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Xiao-Hong Wu

Publications and source records attributed to Xiao-Hong Wu.

At least 19 recordsLinked to original sources
arXiv2018

Signature of heavy sterile neutrinos at CEPC

We study the production of heavy sterile neutrino $N$, $e^+ e^- \to N ν({\bar ν})$, at the Circular Electron Positron Collider(CEPC) and its $ljj$ signal in its decay to three charged fermions. We study background events for this process which are mainly events coming from W pair production. We study the production of a single heavy sterile neutrino and the sensitivity of CEPC to the mixing of sterile neutrino with active neutrinos. We study the production of two degenerate heavy sterile neutrinos in a low energy see-saw model by taking into account the constraints on mixings of sterile neutrinos from the neutrino-less double $β$ decay experiment and the masses and mixings of active neutrinos. We show that CEPC under proposal has a good sensitivity to the mixing of sterile neutrinos with active neutrinos for a mass of sterile neutrino around 100 GeV.

hep-ph↗
arXiv2017

E6 GUT through Effects of Dimension-5 Operators

In the effective field theory framework, quantum gravity can induce effective dimension-5 operators, which have important impacts on grand unified theories. Interestingly, one of main effects is the modification of the usual gauge coupling unification condition. We investigate the gauge coupling unification in $E_{6}$ under modified gauge coupling unification condition at scales $M_X$ in the presence of one or more dimension-5 operators. It is shown that nonsupersymmetric models of $E_6$ unification can be obtained and can easily satisfy the constraints from the proton lifetime. For constructing these models, we consider several maximal subgroups $H=SO(10)\times U(1), H=SU(3)\times SU(3)\times SU(3)$, and $H=SU(2)\times SU(6)$ of $E_{6}$ and the usual breaking chains for a specific maximal subgroup, and derive all of the Clebsch-Gordan coefficients $Φ^{(r)}_{s,z}$ associated with $E_6$ breaking to the Standard Model, which are given in Appendix A.

hep-ph↗
arXiv2015

Charged lepton flavor violation on target at GeV scale

We study the lepton flavor violating process, $e+ T \to τ+T'$, at a few GeV. This process can be studied by experiments directing GeV scale electron or positron beams on internal or fixed targets. We study the effects of some low energy lepton flavor violating interactions on this process. We study the sensitivities of this process on these low energy lepton flavor violating interactions and compare them to the sensitivities of lepton flavor violating $τ$ decay processes. Comparing with $τ$ decay processes, this process provides another way to study the lepton flavor violating effects with $e-τ$ conversion and it can be searched for in facilities with GeV scale electron or positron beams which are available in a number of laboratories in the world.

hep-ph↗
arXiv2014

Distinguishing the right-handed up/charm quarks from top quark via discrete symmetries in the standard model extensions

We propose a class of the two Higgs doublet Standard models (SMs) with a SM singlet and a class of supersymmetric SMs with two pairs of Higgs doublets, where the right-handed up/charm quarks and the right-handed top quark have different quantum numbers under extra discrete symmetries. Thus, the right-handed up and charm quarks couple to one Higgs doublet field, while the right-handed top quark couples to another Higgs doublet. The quark CKM mixings can be generated from the down-type quark sector. As one of phenomenological consequences in our models, we explore whether one can accommodate the observed direct CP asymmetry difference in singly Cabibbo-suppressed D decays. We show that it is possible to explain the measured values of CP violation under relevant experimental constraints.

hep-ph↗
arXiv2014

Effect of interaction with neutrons in matter on flavor conversion of super-light sterile neutrino with active neutrino

A super-light sterile neutrino was proposed to explain the absence of the expected upturn of the survival probability of low energy solar boron neutrinos. This is because this super-light sterile neutrino can oscillate efficiently with electron neutrino through a MSW resonance happened in Sun. One may naturally expect that a similar resonance should happen for neutrinos propagating in Earth matter. We study the flavor conversion of this super-light sterile neutrino with active neutrinos in Earth matter. We find that the scenario of the super-light sterile neutrino can easily pass through possible constraints from experiments which can test the Earth matter effect in oscillation of neutrinos. Interestinlgy, we find that this is because the naively expected resonant conversion disappears or is significantly suppressed due to the presence of a potential $V_n$ which arises from neutral current interaction of neutrino with neutrons in matter. In contrast, the neutron number density in the Sun is negligible and the effect of $V_n$ is effectively switched off. This enables the MSW resonance in Sun needed in oscillation of the super-light sterile neutrino with solar electron neutrinos. It's interesting to note that it is the different situation in the Sun and in the Earth that makes $V_n$ effectively turned off and turned on respectively. This observation makes the scenario of the super-light sterile neutrino quite interesting.

hep-ph↗
arXiv2013

Electron events from the scattering with solar neutrinos in the search of keV scale sterile neutrino dark matter

