Vector field effective action in the open superstring theory

Using a path integral technique we find a closed expression (to all orders in α′) for the abelian, constant field strenght limit of the (tree) effective action for the massless vector field in the open superstring theory. The result is a modification of the Born-Infeld action found in the Bose string theory case. One-loop correction to the effective action is computed and shown to be finite if the gauge group is SO(32). It is demonstrated how the on-shell superstring scattering amplitudes can be calculated in the path-integral approach. We determine the leading (O(α') and O(α′²)) terms in the full non-abelian effective action starting from the known results for the 3-point and 4-point amplitudes. We find that because of the equivalence theorem the coefficients of some of the invariant structures in the effective lagrangian cannot be fixed from the S-matrix. In the path integral approach this ambiguity manifests itself as a 2d renormalization scheme (and Weyl gauge choice) ambiguity. We also discuss the leading terms in the gravitational effective actions in the closed (super) string theories and point out that whether or not the R² terms form the “Gauss-Bonnet” combination depends on choice of a renormalization (massless exchange subtraction) scheme.     

Lepton asymmetry and neutrino oscillations interplay

We discuss the interplay between lepton asymmetry L and ν oscillations in the early Universe. Neutrino oscillations may suppress or enhance previously existing L. On the other hand L is capable to suppress or enhance neutrino oscillations. The mechanism of L enhancement in MSW resonant ν oscillations in the early Universe is numerically analyzed. L cosmological effects through ν oscillations are discussed. We discuss how L may change the cosmological BBN constraints on neutrino and show that BBN model with $\nu_e \leftrightarrow \nu_s$ oscillations is extremely sensitive to L - it allows to obtain the most stringent constraints on L value. We discuss also the cosmological role of active-sterile ν mixing and L in connection with the indications about additional relativistic density in the early Universe, pointed out by BBN, CMB and LSS data and the analysis of global ν data.     

Causal horizons in a bouncing universe

As our understanding of the past in a bouncing universe is limited, it becomes difficult to propose a cosmological model which can give some understanding of the causal structure of the bouncing universe. In this article we address the issue related to the particle horizon problem in the bouncing universe models. It is shown that in many models the particle horizon does not exist, and consequently the horizon problem is trivially solved. In some cases a bouncing universe can have a particle horizon and we specify the conditions for its existence. In the absence of a particle horizon the Hubble surface specifies the causal structure of a bouncing universe. We specify the complex relationship between the Hubble surface and the particle horizon when the particle horizon exists. The article also address the issue related to the event horizon in a bouncing universe. A toy example of a bouncing universe is first presented where we specify the conditions which dictate the presence of a particle horizon. Next we specify the causal structures of three widely used bouncing models. The first case is related to quintom matter bounce model, the second one is loop quantum cosmology based bounce model and lastly f(R) gravity induced bounce model. We present a brief discussion on the horizon problem in bouncing cosmologies. We point out that the causal structure of the various bounce models fit our general theoretical predictions.     

Electron scattering from transitional nuclei

An electron scattering experiment on ¹⁸⁸Os, ¹⁹⁰Os, ¹⁹²Os, ¹⁹⁴Pt and ¹⁹⁶Pt has been performed at momentum transfers q = 0.6 to 3.2 fm⁻¹. Transition charge densities have been determined for the low-lying 2⁺, 3⁻ and 4⁺ states. The 2⁺ densities are well reproduced within the framework of the interacting boson model 2, where we have determined the boson densities α_ν, α_π, β_νv and β_π. The 4⁺ transition densities could not be reproduced indicating the need for including a g-boson. The ground and transition charge densities of ¹⁸⁸Os, ¹⁹²Os and ¹⁹⁶Pt have been compared with a microscopic calculation. The total binding energies and the intrinsic wave functions have been calculated for different values of β and γ with the constrained triaxial Hartree-Fock-Bogoliubov method using the finite range interaction D1SA. These energies are interpreted as potential energy surfaces and used in the Bohr hamiltonian in order to obtain the total nuclear wave functions. We obtain very good agreement with experiment. The calculated potential energy surfaces show these nuclei to be γ-soft with a shallow minimum for triaxial deformations and rigid in the β direction.     

New Parameterized Coherent-Entangled State Representation and Its Applications

Based on EPR’s idea of quantum entanglement, new parameterized coherent-entangled states |α,p〉 _μ,ν are introduced in two-mode Fock space, which can be implemented by using a beam splitter. Possible superpositions of |α,p〉 _μ,ν result in some new entangled states. The asymmetric ket-bra integration from |α,p〉 _μ,ν leads to a new one- and two-mode combinatorial squeezing operator with stronger squeezing, which clearly shows the intrinsic relationship between squeezing mechanism and quantum entanglement.     

