Vacuum microarc

The physics of stationary vacuum microarc in a wide interelectrode gap with the perveance corresponding to a geometry of the Müller electron projector type and the Langmuir-Blodgett function α²≥5 is considered on a qualitative level. Under these conditions, the electric field at the cathode can exhibit a significant (severalfold) increase due to a positive space charge of microarc, which makes field electron emission possible. The most important features of the continuity equation, Poisson equation, and thermal conductivity equation describing this system are considered.     

Vacuum Instability

NAbstract Following fresh attempts to resolve the problem of the energy density of the vacuum, we reconsider the case where the cosmological constant is derived from a higher-dimensional version of general relativity, and interpret the gauge-dependence of Λ as a dynamical effect. This leads to a relation between the change in Λ and the line element (action) which is independent of gauge choices and fundamental constants: dΛds² = −6. This implies that the (classical) vacuum is unstable, with implications for particle production.     

The Light-Front Vacuum

We discuss the relation between the trivial light-front vacuum and the non-trivial Heisenberg vacuum.     

Tensor Vacuum Susceptibility

Using a nonlocal four-quark condensate in the framework of the modified global colour symmetry model, we determine the tensor vacuum susceptibility needed in the QCD sum rule external field method for the coupling of tensor current to hadron and compare it with the previous estimations.     

非微扰QCD真空中夸克真空凝聚的结构(英文)

基于Dyson-Schwinger方程(DSEs)所确定的夸克传播子和算符成积展开(OPE),在彩虹近似下,预言了QCD真空中非定域夸克真空凝聚的结构。这种结构由夸克自能函数Af和Bf决定,通过数值求解DSEs就可以得到这些自能函数。但是,直接数值求解DSEs方程非常复杂,这里采用Roberts和Williams提出的参数化方法,用参数化的夸克传播函数σf v(p2)和σf s(p2)计算夸克自能函数。同时,也计算了定域的夸克真空凝聚值,夸克胶子混合的真空凝聚值,以及夸克的虚度。理论预言和计算结果均与标准QCD求和定则、格点QCD和瞬子模型的理论结果大致相符。和这些模型的结果相比,参数化方法得到的轻夸克(u,d,s)的定域真空凝聚偏大,这主要是由于模型依赖导致的。与u,d夸克相比,s夸克的真空凝聚比较大,这是因为s夸克自身质量较大的缘故。当然,Roberts-Williams参数化的夸克传播子只是一个经验公式,只能近似描述夸克的传播。     

Vacuum Cerenkov radiation

Within the classical Maxwell-Chern-Simons limit of the standard-model extension, the emission of light by uniformly moving charges is studied confirming the possibility of a Cerenkov-type effect. In this context, the exact radiation rate for charged magnetic point dipoles is determined and found in agreement with a phase-space estimate under certain assumptions.     

Vacuum Susceptibility Calculation

The vector susceptibility is investigated numerically in the Dyson-Schwinger approach. The results agree with those obtained analytically previously by using a simple gluon propagator.     

Vacuum phonon tunneling

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.     

Vacuum Boundary Effects

The Casimir effect is highly dependent on the shape and structure of space boundaries. This dependence is encoded in the variation of vacuum energy with the different types of boundary conditions. We analyze from a global perspective the properties of the Casimir energy as a function on the largest space of the consistent boundary conditions M_F\mathcal{M}_{F} for a massless scalar field confined between to homogeneous parallel plates. In particular, we analyze the analytic properties of this function and point out the existence of a third order phase transition at periodic boundary conditions. We also characterize the boundary conditions which give rise to attractive or repulsive Casimir forces. In the interface between both regimes we find a very interesting family of boundary conditions without Casimir effect, and fully characterize the boundary conditions which do not induce any type of Casimir force.     

Vacuum Susceptibility Calculation

The vector susceptibility is investigated numerically in the Dyson-Schwinger approach. The results agree with those obtained analytically previously by using a simple gluon propagator.     

Vacuum driven accelerated expansion

It has been shown that an improved estimation of the quantum vacuum energy can yield not only theoretically acceptable but also experimentally realistic results. Our idea consists in a straightforward extraction of the gravitationally interacting part of the full quantum vacuum energy by means of gauge transformations. The implementation of this idea has been performed, in the background of a Friedmann‐Lemaître‐Robertson‐Walker geometry, by means of the euclidean version of the effective action formalism, in the language of Schwinger's proper time and Seeley‐DeWitt's heat kernel expansion.     

A Characterization of Vacuum

In this note, we use a Killing vector field on a 4-dimensional Lorentzian space-time (M,g), to obtain sufficient conditions for (M,g) to be a vacuum.     

Entanglement from the Vacuum

We explore the entanglement of the vacuum of a relativistic field by letting a pair of causally disconnected probes interact with the field. We find that, even when the probes are initially non-entangled, they can wind up to a final entangled state. This shows that entanglement persists between disconnected regions in the vacuum. However the probe entanglement, unlike correlations, vanishes once the regions become sufficiently separated. The relation between entropy, correlations and entanglement is discussed.     

Vacuum metrics without symmetry

Vacuum metrics admitting null, geodetic, expanding, shear-free congruences are investigated. A new solution is derived which contains three holomorphic functions of a complex variable. It includes, as special cases, a number of well-known solutions such as those of Kerr and Taub-NUT. In general, however, it admits no Killing vectors.This work was supported in part by Air Force Office of Scientific Research, Office of Aerospace Research, United States Air Force, under AFOSR Grant No. 903-67 and National Aeronautics and Space Administration under NASA Grant No. NGL 44-004-001.     

Vacuum Arc Anode Phenomena

This paper briefly reviews anode phenomena in vacuum arcs, specially experimental work. It discusses, in succession, arc modes at the anode, anode temperature measurements, anode ions, transitions of the arc into various modes (principally the anode spot mode), and theoretical explanations of anode phenomena. The two most common anode modes in a vacuum arc are a low current mode where the anode is basically passive, acting only as a collector of particles emitted from the cathode, and a high current mode with a fully developed anode spot. Characteristically this anode spot has a temperature near the atmospheric boiling point of the anode material and is a copious source of vapor and energetic ions. However, other anode modes can exist. A low current vacuum arc with electrodes of readily sputterable material may emit a flux of sputtered atoms from the anode. Usually this sputtered flux will have little effect upon the vacuum arc, but in certain circumstances it could be significant. A vacuum arc doesn't always transfer directly from a low current mode to the anode spot mode. In appropriate experimental conditions, formation of an anode spot may be preceded by the formation of an anode footpoint. This footpoint is luminous, but much cooler than a true anode spot. Finally, (again in appropriate circumstances) several small anode spots may form instead of one large anode spot. With sufficient increase in arc current or arcing time these will usually combine to form a single large active spot.     

Vacuum stability and supersymmetry

Radiative effects are shown to cause breakdown of the semiclassical ground state in a massless theory of fermions and spinless bosons when the coupling of fermions to bosons is larger than the boson self-coupling. Supersymmetry forms the boundary, in coupling constant space, separating theories with and without stable semiclassical vacua.     

Vacuum ultraviolet radiation source

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 509–512, March, 1991.     

Vacuum condensates of QCD

We study the properties of QCD vacuum state in this paper. The values of various local quark vacuum condensates, quark-gluon mixed vacuum condensates, and the structure of non-local quark vacuum condensate are predicted by the solution of Dyson-Schwinger Equations in "rainbow" approximation with three sets of different parameters for effective gluon propagator. The light quark virtuality is also obtained in a consistent way. Our all theoretical results here are in good agreement with the empirical values used widely in literature and many other theoretical calculations.