arXiv subjects

Bo-Qiang Ma

Publications and source records attributed to Bo-Qiang Ma.

At least 127 records · Page 7Linked to original sources

arXiv2014

Transverse single-spin asymmetries of pion production in semi-inclusive DIS at subleading twist

We study the single-spin asymmetries with the $\sinϕ_S$ and $\sin(2ϕ_h -ϕ_S)$ angular dependences for charged and neutral pions produced in semi-inclusive deep inelastic scattering on the transversely polarized proton target. The theoretical interpretations of the two asymmetries are presented in terms of the convolution of the twist-3 quark transverse momentum dependent distributions and twist-2 fragmentation functions. Specifically, we investigate the role of the distributions $f_T$, $h_T$ and $h_T^\perp$ in the $\sinϕ_S$ asymmetry, as well as the role of the distributions $f_T^\perp$, $h_T$ and $h_T^\perp$ in the $\sin(2ϕ_h -ϕ_S)$ asymmetry. We calculate these distributions in a spectator-diquark model and predict the corresponding asymmetries for the first time, considering the kinematics at HERMES, JLab and COMPASS. The numerical estimates show that the asymmetries are sizable, and the dominant contribution to the $\sinϕ_S$ asymmetry comes from the T-odd distribution $f_T$, while $f_T^\perp$ gives the main contribution to the $\sin(2ϕ_h -ϕ_S)$ asymmetry. The future measurements on these asymmetries can shed light on the information of twist-3 transverse momentum dependent distributions.

hep-ph↗

arXiv2014

Generalized form factors of the nucleon in a light-cone spectator-diquark model

We investigate the generalized form factors of the nucleon in a light-cone spectator-diquark model. Compared to the form factors, the generalized form factors contain some more information of the structure of the nucleon. In our calculation, both the scalar and the axial-vector spectator-diquark are taken into account. As a relation between the spin in the instant form and that in the light-cone form, the Melosh-Wigner rotation effect is included for both the quark and the axial-vector diquark. We also provide numerical results from our model calculations, and the results are comparable with those from lattice QCD.

hep-ph↗

arXiv2014

Lorentz Violation of the Photon Sector in Field Theory Models

We compare the Lorentz violation terms of the pure photon sector between two field theory models, namely the minimal standard model extension (SME) and the standard model supplement (SMS). From the requirement of the identity of the intersection for the two models, we find that the free photon sector of the SMS can be a subset of the photon sector of the minimal SME. We not only obtain some relations between the SME parameters, but also get some constraints on the SMS parameters from the SME parameters. The CPT-odd coefficients $(k_{AF})^α$ of the SME are predicted to be zero. There are 15 degrees of freedom in the Lorentz violation matrix $Δ^{αβ}$ of free photons of the SMS related with the same number of degrees of freedom in the tensor coefficients $(k_F)^{αβμν}$, which are independent from each other in the minimal SME, but are inter-related in the intersection of the SMS and the minimal SME. With the related degrees of freedom, we obtain the conservative constraints ($2σ$) on the elements of the photon Lorentz violation matrix. The detailed structure of the photon Lorentz violation matrix suggests some applications to the Lorentz violation experiments for photons.

hep-ph↗

arXiv2014

Extracting Mass Hierarchy Information from Simple Analysis of Neutrino Mass Splitting

Based on the independent measurements on neutrino mass splitting $|Δm^2_{μμ}|$, $|Δm^2_{ee}|$, $Δm^2_{21}$, and recent measurements by the T2K Collaboration, we carry out a simple fitting analysis on $Δm^2_{32}$ and $Δm^2_{31}$ in normal hierarchy and inverse hierarchy respectively, suggesting $Δm^2_{32}=(2.46\pm0.07)\times10^{-3}~\mbox{eV}^2$ and $Δm^2_{31}=(2.53\pm0.07)\times10^{-3}~\mbox{eV}^2$ in normal hierarchy, or $Δm^2_{32}$=$-(2.51\pm0.07)\times10^{-3}~\mbox{eV}^2$ and $Δm^2_{31}$=$-(2.44\pm0.07)\times10^{-3}~\mbox{eV}^2$ in invert hierarchy. The simple analysis indicate that both normal and inverted hierarchy are consistent with current experimental measurements on mass splitting. The p-value for normal hierarchy and that for inverted hierarchy are 62% and 55%, respectively. This reveals a slight favor for the normal hierarchy. It is suggested that further measurements on the mass splitting with higher accuracy are necessary to determine the neutrino mass hierarchy.

