arXiv subjects

Chao-Qiang Geng

Publications and source records attributed to Chao-Qiang Geng.

At least 73 records · Page 4Linked to original sources

arXiv2020

Multicomponent Dark Matter in the Light of CALET and DAMPE

In the light of the latest measurements on the total $e^+ + e^-$ flux by CALET and DAMPE experiments, we revisit the multicomponent leptonically decaying dark matter (DM) explanations to the cosmic-ray electron/positron excesses observed previously. Especially, we use the single and double-component DM models to explore the compatibility of the AMS-02 positron fraction with the new CALET or DAMPE data. It turns out that neither single nor double-component DM models are able to fit the AMS-02 positron fraction and DAMPE total $e^+ + e^-$ flux data simultaneously. On the other hand, for the combined AMS-02 and CALET dataset, both the single and double-component DM models can provide reasonable fits. If we further take into the diffuse $γ$-ray constraints from Fermi-LAT, only the double-component DM models are allowed.

hep-ph↗

arXiv2020

Reducing the $H_{0}$ tension with generalized Proca theory

We investigate the cosmological viability of the generalized proca theory. We first implement the background and linear perturbation equations of motion in the Boltzmann code and then study the constraints on the parameters of the generalized proca theory after running MCMC against the cosmological data set. With Planck + HST data, we obtain the constraint $h=0.7334_{-0.0269}^{+0.0246}$, which indicates that the tension between early universe and late time universe within this theory is removed. By adding other late-time data sets (BAO, RSD, etc.) we show that the tension is reduced, as the 2$σ$ allowed region for $h$ in Proca, $h=0.7041_{-0.0087}^{+0.0094}$, overlaps with the 2$σ$ region of the HST data.

astro-ph.CO↗

arXiv2020

Inverse-Chirp Imprint of Gravitational Wave Signals in Scalar Tensor Theory

The scalar tensor theory contains a coupling function connecting the quantities in the Jordan and Einstein frames, which is constrained to guarantee a transformation rule between frames. We simulate the supernovae core collapse with different choices of coupling functions defined over the viable region of the parameter space and find that a generic inverse-chirp feature of the gravitational waves in the scalar tensor scenario.

gr-qc↗

arXiv2020

Nonleptonic two-body weak decays of $Λ_b$ in modified MIT bag model

We study the nonleptonic two-body weak decays of $Λ_b$ by modifying the MIT bag model without introducing new parameters to construct the momentum eigenstates of the baryons. We find that the branching ratios of $Λ_b^0 \to Λ_c^+ π^-$, $Λ_c^+ K^-$, $p π^-$ and $pK^-$ are $(4.5\pm0.2)\times 10^{-3}$, $(3.4\pm 0.1)\times 10^{-4}$, $(5.0\pm 0.5)\times 10^{-6}$ and $(6.0\pm 0.7) \times 10^{-6}$, which are all well consistent with the current experimental data, respectively. We also explore P and CP asymmetries for the decays of $Λ_b^0 \to p (π^-,K^-)$. In particular, we obtain that the direct CP-violating rate asymmetries in $Λ_b^0 \to p π^-$ and $Λ_b^0 \to p K^-$ are around $-4.4\%$ and $6.7\%$, in comparison with $(-2.5\pm2.9)\%$ and $(-2.5\pm2.2)\%$ from the Particle Data Group in 2020, respectively.

hep-ph↗

arXiv2020

Running vacuum model in non-flat universe

We investigate observational constraints on the running vacuum model (RVM) of $Λ=3ν(H^{2}+K/a^2)+c_0$ in the spatially curved universe, where $ν$ is the model parameter, $K$ corresponds to the spatial curvature constant, and $c_{0}$ is a constant defined by the boundary conditions. As $\dotΛ \ne 0$, there are energy exchanges between vacuum, matter and radiation in RVM. We study the "geometrical degeneracy" of RVM on the CMB power spectra. By fitting the cosmological data, we find that the values of $χ^2$ in RVM and $Λ$CDM are similar to each other for the non-flat universe. Explicitly, we obtain the constraints of $ν\leq O(10^{-4})$ (68 $\%$ C.L.) and $|Ω_K|\leq O(10^{-2})$ (95 $\%$ C.L.) in our study. In addition, we show that the cosmological constraints of $Σm_ν=0.416^{+0.311}_{-0.407}$ (RVM) and $Σm_ν=0.497^{+0.335}_{-0.387}$ ($Λ$CDM) at 95$\%$ C.L. for the neutrino mass sum are relaxed in both models in the spatially curved universe.

