arXiv subjects

Q. Y. Liu

Publications and source records attributed to Q. Y. Liu.

At least 19 recordsLinked to original sources

arXiv2023

The chromatic Point Spread Function of weak lensing measurement in Chinese Space Station survey Telescope

The weak gravitational lensing is a powerful tool in modern cosmology. To accurately measure the weak lensing signal, one has to control the systematic bias to a small level. One of the most difficult problems is how to correct the smearing effect of the Point Spread Function (PSF) on the shape of the galaxies. The chromaticity of PSF for a broad-band observation can lead to new subtle effects. Since the PSF is wavelength dependent and the spectrum energy distributions between stars and galaxies are different, the effective PSF measured from the star images will be different from that smears the galaxies. Such a bias is called colour bias. We estimate it in the optical bands of the Chinese Space Station Survey Telescope from simulated PSFs, and show the dependence on the colour and redshift of the galaxies. Moreover, due to the spatial variation of spectra over the galaxy image, there exists another higher-order bias, colour gradient bias. Our results show that both colour bias and colour gradient bias are generally below $0.1$ percent in CSST. Only for small-size galaxies, one needs to be careful about the colour gradient bias in the weak lensing analysis using CSST data.

astro-ph.CO↗

arXiv2022

$B$-flavor tagging at Belle II

We report on new flavor tagging algorithms developed to determine the quark-flavor content of bottom ($B$) mesons at Belle II. The algorithms provide essential inputs for measurements of quark-flavor mixing and charge-parity violation. We validate and evaluate the performance of the algorithms using hadronic $B$ decays with flavor-specific final states reconstructed in a data set corresponding to an integrated luminosity of $62.8$ fb$^{-1}$, collected at the $Υ$(4$S$) resonance with the Belle II detector at the SuperKEKB collider. We measure the total effective tagging efficiency to be $\varepsilon_{\rm eff} = \big(30.0 \pm 1.2(\text{stat}) \pm 0.4(\text{syst})\big)\%$ for a category-based algorithm and $\varepsilon_{\rm eff} = \big(28.8 \pm 1.2(\text{stat}) \pm 0.4(\text{syst})\big)\%$ for a deep-learning-based algorithm.

hep-ex↗

arXiv2018

Ultralow-temperature heat transport in the quantum spin liquid candidate Ca10Cr7O28 with bilayer kagome lattice

Recently, a novel material with bilayer kagome lattice Ca$_{10}$Cr$_7$O$_{28}$ was proposed to be a gapless quantum spin liquid, due to the lack of long-range magnetic order and the observation of broad diffuse excitations. Here, we present the ultralow-temperature thermal conductivity measurements on single crystals of Ca$_{10}$Cr$_7$O$_{28}$ to detect its low-lying magnetic excitations. At finite temperatures, with increasing the magnetic fields, the thermal conductivity exhibits a clear dip around 6 T, which may correspond to a crossover in the magnetic ground state. At the zero-temperature limit, no residual linear term is found at any fields, indicating the absence of gapless itinerant fermionic excitations. Therefore, if the spinons do exist, they are either localized or gapped. In the gapped case, the fitting of our data gives a small gap $Δ\sim$ 0.27(2) K. These results put strong constraints on the theoretical description of the ground state in this quantum spin liquid candidate.

cond-mat.str-el↗

arXiv2013

Update of Short-Baseline Electron Neutrino and Antineutrino Disappearance

We present a complete update of the analysis of electron neutrino and antineutrino disappearance experiments in terms of neutrino oscillations in the framework of 3+1 neutrino mixing, taking into account the Gallium anomaly, the reactor anomaly, solar neutrino data and nu_e-C scattering data. We discuss the implications of a recent 71Ga(3He,3H)71Ge measurement which give information on the neutrino cross section in Gallium experiments. We discuss the solar bound on active-sterile mixing and present our numerical results. We discuss the connection between the results of the fit of neutrino oscillation data and the heavy neutrino mass effects in beta-decay experiments (considering new Mainz data) and neutrinoless double-beta decay experiments (considering the recent EXO results).