hep-ph↗

arXiv2014

Lorentz violation from gamma-ray bursts

The constancy of light speed is a basic assumption in Einstein's special relativity, and consequently the Lorentz invariance is a fundamental symmetry of space-time in modern physics. However, it is speculated that the speed of light becomes energy-dependent due to the Lorentz invariance violation~(LV) in various new physics theories. We analyse the data of the energetic photons from the gamma-ray bursts (GRBs) by the Fermi Gamma-Ray Space Telescope, and find more events to support the energy dependence in the light speed with both linear and quadratic form corrections. We provide two scenarios to understand all the new-released Pass~8 data of bright GRBs by the Fermi-LAT Collaboration, with predictions from such scenarios being testable by future detected GRBs.

hep-ph↗

arXiv2014

Present status on experimental search for pentaquarks

It has been ten years since the first report for a positive strangeness pentaquark-like baryon state. However the existence of the pentaquark state is still controversial. Some contradictions between the experiments are unsolved. In this paper we review the experimental search for the pentaquark candidates $Θ^+$, $Θ^{++}$, $Ξ^{--}$, $Θ_c^0$ and $N^*$ in details. We review the experiments with positive results and compare the experiments with similar conditions but opposite results.

hep-ex↗

arXiv2014

Baryon spectrum in a finite-temperature AdS/QCD model

We propose a model for baryons at finite temperature using AdS/QCD correspondence. In this model, we modify the AdS spacetime into the AdS-Schwarzchild spacetime and consider a couple of bulk spinors in this background. Solving this model, we get an eigenvalue equation for the baryon masses. We then investigate the effects of temperature on the baryon masses numerically, and find an interesting temperature dependence. Our result is consistent with the results from lattice QCD and other phenomenological models.

hep-ph↗

arXiv2013

Quark to $Λ$-hyperon spin transfers in the current-fragmentation region

We perform a study on the struck quark to the $Λ$-hyperon fragmentation processes by taking into account the anti-quark fragmentations and intermediate decays from other hyperons. We concentrate on how the longitudinally polarized quark fragments to the longitudinally polarized $Λ$, how unpolarized quark and anti-quark fragment to the unpolarized $Λ$, and how quark and anti-quark fragment to the $Λ$ through the intermediate decay processes. We calculate the effective fragmentation functions in the light-cone SU(6) quark-spectator-diquark model via the Gribov-Lipatov relation, with the Melosh-Wigner rotation effect also included. The calculated results are in reasonable agreement with the HERMES semi-inclusive $ep$ experimental data and the OPAL and ALEPH $e^{+}e^{-}$ annihilation experimental data.

hep-ph↗

arXiv2013

A Theoretical Diagnosis on Light Speed Anisotropy from GRAAL Experiment

The light speed anisotropy, i.e., the variation of the light speed with respect to the direction in an "absolute" reference frame, is a profound issue in physics. The one-way experiment, performed at the GRAAL facility of the European Synchrotron Radiation Facility (ESRF) in Grenoble, reported results on the light speed anisotropy by Compton scattering of laser photons on high-energy electrons. So far, most articles concerned with the GRAAL data have established only the upper bounds on the anisotropy parameters based on available theories. We use a new theory of the Lorentz invariance violation to analyse the available GRAAL data and obtain the stringent upper limit of the order $2.4\times10^{-14}$ on the Lorentz violation parameters. In the meantime, we also can reproduce the allowed light speed anisotropy appearing in the azimuthal distribution of the GRAAL experimental data, and find that the best-fit parameters are compatible with the competitive upper bounds.

hep-ph↗

arXiv2013

New mixing pattern for neutrinos

We propose a new mixing pattern for neutrinos with a nonzero mixing angle $θ_{13}$. Under a simple form, it agrees well with current neutrino oscillation data and displays a number of intriguing features including the $μ$-$τ$ interchange symmetry $|U_{μi}|=|U_{τi}|$, $(i=1,2,3)$, the trimaximal mixing $|U_{\e 2}|=|U_{μ2}|=|U_{τ2}|=1/\sqrt{3}$, the self-complementarity relation $θ_1+θ_3=45°$, together with the maximal Dirac CP violation as a prediction.

hep-ph↗

arXiv2013

Neutrino speed anomaly as signal of Lorentz violation

We make a reanalysis on the issue of neutrino speed anomaly by taking into account the newly reported data from the ICARUS experiment and other CNGS collaborations. We examine the consequence of the Lorentz violation on the neutrino speed in a new framework of standard model supplement (SMS), and find that the Lorentz violating parameters are constrained at least one order stronger than that of the earlier OPERA report. The combination with other phenomenological considerations puts more stringent constraints on the Lorentz violation of neutrinos.

hep-ph↗

arXiv2013

Quark helicity distributions in transverse momentum space and transverse coordinate space