astro-ph.CO↗

arXiv2020

Viable Constraint on Scalar Field in Scalar-Tensor Theory

The scalar-tensor theory can be formulated in both Jordan and Einstein frames, which are conformally related together with a redefinition of the scalar field. As the solution to the equation of the scalar field in the Jordan frame does not have the one-to-one correspondence with that in the Einstein frame, we give a criterion along with some specific models to check if the scalar field in the Einstein frame is viable or not by confirming whether this field is reversible back to the Jordan frame. We further show that the criterion in the first parameterized post-Newtonian approximation can be determined by the parameters of the osculating approximation of the coupling function in the Einstein frame and can be treated as a viable constraint on any numerical study in the scalar-tensor scenario. We also demonstrate that the Brans-Dicke theory with an infinite constant parameter $ω_{\text{BD}}$ is a counterexample of the equivalence between two conformal frames due to the violation of the viable constraint.

gr-qc↗

arXiv2020

Constraints on a special running vacuum model

We study a special running vacuum model (RVM) with $Λ= 3 αH^2+3βH_0^4 H^{-2}+Λ_0$, where $α$, $β$ and $Λ_0$ are the model parameters and $H$ is the Hubble one. This RVM has non-analytic background solutions for the energy densities of matter and radiation, which can only be evaluated numerically. From the analysis of the CMB power spectrum and baryon acoustic oscillation along with the prior of $α>0$ to avoid having a negative dark energy density, we find that $α<2.83\times 10^{-4}$ and $β=(-0.2^{+3.9}_{-4.5})\times 10^{-4}$ (95$\%$ C.L.). We show that the RVM fits the cosmological data comparably to the $Λ$CDM. In addition, we relate the fluctuation amplitude $σ_8$ to the neutrino mass sum $Σm_ν$.

astro-ph.CO↗

arXiv2020

Modified Cosmology Models from Thermodynamical Approach

We apply the first law of thermodynamics to the apparent horizon of the universe with the power-law corrected and non-extensive Tsallis entropies rather than the Bekenstein-Hawking one. We examine the cosmological properties in the two entropy models by using the CosmoMC package. In particular, the first numerical study for the cosmological observables with the power-law corrected entropy is performed. We also show that the neutrino mass sum has a non-zero central value with a relaxed upper bound in the Tsallis entropy model comparing with that in the $Λ$CDM one.

astro-ph.CO↗

arXiv2019

Up-down asymmetries of charmed baryon three-body decays

We study the up-down asymmetries in the three-body anti-triplet charmed baryon decays of ${\bf B_c}\to{\bf B_n}MM' $ with the $SU(3)_f$ flavor symmetry, where ${\bf B_c}$ presents the anti-triplet charmed baryon of $(Ξ_c^0,-Ξ_c^+,Λ_c^+)$, while ${\bf B_n}$ and $M^{(')}$ denote octet baryon and meson states, respectively. By assuming the s-wave meson-pairs to be the dominant constituents in final state configurations, we can write the spin-dependent decay amplitude into parity-conserving and parity-violating parts, parametrized by 6 real parameters under $SU(3)_f$, respectively. Fitting these parameters by 16 experimental data points with the minimum $χ^2$ method, we obtain that $χ^2/d.o.f=2.4$. With the fitted parameters, we evaluate the up-down asymmetries along with the decay branching ratios of ${\bf B_c}\to{\bf B_n}MM' $. Some of these up-down asymmetries are accessible to the experiments at BESIII, BELLE-II and LHCb.