In a previous work we showed that keV scale sterile neutrino dark matter $ν_s$ is possible to be detected in $β$ decay experiment using radioactive sources such as $^3$T or $^{106}$Ru. The signals of this dark matter candidate are mono-energetic electrons produced in neutrino capture process $ν_s + N' \to N +e^-$. These electrons have energy greater than the maximum energy of the electrons produced in the associated decay process $N' \to N +e^- + {\bar ν}_e$. Hence, signal electron events are well beyond the end point of the $β$ decay spectrum and are not polluted by the $β$ decay process. Another possible background, which is a potential threat to the detection of $ν_s$ dark matter, is the electron event produced by the scattering of solar neutrinos with electrons in target matter. In this article we study in detail this possible background and discuss its implication to the detection of keV scale sterile neutrino dark matter. In particular, bound state features of electrons in Ru atom are considered with care in the scattering process when the kinetic energy of the final electron is the same order of magnitude of the binding energy.

hep-ph↗
arXiv2010

Strange meson form factors in holographic QCD

We consider the electromagnetic form factors of strange vector, axial vector and pseudoscalar mesons in a holographic QCD model. We find the charge radius of charged kaon agrees with the experiment, while the charge radius of charged pion is a little bit smaller than the experimental value, as obtained in other calculations in the hard-wall holographic QCD models. The charge radii of charged rho and $K^\ast$ quantitatively agree with a recent Dyson-Schwinger equation calculation. We also present the electric form factors of vector, axial vector and pseudoscalar mesons in both space-like and time-like regions. We find the charged kaon form factor is in agreement with the experiment data.

hep-ph↗
arXiv2008

Holographic QCD beyond the leading order

We consider a holographic QCD model for light mesons beyond the leading order in the context of 5-dim gauged linear sigma model on the interval in the AdS$_5$ space. We include two dimension-6 operators in addition to the canonical bulk kinetic terms, and study chiral dynamics of $π$, $ρ$, $a_1$ and some of their KK modes. As novel features of dim-6 operators, we get non-vanishing Br$(a_1 \to πγ)$, the electromagnetic form factor and the charge radius of a charged pion, which improve the leading order results significantly and agree well with the experimental results.

hep-ph↗
arXiv2008

Direct CP violation of $B \to l ν$ in unparticle physics

We have investigated the effects of unparticles in decays $B \to l ν$. It is found that the direct CP violation in the decays, which is zero in SM, can show up due to the CP conserving phase intrinsic in unparticle physics. For $l=τ$, the direct CP asymmetry can reach 30% for the scalar unparticle contribution, and 100% for the longitudinal vector unparticle contribution under the constraints of ${\rm Br}(B\toτν)$ and $νe$ elastic scattering. If both unparticle-lepton coupling universality and unparticle-quark coupling universality are assumed the constraint from $Br(π\to μν)$ leads that the direct CP violation in $B\to lν$ can only reach at most 8% and 1% for scalar and vector unparticle contributions respectively if $d_{\cal U} < 2$. If the direct CP violation is observed in the future it would give strong evidence for the existence of unparticle stuff.

hep-ph↗
arXiv2007

Spectra, triple and quartic gauge couplings in a Higgsless model

Spectra, triple and quartic gauge couplings of the Higgsless model with gauge group $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ defined in warped space are explored with numerical method. We extend the equation of motions, boundary conditions and formalism of multi-gauge-boson vertices to the Hirn-Sanz scenario. By assuming the ideally delocalized fermion profile, we study the spectra of vector bosons as well as the triple and quartic gauge couplings among vector bosons. It is found that mass spectra can be greatly modified by the parameters of QCD power corrections. Meanwhile, the triple and quartic gauge couplings can deviate from the values of the standard model to at least $\pm 10%$ and can saturate the LEP2 bounds. We find the triple gauge couplings of $Z{\bar W}W$ can be $ 50 %$ smaller than the unitarity bounds. While the triple gauge couplings of ${\bar Z}WW$ is 20% smaller than the unitarity bounds, which might challenge the detection of ${\bar Z}$ via s channel at LHC if $m_{\bar Z}> 500$ GeV.

hep-ph↗
arXiv2007

Antisymmetric rank--2 tensor unparticle physics

We present the phenomenology of antisymmetric rank-2 tensor unparticle operator ${\cal O}_{\cal U,A}^{μν}$ with scaling dimension $d_{\cal U}$. We consider the physical effects of operator $O_{\cal U,A}^{μν}$ in $Z^0$ boson invisible decays $Z^0 \to {\cal U}$, $Z^0 \to b \bar{b}$ channel, the electroweak precision observable $S$ parameter, and the muon anomalous magnetic dipole moment. The $Z^0$ boson invisible decay gives a very stringent constraint in the $(Λ_{\cal U}, M_{\cal U})$ plane, and only small $r \equiv Λ_{\cal U} / M_{\cal U} \lesssim 0.1$ is favored, when $Λ_{\cal U}$ is order of several 100 GeV. When the phenomenological parameter $μ$, which parameterizes the scale invariance breaking, goes to 0, the $S$ parameter and the muon $(g-2)$ diverge for $1 < d_{\cal U} < 2$, while for non-zero $μ$, there will be constraints on $(Λ_{\cal U}, M_{\cal U})$ which are more stringent than those obtained from collider experiments.

