关于μ俘获中有效赝标量耦合项的符号

最近的实验有迹象表明,μ俘获中有效赝标量项的符号与从V-A理论用色散关系求得的相反。本文对这个符号的差别提出了一个可能的解释。在本文中指出,汉密顿量中一很小的赝标耦合项(约为有效赝标耦合项的1/100)即能改变有效赝标耦合项的符号。将这一赝标项加以变换,使之成为普适赝矢量电流的一部分,则可证明新添的这一项对β衰变和π→e+v衰变不产生任何可观察的效应,因而不破坏V-A理论的普适性。文章最后讨论了超子对对有效赝标项符号的影响的问题。     

Ambiguities in chiral-symmetry breaking using the effective potential approach

Using a form of the effective potential for composite operators with a variational approach we show that it is possible to get different directions of the chiral phase transition in QCD. Which one occurs depends on the way the Schwinger-Dyson equation for the fermion self-energy is used in the 2-loop term of the effective potential. We must choose the 2-loop term which agrees with phenomenology in each form of the effective potential.     

Modeling multibody effects in ionic solutions with a concentration dependent dielectric permittivity

We report a new strategy to parametrize effective ion-ion potentials for implicit solvent simulations of charged systems. The effective potential includes a pair term and a Coulomb term that by means of a concentration dependent dielectric permittivity takes into account multibody effects. We demonstrate that this approach allows us to accurately reproduce the solution osmotic properties and the ion coordination up to concentrations of 2.8 M aqueous NaCl.     

SOLUTION OF CHIRAL QCD2 IN 1+1 DIMENSIONAL CURVED SPACETIME

The effective Lagrangian of chiral QCD₂ in 1+1 dimensional curved spacetime is derived by using pathintegral approach.It is shown that vector bosons may have a mass generation and interaction of gravity with gauge field may exist.Besides,the effective Lagrangian contains a term corresponding to the analog of the gauged Wess-Zumino-Witten term in 2-dimensional flat space-time.     

Effective lagrangian and topological interactions in supersolids

We construct a low-energy effective Lagrangian describing zero temperature supersolids. Galilean invariance imposes strict constraints on the form of the effective Lagrangian. We identify a topological term in the Lagrangian that couples superfluid and crystalline modes. For small superfluid fractions, this interaction term is dominant in problems involving defects. As an illustration, we compute the differential cross section of scatterings of low-energy transverse elastic phonons by a superfluid vortex. The result is model independent.     

Band structures of a slowly rotating dipolar Bose-Einstein condensate with a quantized vortex along a one-dimensional optical lattice

We derive the effective Gross-Pitaevskii equation for a slowly rotating dipolar Bose-Einstein condensate (BEC) with a quantized vortex along a one-dimensional optical lattice and calculate its band structures. The band structure of a slowly rotating BEC in a lattice becomes interesting when dipole-dipole interaction (DDI) is involved. Under rotation, a dipolar rotating term emerges from the DDI potential. The dipolar rotating term makes a BEC with an attractive DDI more stable than one with a repulsive DDI. The dipolar rotating term changes and generalizes the definition for the type of BEC, which cannot be simply determined by an s-wave scattering length or an effective contact interaction term. The dipolar rotating term also makes the band structure fascinating and tunable. A so-called swallowtail band structure, i.e., a multi-valued solution due to nonlinear interaction, can either elongate or shrink as the band index increases, in contrast to a non-rotating dipolar BEC system with a monotonic dependence. With the dipolar rotating term, various band structures as well as an attractive BEC without collapse can be easily achieved. We demonstrate that a rotating dipolar BEC system subject to an optical lattice combines features of a crystal and a superfluid and promises wide applications.     

