arXiv subjects

Chao-Qiang Geng

Publications and source records attributed to Chao-Qiang Geng.

At least 109 records · Page 6Linked to original sources

arXiv2016

Observational constraints on varying neutrino-mass cosmology

We consider generic models of quintessence and we investigate the influence of massive neutrino matter with field-dependent masses on the matter power spectrum. In case of minimally coupled neutrino matter, we examine the effect in tracker models with inverse power-law and double exponential potentials. We present detailed investigations for the scaling field with a steep exponential potential, non-minimally coupled to massive neutrino matter, and we derive constraints on field-dependent neutrino masses from the observational data.

astro-ph.CO↗

arXiv2015

CP Violation in Predictive Neutrino Mass Structures

We study the CP violation effects from two types of neutrino mass matrices with (i) $(M_ν)_{ee}=0$, and (ii) $(M_ν)_{ee}=(M_ν)_{eμ}=0$, which can be realized by the high dimensional lepton number violating operators $\bar \ell_R^cγ^μL_L (D_μΦ)Φ^2$ and $\bar \ell_R^c l_R (D_μΦ)^2Φ^2$, respectively. In (i), the neutrino mass spectrum is in the normal ordering with the lightest neutrino mass within the range $0.002\,{\rm eV}\lesssim m_0\lesssim 0.007\,{\rm eV}$. Furthermore, for a given value of $m_0$, there are two solutions for the two Majorana phases $α_{21}$ and $α_{31}$, whereas the Dirac phase $δ$ is arbitrary. For (ii), the parameters of $m_0$, $δ$, $α_{21}$, and $α_{31}$ can be completely determined. We calculate the CP violating asymmetries in neutrino-antineutrino oscillations for both mass textures of (i) and (ii), which are closely related to the CP violating Majorana phases.

hep-ph↗

arXiv2015

Resolving Fermi, PAMELA and ATIC anomalies in split supersymmetry without R-parity

A long-lived decaying dark matter as a resolution to Fermi, PAMELA and ATIC anomalies is investigated in the framework of split supersymmetry (SUSY) without R-parity, where the neutralino is regarded as the dark matter and the extreme fine-tuned couplings for the long-lived neutralino are naturally evaded in the usual approach.

hep-ph↗

arXiv2015

Constraints on the Combined Models with $R^{2-q}$ Inflation and Viable $f(R)$ Dark Energy

We investigate the observational constraints on the modified gravity, which combines the $R^{2-q}$ inflation with the power-law (exponential) type of the viable $f(R)$ dark energy models. We discuss the difference between the combined model and $R^{2-q}$ gravity in the inflationary epoch and obtain the constraints on the deviation power $q$ as well as the parameters in $f(R)$ by using the CosmoMC package. The allowed ranges of the spectral index and tensor-to-scalar ratio from the Planck data are highly restricted, resulting in $q < 2.66 \times 10^{-2}$ and $2.17 \times 10^{-2}$ for the power-law and exponential types of $f(R)$ gravity, respectively.

astro-ph.CO↗

arXiv2015

Connecting Neutrino Masses and Dark Matter by High-dimensional Lepton Number Violation Operator

We propose a new model with the Majorana neutrino masses generated at two-loop level, in which the lepton number violation (LNV) processes, such as neutrinoless double beta decays, are mainly induced by the dimension-7 LNV effective operator O_7=\bar l_R^c γ^μL_L(D_mu Φ) ΦΦ. Note that it is necessary to impose an Z_2 symmetry in order that O_7 dominates over the conventional dimension-5 Weinberg operator, which naturally results in a stable Z_2-odd neutral particle to be the cold dark matter candidate. More interestingly, due to the non-trivial dependence of the charged lepton masses, the model predicts the neutrino mass matrix to be in the form of the normal hierarchy. We also focus on a specific parameter region of great phenomenological interests, such as electroweak precision tests, dark matter direct searches along with its relic abundance, and lepton flavor violation processes.

