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Xin Zhang

Publications and source records attributed to Xin Zhang.

At least 1,081 records · Page 60Linked to original sources
arXiv2018

$R_{D^{(\ast)}}$, $R_{K^{(\ast)}}$ and neutrino mass in the 2HDM-III with right-handed neutrinos

Given that the two-Higgs-doublet model of type III (2HDM-III) has the potential to address the $R_{D^{(\ast)}}$ anomalies while the resolution to the $R_{K^{(\ast)}}$ deficits requires new degrees of freedom within this framework, we consider in this paper a unified scenario where the low-scale type-I seesaw mechanism is embedded into the 2HDM-III, so as to accommodate the $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$ anomalies as well as the neutrino mass. We first revisit the $R_{D^{(\ast)}}$ anomalies and find that the current world-averaged results can be addressed at $2σ$ level without violating the bound from the branching ratio $\mathcal{B}(B_c^-\rightarrow τ^- \barν)\leqslant 30\%$. The scenario predicts two sub-eV neutrino masses based on a decoupled heavy Majorana neutrino and two nearly degenerate Majorana neutrinos with mass around the electroweak scale. For the $R_{K^{(\ast)}}$ anomalies, the same scenario can generate the required Wilson coefficients in the direction $ C_{9 μ}^{\rm NP}=-C_{10 μ}^{\rm NP}<0$, with $\mathcal{O}(1)$ Yukawa couplings for the muon and the top quark.

hep-ph↗
arXiv2018

Open-Loop and Closed-Loop Solvabilities for Stochastic Linear Quadratic Optimal Control Problems of Markov Regime-Switching System

This paper investigates the stochastic linear quadratic (LQ, for short) optimal control problem of Markov regime switching system. The representation of the cost functional for the stochastic LQ optimal control problem of Markov regime switching system is derived using the technique of It{ô}'s formula. For the stochastic LQ optimal control problem of Markov regime switching system, we establish the equivalence between the open-loop (closed-loop) solvability and the existence of an adapted solution to the corresponding forward-backward stochastic differential equation with constraint (the existence of a regular solution to the Riccati equation). Also, we analyze the interrelationship between the strongly regular solvability of the Riccati equation and the uniform convexity of the cost functional.

math.OC↗
arXiv2018

A note on the edge partition of graphs containing either a light edge or an alternating 2-cycle

Let $\mathcal{G}_α$ be a hereditary graph class (i.e, every subgraph of $G_α\in \mathcal{G}_α$ belongs to $\mathcal{G}_α$) such that every graph $G_α$ in $\mathcal{G}_α$ has minimum degree at most 1, or contains either an edge $uv$ such that $d_{G_α}(u)+d_{G_α}(v)\leq α$ or a 2-alternating cycle. It is proved that every graph in $\mathcal{G}_α$ ($α\geq 5$) with maximum degree $Δ$ can be edge-partitioned into two forests $F_1$, $F_2$ and a subgraph $H$ such that $Δ(F_i)\leq \max\{2,\lceil\frac{Δ-α+6}{2}\rceil\}$ for $i=1,2$ and $Δ(H)\leq α-5$.

math.CO↗
arXiv2018

Interpreting Neural Network Judgments via Minimal, Stable, and Symbolic Corrections

We present a new algorithm to generate minimal, stable, and symbolic corrections to an input that will cause a neural network with ReLU activations to change its output. We argue that such a correction is a useful way to provide feedback to a user when the network's output is different from a desired output. Our algorithm generates such a correction by solving a series of linear constraint satisfaction problems. The technique is evaluated on three neural network models: one predicting whether an applicant will pay a mortgage, one predicting whether a first-order theorem can be proved efficiently by a solver using certain heuristics, and the final one judging whether a drawing is an accurate rendition of a canonical drawing of a cat.

cs.LG↗
arXiv2018

Exploring neutrino mass and mass hierarchy in the scenario of vacuum energy interacting with cold dark matter

