arXiv subjects

Xu Feng

Publications and source records attributed to Xu Feng.

At least 73 records · Page 4Linked to original sources

arXiv2022

Lattice QCD Study of Transverse-Momentum Dependent Soft Function

In this work, we perform a lattice QCD study of the intrinsic, rapidity-independent soft function within the framework of large momentum effective theory. The computation is carried out using a gauge ensemble of $N_f=2+1+1$ clover-improved twisted mass fermion. After applying an appropriate renormalization procedure and the removal of significant higher-twist contamination, we obtain the intrinsic soft function that is comparable to the one-loop perturbative result at large external momentum. The determination of the nonperturbative soft function from first principles is crucial to sharpen our understanding of the processes with small transverse momentum such as the Drell-Yan production and the semi-inclusive deep inelastic scattering. Additionally, we calculate the Collins-Soper evolution kernel using the quasi-transverse-momentum-dependent wave function as input.

hep-lat↗

arXiv2022

In vivo stiffness measurement of epidermis, dermis, and hypodermis using broadband Rayleigh-wave optical coherence elastography

Traveling-wave optical coherence elastography (OCE) is a promising technique to measure the stiffness of biological tissues. While OCE has been applied to relatively homogeneous samples, tissues with significantly varying elasticity through depth pose a challenge, requiring depth-resolved measurement with sufficient resolution and accuracy. Here, we develop a broadband Rayleigh-wave OCE technique capable of measuring the elastic moduli of the 3 major skin layers (epidermis, dermis, and hypodermis) reliably by analyzing the dispersion of leaky Rayleigh surface waves over a wide frequency range of 0.1-10 kHz. We show that a previously unexplored, high frequency range of 4-10 kHz is critical to resolve the thin epidermis, while a low frequency range of 0.2-1 kHz is adequate to probe the dermis and deeper hypodermis. We develop a dual bilayer-based inverse model to determine the elastic moduli in all 3 layers and verify its high accuracy with finite element analysis and skin-mimicking phantoms. Finally, the technique is applied to measure the forearm skin of healthy volunteers. The Young's modulus of the epidermis (including the stratum corneum) is measured to be ~ 4 MPa at 4-10 kHz, whereas Young's moduli of the dermis and hypodermis are about 40 and 15 kPa, respectively, at 0.2-1 kHz. Besides dermatologic applications, this method may be useful for the mechanical analysis of various other layered tissues with sub-mm depth resolution.

physics.med-ph↗

arXiv2022

Pion electric polarizabilities from lattice QCD

We report a first principle lattice calculation of the pion electric polarizability $α_π$ at the physical pion mass. First, we derive the master formula, which relates the pion polarizabilities with the position space hadronic Compton tensor, $\langle π| J_μ(x) J_ν(0) | π\rangle$. The finite volume error of the master formula is exponentially suppressed by the spatial extent of the lattice. Then, the hadronic tensor is calculated using domain wall fermions (DWF) directly at physical pion mass. The gauge ensembles are generated by the RBC-UKQCD collaborations.

hep-lat↗

arXiv2021

Coulomb corrections to pi-pi scattering

The relationship between finite volume multi-hadron energy levels and matrix elements and two particle scattering phase shifts and decays is well known, but the inclusion of long range interactions such as QED is non-trivial. Inclusion of QED is an important systematic error correction to $K\toππ$ decays. In this talk, we present a method of including a truncated, finite-range Coulomb interaction in a finite-volume lattice QCD calculation. We show how the omission caused by the truncation can be restored by an infinite-volume analytic calculation so that the final result contains no power-law finite-volume errors beyond those usually present in Luscher's finite-volume phase shift determination. This approach allows us to calculate the QED corrected infinite-volume phase shift for $ππ$ scattering in Coulomb gauge, a necessary ingredient to $K\toππ$, while neglecting the transverse radiation for now.

hep-lat↗

arXiv2021

Model-Independent Error Mitigation in Parametric Quantum Circuits and Depolarizing Projection of Quantum Noise

Finding ground states and low-lying excitations of a given Hamiltonian is one of the most important problems in many fields of physics. As a novel approach, quantum computing on Noisy Intermediate-Scale Quantum (NISQ) devices offers the prospect to efficiently perform such computations and may eventually outperform classical computers. However, current quantum devices still suffer from inherent quantum noise. In this work, we propose an error mitigation scheme suitable for parametric quantum circuits. This scheme is based on projecting a general quantum noise channel onto depolarization errors. Our method can efficiently reduce errors in quantum computations, which we demonstrate by carrying out simulations both on classical and IBM's quantum devices. In particular, we test the performance of the method by computing the mass gap of the transverse-field Ising model using the variational quantum eigensolver algorithm.

