arXiv subjects

Yue-Liang Wu

Publications and source records attributed to Yue-Liang Wu.

At least 109 records · Page 6Linked to original sources

arXiv2014

Thermal Spectral Function and Deconfinement Temperature in Bulk Holographic AdS/QCD with Back Reaction of Bulk Vacuum

Based on the IR-improved bulk holographic AdS/QCD model which provides a consistent prediction for the mass spectra of resonance scalar, pseudoscalar, vector and axial vector mesons, we investigate its finite temperature behavior. By analyzing the spectral function of mesons and fitting it with a Breit-Wigner form, we perform an analysis for the critical temperature of mesons. The back-reaction effects of bulk vacuum are considered, the thermal mass spectral function of resonance mesons is calculated based on the back-reaction improved action. A reasonable melting temperature is found to be $T_c \simeq 150 \pm 7$ MeV, which is consistent with the recent results from lattice QCD simulations.

hep-ph↗

arXiv2014

Leptonic CP Violation and Wolfenstein Parametrization for Lepton Mixing

We investigate a general structure of lepton mixing matrix resulting from the SU$_F$(3) gauge family model with an appropriate vacuum structure of SU$_F$(3) symmetry breaking. It is shown that the lepton mixing matrix can be parametrized by using the Wolfenstein parametrization method to characterize its deviation from the tri-bimaximal mixing. A general analysis for the allowed leptonic CP-violating phase $δ_e$ and the leptonic Wolfenstein parameters $λ_e$, $A_e$, $ρ_e$ is carried out based on the observed lepton mixing angles. We demonstrate how the leptonic CP violation correlates to the leptonic Wolfenstein parameters. It is found that the phase $δ_e$ is strongly constrained and only a large or nearly maximal leptonic CP-violating phase $|δ_e| \simeq 3π/4 \sim π/2$ is favorable when $λ_e > 0.15 $. In particular, when taking $λ_e$ to be the Cabbibo angle $\gl_e\simeq λ\simeq 0.225$, a sensible result for leptonic Wolfenstein parameters and CP violation is obtained with $ A_e=1.40$, $ρ_e=0.20$, $δ_{e}\sim 101.76\;^o$, which is compatible with the one in quark sector. An interesting correlation between leptons and quarks is observed, which indicates a possible common origin of masses and mixing for the charged-leptons and quarks.

hep-ph↗

arXiv2014

Direct detection and solar capture of spin-dependent dark matter

We investigate the implication of different spin-dependent (SD) operators on both the direct and indirect detections of the Weakly Interacting Massive Particle (WIMP). Six representative building blocks of SD operators, together with their counterparts with a massless mediator are considered to interpret the direct detection experiments(Xenon100, SIMPLE, and COUPP) in a comprehensive way. We also study the solar capture and annihilation of WIMPs with these effective SD operators and place the constraints on the relevant annihilation rate from neutrino detection experiments Super-Kamionkande and IceCube. Upper limits on the WIMP-nucleon couplings drawn from direct detections are also projected to the annihilation rate for contrast and complementarity. We find that the efficiency of these mentioned detection strategies depends specifically on the six SD operators, while the neutrino-based detections are more effective in exploring the parameter space for the massless mediator scenario.

hep-ph↗

arXiv2014

Quantum Structure of Field Theory and Standard Model Based on Infinity-free Loop Regularization/Renormalization

To understand better the quantum structure of field theory and standard model in particle physics, it is necessary to investigate carefully the divergence structure in quantum field theories (QFTs) and work out a consistent framework to avoid infinities. The divergence has got us into trouble since developing quantum electrodynamics in 1930s, its treatment via the renormalization scheme is satisfied not by all physicists, like Dirac and Feynman who have made serious criticisms. The renormalization group analysis reveals that QFTs can in general be defined fundamentally with the meaningful energy scale that has some physical significance, which motivates us to develop a new symmetry-preserving and infinity-free regularization scheme called loop regularization (LORE). A simple regularization prescription in LORE is realized based on a manifest postulation that a loop divergence with a power counting dimension larger than or equal to the space-time dimension must vanish. The LORE method is achieved without modifying original theory and leads the divergent Feynman loop integrals well-defined to maintain the divergence structure and meanwhile preserve basic symmetries of original theory. The crucial point in LORE is the presence of two intrinsic energy scales which play the roles of ultraviolet cut-off $M_c$ and infrared cut-off $μ_s$ to avoid infinities. The key concept in LORE is the introduction of irreducible loop integrals (ILIs) on which the regularization prescription acts, which leads to a set of gauge invariance consistency conditions between the regularized tensor-type and scalar-type ILIs. The evaluation of ILIs with ultraviolet-divergence-preserving (UVDP) parametrization naturally leads to Bjorken-Drell's analogy between Feynman diagrams and electric circuits. The LORE method has been shown to be applicable to both underlying and effective QFTs.