Implications of Time Varying Cosmological Constant on Kaluza-Klein Cosmological Model

In this paper, the cosmological model with variable $\varLambda= \alpha \frac{\dot{R}^{2}}{R^{2}} + \beta\frac{1}{R^{2}}$ in Kaluza-Klein metric have been studied. Here α and β are dimensionless parameters. The solutions to Einstein field equations which assume that the Universe is filled with perfect fluid have been obtained by using the Gamma Law Equation p=(γ?1)ρ; in which the parameter γ is constant and power law equation A(t)=R ⁿ (t)—where A(t) is scale factor for extra dimension and R(t) is scale factor for space dimensions. The fifth dimension for the radiation dominated phases is more prominent with this model. Other physical parameters i.e. density, pressure, deceleration parameter, Hubble parameter have been determined for this model. It is observed physical parameters depends upon constants α, β and n. Neo-classical tests have also been studied in this paper.     

具有广义协变的包含重力场贡献的重力场方程

利用半度规λ^(α)_μ表象的数学工具定义一个对广义坐标具有协变形式的重力场矢势函数ω^(α)_μ≡-cλ^(α)_μ，给出一个具有广义协变的包含重力场贡献的重力场方程R_μν-g_μνR/2+Λg_μν=8πG(T^(Ⅰ)_μν+T^(Ⅱ)_μν) 关键词： 重力场方程 协变形式 能量-动量张量 量子化     

Proton decay in supersymmetric models

We discuss proton decay in supersymmetric theories. We find that it is possible to obtain rates which are comparable with those of standard SU(5). In the presence of a discrete symmetry which occurs in an SU(5) supersymmetric unified model we obtain a definite prediction for the dominant decay mode, i.e. p → K^+?ν_μ and n → K^0?ν_μ.     

Higher-dimensional perfect fluids and empty singular boundaries

In order to find out whether empty singular boundaries can arise in higher dimensional Gravity, we study the solution of Einstein’s equations consisting in a (N + 2)-dimensional static and hyperplane symmetric perfect fluid satisfying the equation of state ρ = ηp, being η an arbitrary constant and N ≥ 2. We show that this spacetime has some weird properties. In particular, in the case η > −1, it has an empty (without matter) repulsive singular boundary. We also study the behavior of geodesics and the Cauchy problem for the propagation of massless scalar field in this spacetime. For η > 1, we find that only vertical null geodesics touch the boundary and bounce, and all of them start and finish at z = ∞; whereas non-vertical null as well as all time-like ones are bounded between two planes determined by initial conditions. We obtain that the Cauchy problem for the propagation of a massless scalar field is well-posed and waves are completely reflected at the singularity, if we only demand the waves to have finite energy, although no boundary condition is required.     

The $$B\rightarrow \bar{K}\pi \ell \ell $$ distribution at low hadronic recoil

The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable Λ and G and bulk viscosity have been considered. We discuss three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity (ξ), cosmological constant (Λ), gravitational parameter (G) and deceleration parameter (q) for different equations of state. The model describes an accelerating Universe for large value of time t, wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.     

An Analytic Approximation for Researching Tunneling Rate from Black Hole in Proca Field

The analytic solution of a static spherical symmetrical Proca black hole is discussed in this paper. As in the massive vector field, Proca black hole can be considered as the analogy of RN background plus a perturbation with the same order as μ ² due to the mass of vector particle μ satisfying μ ² ? 1. Through the action of Proca field, we find the analytic form with the first and arbitrary order approximation. Furthermore, we divide the results into 3 groups according to the real zero solutions of the background (i.e., spacetime in massless vector field). Finally we analyze the Hawking radiation of such black hole, which is significant for constructing black hole thermodynamic.     

Expanding and collapsing scalar field thin shell

This paper deals with the dynamics of scalar field thin shell in the Reissner-Nordstr?m geometry. The Israel junction conditions between Reissner-Nordstr?m spacetimes are derived, which lead to the equation of motion of scalar field shell and Klien–Gordon equation. These equations are solved numerically by taking scalar field model with the quadratic scalar potential. It is found that solution represents the expanding and collapsing scalar field shell. For the better understanding of this problem, we investigate the case of massless scalar field (by taking the scalar field potential zero). Also, we evaluate the scalar field potential when p is an explicit function of R. We conclude that both massless as well as massive scalar field shell can expand to infinity at constant rate or collapse to zero size forming a curvature singularity or bounce under suitable conditions.     