We investigate the constraints on total neutrino mass in the scenario of vacuum energy interacting with cold dark matter. We focus on two typical interaction forms, i.e., $Q=βHρ_{\rm c}$ and $Q=βHρ_Λ$. To avoid the occurrence of large-scale instability in interacting dark energy cosmology, we adopt the parameterized post-Friedmann approach to calculate the perturbation evolution of dark energy. We employ observational data, including the Planck cosmic microwave background temperature and polarization data, baryon acoustic oscillation data, a JLA sample of type Ia supernovae observation, direct measurement of the Hubble constant, and redshift space distortion data. We find that, compared with those in the $Λ$CDM model, much looser constraints on $\sum m_ν$ are obtained in the $Q=βHρ_{\rm c}$ model, whereas slightly tighter constraints are obtained in the $Q=βHρ_Λ$ model. Consideration of the possible mass hierarchies of neutrinos reveals that the smallest upper limit of $\sum m_ν$ appears in the degenerate hierarchy case. By comparing the values of $χ^2_{\rm min}$, we find that the normal hierarchy case is favored over the inverted one. In particular, we find that the difference $Δχ^2_{\rm min} \equiv χ^2_{\rm IH; min}-χ^2_{\rm NH; min}> 2$ in the $Q=βHρ_{\rm c}$ model. In addition, we find that $β=0$ is consistent with the current observations in the $Q=βHρ_{\rm c}$ model, and $β< 0$ is favored at more than the $1σ$ level in the $Q=βHρ_Λ$ model.

astro-ph.CO↗
arXiv2018

Natural explanation for 21cm absorption signals via axion-induced cooling

The EDGES Collaboration has reported an anomalously strong 21cm absorption feature corresponding to the era of first star formation, which may indirectly betray the influence of dark matter during this epoch. We demonstrate that, by virtue of the ability to mediate cooling processes whilst in the condensed phase, a small amount of axion dark matter can explain these observations within the context of standard models of axions and axion-like-particles. The EDGES best-fit result favours an axion-like-particles mass in the (10, 450) meV range, which can be compressed for the QCD axion to (100, 450) meV in the absence of fine tuning. Future experiments and large scale surveys, particularly the International Axion Observatory (IAXO) and EUCLID, should have the capability to directly test this scenario.

hep-ph↗
arXiv2018

$T$-$Q$ relations for the integrable two-species asymmetric simple exclusion process with open boundaries

We study the integrable two-species asymmetric simple exclusion process (ASEP) for two inequivalent types of open, non particle conserving boundary conditions. Employing the nested off-diagonal Bethe ansatz method, we construct for each case the corresponding homogeneous $T$-$Q$ relations and obtain the Bethe ansatz equations. Numerical checks for small system sizes show completeness for some Bethe ansatz equations, and partial completeness for others.

math-ph↗
arXiv2018

Testing photometric redshift measurements with filter definition of the Chinese Space Station Optical Survey (CSS-OS)

The Chinese Space Station Optical Survey (CSS-OS) is a major science project of the Space Application System of the China Manned Space Program. This survey is planned to perform both photometric imaging and slitless spectroscopic observations, and it will focus on different cosmological and astronomical goals. Most of these goals are tightly dependent on the accuracy of photometric redshift (photo-z) measurement, especially for the weak gravitational lensing survey as a main science driver. In this work, we assess if the current filter definition can provide accurate photo-z measurement to meet the science requirement. We use the COSMOS galaxy catalog to create a mock catalog for the CSS-OS. We compare different photo-z codes and fitting methods that using the spectral energy distribution (SED) template-fitting technique, and choose to use a modified LePhare code in photo-z fitting process. Then we investigate the CSS-OS photo-z accuracy in certain ranges of filter parameters, such as band position, width, and slope. We find that the current CSS-OS filter definition can achieve reasonably good photo-z results with sigma_z~0.02 and outlier fraction ~3%.

astro-ph.IM↗
arXiv2018

Constraints on brane inflation after Planck 2015: Impacts of the latest local measurement of the Hubble constant