hep-ph↗

arXiv2015

Quintessential inflation with canonical and noncanonical scalar fields and Planck 2015 results

We investigate two classes of models of quintessential inflation, based upon canonical as well as noncanonical scalar fields. In particular, introducing potentials steeper than the standard exponential, we construct models that can give rise to a successful inflationary phase, with signatures consistent with Planck 2015 results. Additionally, using nonminimal coupling of the scalar field with massive neutrino matter, we obtain the standard thermal history of the Universe, with late-time cosmic acceleration as the last stage of evolution. In both cases, inflation and late-time acceleration are connected by a tracker solution.

gr-qc↗

arXiv2015

Revisiting Multi-Component Dark Matter with New AMS-02 Data

We revisit the multi-component leptonically decaying dark matter (DM) scenario to explain the possible electron/positron excesses with the recently updated AMS-02 data. We find that both the single- and two-component DM models can fit the positron fraction and $e^+/e^-$ respective fluxes, in which the two-component ones provide better fits. However, for the single-component models, the recent AMS-02 data on the positron fraction limit the DM cutoff to be smaller than 1 TeV, which conflicts with the high-energy behavior of the AMS-02 total $e^++e^-$ flux spectrum, while the two-component DM models do not possess such a problem. We also discuss the constraints from the Fermi-LAT measurement of the diffuse $γ$-ray spectrum. We show that the two-component DM models are consistent with the current DM lifetime bounds. In contrast, the best-fit DM lifetimes in the single-component models are actually excluded.

hep-ph↗

arXiv2015

Comment on "A three-loop radiative neutrino mass model with dark matter" [Phys. Lett. B 741 (2015) 163]

We revisit the calculation of the three-loop diagrams for the radiative neutrino mass generation and consider some relevant constraints on the model recently proposed by L. Jin {\it et al} [Phys. Lett. B 741 (2015) 163]. We find that the previous approximation is inappropriate due to the neglect of some important contributions, and the benchmark point proposed can neither give rise to enough neutrino masses nor accommodate these additional constraints, such as the validity of the perturbation theory, the electroweak precision measurements, and the neutrinoless double beta decays.

hep-ph↗

arXiv2015

Constraints on the septet-doublet mixing models from oblique parameters

The limitations of the doublet-septet mixing models by the deviations of electroweak oblique parameters $ΔS$ and $ΔT$ are studied. In the minimal model, the mixture of the septet $η$ and the scalar doublet in the standard model (SM) is driven by a non-Hermitian dimension-7 operator. For a smaller bare mass of the septet, $ΔS$ gives a stringent constraint on the mixing angle $\sinβ$ between the CP-odd neutral parts of the SM Higgs doublet and $η$. In general, increasing the mass of the scalar septet $M_η$ will enhance the deviation of $T$ from the SM, whereas it decreases the magnitude of $ΔS$ for a larger bare mass within the range $M_η\lesssim 400\,{\rm GeV}$. We also examine two extended models from the ordinary doublet-septet mixture pattern. One of them is based on a inert doublet-septet mixing pattern, in which there is no vacuum expectation value for the neutral component of $η$, and a stable dark matter could naturally exist. For a benchmark point with this inner doublet mass of $M_χ=250{\rm}$ and $M_η=400\,{\rm GeV}$ in this model, the mixing coefficient is found to be less than $1.8$. The other extension is constructed by imposing a doubly charged scalar mixed with the doubly charged component of the septet. Apart from the contribution by the septet-doublet admixture, $ΔS$ is suppressed by a factor of $s_W^2$ and $ΔT$ has a significant constraint due to the vanishing vacuum polarization of $Z$ at the momentum transfer $p^2=0$.