hep-ph↗
arXiv2006

Search for new physics from $B\toπϕ$

We investigate the pure penguin process $B^-\to π^-ϕ$ using QCD factorization approach to calculate hadronic matrix elements to the $α_s$ order in some well-known NP models. It is shown that the NP contributions in R-parity conserved SUSY models and 2HDMs are not enough to saturate the experimental upper bounds for $B\to ϕπ$. We have shown that the flavor changing $Z^\prime$ models can make the branching ratios of $B\to ϕπ$ to saturate the bound under all relevant experimental constraints.

hep-ph↗
arXiv2006

Implications for new physics from ${\bar B}^0\to π^0π^0$ and ${\bar B}^0\to {\bar K}^0K^0$

We have analyzed the ${\bar B}^0\to π^0π^0$ puzzle in three kinds of models beyond the standard model (SM). It is shown that the minimal flavor violation (MFV) models, the minimal supersymmetric standard model (MSSM), and the two Higgs doublet models (2HDM) I and II can not give an explanation of the ${\bar B}^0\to π^0π^0$ puzzle within $1 σ$ experimental bounds and the model III 2HDM can explain the puzzle without a conflict with other experimental measurements. If the constraint on $C_{8g}$ from $b\to s g$ is not imposed, for all kinds of insertions considered there are regions of parameter space, where the scalar quark mass is larger (much larger) than the gluino mass in the case of LR or RL (LL or RR), in which the puzzle can be resolved within $1 σ$ experimental bounds.

hep-ph↗
arXiv2006

MSSM Anatomy of the Polarization Puzzle in B --> phi K* Decays

We analyze the $B \to ϕK^{*}$ polarization puzzle in the Minimal Supersymmetric Standard Model (MSSM) including the neutral Higgs boson (NHB) contributions. To calculate the non-factorizable contributions to hadronic matrix elements of operators, we have used the QCD factorization framework to the $α_s $ order. It is shown that the recent experimental results of the polarization fractions in $B\to ϕK^{*}$ decays, which are difficult to be explained in SM, could be explained in MSSM if there are flavor non-diagonal squark mass matrix elements of 2nd and 3rd generations, which also satisfy all relevant constraints from known experiments ($B\to X_sγ, B_s\to μ^+μ^-, B\to X_s μ^+μ^-, B\to X_s g, ΔM_s$, etc.). We have shown in details that the experimental results can be accommodated with the flavor non-diagonal mass insertion of chirality RL, RL+LR, RR, or LL+ RR when the NHB contributions as well as $\mathcal{O}(α_s)$ corrections of hadronic matrix elements of operators are included. However the branching ratios for the decay are smaller than the experimental measurements.

hep-ph↗
arXiv2004

CP asymmetry in B \to phi K_S in a SUSY SO(10) GUT

We study the $B\to ϕK_S$ decay in a SUSY SO(10) GUT. We calculate the mass spectrum of sparticles for a given set of parameters at the GUT scale. We complete the calculations of the Wilson coefficients of operators including the new operators which are induced by NHB penguins at LO using the MIA with double insertions. It is shown that the recent experimental results on the time-dependent CP asymmetry $S_{ϕK}$ in $B\to ϕK_S$, which is negative and can not be explained in SM, can be explained in the model where there are flavor non-diagonal right-handed down squark mass matrix elements of 2nd and 3rd generations whose size satisfies all relevant constraints from known experiments ($τ\to μγ$, $B\to X_Sγ, B_s\to μ^+μ^-, B\to X_s μ^+μ^-, B\to X_s g, ΔM_s$, etc.). At the same time, the branching ratio for the decay can also be in agreement with experimental measurements.

hep-ph↗
arXiv2004

CP asymmetries in $B\to ϕK_S$ and $B\to η' K_S$ in MSSM

We study the $B\to ϕK_S$ and $B\to \ep K_S$ decays in MSSM by calculating hadronic matrix elements of operators with QCD factorization approach and including neutral Higgs boson (NHB) contributions. We calculate the Wilson coefficients of operators including the new operators which are induced by NHB penguins at LO using the MIA with double insertions. We calculate the $α_s$ order hadronic matrix elements of the new operators for $B\to ϕK_s$ and $B\to η^\prime K_s$. It is shown that the recent experimental results on the time-dependent CP asymmetries in $B\to ϕK_S$ and $B\to \ep K_S$, $S_{ϕK}$ is negative and $S_{η^{\prime} K}$ is positive, which can not be explained in SM, can be explained in MSSM if there are flavor non-diagonal squark mass matrix elements of 2nd and 3rd generations whose size satisfies all relevant constraints from known experiments ($B\to X_Sγ, B_s\to μ^+μ^-, B\to X_s μ^+μ^-, B\to X_s g, ΔM_s$, etc.). In particular, we find that one can explain the experimental results with a flavor non-diagonal mass insertion of any chirality when $α_s$ corrections of hadronic matrix elements of operators are included, in contrast with the claim in the literature. At the same time, the branching ratios for the two decays can also be in agreement with experimental measurements.

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