguin-annihilation induced power corrections are taken into account. However, this will destroy the agreement between theory and experiment for $B\to K_0^*(1430)(η^{(')},ρ,ω,ϕ)$. Contrary to the pseudoscalar meson sector where $B\to Kη'$ has the largest rate in 2-body decays of the $B$ meson, we show that $Br(B\to K_0^*η')<\B(B\to K_0^*η)$. The decay $\ov B^0\to a_0(980)^+K^-$ is found to have a rate much smaller than that of $\ov B^0\to a_0(980)^+π^-$ in QCDF, while it is the other way around in pQCD. Experimental measurements of these two modes will help discriminate between these two different approaches. Assuming 2-quark bound states for $f_0(980)$ and $f_0(500)$, the observed large rates of $f_0(980)K$ and $f_0(980)K^*$ modes can be explained in QCDF with the $f_0(980)\!-\!f_0(500)$ mixing angle $θ$ in the vicinity of $20^\circ$.

hep-ph↗

arXiv2012

Galactic Dark Matter in the Phantom Field

We investigate the possibility that the galactic dark matter exists in an scenario where the phantom field is responsible for the dark energy. We obtain the statically and spherically approximate solution for this kind of the galaxy system with a supermassive black hole at its center. The solution of the metric functions is satisfied with $g_{tt} = - g_{rr}^{-1}$. Constrained by the observation of the rotational stars moving in circular orbits with nearly constant tangential speed in a spiral galaxy, the background of the phantom field which is spatially inhomogeneous has an exponential potential. To avoid the well-known quantum instability of the vacuum at high frequencies, the phantom field defined in an effective theory is valid only at low energies. Under this assumption, we further investigate the following properties. The absorption cross section of the low-energy $S$-wave excitations of the phantom field into the central black hole is shown to be the horizontal area of the central black hole. Because the infalling phantom particles have a total negative energy, the accretion of the phantom energy is related to the decrease of the black hole mass which is estimated to be much less than a solar mass in the lifetime of the Universe. Using a simple model with the cold dark matter very weakly coupled to the "{\it low-frequency}" phantom particles which are generated from the background, we show that these two densities can be quasi-stable in the galaxy.

astro-ph.CO↗

arXiv2012

$1^{++}$ Nonet Singlet-Octet Mixing Angle, Strange Quark Mass, and Strange Quark Condensate

Two strategies are taken into account to determine the $f_1(1420)$-$f_1(1285)$ mixing angle $θ$. (i) First, using the Gell-Mann-Okubo mass formula together with the $K_1(1270)$-$K_1(1400)$ mixing angle $θ_{K_1}=(-34\pm 13)^\circ$ extracted from the data for ${\cal B}(B\to K_1(1270) γ), {\cal B}(B\to K_1(1400) γ), {\cal B}(τ\to K_1(1270) ν_τ)$, and ${\cal B}(τ\to K_1(1420) ν_τ)$, gave $θ= (23^{+17}_{-23})^\circ$. (ii) Second, from the study of the ratio for $f_1(1285) \to ϕγ$ and $f_1(1285) \to ρ^0γ$ branching fractions, we have two-fold solution $θ=(19.4^{+4.5}_{-4.6})^\circ$ or $(51.1^{+4.5}_{-4.6})^\circ$. Combining these two analyses, we thus obtain $θ=(19.4^{+4.5}_{-4.6})^\circ$. We further compute the strange quark mass and strange quark condensate from the analysis of the $f_1(1420)-f_1(1285)$ mass difference QCD sum rule, where the operator-product-expansion series is up to dimension six and to ${\cal O}(α_s^3, m_s^2 α_s^2)$ accuracy. Using the average of the recent lattice results and the $θ$ value that we have obtained as inputs, we get $<\bar{s} s>/<\bar{u} u> =0.41 \pm 0.09$.

hep-ph↗

arXiv2011

B -> K1 l^+l^- Decays in a Family Non-universal Z' Model

The implications of the family non-universal $Z^\prime$ model in the $B\to K_{1}(1270,1400)\ell^{+}\ell^{-}(\ell=e\,,μ\,,τ)$ decays are explored, where the mass eigenstates $K_{1}(1270,1400)$ are the mixtures of $^{1}{P}_{1}$ and $^{3}{P}_{1}$ states with the mixing angle $θ$. In this work, considering the $Z^\prime$ boson and setting the mixing angle $θ=(-34\pm13)^{\circ}$, we analyze the branching ratio, the dilepton invariant mass spectrum, the normalized forward-backward asymmetry and lepton polarization asymmetries of each decay mode. We find that all observables of $B\to K_{1}(1270)μ^{+}μ^{-}$ are sensitive to the $Z^{\prime}$ contribution. Moreover, the observables of $B\to K_{1}(1400)μ^{+}μ^{-}$ are relatively strong $θ$-dependence; thus, the $Z^{\prime}$ contribution will be buried by the uncertainty of the mixing angle $θ$. Furthermore, the zero crossing position in the FBA spectrum of $B\to K_{1}(1270)μ^{+}μ^{-}$ at low dilepton mass will move to the positive direction with $Z^\prime$ contribution. For the tau modes, the effects of $Z^\prime$ are not remarkable due to the small phase space. These results could be tested in the running LHC-b experiment and Super-B factory.

hep-ph↗

arXiv2011

Non-Gaussianities of Single Field Inflation with Non-minimal Coupling

We investigate the non-Gaussianities of inflation driven by a single scalar field coupling non-minimally to the Einstein Gravity. We assume that the form of the scalar field is very general with an arbitrary sound speed. For convenience to study, we take the subclass that the non-minimal coupling term is linear to the Ricci scalar $R$. We define a parameter $μ\equivε_h/ε_θ$ where $ε_h$ and $ε_θ$ are two kinds of slow-roll parameters, and obtain the dependence of the shape of the 3-point correlation function on $μ$. We also show the estimator $F_{NL}$ in the equilateral limit. Finally, based on numerical calculations, we present the non-Gaussianities of non-minimal coupling chaotic inflation as an explicit example.

hep-th↗