hep-ph↗

arXiv2015

Study of Two-Loop Neutrino Mass Generation Models

We study the models with the Majorana neutrino masses generated radiatively by two-loop diagrams due to the Yukawa $ρ\bar \ell_R^c \ell_R$ and effective $ρ^{\pm\pm} W^\mp W^\mp$ couplings along with a scalar triplet $Δ$, where $ρ$ is a doubly charged singlet scalar, $\ell_R$ the charged lepton and $W$ the charged gauge boson. A generic feature in these types of models is that the neutrino mass spectrum has to be a normal hierarchy. Furthermore, by using the neutrino oscillation data and comparing with the global fitting result in the literature, we find a unique neutrino mass matrix and predict the Dirac and two Majorana CP phases to be $1.40π$, $1.11π$ and $1.47π$, respectively. We also discuss the model parameters constrained by the lepton flavor violating processes and electroweak oblique parameters. In addition, we show that the rate of the neutrinoless double beta decay $(0νββ)$ can be as large as the current experimental bound as it is dominated by the short-range contribution at tree level, whereas the traditional long-range one is negligible.

hep-ph↗

arXiv2015

Constraints on a $ϕ$CDM model from strong gravitational lensing and updated Hubble parameter measurements

We constrain the scalar field dark energy model with an inverse power-law potential, i.e., $V(ϕ)\propto ϕ^{-α}$ ($α>0$), from a set of recent cosmological observations by compiling an updated sample of Hubble parameter measurements including 30 independent data points. Our results show that the constraining power of the updated sample of $H(z)$ data with the HST prior on $H_0$ is stronger than those of the SCP Union2 and Union2.1 compilations. A recent sample of strong gravitational lensing systems is also adopted to confine the model even though the results are not significant. A joint analysis of the strong gravitational lensing data with the more restrictive updated Hubble parameter measurements and the Type Ia supernovae data from SCP Union2 indicates that the recent observations still can not distinguish whether dark energy is a time-independent cosmological constant or a time-varying dynamical component.

astro-ph.CO↗

arXiv2015

Constraints on the exponential $f(R)$ model from latest Hubble parameter measurements

We investigate the viable exponential $f(R)$ gravity in the metric formalism with $f(R)=-βR_s (1-e^{-R/R_s})$. The latest sample of the Hubble parameter measurements with 23 data points is used to place bounds on this $f(R)$ model. A joint analysis is also performed with the luminosity distances of Type Ia supernovae and baryon acoustic oscillations in the clustering of galaxies, and the shift parameters from the cosmic microwave background measurements, which leads to $0.240<Ω_m^0<0.296$ and $β>1.47$ at 1$σ$ confidence level. The evolutions of the deceleration parameter $q(z)$ and the effective equations of state $ω_{de}^{eff}(z)$ and $ω_{tot}^{eff}(z)$ are displayed. By taking the best-fit parameters as prior values, we work out the transition redshift (deceleration/acceleration) $z_T$ to be about 0.77. It turns out that the recent observations are still unable to distinguish the background dynamics in the $Λ$CDM and exponential $f(R)$ models.

astro-ph.CO↗

arXiv2014

Correlation Between Muon $g-2$ and $μ\rightarrow{e}γ$

While the muon $g-2$ anomaly can be successfully explained by some new physics models, most of them are severely constrained by the $μ\to e γ$ bound. This tension is more transparent from the effective field theory perspective, in which the two phenomena are encoded in two very similar operators. However, with the ${\cal O}(1)$ Wilson coefficients, the current upper bound on $μ\to e γ$ indicates a new-physics cutoff scale five orders smaller than that needed to eliminate the $(g-2)_μ$ anomaly. By summarizing all the formulae from the one-loop contributions to the muon $g-2$ with the internal-particle spin not larger than 1, we point out two general methods to reconcile the conflict between the muon $g-2$ and $μ\to e γ$: the GIM mechanism and the non-universal couplings. For the latter method, we use a simple scalar leptoquark model as an illustration.