hep-th↗

arXiv2013

Direct detection and solar capture of dark matter with momentum and velocity dependent elastic scattering

We explore the momentum and velocity dependent elastic scattering between the dark matter (DM) particles and the nuclei in detectors and the Sun. In terms of the non-relativistic effective theory, we phenomenologically discuss ten kinds of momentum and velocity dependent DM-nucleus interactions and recalculate the corresponding upper limits on the spin-independent DM-nucleon scattering cross section from the current direct detection experiments. The DM solar capture rate is calculated for each interaction. Our numerical results show that the momentum and velocity dependent cases can give larger solar capture rate than the usual contact interaction case for almost the whole parameter space. On the other hand, we deduce the Super-Kamiokande's constraints on the solar capture rate for eight typical DM annihilation channels. In contrast to the usual contact interaction, the Super-Kamiokande and IceCube experiments can give more stringent limits on the DM-nucleon elastic scattering cross section than the current direct detection experiments for several momentum and velocity dependent DM-nucleus interactions. In addition, we investigate the mediator mass's effect on the DM elastic scattering cross section and solar capture rate.

hep-ph↗

arXiv2013

Implications of the first AMS-02 measurement for dark matter annihilation and decay

In light of the first measurement of the positron fraction by the AMS-02 experiment, we perform a detailed global analysis on the interpretation of the latest data of PAMELA, Fermi-LAT, and AMS-02 in terms of dark matter (DM) annihilation and decay in various propagation models. The allowed regions for the DM particle mass and annihilation cross section or decay life-time are obtained for channels with leptonic final states: $2e$, $2μ$, $2τ$, $4e$, $4μ$ and $4τ$. We show that for the conventional astrophysical background the AMS-02 positron fraction data alone favour a DM particle mass $\sim 500 \ (800)$ GeV if DM particles annihilate dominantly into $2μ\ (4μ)$ final states, which is significantly lower than that favoured by the Fermi-LAT data of the total flux of electrons and positrons. The allowed regions by the two experiments do not overlap at a high confidence level ($99.99999\%$C.L.). We consider a number of propagation models with different halo height $Z_{h}$, diffusion parameters $D_{0}$ and $δ_{1/2}$, and power indices of primary nucleon sources $γ_{p1/p2}$. The normalization and the slope of the electron background are also allowed to vary. We find that the tension between the two experiments can be only slightly reduced in the propagation model with large $Z_{h}$ and $D_{0}$. The consistency of fit is improved for annihilation channels with $2τ$ and $4τ$ final states which favour TeV scale DM particle with large cross sections above $\sim 10^{-23} \text{cm}^3\text{s}^{-1}$. In all the considered leptonic channels, the current data favour the scenario of DM annihilation over DM decay. In the decay scenario, the charge asymmetric DM decay is slightly favoured.

hep-ph↗

arXiv2013

Hydrodynamics and transport coefficients in an infrared-deformed soft-wall AdS/QCD model at finite temperature

We extend an infrared-deformed soft-wall anti de-Sitter/QCD model at zero temperature to a model at finite temperature and perform hydrodynamics. To have the infalling boundary condition to make the hydrodynamic analysis possible, we treat the infrared energy scale factor in our metric as a temperature-depending parameter. Then, by carrying out the hydrodynamic analysis, we compute the transport coefficients, the diffusion constant, and the shear viscosity, through the linear response theory.