hep-ph↗

arXiv2009

Corrections to Tribimaximal Mixing from Nondegenerate Phases

We propose a seesaw scenario that possible corrections to the tribimaximal pattern of lepton mixing are due to the small phase splitting of the right-handed neutrino mass matrix. we show that the small deviations can be expressed analytically in terms of two splitting parameters($δ_1$ and $δ_2$) in the leading order. The solar mixing angle $θ_{12}$ favors a relatively smaller value compared to zero order value ($35.3^\circ$), and the Dirac type CP phase $δ$ chooses a nearly maximal one. The two Majorana type CP phases $ρ$ and $σ$ turn out to be a nearly linear dependence. Also a normal hierarchy neutrino mass spectrum is favored due to the stability of perturbation calculations.

hep-ph↗

arXiv2009

Bayesian Constraints on theta_{13} from Solar and KamLAND Neutrino Data

We present the results of a Bayesian analysis of solar and KamLAND neutrino data in the framework of three-neutrino mixing. We adopt two approaches for the prior probability distribution of the oscillation parameters Delta m^2_{21}, sin^2 theta_{12}, sin^2 theta_{13}: 1) a traditional flat uninformative prior; 2) an informative prior which describes the limits on sin^2 theta_{13} obtained in atmospheric and long-baseline accelerator and reactor neutrino experiments. In both approaches, we present the allowed regions in the sin^2 theta_{13} - Delta m^2_{21} and sin^2 theta_{12} - sin^2 theta_{13} planes, as well as the marginal posterior probability distribution of sin^2 theta_{13}. We confirm the 1.2 sigma hint of theta_{13} > 0 found in hep-ph/0806.2649 from the analysis of solar and KamLAND neutrino data. We found that the statistical significance of the hint is reduced to about 0.8 sigma by the constraints on sin^2 theta_{13} coming from atmospheric and long-baseline accelerator and reactor neutrino data, in agreement with arXiv:0808.2016.

hep-ph↗

arXiv2008

Small Neutrino Masses From Structural cancellation In Left-Right Symmetric Model

The Type I, II and hybrid (I+II) seesaw mechanism, which explain why neutrinos are especially light, are consequences of the left-right symmetric model (LRSM). They can be classified by the ranges of parameters of LRSM. We show that a nearly cancellation in general Type-(I+II) seesaw is more natural than other types of seesaw in the LRSM if we consider their stability against radiative correction. In this scenario the small neutrino masses are due to the structure cancellation, and the masses of the right handed neutrino can be of order of O(10)TeV. The realistic model for non-zero neutrino masses, charged lepton masses and lepton tribimaximal mixing can be implemented by embedding $A_4$ flavor symmetry in the model with perturbations to the textures.

hep-ph↗

arXiv2006

Testing the Stability of the Solar Neutrino LMA Solution with a Bayesian Analysis

We analyze with the Bayesian method the solar and KamLAND neutrino data in terms of neutrino oscillations. We show that Bayesian credible regions with a flat prior in the tan^2(theta12)--(Delta m^2)_21 plane strongly support the LMA solution, in agreement with the usual chi-square analysis. Other reasonable priors are considered in order to test the stability of the LMA solution. We show that priors which favor small or large values of the mixing angle lead to minor changes of the allowed LMA region, affecting mainly its large tan^2(theta12) part.