The transverse momentum dependent helicity distributions of valence quarks are calculated in the light-cone diquark model by adopting two different approaches. We use the model results to analyze the $P_{h\perp}$-dependent double spin asymmetries for $π^+$, $π^-$ and $π^0$ productions in semi-inclusive deep inelastic scattering, and find that the asymmetries agree with the CLAS data in one of the approaches. By taking the Fourier transform of the transverse momentum dependent helicity distributions, we obtain the helicity distributions of valence quarks in the transverse coordinate space, and then apply them further to predict the Bessel-weighted double spin asymmetries of $π^+$, $π^-$ and $π^0$ productions in semi-inclusive deep inelastic scattering at CLAS, COMPASS and HERMES for the first time. The shape of the Bessel-weighted double spin asymmetry thereby provides a direct probe on the transverse structure of longitudinally polarized quarks.

hep-ph↗

arXiv2013

Simple parametrization of neutrino mixing matrix

We propose simple forms of neutrino mixing matrix in analogy with the Wolfenstein parametrization of quark mixing matrix, by adopting the smallest mixing angle $θ_{13}$ as a measure of expansion parameters with the tribimaximal pattern as the base matrix. The triminimal parametrization technique is utilized to expand the mixing matrix under two schemes, i.e., the standard Chau-Keung (CK) scheme and the original Kobayashi-Maskawa (KM) scheme. The new parametrizations have their corresponding Wolfenstein-like parametrizations of quark mixing matrix, and therefore they share the same intriguing features of the Wolfenstein parametrization. The newly introduced expansion parameters for neutrinos are connected to the Wolfenstein parameters for quarks via the quark-lepton complementarity.

hep-ph↗

arXiv2012

Quark-lepton complementarity and self-complementarity in different schemes

With the progress of increasingly precise measurements on the neutrino mixing angles, phenomenological relations such as quark-lepton complementarity (QLC) among mixing angles of quarks and leptons and self-complementarity (SC) among lepton mixing angles have been observed. Using the latest global fit results of the quark and lepton mixing angles in the standard Chau-Keung scheme, we calculate the mixing angles and CP-violating phases in the other eight different schemes. We check the dependence of these mixing angles on the CP-violating phases in different phase schemes. The dependence of QLC and SC relations on the CP phase in the other eight schemes is recognized and then analyzed, suggesting that measurements on CP-violating phases of the lepton sector are crucial to the explicit forms of QLC and SC in different schemes.

hep-ph↗

arXiv2012

Correlating lepton mixing angles and mixing matrix with Wolfenstein parameters

Inspired by a new relation $θ_{13}^{\rm PMNS}={θ_C}/{\sqrt{2}}$ observed from the relatively large $θ_{13}^{\rm PMNS}$, we find that the combination of this relation with the quark-lepton complementarity and the self-complementarity results in correlations of the lepton mixing angles with the quark mixing angles. We find that the three mixing angles in the PMNS matrix are all related to the Wolfenstein parameter $λ$ in the quark mixing, so they are also correlated. Consequently, the PMNS matrix can be parameterized by $λ$, A, and a Dirac CP-violating phase $δ$. Such parametrizations for the PMNS matrix have the same explicitly hierarchical structure as the Wolfenstein parametrization for the CKM matrix in the quark mixing, and the bimaximal mixing pattern is deduced at the leading order. We also discuss implications of these phenomenological relations in parametrizations.

hep-ph↗

arXiv2012

Boer-Mulders function of the pion in the MIT bag model

We apply the MIT bag model to study the Boer-Mulders function of the pion, a $T$-odd function that describes the transverse polarization distribution of the quark inside the pion. We simulate the effect of the gauge link through the "one-gluon-exchange" approximation. We consider both the quark helicity nonflip and double-flip contributions. The result in the MIT bag model is compared with those in the spectator models.

hep-ph↗

arXiv2012

Proton spin in a light-cone chiral quark model

We discuss the spin structure of the proton in a light-cone treatment of the chiral quark model. Based on the fact that the quark helicity ($Δq$) measured in polarized deep inelastic scattering experiments is actually the quark spin defined in the light-cone formalism, rather than the quark spin ($Δq_{QM}$) defined in the conventionally quark model (or in the rest frame of the nucleon), we calculate the $x$-dependence of the polarized quark distribution functions $Δq(x)$, and the polarized structure functions $g_1 (x)$. Special attention is focused on the Melosh-Wigner rotation due to the transversal motions of quarks inside the nucleon and its effects on the bare quark input. It is shown that our results match the experimental data well.

hep-ph↗

arXiv2012

Wave Packet Approach to Neutrino Oscillations with Matter Effects

The complete description of neutrino oscillations require the wave packet treatment. For terrestrial experiments the contribution from the interaction of neutrino with the Earth matter would modify oscillation pattern, i.e., the dependence of the flavor transition probability on baseline $L$ and energy $E$. We thus combine the wave packet approach and the matter effects, in order to have more accurate descriptions of neutrino oscillation. The general expression for the transition probability of oscillations with arbitrary numbers of neutrinos are derived. As an example the two-neutrino oscillation is studied in detail.

hep-ph↗