We investigate the observational constraints on three typical brane inflation models by considering the latest local measurement of the Hubble constant in the global fit. We also employ other observational data, including the Planck 2015 CMB data, the BICEP2/Keck Array B-mode data, and the baryon acoustic oscillations data, in our analysis. Previous studies have shown that the addition of the latest local $H_{0}$ measurement favors a larger spectral index, and can exert a significant influence on the model selection of inflation. In this work, we investigate its impacts on the status of brane inflation models. We find that, when the direct $H_{0}$ measurement is considered, the prototype model of brane inflation is still in good agreement with the current observational data within the $2σ$ level range. For the KKLMMT model, the consideration of the $H_{0}$ measurement allows the range of the parameter $β$ to be amplified to ${\cal O}(10^{-2})$, which slightly alleviates the fine-tuning problem. For the IR DBI model, the addition of the $H_{0}$ measurement does not provide a better fit. These results show that the consideration of the new $H_{0}$ prior can exert a considerable influence on the brane inflation models. At last, we show that, when $β\lesssim 1.1$, the equilateral non-Gaussianity in the IR DBI inflation model is compatible with the current CMB data at the 1$σ$ level.

astro-ph.CO↗
arXiv2018

An efficient quantum circuits optimizing scheme compared with QISKit

Recently, the development of quantum chips has made great progress-- the number of qubits is increasing and the fidelity is getting higher. However, qubits of these chips are not always fully connected, which sets additional barriers for implementing quantum algorithms and programming quantum programs. In this paper, we introduce a general circuit optimizing scheme, which can efficiently adjust and optimize quantum circuits according to arbitrary given qubits' layout by adding additional quantum gates, exchanging qubits and merging single-qubit gates. Compared with the optimizing algorithm of IBM's QISKit, the quantum gates consumed by our scheme is 74.7%, and the execution time is only 12.9% on average.

cs.ET↗
arXiv2018

Prospect for cosmological parameter estimation using future Hubble parameter measurements

We constrain cosmological parameters using only Hubble parameter data and quantify the impact of future Hubble parameter measurements on parameter estimation for the most typical dark energy models. We first constrain cosmological parameters using 52 current Hubble parameter data including the Hubble constant measurement from the Hubble Space Telescope. Then we simulate the baryon acoustic oscillation signals from WFIRST (Wide-Field Infrared Survey Telescope) covering the redshift range of $z\in [0.5, 2]$ and the redshift drift data from E-ELT (European Extremely Large Telescope) in the redshift range of $z\in [2,5]$. It is shown that solely using the current Hubble parameter data could give fairly good constraints on cosmological parameters. Compared to the current Hubble parameter data, with the WFIRST observation the $H(z)$ constraints on dark energy would be improved slightly, while with the E-ELT observation the $H(z)$ constraints on dark energy is enormously improved.

astro-ph.CO↗
arXiv2018

Probing signatures of bounce inflation with current observations

The aim of this paper is to probe the features of the bouncing cosmology with the current observational data. Basing on bounce inflation model, with high derivative term, we propose a general parametrization of primordial power spectrum which includes the typical bouncing parameters, such as bouncing time-scale, and energy scale. By applying Markov Chain Monto Carlo analysis with current data combination of Planck 2015, BAO and JLA, we report the posterior probability distributions of the parameters. We find that, bouncing models can well explain CMB observations, especially the deficit and oscillation on large scale in TT power spectrum.

astro-ph.CO↗
arXiv2018

Finite- Size Scaling of Correlation Function

We propose the finite-size scaling of correlation function in a finite system near its critical point. At a distance ${\bf r}$ in the finite system with size $L$, the correlation function can be written as the product of $|{\bf r}|^{-(d-2+η)}$ and its finite-size scaling function of variables ${\bf r}/L$ and $tL^{1/ν}$, where $t=(T-T_c)/T_c$. The directional dependence of correlation function is nonnegligible only when $|{\bf r}|$ becomes compariable with $L$. This finite-size scaling of correlation function has been confirmed by correlation functions of the Ising model and the bond percolation in two-diemnional lattices, which are calculated by Monte Carlo simulation. We can use the finite-size scaling of correlation function to determine the critical point and the critical exponent $η$.

