arXiv subjects

Feng Wu

Publications and source records attributed to Feng Wu.

At least 271 records · Page 15Linked to original sources

arXiv2014

Superconducting anisotropy in the electron-doped high-T$_{c}$ superconductors Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$

We report superconducting anisotropy measurements in the electron-doped high-$T_{c}$ superconductors (HTSCs) Pr$_{2-x}$Ce$_{x}$CuO$_{4-y}$ (PCCO, $x$ = 0.15 and 0.17) with applied magnetic field ($H_{0}$) up to 28 T. Our results show that the upper critical field [$H_{c2}(T)$] is highly anisotropic, and as temperature $T$ $\rightarrow$ 0 the value of it at $H_{0}$ $\parallel$ $c$ [$H_{c2,\parallel c}$(0)] is far less than the Pauli limit, which is very different from that at $H_{0}$ $\perp$ $c$. The $H_{c2}(0)$ character along with the evaluated zero $T$ coherence length $[ξ_{ab(c)}(0)]$ and penetration depth $[λ_{ab(c)}(0)]$ is compared with those of the hole-doped cuprate HTSCs and typical Fe-based superconductors. We find that the low temperature anisotropic character of PCCO is rather similar to that of hole-doped cuprate HTSCs, but apparently larger than that of typical Fe-based superconductors. This study also proves a new sensitive probe of detecting rich properties of unconventional superconductors with the use of the resonant frequency of a NMR probe circuit.

cond-mat.supr-con↗

arXiv2013

Regret-Based Multi-Agent Coordination with Uncertain Task Rewards

Many multi-agent coordination problems can be represented as DCOPs. Motivated by task allocation in disaster response, we extend standard DCOP models to consider uncertain task rewards where the outcome of completing a task depends on its current state, which is randomly drawn from unknown distributions. The goal of solving this problem is to find a solution for all agents that minimizes the overall worst-case loss. This is a challenging problem for centralized algorithms because the search space grows exponentially with the number of agents and is nontrivial for standard DCOP algorithms we have. To address this, we propose a novel decentralized algorithm that incorporates Max-Sum with iterative constraint generation to solve the problem by passing messages among agents. By so doing, our approach scales well and can solve instances of the task allocation problem with hundreds of agents and tasks.

cs.AI↗

arXiv2013

Aspects of Electrodynamics Modified by Some Dimension-five Lorentz Violating Interactions

Assuming Lorentz symmetry is broken by some fixed vector background, we study the spinor electrodynamics modified by two dimension-five Lorentz-violating interactions between fermions and photons. The effective polarization and magnetization are identified from the modified Maxwell equations, and the theoretical consequences are investigated. We also compute the corrections to the relativistic energy levels of hydrogen atom induced by these Lorentz-violating operators in the absence and presence of uniform external fields in first-order perturbation theory. We find that the hydrogen spectrum is insensitive to the breakdown of Lorentz boost symmetry.

hep-th↗

arXiv2012

Common dependence on earthquake magnitudes for the trapped particles bursts approaching the earthquake

Trapped particles bursts have long been observed to be frequently occurred several hours before earthquakes, especially for strong earthquakes, from several space experiments during past decades. However, the validity of earthquake origin of particles bursts events is still unsolved. In this paper, we firstly reported the frequency distribution and time evolution of particles bursts within different time windows centered around earthquakes for various magnitudes. The results showed nearly the same systematic dependence of particle bursts frequency on earthquake magnitude and characteristic time decay behavior of average number of particles bursts for various magnitudes. These findings should strengthen the validity of earthquake origin of particles bursts and further understanding of particles bursts as possible precursor of earthquake.

physics.space-ph↗

arXiv2012

Rollout Sampling Policy Iteration for Decentralized POMDPs

We present decentralized rollout sampling policy iteration (DecRSPI) - a new algorithm for multi-agent decision problems formalized as DEC-POMDPs. DecRSPI is designed to improve scalability and tackle problems that lack an explicit model. The algorithm uses Monte- Carlo methods to generate a sample of reachable belief states. Then it computes a joint policy for each belief state based on the rollout estimations. A new policy representation allows us to represent solutions compactly. The key benefits of the algorithm are its linear time complexity over the number of agents, its bounded memory usage and good solution quality. It can solve larger problems that are intractable for existing planning algorithms. Experimental results confirm the effectiveness and scalability of the approach.