quant-ph↗

arXiv2021

$π-π$ scattering, QED and finite-volume quantization

Using the Coulomb gauge formulation of QED we present a lattice QCD procedure to calculate the $π^+π^+$ scattering phase shift including the effects of the Coulomb potential which appears in this formulation. The approach described here incorporates the effects of relativity and avoids finite-volume corrections that vanish as a power of the volume in which the lattice calculation is performed. This is the first step in developing a complete lattice QCD calculation of the electromagnetic and isospin-breaking light-quark mass contributions to $\varepsilon'$, the parameter describing direct CP violating effects in $K_L\toππ$ decay.

hep-lat↗

arXiv2021

Supershear surface waves reveal prestress and anisotropy of soft materials

Surface waves play important roles in many fundamental and applied areas from seismic detection to material characterizations. Supershear surface waves with propagation speeds greater than bulk shear waves have recently been reported, but their properties are not well understood. In this Letter, we describe theoretical and experimental results on supershear surface waves in rubbery materials. We find that supershear surface waves can be supported in viscoelastic materials with no restriction on the shear quality factor. Interestingly, the effect of prestress on the speed of the supershear surface wave is opposite to that of the Rayleigh surface wave. Furthermore, anisotropy of material affects the supershear wave much more strongly than the Rayleigh surface wave. We offer heuristic interpretation as well as theoretical verification of our experimental observations. Our work points to the potential applications of supershear waves for characterizing the bulk mechanical properties of soft solid from the free surface.

cond-mat.soft↗

arXiv2021

Lattice QCD calculation of the electroweak box diagrams for the kaon semileptonic decays

We present a lattice QCD calculation of the axial $γW$-box diagrams relevant for the kaon semileptonic decays. We utilize a recently proposed method, which connects the electroweak radiative corrections in Sirlin's representation to that in chiral perturbation theory. It allows us to use the axial $γW$-box correction in the SU(3) limit to obtain the low energy constants for chiral perturbation theory. From first principles our results confirm the previously used low energy constants provided by the minimal resonance model with a significant reduction in uncertainties.

hep-lat↗

arXiv2021

Electron-Ion Collider in China

Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a polarization of $\sim$80%) and protons (with a polarization of $\sim$70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2-3) $\times$ 10$^{33}$ cm$^{-2}$ s$^{-1}$. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC. The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies. This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.

nucl-ex↗

arXiv2020

New method for calculating electromagnetic effects in semileptonic beta-decays of mesons

We construct several classes of hadronic matrix elements and relate them to the low-energy constants in Chiral Perturbation Theory that describe the electromagnetic effects in the semileptonic beta decay of the pion and the kaon. We propose to calculate them using lattice QCD, and argue that such a calculation will make an immediate impact to a number of interesting topics at the precision frontier, including the outstanding anomalies in $|V_{us}|$ and the top-row Cabibbo-Kobayashi-Maskawa matrix unitarity.

hep-lat↗

arXiv2020

Finite-volume effects in long-distance processes with massless leptonic propagators

In Ref. [1], a method was proposed to calculate QED corrections to hadronic self energies from lattice QCD without power-law finite-volume errors. In this paper, we extend the method to processes which occur at second-order in the weak interaction and in which there is a massless (or almost massless) leptonic propagator. We demonstrate that, in spite of the presence of the propagator of an almost massless electron, such an infinite-volume reconstruction procedure can be used to obtain the amplitude for the rare kaon decay $K^+\toπ^+ν\barν$ from a lattice quantum chromodynamics computation with only exponentially small finite-volume corrections.

hep-lat↗

arXiv2020

Field sparsening for the construction of the correlation functions in lattice QCD

Two field-sparsening methods, namely the sparse-grid method and the random field selection method, are used in this paper for the construction of the 2-point and 3-point correlation functions in lattice QCD. We argue that, due to the high correlation among the lattice correlators at different field points associated with source, current, and sink locations, one can save a lot of computational time by performing the summation over a subset of the lattice sites. Furthermore, with this strategy, one only needs to store a small fraction of the full quark propagators. It is found that the number of field points can be reduced by a factor of $\sim$100 for the point-source operator and a factor of $\sim$1000 for the Gaussian-smeared operator, while the uncertainties of the correlators only increase by $\sim$15\%. Therefore, with a modest cost of the computational resources, one can approach the precision of the all-to-all correlators using the field-sparsening methods.

hep-lat↗

arXiv2020

Parton distribution functions of $Δ^+$ on the lattice

We perform a first calculation for the unpolarized parton distribution function of the $Δ^+$ baryon using lattice QCD simulations within the framework of Large Momentum Effective Theory. Two ensembles of $N_f=2+1+1$ twisted mass fermions are utilized with a pion mass of 270 MeV and 360 MeV, respectively. The baryon, which is treated as a stable single-particle state, is boosted with momentum $P_3$ with values $\{0.42,0.83,1.25\}$ GeV, and we utilize momentum smearing to improve the signal. The unpolarized parton distribution function of $Δ^+$ is obtained using a non-perturbative renormalization and a one-loop formula for the matching, with encouraging precision. In particular, we compute the $\overline{d}(x)-\overline{u}(x)$ asymmetry and compare it with the same quantity in the nucleon, in a first attempt towards resolving the physical mechanism responsible for generating such asymmetry.