Time Varying Gravitational Constant G via Entropic Force

If the uncertainty principle applies to the Verlinde entropic idea, it leads to a new term in the Newton's second law of mechanics in the Planck's scale. This curious velocity dependent term inspires a frictional feature of the gravity. In this short letter we address that this new term modifies the effective mass and the Newtonian constant as the time dependentquantities. Thus we must have a running on the value of the effective mass on the particle mass m near the holographic screen and the G. This result has a nigh relation with the Dirac hypothesis about the large numbers hypothesis (L.N.H.). We propose that the corrected entropic terms via Verlinde idea can be brought as a holographic evidence for the authenticity of the Dirac idea.     

Symmetry breaking and restoration in Lifshitz type theories

We consider the one-loop effective potential at zero and finite temperature in scalar field theories with anisotropic space-time scaling. For z=2, there is a symmetry breaking term induced at one loop at zero temperature and we find symmetry restoration through a first-order phase transition at high temperature. For z=3, we considered at first the case with a positive mass term at tree level and found no symmetry breaking effects induced at one loop, and then we study the case with a negative mass term at tree level where we cannot conclude about symmetry restoration effects at high temperature because of the imaginary parts that appear in the effective potential for small values of the scalar field.     

Black Hole Fluctuations and Backreaction in Stochastic Gravity

We present a framework for analyzing black hole backreaction from the point of view of quantum open systems using influence functional formalism. We focus on the model of a black hole described by a radially perturbed quasi-static metric and Hawking radiation by a conformally coupled massless quantum scalar field. It is shown that the closed-time-path (CTP) effective action yields a non-local dissipation term as well as a stochastic noise term in the equation of motion, the Einstein–Langevin equation. Once the thermal Green's function in a Schwarzschild background becomes available to the required accuracy, the strategy described here can be applied to obtain concrete results on backreaction. We also present an alternative derivation of the CTP effective action in terms of the Bogolyubov coefficients, thus making a connection with the interpretation of the noise term as measuring the difference in particle production in alternative histories.     

N = 4 SYM low-energy effective action in N = 4 harmonic superspace

We apply the N = 4 harmonic superspace with USp(4) harmonic variables for describing the N = 4 SYM low-energy effective action. Scale invariance and gauge symmetry fix the leading term in the low-energy effective action uniquely, up to a constant. The value of the remaining constant can be fixed by the topological quantization condition for the Wess-Zumino term which is present in the component structure of this action.     

Non-commutative Chiral QCD2 Model

The effective action of chiral QCD2 was studied in two-dimensional non-commutative space-time by usingpath integral approach. It is shown that vector boson has a mass generation and the effective Lagrangian contains aterm corresponding to a Wess-Zumino-Witten-like term.     

Soliton solutions in an effective action for SU(2) Yang—Mills theory: including effects of higher-derivative term

The Skyrme-Faddeev-Niemi (SFN) model, which is an O(3) σ model in three dimensional space, upto fourth-order in the first derivative is regarded as a low-energy effective theory of SU(2) Yang-Mills theory. One can show from the Wilsonian renormalization group argument that the effective action of Yang-Mills theory recovers the SFN in the infrared region. However, the theory contains an additional fourth-order term which destabilizes the soliton solution. In this paper, we derive the second-derivative term perturbatively and show that the SFN model with the second-derivative term possesses soliton solutions. Presented at the International Colloquium “Integrable Systems and Quantum Symmetries”, Prague, 16–18 June 2005.     

The anomalous effective action in three-dimensional gauge theories

Summary We analyse the effective action for gauge fields in odd dimensions, obtained by integrating out the fermions in the Feynman path integral. In particular, we discuss the generation of a Chern-Simons term by massless fermions minimally coupled to an Abelian gauge field. We review two methods of revealing the presence of a Chern-Simons term in the effective action: first, as the consequence of a nontrivial holonomy of the fermionic ground state, then as the result of the generation of an anomalous imaginary part of the effective action. We derive the most general form of the anomalous effective action at the lowest nontrivial order of a derivative expansion in time. We discuss the implications of our analysis for the theory of the fractional quantum Hall effect as well as for the quantization of anomalous theories. To speed up publication, the authors have agreed not to receive proofs which have been supervised by the Scientific Committee.     