Big bounce from spin and torsion

The Einstein-Cartan-Sciama-Kibble theory of gravity naturally extends general relativity to account for the intrinsic spin of matter. Spacetime torsion, generated by spin of Dirac fields, induces gravitational repulsion in fermionic matter at extremely high densities and prevents the formation of singularities. Accordingly, the big bang is replaced by a bounce that occurred when the energy density e μ gT⁴{\epsilon \propto gT^4} was on the order of n²/m_Pl²{n^2/m_{\rm Pl}^2} (in natural units), where n μ gT³{n \propto gT^3} is the fermion number density and g is the number of thermal degrees of freedom. If the early Universe contained only the known standard-model particles (g ≈ 100), then the energy density at the big bounce was about 15 times larger than the Planck energy. The minimum scale factor of the Universe (at the bounce) was about 10³² times smaller than its present value, giving ≈ 50 μm. If more fermions existed in the early Universe, then the spin-torsion coupling causes a bounce at a lower energy and larger scale factor. Recent observations of high-energy photons from gamma-ray bursts indicate that spacetime may behave classically even at scales below the Planck length, supporting the classical spin-torsion mechanism of the big bounce. Such a classical bounce prevents the matter in the contracting Universe from reaching the conditions at which a quantum bounce could possibly occur.     

Renormalization group and dynamical symmetry breakdown in abelian gauge theories

Generalized renormalization group equations are used to analyze the dynamical mechanism of particle mass generation in terms of the Cornwall-Norton model both with and without cut-off. We look for solutions which contain non-zero physical masses of the two fermions (m₁, m₂) and of one of the vector bosons (μ) when the bare masses m_1Λ, m_2Λ, μ_Λ approach zero. For a theory without cut-off we obtain results which are similar to those of Cornwall. For a theory with cut-off the mass generation mechanism may only occur when a bare coupling constant α_Λ of the A_μ vector boson, which remains massless, exceeds some critical value α_c. In this case the fermion masses turn out to be of the superconductivity type.The model's “memory” of the nature of spontaneous symmetry breaking lim_{m1Λ, m2Λ → 0}m_1Λ/m_2Λ ≠ 1 is an indispensible factor for the vector boson to acquire a mass.     

Limits on neutrino oscillations derived from the ratio of neutral- to charged-current cross sections of neutrinos measured at the CERN SPS NBB

We present an analysis, in terms of neutrino oscillations, of the recent measurements of the ratio R of neutral-current to charged-current neutrino cross sections performed by the CDHS and CHARM Collaborations at the CERN Super Proton Synchroton narrow-band beam. The measurementswere aimed at the determination of sin² θ_w. Our analysis is based on the observation that muon-neutrino oscillations would decrease the number of interactions with a muon in the final state. The effect of oscillations on R can be studied, comparing the actual measurements with the value of R predicted by an independent measurement of sin² θ_w. Limits on ν_μ−ν_e, ν_μ−ν_τ, and ν_μ−ν_x oscillations are presented. They refer to a region of high mass squared difference of the two oscillating neutrinos (Δm² > 3 eV²). For high Δm² the limits on the mixing angle θ are very restrictive. In particular, for the transition ν_μ−ν_x (x≠e, τ) they represent the best available results for large intervals in Δm².     

Friedmann Cosmology with Matter Creation in Modified <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>) Gravity

The theoretical and observational consequences of thermodynamics of open systems which allow matter creation, are investigated in modified f(R, T) (R is the Ricci scalar and T is the trace of energy-momentum tensor) theory of gravity within the framework of a flat Friedmann-Robertson-Walker line element. The simplest model f(R, T)=R+2f(T) with “gamma-law” equation of state p = (γ?1)ρ is assumed to obtain the exact solution. A power-law expansion model is proposed by considering the natural phenomenological particle creation rate ψ = 3β n H, where β is a pure number of the order of unity, n the particle number density and H is the Hubble parameter. A Big Rip singularity is observed for γ<0 describing phantom cosmology. The accelerated expansion of the Universe is driven by the particle creation. The density parameter shows the negative curvature of the Universe due to particle creation. The entropy increases with the evolution of the Universe. Some kinematics tests such as lookback time, luminosity distance, proper distance, angular diameter versus redshift are discussed in detail to observe the role of particle creation in early and late time evolution of the Universe.     

Supersymmetry and classical solutions

We obtain classical solutions to the field equations of the massless supersymmetric Wess-Zumino model and to the field equations of the interacting SU(2) gauge supermultiplet. This is done by applying finite supersymmetry transformations to the known solutions of the scalar field equation with ?⁴ interaction and the Yang-Mills field equations. The relevance of supersymmetry to the solution of classical field equations involving anticommuting fermion fields is discussed.     

The casimir effect as a screening effect in quantized field theory

We study the vacuum energy and the vacuum force in a system of quantized scalar fields (massive and massless) in interaction with a given screening medium. Regularization of the energy is studied and the types of determinable forces are clarified. The Casimir effect—the attraction between two conducting plates in a vacuum, and its extension to different geometries —is re-examined in this framework. Instead of the puzzling repulsion for a spherical shell conductor, an attractive force is obtained in our case. As a by-product, we obtain a potential energy between two balls of large screening power and at remote distance R, ?a₁a₂/4πR³, where a_i are the ball radii.