cs.AI↗

arXiv2010

Nonrelativistic Cousin of QCD

Based on the uniqueness and universality of gravity, it is clear that theories with different dynamical exponents are related in the holographic approach. Concretely, we construct an M-theory background from pure QCD dual and show that a deformed $Sch_{6}^{4}$ geometry is obtained by compactification from the same background. The deformed $Sch_{6}^{4}$ geometry is considered as the geometrical realization of a four-dimensional nonrelativistic field theory. Several aspects of this nonrelativistic field theory are studied in the holographic picture.

hep-th↗

arXiv2009

Higher Derivative Operators in the Noncommutative Schwinger Model

A study of the noncommutative Schwinger model is presented. It is shown that the Schwinger mass is not modified by the noncommutativity of spacetime till the first nontrivial order in the noncommutative parameter. Instead, a higher derivative kinetic term is dynamically generated by the lowest-order vacuum polarization diagrams. We argue that in the framework of the Seiberg-Witten map the feature of non-unitarity for a field theory with space-time noncommutativity is characterized by the presence of higher derivative kinetic terms. The $θ$-expanded version of a unitary theory will not generate the lowest-order higher derivative quadratic terms.

hep-th↗

arXiv2008

TeV Scale Lee-Wick Fields out of Large Extra Dimensional Gravity

We study the gravitational corrections to the Maxwell, Dirac and Klein-Gorden theories in the large extra dimension model in which the gravitons propagate in the (4+n)-dimensional bulk, while the gauge and matter fields are confined to the four-dimensional world. The corrections to the two-point Green's functions of the gauge and matter fields from the exchanges of virtual Kaluza-Klein gravitons are calculated in the gauge independent background field method. In the framework of effective field theory, we show that the modified one-loop renormalizable Lagrangian due to quantum gravitational effects contains a TeV scale Lee-Wick partner of every gauge and matter field as extra degrees of freedom in the theory. Thus the large extra dimension model of gravity provides a natural mechanism to the emergence of these exotic particles which were recently used to construct an extension of the Standard Model.

hep-ph↗

arXiv2008

Correction to the Running of Gauge Couplings out of Extra Dimensional Gravity

We study the gravitational correction to the gauge couplings in the extra dimension model where the gravity propagates in the (4+n)-dimensional bulk. We show by explicit calculation in the background field method that the one-loop correction coming from graviton Kaluza-Klein states is nontrivial and tends to make the theory anti-asymptotically free. For the theory characterized with asymptotic freedom, the correction will induce a nontrivial UV-stable fixed point. This may lead to an interesting possibility that the non-abelian gauge coupling constants $g_2$ and $g_3$ in the SM and that of the gravity $g_κ$ unify at the fixed point in the limit of high energy scale.

hep-ph↗

arXiv2007

The Lee-Wick Fields out of Gravity

We study the Maxwell-Einstein theory in the framework of effective field theories. We show that the modified one-loop renormalizable Lagrangian due to quantum gravitational effects contains a Lee-Wick vector field as an extra degree of freedom in the theory. Thus gravity provides a natural mechanism for the emergence of this exotic particle.

hep-ph↗

arXiv2006

AdS/QCD Phenomenological Models from a Back-Reacted Geometry

We construct a fully back-reacted holographic dual of a four-dimensional field theory which exhibits chiral symmetry breaking. Two possible models are considered by studying the effects of a five-dimensional field, dual to the $q\bar{q}$ operator. One model has smooth geometry at all radii and the other dynamically generates a cutoff at finite radius. Both of these models satisfy Einstein's field equations. The second model has only three free parameters, as in QCD, and we show that this gives phenomenologically consistent results. We also discuss the possibility that in order to obtain linear confinement from a back-reacted model it may be necessary to consider the condensate of a dimension two operator.

hep-ph↗

arXiv2006

Z_3 Symmetry and Neutrino Mixing in Type II Seesaw

Neutrino mixing matrix satisfying the current experimental data can be well described by the HPS tri-bimaximal mixing matrix. We propose that its origin can be understood within the seesaw framework by a hidden condition on the mass matrix of heavy right-handed neutrinos under the transformation of the Abelian finite group Z_3 on the flavor basis. Ignoring CP phases, we show that it can lead to the generic form of the effective light neutrino mass matrix from which the HPS mixing matrix appears naturally, as well as an expeimentally allowed non-zero \sinθ_{13}. We show that the model based on our proposal is in good agreement with the current experimental data.

hep-ph↗

arXiv2006

Embedding Flipped SU(5) into SO(10)