hep-ph↗

arXiv2019

Cosmological evolutions in Tsujikawa model of $f(R)$ Gravity

We concentrate on the cosmological properties in the Tsujikawa model (TM) of viable $f(R)$ gravity with the dynamical background evolution and linear perturbation theory by using the CosmoMC package. We study the constraints of the cosmological variables along with the model parameter from the current observational data. In particular, we show that the matter density fluctuation is suppressed and the constraint of the neutrino mass sum is relaxed in the TM, which are similar to other viable $f(R)$ models. In addition, we discuss the parameters of the deceleration and equation of state for dark energy in the TM and compare them with those in the $Λ$CDM model.

gr-qc↗

arXiv2019

The Buchdahl Stability Bound in Eddington-inspired Born-Infeld Gravity

We give the Buchdahl stability bound in Eddington-inspired Born-Infeld (EiBI) gravity. We show that this bound depends on an energy condition controlled by the model parameter $κ$. From this bound, we can constrain $κ\lesssim 10^{8}\text{m}^2$ if a neutron star with a mass around $3M_{\odot}$ is observed in the future. In addition, to avoid the potential pathologies in EiBI, a \emph{Hagedorn-like} equation of state associated with $κ$ at the center of a compact star is inevitable, which is similar to the Hagedorn temperature in string theory.

gr-qc↗

arXiv2019

Charmed Baryon Weak Decays with Decuplet Baryon and SU(3) Flavor Symmetry

We study the branching ratios and up-down asymmetries in the charmed baryon weak decays of ${\bf B}_c\to {\bf B}_DM$ with ${\bf B}_{c(D)}$ anti-triplet charmed (decuplet) baryon and $M$ pseudo-scalar meson states based on the flavor symmetry of $SU(3)_F$. We propose equal and physical-mass schemes for the hadronic states to deal with the large variations of the decuplet baryon momenta in the decays in order to fit with the current experimental data. We find that our fitting results of ${\cal B}({\bf B}_c\to {\bf B}_DM) $ are consistent with the current experimental data in both schemes, while the up-down asymmetries in all decays are found to be sizable, consistent with the current experimental data, but different from zero predicted in the literature. We also examine the processes of $Ξ_c^0 \to Σ^{\prime 0}K_S/K_L$ and derive the asymmetry between the $K_L/K_S$ modes being a constant.

hep-ph↗

arXiv2019

Resolving $B$-meson anomalies by flavor-dependent gauged symmetries $\displaystyle \prod_{i=1}^3U(1)_{B_i-L_i}$

We propose a model with flavor dependent gauged symmetries of $\displaystyle \prod_{i=1}^3 U(1)_{B_i-L_i}$ with $i$ the family indices. After formulating the renormalizable Yukawa Lagrangian, Higgs potential and kinetic term, we study the lepton sector based on a successful two-zero texture without introducing extra scalar bosons to avoid the dangerous Goldstone bosons. In particular, we discuss the muon related phenomenologies via additional neutral gauge bosons. In our numerical analysis, we explore the allowed parameter space, in which the anomaly of $B \to K^* \bar μμ$ can be explained.

hep-ph↗

arXiv2019

Semileptonic decays of anti-triplet charmed baryons

We study the semileptonic decays ${\bf B_c} \to {\bf B_n} \ell^+ ν_{\ell}$ where ${\bf B_{c(n)}}$ is the anti-triplet-charmed (octet) baryon with the $SU(3)_f$ flavor symmetry and helicity formalism. In particular, we present the decay branching ratios of $ {\bf B_c} \to {\bf B_n}\ell^+ ν_\ell$ in three scenarios: (a) an exact $SU(3)_f$ symmetry with equal masses for the anti-triplet-charmed (octet) baryon states of ${\bf B_c}$ (${\bf B_n}$), (b) $SU(3)_f$ parameters without the baryonic momentum-transfer dependence, and (c) $SU(3)_f$ with baryonic transition form factors in the heavy quark limit. We show that our results are all consistent with the existing data. Explicitly, we predict that ${\cal B}( Ξ_c^+ \to Ξ^0 e^+ ν_{e})=(11.9\pm1.3, 9.8\pm 1.1, 10.7\pm 0.9)\times 10^{-2}$ and ${\cal B}( Ξ_c^0 \to Ξ^- e^+ ν_{e})=(3.0\pm0.3, 2.4\pm 0.3, 2.7\pm 0.2)\times 10^{-2}$ in the scenarios (a), (b) and (c) agree with the data of $(14.0^{+8.3}_{-8.7})\times 10^{-2}$ and $(5.6\pm2.6)\times 10^{-2}$ from the CLEO Collaboration, respectively. In addition, we obtain that ${\cal B}(Λ_c^+\to n e^+ ν_e)=(2.8\pm 0.4, 4.9\pm0.4, 5.1\pm0.4)\times 10^{-3}$ in (a), (b) and (c). We also examine the longitudinal asymmetry parameters of $α({\bf B_c} \to {\bf B_n} \ell^+ ν_{\ell})$, which are sensitive to the different scenarios with $SU(3)_f$. Some of the decay branching ratios and asymmetries can be observed by the ongoing experiments at BESIII and LHCb as well as the future searches by BELLEII.