hep-ph↗

arXiv2013

Sommerfeld enhancements with vector, scalar and pseudoscalar force-carriers

The first AMS-02 measurement confirms the existence of an excess in the cosmic-ray positron fraction previously reported by the PAMELA and Fermi-LAT experiments. If interpreted in terms of thermal dark matter (DM) annihilation, the AMS-02 result still suggests that the DM annihilation cross section in the present day should be significantly larger than that at freeze out. The Sommerfeld enhancement of DM annihilation cross section as a possible explanation for the observed excesses is subject to constraint from the DM thermal relic density, mainly due to the annihilation of DM particles into force-carrier particles introduced by the mechanism. We show that the effect of the Sommerfeld enhancement and the relic density constraint depend significantly on the nature of the force-carrier. Three cases where the force-carrier is a vector boson, scalar and pseudoscalar particle are investigated and compared with each other. The results show that for the vector force-carrier, the Sommerfeld enhancement can marginally account for the AMS-02 data for $2μ$ final states, while for scalar force-carrier the allowed Sommerfeld enhancement can be larger by a factor of two. For the case with a pesudoscalar force-carrier, the Sommerfeld enhancement can be large enough to accommodate the AMS-02 and Fermi-LAT result for a variety of DM annihilation final states.

hep-ph↗

arXiv2013

Thermal Mass Spectra of Scalar and Pseudo-Scalar Mesons in IR-improved Soft-Wall AdS/QCD Model with Finite Chemical Potential

The thermal mass spectra of scalar and pseudo scalar mesons are studied in an IR-improved soft-wall AdS/QCD model. The Reissner-Nordstrom AdS black hole metric is introduced to describe both the finite temperature and density effects. The thermal spectral function is computed, which shows that the position of peak moves towards a smaller value and the width of peak also broadens to a larger value as the temperature increases. The critical temperature at which the peaks are completely dissolved has been found to be around $T_{c}\simeq 160\sim 200\MeV$. The effect of chemical potential is shown to be the same as the one caused by the temperature. It is found that when the temperature approaches to zero $T\approx 0$, the melting down of mesons occurs at the scaled critical chemical potential $μ_0/κ\approx 2.2\sim 2.4 \GeV$.

hep-ph↗

arXiv2013

Consistency of Loop Regularization Method and Divergence Structure of QFTs Beyond One-Loop Order

We study the problem how to deal with tensor-type two-loop integrals in the Loop Regularization (LORE) scheme. We use the two-loop photon vacuum polarization in the massless Quantum Electrodynamics (QED) as the example to present the general procedure. In the processes, we find a new divergence structure: the regulated result for each two-loop diagram contains a gauge-violating quadratic harmful divergent term even combined with their corresponding counterterm insertion diagrams. Only when we sum up over all the relevant diagrams do these quadratic harmful divergences cancel, recovering the gauge invariance and locality.

hep-ph↗

arXiv2013

Note on 125 GeV Spin-2 particle

A new boson around 125 GeV without specific spin has been observed by both ATLAS and CMS at the LHC. Since its decay into a diphoton excludes the spin-1 case by the Landau-Yang theorem,it leaves 0 or 2 as the possible lowest spin for the new boson. Instead of the well-established spin-0 Higgs-like boson, we take this new boson to be a spin-2 massive Graviton-like particle denoted as $G$, which exists copiously in extra-dimension theories, and concentrate on its phenomenology. In particular, we calculate the three-body decays of $G\rightarrow V f\bar{f}'$ with $V$ and $f^{(\prime)}$ the gauge boson and fermions in the standard model (SM) and compare our results with those of the SM Higgs boson. The couplings between $G$ and $V$s are also estimated by fitting the data. A new observable that can distinguish $G$ from the Higgs is proposed.

hep-ph↗

arXiv2012

Exploring the singlet scalar dark matter from direct detections and neutrino signals via its annihilation in the Sun

We explore the singlet scalar dark matter (DM) from direct detections and high energy neutrino signals generated by the solar DM annihilation. Two singlet scalar DM models are discussed, one is the real singlet scalar DM model as the simple extension of the standard model (SSDM-SM) with a discrete Z_2 symmetry, and another is the complex singlet scalar DM model as the simple extension of the left-right symmetric two Higgs bidoublet model (SSDM-2HBDM) with $P$ and CP symmetries. To derive the Sun capture rate, we consider the uncertainties in the hadronic matrix elements and calculate the spin-independent DM-nucleon elastic scattering cross section. We find that the predicted neutrino induced upgoing muon fluxes in the region 3.7 GeV < m_D < 4.2 GeV slightly exceed the Super-Kamiokande limit in the SSDM-SM. However, this exceeded region can be excluded by the current DM direct detection experiments. For the SSDM-2HBDM, one may adjust the Yukawa couplings to avoid the direct detection limits and enhance the predicted muon fluxes. For the allowed parameter space of the SSDM-SM and SSDM-2HBDM, the produced muon fluxes in the Super-Kamiokande and muon event rates in the IceCube are less than the experiment upper bound and atmosphere background, respectively.