hep-ph↗

arXiv2006

A Paradox on Quantum Field Theory of Neutrino Mixing and Oscillations

Neutrino mixing and oscillations in quantum field theory framework had been studied before, which shew that the Fock space of flavor states is unitarily inequivalent to that of mass states (inequivalent vacua model). A paradox emerges when we use these neutrino weak states to calculate the amplitude of $W$ boson decay. The branching ratio of W(+) -> e(+) + nu_mu to W(+) -> e(+) + nu_e is approximately at the order of O({m_i^2}/{k^2}). The existence of flavor changing currents contradicts to the Hamiltonian we started from, and the usual knowledge about weak processes. Also, negative energy neutrinos (or violating the principle of energy conservation) appear in this framework. We discuss possible reasons for the appearance of this paradox.

hep-ph↗

arXiv2005

Solving Solar Neutrino Puzzle via LMA MSW Conversion

We analyze the existing solar neutrino experiment data and show the allowed regions. The result from SNO's salt phase itself restricts quite a lot the allowed region's area. Reactor neutrinos play an important role in determining oscillation parameters. KamLAND gives decisive conclusion on the solution to the solar neutrino puzzle, in particular, the spectral distortion in the 766.3 Ty KamLAND data gives another new improvement in the constraint of solar MSW-LMA solutions. We confirm that at 99.73% C.L. the high-LMA solution is excluded.

hep-ph↗

arXiv2005

Entangled state representations in noncommutative quantum mechanics

We introduce new representations to formulate quantum mechanics on noncommutative coordinate space, which explicitly display entanglement properties between degrees of freedom of different coordinate components and hence could be called entangled state representations. Furthermore, we derive unitary transformations between the new representations and the ordinary one used in noncommutative quantum mechanics (NCQM) and obtain eigenfunctions of some basic operators in these representations. To show the potential applications of the entangled state representations, a two-dimensional harmonic oscillator on the noncommutative plane with both coordinate-coordinate and momentum-momentum couplings is exactly solved.

hep-th↗

arXiv2004

Does Reactor Neutrino Experiment Play an Important Role in Theta_{13} of Lepton Mixing (PMNS) Matrix ?

Reactor neutrinos play an important role in determining parameter theta_{13} in the lepton mixing (PMNS) matrix. A next important step on measuring PMNS matrix could be to build another reactor neutrino experiment, for example, DaYa bay in China, to search the possible oscillations via sin^2 (2theta_{13}) and Delta m^2_{13}. We consider 4 different schemes for positions of three 8-ton detectors of this experiment, and simulate the results with respect to an array of assumed ''true'' values of physics parameters. Using three kinds of analysis method, we suggest a best scheme for this experiment which is to place a detector 2200m ~ 2500m symmetrically away from two reactors, and to put the other two detectors closer to their corresponding reactors respectively, almost at a 100m ~ 200m distance. Moreover, with conservative assumption on the experimental technique, we construct series of allowed regions from our simulation results, and give detailed explanations therein.

hep-ph↗

arXiv1999

Operator for Describing Polarization States of a Photon

Based on the quantized electromagnetic field described by the Riemann-Silberstein complex vector $F$, we construct the eigenvector set of $% F$, which makes up an orthonormal and complete representation. In terms of $% F $ we then introduce a new operator which can describe the relative ratio of the left-handed and right-handed polarization states of a polarized photon .In $F^{\prime}s$ eigenvector basis the operator manifestly exhibits a behaviour which is similar to a phase difference between two orientations of polarization of a light beam in classical optics.

quant-ph↗

arXiv1999

Uncertainty of the Solar Neutrino Energy Spectrum

The solar neutrino spectrum measured by the Super-Kamiokande shows an excess in high energy bins, which may be explained by vacuum oscillation solution or $hep$ neutrino effect. Here we reconsider an uncertainty of the data caused by the tail of the energy resolution function. Events observed at energy higher than 13.5 MeV are induced by the tail of the resolution. At Super-Kamiokande precision level this uncertainty is no more than few percent within a Gaussian tail. But a power-law decay tail at 3 $σ$ results considerable excesses in these bins, which may be another possible explanation of the anomaly in 708d(825d) data.