hep-ph↗

arXiv2014

Matter Power Spectra in Viable $f(R)$ Gravity Models with Massive Neutrinos

We investigate the matter power spectra in the power law and exponential types of viable $f(R)$ theories along with massive neutrinos. The enhancement of the matter power spectrum is found to be a generic feature in these models. In particular, we show that in the former type, such as the Starobinsky model, the spectrum is magnified much larger than the latter one, such as the exponential model. A greater scale of the total neutrino mass, $Σm_ν$, is allowed in the viable $f(R)$ models than that in the $Λ$CDM one. We obtain the constraints on the neutrino masses by using the CosmoMC package with the modified MGCAMB. Explicitly, we get $Σm_ν < 0.451 \ (0.214)\ \mathrm{eV}$ at 95% C.L. in the Starobinsky (exponential) model, while the corresponding one for the $Λ$CDM model is $Σm_ν < 0.200\ \mathrm{eV}$. Furthermore, by treating the effective number of neutrino species $N_{\mathrm{eff}}$ as a free parameter along with $Σm_ν$, we find that $N_{\mathrm{eff}} = 3.78^{+0.64}_{-0.84} (3.47^{+0.74}_{-0.60})$ and $Σm_ν = 0.533^{+0.254}_{-0.411}$ ($< 0.386) \ \mathrm{eV}$ at 95% C.L. in the Starobinsky (exponential) model.

astro-ph.CO↗

arXiv2014

Loop-induced Neutrino Masses: A Case Study

We study the cocktail model in which the Majorana neutrino masses are generated by the so-called "cocktail" three-loop diagrams with the dark matter particle running in the loops. In particular, we give the correct analytic expressions of the neutrino masses in the model by the detailed calculation of the cocktail diagrams. Based on the reliable numerical calculation of the loop integrals, we explore the parameter space which can give the correct orders of neutrino masses while satisfying other experimental constraints, such as those from the neutrinoless double beta decay, low-energy lepton flavor violation processes, electroweak precision tests, and collider searches. As a result, the large couplings and the large mass difference between the two singly-charged (neutral) scalars are required.

hep-ph↗

arXiv2014

Kaluza-Klein theory for teleparallel gravity

We study teleparallel gravity in the \emph{original} Kaluza-Klein (KK) scenario. Our calculation of the KK reduction of teleparallel gravity indicates that the 5-dimensional torsion scalar $^{(5)}T$ generates the non-Brans-Dicke type effective Lagrangian in 4-dimension due to an additional coupling between the derivative of the scalar field and torsion, but the result is equivalent to that in general relativity. We also discuss the cosmological behavior in the FLRW universe based on the effective teleparallel gravity.

gr-qc↗

arXiv2014

X-ray Line from the Dark Transition Electric Dipole

We study a two-component dark matter (DM) model in which the two Majorana fermionic DM components with nearly degenerate masses are stabilized by an $Z_2$ symmetry and interact with the right-handed muon and tau only via real Yukawa couplings, together with an additional $Z_2$-odd singly-charged scalar. In this setup, the decay from the heavy DM to the lighter one via the transition electric dipole yields the 3.55 keV X-ray signal observed recently. The Yukawa couplings in the dark sector are assumed to be hierarchical, so that the observed DM relic abundance can be achieved with the leading s-wave amplitudes without a fine-tuning. We also consider the constraints from flavor physics, DM direct detections and collider searches, respectively.

hep-ph↗

arXiv2014

Teleparallel Gravity in Five Dimensional Theories

We study teleparallel gravity in five-dimensional spacetime with particular discussions on Kaluza-Klein (KK) and braneworld theories. We directly perform the dimensional reduction by differential forms. In the braneworld theory, the teleparallel gravity formalism in the Friedmann-Lemaître-Robertson-Walker cosmology is equivalent to GR due to the same Friedmann equation, whereas in the KK case the reduction of our formulation does not recover the effect as GR of 4-dimensional spacetime.

hep-th↗