We embed the flipped SU(5) models into the SO(10) models. After the SO(10) gauge symmetry is broken down to the flipped SU(5) \times U(1)_X gauge symmetry, we can split the five/one-plets and ten-plets in the spinor \mathbf{16} and \mathbf{\bar{16}} Higgs fields via the stable sliding singlet mechanism. As in the flipped SU(5) models, these ten-plet Higgs fields can break the flipped SU(5) gauge symmetry down to the Standard Model gauge symmetry. The doublet-triplet splitting problem can be solved naturally by the missing partner mechanism, and the Higgsino-exchange mediated proton decay can be suppressed elegantly. Moreover, we show that there exists one pair of the light Higgs doublets for the electroweak gauge symmetry breaking. Because there exist two pairs of additional vector-like particles with similar intermediate-scale masses, the SU(5) and U(1)_X gauge couplings can be unified at the GUT scale which is reasonably (about one or two orders) higher than the SU(2)_L \times SU(3)_C unification scale. Furthermore, we briefly discuss the simplest SO(10) model with flipped SU(5) embedding, and point out that it can not work without fine-tuning.

hep-ph↗

arXiv2006

Three Flavour QCD from the Holographic Principle

Building on recent research into five-dimensional holographic models of QCD, we extend this work by including the strange quark with an SU(3)_L\times SU(3)_R gauge symmetry in the five-dimensional theory. In addition we deform the naive $AdS$ metric with a single parameter, thereby breaking the conformal symmetry at low energies. The vector and axial vector sectors are studied in detail and both the masses and decay constants are calculated with the additional parameters. It is shown that with a single extra degree of freedom, exceptional agreement with experimental results can be obtained in the light quark sector while the kaon sector is found to give around 10% agreement with lattice results. We propose some simple extensions to this work to be taken up in future research.

hep-ph↗

arXiv2006

Physical foundation of the mathematical concepts in the nonstandard analysis theory of turbulence

The physical foundation of the main mathematical concepts in the nonstandard analysis theory of turbulence are presented and discussed. The basic fact is that there does not exist the absolute zero fluid-volume. Therefore, the corresponding physical object to the absolute point is just the uniform fluid-particle. The fluid-particle, in general, corresponds to the monad. The uniform fluid-particle corresponds to the uniform monad, the nonuniform fluid-particle to the nonuniform monad. There are two kinds of the differentiations, one based on the absolute point, another based on the monad. The former is adopted in the Navier-Stokes equations, the latter in the fundamental equations, the closed forms are the equations (7)-(11) in this article, in the nonstandard analysis theory of turbulence. The continuity of fluid is shown by virtue of the concepts of the fluid-particle and fluid-particle in lower level. The character of the continuity in two cases, the standard and nonstandard analysis, is presented in the paper. And the difference in the discretization between the Navier-Stokes equations and the equations (7)-(11) is pointed out too.

physics.flu-dyn↗

arXiv2005

Some Important Concepts in Nonstandard Analysis Theory of Turbulence(The revised)

Some important concepts in the nonstandard analysis theory of turbulence are presented in this article. The structure of point, on which differential equations are defined, is analyzed. The distinction between the uniform point and the non-uniform point, as well as between the standard point and the nonstandard point, is showed. A new kind of equations, which differ essentially from those in existent theory, is emphasized. These new equations can hold at non-uniform points. The applicability of the Navier-Stokes equations to turbulence is discussed. Some illustrations of the nonstandard analysis theory of turbulence are given too.

physics.flu-dyn↗

arXiv2005

Strong Phases in the Decays B to pi pi

Two sources of strong phases in the decays $B$ to $ππ$ are identified: (1) "quasi-elastic scattering" corresponding to intermediate states like $ππ$ and $ρρ$, (2) ``$c\bar{c}$'' corresponding to intermediate states like $D\bar{D}$ and $D^{*}\bar{D}^{*}$. Possibilities of using data to identify these two sources are discussed and illustrated. Present data suggests both sources may be significant.

hep-ph↗

arXiv2005

Governing Equations of Compressible Turbulence

By the nonstandard analysis theory of turbulence, the governing equations of compressible turbulence are given. The equations can hold at non-uniform points, in fact, are new kind of equations. There are three choices. In the choice one, the second-order infinitesimal quantities are neglected, the closed equations about the point(monad)-average quantities are obtained. In other two choices, the closed equations, in which the third-order infinitesimal quantities are omitted, are given and about the instantaneous, point-averaged and fluctuant quantities.

physics.flu-dyn↗