hep-ph↗

arXiv1999

Coherence and the Day - Night Asymmetry in the Solar Neutrino Flux

We consider the day-night asymmetries predicted by MSW solutions of the solar neutrino problem. The integration over the neutrino energy, as well as over the production region or over the time intervals of more than a day leads to the averaging of oscillations on the way to the earth. This is equivalent to considering the neutrino state arriving at the surface of the earth as an incoherent mixture of the neutrino mass eigenstates (even if there is no divergence of wavepackets). As a consequence, the $ν_e$-regeneration effect inside the earth is incoherent, in contrast with the result in hep-ph/9902435.

hep-ph↗

arXiv1998

Neutrino Mass Spectrum with $ν_μ$ $\to$ $ν_s$ Oscillations of Atmospheric Neutrinos

We consider the ``standard'' spectrum of the active neutrinos (characterized by strong mass hierarchy and small mixing) with additional sterile neutrino, $ν_s$. The sterile neutrino mixes strongly with the muon neutrino, so that $ν_μ \leftrightarrow ν_s$ oscillations solve the atmospheric neutrino problem. We show that the parametric enhancement of the $ν_μ \leftrightarrow ν_s$ oscillations occurs for the high energy atmospheric neutrinos which cross the core of the Earth. This can be relevant for the anomaly observed by the MACRO experiment. Solar neutrinos are converted both to $ν_μ$ and $ν_s$. The heaviest neutrino ($\approx ν_τ$) may compose the hot dark matter of the Universe. Phenomenology of this scenario is elaborated and crucial experimental signatures are identified. We also discuss properties of the underlying neutrino mass matrix.

hep-ph↗

arXiv1998

Parametric Resonance in Oscillations of Atmospheric Neutrinos?

We consider a solution of the atmospheric neutrino problem based on oscillations of muon neutrinos to sterile neutrinos: $ν_μ$ $\leftrightarrow$ $ν_s$. The zenith angle ($Θ$) dependences of the neutrino and upward-going muon fluxes in presence of these oscillations are studied. The dependences have characteristic form with two dips: at $\cos Θ= -0.6 ÷-0.2$ and $\cos Θ= -1.0 ÷-0.8$. The latter dip is due to parametric resonance in oscillations of neutrinos which cross the core of the earth. A comparison of predictions with data from the MACRO, Baksan and Super-Kamiokande experiments is given.

hep-ph↗

arXiv1997

Solar neutrinos and grand unification

We consider the Grand Unification (GU) scenario for neutrino masses which is based on the see-saw mechanism with the mass of the heaviest right handed (RH) neutrino at the GU-scale: $M_3 \sim Λ_{GU}$, and on the quark-lepton symmetry for fermions from the third generation. The scenario predicts for the light neutrinos: $m_3 \sim (2 - 4) \cdot 10^{-3}$ eV and $m_2 \sim (0.3 - 3) \cdot 10^{-5}$ eV (in the case of a linear mass hierarchy of the RH neutrinos or/and in presence of the Planck scale suppressed non-renormalizable operators). It also predicts large $ν_e - ν_μ$ mixing: $~\sin^2 2θ_{eμ} \stackrel{_>}{_\sim} 0.2$. In this scenario the solar neutrinos ($ν_{\odot}$) undergo both the \nue $\to$ \nutau resonance conversion in the Sun and substantial \nue $\to$ \numu vacuum oscillations on the way from the Sun to the Earth. The interplay of both effects enlarges the range of neutrino parameters which solve the $ν_{\odot}$-problem. In particular, $ν_e - ν_τ$ mixing angle can be as small as the corresponding quark mixing: $\sin^2 2θ_{eτ} \geq (2~-~5) \cdot 10^{-4}$. The scenario predicts peculiar (oscillatory) distortion of the boron neutrino energy spectrum and seasonal variations of signals. Manifestations of these effects in the Super-Kamiokande and SNO experiments are studied.

hep-ph↗