cond-mat.stat-mech↗
arXiv2018

Covariate-Adjusted Tensor Classification in High-Dimensions

In contemporary scientific research, it is of great interest to predict a categorical response based on a high-dimensional tensor (i.e. multi-dimensional array) and additional covariates. This mixture of different types of data leads to challenges in statistical analysis. Motivated by applications in science and engineering, we propose a comprehensive and interpretable discriminant analysis model, called CATCH model (in short for Covariate-Adjusted Tensor Classification in High-dimensions), which efficiently integrates the covariates and the tensor to predict the categorical outcome. The CATCH model jointly models the relationships among the covariates, the tensor predictor, and the categorical response. More importantly, it preserves and utilizes the structures of the data for maximum interpretability and optimal prediction. To tackle the new computational and statistical challenges arising from the intimidating tensor dimensions, we propose a penalized approach to select a subset of tensor predictor entries that has direct discriminative effect after adjusting for covariates. We further develop an efficient algorithm that takes advantage of the tensor structure. Theoretical results confirm that our method achieves variable selection consistency and optimal classification error, even when the tensor dimension is much larger than the sample size. The superior performance of our method over existing methods is demonstrated in extensive simulated and real data examples.

stat.ME↗
arXiv2018

Gravitational clustering of cosmic relic neutrinos in the Milky Way

The standard model of cosmology predicts the existence of cosmic neutrino background in the present Universe. To detect cosmic relic neutrinos in the vicinity of the Earth, it is necessary to evaluate the gravitational clustering effects on relic neutrinos in the Milky Way. Here we introduce a reweighting technique in the N-one-body simulation method, so that a single simulation can yield neutrino density profiles for different neutrino masses and phase space distributions. In light of current experimental results that favor small neutrino masses, the neutrino number density contrast around the Earth is found to be almost proportional to the square of neutrino mass. The density contrast-mass relation and the reweighting technique are useful for studying the phenomenology associated with the future detection of the cosmic neutrino background.

astro-ph.CO↗
arXiv2018

Impacts of gravitational-wave standard siren observation of the Einstein Telescope on weighing neutrinos in cosmology

We investigate the impacts of the gravitational-wave (GW) standard siren observation of the Einstein Telescope (ET) on constraining the total neutrino mass. We simulate 1000 GW events that would be observed by the ET in its 10-year observation by taking the standard $Λ$CDM cosmology as a fiducial model. We combine the simulated GW data with other cosmological observations including cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and type Ia supernovae (SN). We consider three mass hierarchy cases for the neutrino mass, i.e., normal hierarchy (NH), inverted hierarchy (IH), and degenerate hierarchy (DH). Using Planck+BAO+SN, we obtain $\sum m_ν<0.175$ eV for the NH case, $\sum m_ν<0.200$ eV for the IH case, and $\sum m_ν<0.136$ eV for the DH case. After considering the GW data, i.e., using Planck+BAO+SN+GW, the constraint results become $\sum m_ν<0.151$ eV for the NH case, $\sum m_ν<0.185$ eV for the IH case, and $\sum m_ν<0.122$ eV for the DH case. We find that the GW data can help reduce the upper limits of $\sum m_ν$ by 13.7%, 7.5%, and 10.3% for the NH, IH, and DH cases, respectively. In addition, we find that the GW data can also help break the degeneracies between $\sum m_ν$ and other parameters. We show that the GW data of the ET could greatly improve the constraint accuracies of cosmological parameters.

astro-ph.CO↗
arXiv2018

A convenient basis for the Izergin-Korepin model

We propose a convenient orthogonal basis of the Hilbert space for the Izergin-Korepin model (or the quantum spin chain associated with the $A^{(2)}_{2}$ algebra). It is shown that the monodromy-matrix elements acting on the basis take relatively simple forms (c.f. acting on the original basis ), which is quite similar as that in the so-called F-basis for the quantum spin chains associated with $A$-type (super)algebras. As an application, we present the recursive expressions of Bethe states in the basis for the Izergin-Korepin model.

math-ph↗