Generalized Chern–Simons modified gravity in first-order formalism

We propose a generalization of Chern–Simons (CS) modified gravity in first-order formalism. CS modified gravity action has a term that comes from the chiral anomaly which is Pontryagin invariant. First-order CS modified gravity is a torsional theory and in a space-time with torsion the chiral anomaly includes a torsional topological term called Nieh-Yan invariant. We generalize the CS modified gravity by adding the Nieh-Yan term to the action and find the effective theory. We compare the generalized theory with the first-order CS modified gravity and comment on the similarities and differences.     

Asymptotic results for a persistent diffusion model of Taylor dispersion of particles

We study Taylor diffusion for the case when the diffusion transverse to the bulk motion is a persistent random walk on a one-dimensional lattice. This is mapped onto a Markovian walk where each lattice site has two internal states. For such a model we find the effective diffusion coefficient which depends on the rate of transition among internal states of the lattice. The Markovian limit is recovered in the limit of infinite rate of transitions among internal states; the initial conditions have no role in the leading-order time-dependent term of the effective dispersion, but a strong effect on the constant term. We derive a continuum limit of the problem presented and study the asymptotic behavior of such limit.     

Model for gravity at large distances

We construct an effective model for gravity of a central object at large scales. To leading order in the large radius expansion we find a cosmological constant, a Rindler acceleration, a term that sets the physical scales, and subleading terms. All these terms are expected from general relativity, except for the Rindler term. The latter leads to an anomalous acceleration in geodesics of test particles.     

Systematic effective field theory investigation of spiral phases in hole-doped antiferromagnets on the honeycomb lattice

Motivated by possible applications to the antiferromagnetic precursor of the high-temperature superconductor Na_xCoO₂.yH₂O, we use a systematic low-energy effective field theory for magnons and holes to study different phases of doped antiferromagnets on the honeycomb lattice. The effective action contains a leading single-derivative term, similar to the Shraiman-Siggia term in the square lattice case, which gives rise to spirals in the staggered magnetization. Depending on the values of the low-energy parameters, either a homogeneous phase with four or a spiral phase with two filled hole pockets is energetically favored. Unlike in the square lattice case, at leading order the effective action has an accidental continuous spatial rotation symmetry. Consequently, the spiral may point in any direction and is not necessarily aligned with a lattice direction.     

双光子激光器的量子理论

从双光子激光器三能级模型的微观哈密顿量出发,应用慢变幅度近似和双光子旋波近似,在双光子过程压倒其它辐射过程的情形下,导出二能级双光子模型的等效哈密顿量,从而建立三能级模型与二能级双光子模型的正确关系。得到的等效哈密顿量包含通常讨论中所忽略的光学斯塔克效应项,其系数在一般情形下可与等效互作用常数具有相间的数量级。根据这等效哈密顿量,应用Haken激光理论的标准方法研究定态的阈值,平均光子数,自生频移,光子统计和涨落,并与以前未计及光学斯塔克效应的结果作比较。 关键词：     

Vacuum structure in quantum gravity

The physical interpretation of the Eguchi-Hanson (EH) instanton solution is suggested. This solution describes the tunneling transition which connects vacua with opposite orientations. The diagonal vacuum states are symmetric and antisymmetric superpositions of states with a given orientation. The EH instantons lead to appearance of the induced Einstein term and of the large induced cosmological term in the effective action of the conformal gravity theory.     

Derivative expansions of fermion-number currents

It is shown, by constructing an appropriate homotopy operator on differential forms, that the derivative expansion of a conserved fermion-number current can be written term-by-term as a total divergence, apart from the leading gauged topological term. As a corollary, it is shown that the derivative expansion of the effective action for massive chiral fermions is local and chiral gauge invariant, apart from the gauged Wess-Zumino term which produces the chiral anomaly.