hep-ph↗

arXiv2012

Analysis on a General Class of Holographic Type Dark Energy Models

We present a detail analysis on a general class of holographic type dark energy models characterized by the length scale $L=\frac1{a^n(t)}\int_0^t dt' a^m(t')$. We show that $n \geq 0$ is required by the recent cosmic accelerated expansion of universe. In the early universe dominated by the constituent with constant equation of state $w_m$, we have $w_{de}\simeq -1-\frac{2n}{3}$ for $n \geq 0$ and $m<0$, and $w_{de}\simeq-\frac23(n-m)+w_m$ for $n > m \geq 0$. The models with $n > m \geq 0$ become single-parameter models like the $Λ$CDM model due to the analytic feature $Ω_{de}\simeq \frac{d^2}4(2m+3w_m+3)^2a^{2(n-m)}$ at radiation- and matter-dominated epoch. Whereas the cases $n=m\geq 0$ should be abandoned as the dark energy cannot dominate the universe forever and there might be too large fraction of dark energy in early universe, and the cases $m> n \geq 0$ are forbidden by the self-consistent requirement $Ω_{de}\ll1 $ in the early universe. Thus a detailed study on the single-parameter models corresponding to cases $n >m \geq 0$ is carried out by using recent observations. The best-fit analysis indicates that the conformal-age-like models with $n=m+1$, i.e. $L\propto\frac1{Ha}$ in early universe, are more favored and also the models with smaller $n$ for the given $n-m$ are found to fit the observations better. The equation of state of the dark energy in models with $n=m+1 >0$ transits from $w_{de}<-1$ during inflation to $w_{de}>-1$ in radiation- and matter-dominated epoch, and then back to $w_{de}<-1$ eventually. The best-fit result of the case $(n=0, m=-1)$ which is so-called $η$HDE model proposed in \cite{Huang:2012xm} is the most favorable model and compatible with the $Λ$CDM model.

gr-qc↗

arXiv2012

SU(3) Gauge Family Symmetry and Prediction for the Lepton-Flavor Mixing and Neutrino Masses with Maximal Spontaneous CP Violation

A model for the lepton-flavor mixing and CP violation is proposed based on the SU$_F$(3) gauge family symmetry and the Majorana feature of neutrinos. A consistent prediction for the lepton-flavor mixing and masses is shown to be resulted from the appropriate vacuum structure of SU$_F$(3) gauge symmetry breaking. By choosing the SU$_F$(3) gauge fixing condition to possess a residual $Z_2$ symmetry and requiring the vacuum structure of spontaneous symmetry breaking to have approximate global U(1) family symmetries, we obtain naturally the tri-bimaximal mixing matrix and largely degenerate neutrino masses in the neutrino sector and the small mixing matrix in the charged-lepton sector. With a simple ansatz that all the smallness due to the approximate global U(1) family symmetries is characterized by a single Wolfenstein parameter $λ\simeq 0.22$, and the charged-lepton mixing matrix has a similar hierarchy structure as the CKM quark mixing matrix, we arrive at a consistent prediction for the MNSP lepton-flavor mixing with a maximal spontaneous CP violation: $δ=π/2$, $\sin^2θ_{13} \simeq 1/2λ^2 \simeq 0.024$ ($\sin^22θ_{13} \simeq 0.094$), $\sin^2θ_{12} \simeq 1/3{3}(1 - 2λ^3) \simeq 0.326$ and $\sin^2θ_{23} \simeq 1/2(1 - λ^2) \simeq 0.48$, which agree well with the current experimental data. The CP-violating Jarlskog-invariant is obtained to be $J_{CP} \simeq 1/6λ(1-λ^2/2-λ^3)\sinδ\simeq 0.035$, which is detectable in next generation neutrino experiment. The largely degenerate neutrino masses with the normal hierarchy and inverse hierarchy are discussed and found be at the order $m_{ν_i} \simeq O(λ^2) \simeq 0.04\sim 0.06$ eV with a total mass $\sum m_ν \sim 0.15$ eV, which is testable in future precision astrophysics and cosmology.

hep-ph↗

arXiv2012

Consistency and Advantage of Loop Regularization Method Merging with Bjorken-Drell's Analogy Between Feynman Diagrams and Electrical Circuits