hep-lat↗

arXiv2020

Joint lattice QCD - dispersion theory analysis confirms the quark-mixing top-row unitarity deficit

Recently, the first ever lattice computation of the $γW$-box radiative correction to the rate of the semileptonic pion decay allowed for a reduction of the theory uncertainty of that rate by a factor of $\sim3$. A recent dispersion evaluation of the $γW$-box correction on the neutron also led to a significant reduction of the theory uncertainty, but shifted the value of $V_{ud}$ extracted from the neutron and superallowed nuclear $β$ decay, resulting in a deficit of the CKM unitarity in the top row. A direct lattice computation of the $γW$-box correction for the neutron decay would provide an independent cross-check for this result but is very challenging. Before those challenges are overcome, we propose a hybrid analysis, converting the lattice calculation on the pion to that on the neutron by a combination of dispersion theory and phenomenological input. The new prediction for the universal radiative correction to free and bound neutron $β$-decay reads $Δ_R^V=0.02477(24)$, in excellent agreement with the dispersion theory result $Δ_R^V=0.02467(22)$. Combining with other relevant information, the top-row CKM unitarity deficit persists.

hep-ph↗

arXiv2020

Finite-volume formalism in the $2 \xrightarrow[]{H_I+H_I} 2$ transition: an application to the lattice QCD calculation of double beta decays

We present the formalism for connecting a second-order electroweak $2\xrightarrow[]{H_I+H_I}2$ transition amplitudes in the finite volume (with two hadrons in the initial and final states) to the physical amplitudes in the infinite volume. Our study mainly focus on the case where the low-lying intermediate state consists of two scattering hadrons. As a side product we also reproduce the finite-volume formula for $2\xrightarrow[]{H_I}2$ transition, originally obtained by Briceño and Hansen. With the available finite-volume formalism, we further discuss how to treat with the finite-volume problem in the double beta decays $nn\to pp ee\barν\barν$ and $nn\to pp ee$.

hep-lat↗

arXiv2020

First-principles calculation of electroweak box diagrams from lattice QCD

We present the first realistic lattice QCD calculation of the $γW$-box diagrams relevant for beta decays. The nonperturbative low-momentum integral of the $γW$ loop is calculated using a lattice QCD simulation, complemented by the perturbative QCD result at high momenta. Using the pion semileptonic decay as an example, we demonstrate the feasibility of the method. By using domain wall fermions at the physical pion mass with multiple lattice spacings and volumes, we obtain the axial $γW$-box correction to the semileptonic pion decay, $\Box_{γW}^{VA}\big|_π=2.830(11)_{\mathrm{stat}}(26)_{\mathrm{sys}}\times10^{-3}$, with the total uncertainty controlled at the level of $\sim1$\%. This study sheds light on the first-principles computation of the $γW$-box correction to the neutron decay, which plays a decisive role in the determination of $|V_{ud}|$.

hep-lat↗

arXiv2020

Lattice QCD calculation of the pion charge radius using a model-independent method

We use a method to calculate the hadron's charge radius without model-dependent momentum extrapolations. The method does not require the additional quark propagator inversions on the twisted boundary conditions or the computation of the momentum derivatives of quark propagators and thus is easy to implement. We apply this method to the calculation of pion charge radius $\langle r_π^2\rangle$. For comparison, we also determine $\langle r_π^2\rangle$ with the traditional approach of computing the slope of the form factors. The new method produces results consistent with those from the traditional method and with statistical errors 1.5-1.9 times smaller. For the four gauge ensembles at the physical pion masses, the statistical errors of $\langle r_π^2\rangle$ range from 2.1% to 4.6% by using $\lesssim50$ configurations. For the ensemble at $m_π\approx 340$ MeV, the statistical uncertainty is even reduced to a sub-percent level.

hep-lat↗

arXiv2020

Calculating the Two-photon Contribution to $π^0 \rightarrow e^+ e^-$ Decay Amplitude

We develop a new method that allows us to deal with two-photon intermediate states in a lattice QCD calculation. We apply this method to perform a first-principles calculation of the $π^0 \rightarrow e^+ e^-$ decay amplitude. Both the real and imaginary parts of amplitude are calculated. The imaginary part is compared with the prediction of optical theorem to demonstrate the effectiveness of this method. Our result for the real part of decay amplitude is $19.68(52)(1.10) \ \text{eV}$, where the first error is statistical and the second is systematic.

hep-lat↗