hep-ph↗

arXiv2019

Thermodynamics of $f(R)$ Gravity with Disformal Transformation

We study thermodynamics in $f(R)$ gravity with the disformal transformation. The transformation applied to the matter Lagrangian has the form of $\g_{\m\n} = A(ϕ,X)g_{\m\n} + B(ϕ,X)\pa_\m\f\pa_\n\f$ with the assumption of the Minkowski matter metric $\g_{\m\n} = \e_{\m\n}$, where $ϕ$ is the disformal scalar and $X$ is the corresponding kinetic term of $ϕ$. We verify the generalized first and second laws of thermodynamics in this disformal type of $f(R)$ gravity in the Friedmann-Lemaître-Robertson-Walker (FLRW) universe. In addition, we show that the Hubble parameter contains the disformally induced terms, which define the effectively varying equations of state for matter.

gr-qc↗

arXiv2019

Matter Power Spectra in Viable $f(R)$ Gravity Models with Dynamical Background

We study the matter power spectra in the viable $f(R)$ gravity models with the dynamical background evolution and linear perturbation theory by using the CosmoMC package. We show that these viable $f(R)$ models generally shorten the age of the universe and suppress the matter density fluctuation. We examine the allowed ranges of the model parameters and the constraints of the cosmological variables from the current observational data, and find that the dynamical evolution of $ρ_{DE}(z)$ plays an important role to constrain the neutrino masses.

gr-qc↗

arXiv2019

Singly Cabibbo suppressed decays of $Λ_{c}^+$ with SU(3) flavor symmetry

We analyze the weak processes of anti-triplet charmed baryons decaying to octet baryons and mesons with the SU(3) flavor symmetry and topological quark diagram scheme. We study the decay branching ratios without neglecting the contributions from ${\cal O}(\overline{15})$ for the first time in the SU(3) flavor symmetry approach. The fitting results for the Cabibbo allowed and suppressed decays of $Λ_{c}^+$ are all consistent with the experimental data. We predict all singly Cabibbo suppressed decays. In particular, we find that ${\cal B}(Λ_c^+\to p π^0)=(1.3\pm0.7)\times 10^{-4}$, which is slightly below the current experimental upper limit of $2.7\times 10^{-4}$ and can be tested by the ongoing experiment at BESIII as well as the future one at Belle-II.

hep-ph↗

arXiv2018

Observational constraints on running vacuum model

We investigate the power spectra of the CMB temperature and matter density in the running vacuum model (RVM) with the time-dependent cosmological constant of $Λ= 3 νH^2 + Λ_0$, where $H$ is the Hubble parameter. In this model, dark energy decreases in time and decays to both matter and radiation. By using the Markov chain Monte Carlo method, we constrain the model parameter $ν$ as well as the cosmological observables. Explicitly, we obtain $ν\leq 1.54 \times 10^{-4}$ (68\% confidence level) in the RVM with the best-fit $χ^2_{\mathrm{RVM}} = 13968.8$, which is slightly smaller than $χ^2_{Λ\mathrm{CDM}} = 13969.8$ in the $Λ$CDM model of $ν=0$.

astro-ph.CO↗