The consistency of loop regularization (LORE) method is explored in multiloop calculations. A key concept of the LORE method is the introduction of irreducible loop integrals (ILIs) which are evaluated from the Feynman diagrams by adopting the Feynman parametrization and ultraviolet-divergence-preserving(UVDP) parametrization. It is then inevitable for the ILIs to encounter the divergences in the UVDP parameter space due to the generic overlapping divergences in the 4-dimensional momentum space. By computing the so-called $αβγ$ integrals arising from two loop Feynman diagrams, we show how to deal with the divergences in the parameter space with the LORE method. By identifying the divergences in the UVDP parameter space to those in the subdiagrams, we arrive at the Bjorken-Drell's analogy between Feynman diagrams and electrical circuits. The UVDP parameters are shown to correspond to the conductance or resistance in the electrical circuits, and the divergence in Feynman diagrams is ascribed to the infinite conductance or zero resistance. In particular, the sets of conditions required to eliminate the overlapping momentum integrals for obtaining the ILIs are found to be associated with the conservations of electric voltages, and the momentum conservations correspond to the conservations of electrical currents, which are known as the Kirchhoff's laws in the electrical circuits analogy. As an application to the massive scalar $ϕ^4$ theory, it enables us to obtain the well-known logarithmic running of the coupling constant and the consistent power-law running of the scalar mass at two loop level. Especially, we present an explicit demonstration on the general procedure of applying the LORE method to the multiloop calculations of Feynman diagrams when merging with the advantage of Bjorken-Drell's circuit analogy.

hep-ph↗

arXiv2012

Two Higgs Bi-doublet Model With Spontaneous P and CP Violation and Decoupling Limit to Two Higgs Doublet Model

The two Higgs bi-doublet left-right symmetric model (2HBDM) as a simple extension of the minimal left-right symmetric model with a single Higgs bi-doublet is motivated to realize both spontaneous P and CP violation while consistent with the low energy phenomenology without significant fine tuning. By carefully investigating the Higgs potential of the model, we find that sizable CP-violating phases are allowed after the spontaneous symmetry breaking. The mass spectra of the extra scalars in the 2HBDM are significantly different from the ones in the minimal left-right symmetric model. In particular, we demonstrate in the decoupling limit when the right-handed gauge symmetry breaking scale is much higher than the electroweak scale, the 2HBDM decouples into general two Higgs doublet model (2HDM) with spontaneous CP violation and has rich induced sources of CP violation. We show that in the decoupling limit, it contains extra light Higgs bosons with masses around electroweak scale, which can be directly searched at the ongoing LHC and future ILC experiments.

hep-ph↗

arXiv2012

Thermal Mass Spectra of Vector and Axial-Vector Mesons in Predictive Soft-Wall AdS/QCD Model

We extend the predictive soft-wall AdS/QCD model to a thermodynamic model by considering the black hole metric. A modified bulk vacuum expectation value and a modified coefficient for the quartic term in the bulk scalar potential are introduced to obtain a smooth dilaton solution for computing the spectral functions of the vector and axial-vector mesons. It is demonstrated that the peaks appearing in the spectral functions characterize the thermal mass spectra of vector and axial-vector mesons, where the location of the peak moves to a lower value and the width of the peak becomes wider when increasing the temperature. We observe that the peak disappears completely at the critical temperature around $T_c=200$ MeV, which implies the deconfinement of quark and the restoration of chiral symmetry breaking. A numerical study by fitting the spectral function in terms of the Breit-Wigner form has been made to show how the peak dissolves quantitatively when the temperature is increased to the critical point.

hep-ph↗

arXiv2012

Holographic Dark Energy Characterized by the Total Comoving Horizon and Insights to Cosmological Constant and Coincidence Problem

The observed acceleration of the present universe is shown to be well explained by the holographic dark energy characterized by the total comoving horizon of the universe ($η$HDE). It is of interest to notice that the very large primordial part of the comoving horizon generated by the inflation of early universe makes the $η$HDE behave like a cosmological constant. As a consequence, both the fine-tuning problem and the coincidence problem can reasonably be understood with the inflationary universe and holographical principle. We present a systematic analysis and obtain a consistent cosmological constraint on the $η$HDE model based on the recent cosmological observations. It is found that the $η$HDE model gives the best-fit result $Ω_{m0}=0.270$ ($Ω_{de0}=0.730$) and the minimal $χ^2_{min}=542.915$ which is compatible with $χ^2_{Λ{\rm CDM}}=542.919$ for the $Λ$CDM model.

gr-qc↗