Charge density of the fermionic vacuum

We examine the properties of the matter vacuum in the absence of fermion-photon interactions. We calculate the spatial distribution of the vacuum’s charge density associated with model nuclear interactions and show that even in the absence of photons, the fermionic vacuum can screen off the Coulomb field around a nucleus. For force fields that vary on spatial scales larger than the electron’s Compton wavelength, the resulting charge density is proportional to the spatial derivative of the nuclear force field. As a result we can estimate the electric permeability of the one-dimensional fermionic vacuum to be 5.1 × 10^?7.     

CP noninvariance and the possibility of a sizable neutron electric dipole moment

The electric dipole moment of the neutron will be measured to a precision of 10^?25 e-cm in the near future. We explore a new theoretical possibility that P and CP noninvariance leads to a sizable electric dipole moment. We calculate an electric dipole moment of about 10^?25 e-cm. In this phenomenological theory, we calculate CP-violating observables in non-leptonic decays from theK ⁰ ? \(\bar K^0 \) ,Λ ⁰ ?Λ ⁰ andK ⁺?K ^? systems. In connection with CP noninvariance, the possible observable occurrence of ΔS=2 decays is discussed. We calculate possible branching ratios; in particular that forΞ ⁰ → π^? p can be as high as about 10^?6. The possible existence of a weakly interacting, neutral scalar boson, which violates P and CP in the course of its propagation as a virtual particle, is considered.     

Creation of electron-positron plasma with superstrong laser field

We present a short review of recent progress in studying QED effects within the interaction of ultra-relativistic laser pulses with vacuum and e ^? e ⁺ plasma. Current development in laser technologies promises very rapid growth of laser intensities in the near future. Two exawatt class facilities (ELI and XCELS, Russia) in Europe are already in the planning stage. Realization of these projects will make available a laser intensity of ～ 10²⁶?W/cm² or even higher. Therefore, discussion of nonlinear optical effects in vacuum are becoming compelling for experimentalists and are currently gaining much attention. We show that, in spite of the fact that the expected field strength is still essentially less than E _S = m ² c ³/e? = 1.32 · 10¹⁶?V/cm, the nonlinear vacuum effects will be accessible for observation at the ELI and XCELS facilities. The most promissory effect for observation is pair creation by a laser pulse in vacuum. It is shown, that at intensities ～ 5 · 10²⁵?W/cm², creation even of a single pair is accompanied by the development of an avalanche QED cascade. There exists a distinctive feature of the laser-induced cascades, as compared with the air showers arising due primarily to cosmic rays entering the atmosphere. In our case the laser field plays not only the role of a target (similar to a nucleus in the case of air showers) but is also responsible for the acceleration of slow particles. It is shown that the effect of pair creation imposes a natural limit for the attainable laser intensity and, apparently, the field strength E ～ E _S is not accessible for a pair-creating electromagnetic field at all.     

A novel strong coupling expansion of the QCD Hamiltonian

Introducing an infinite spatial lattice with box length a, a systematic expansion of the physical QCD Hamiltonian in λ = g ^?2/3 can be obtained, with the free part being the sum of the Hamiltonians of the quantum mechanics of spatially constant fields for each box, and interaction terms proportional to λ ⁿ with n spatial derivatives connecting different boxes. As an example, the energy of the vacuum and the lowest scalar glueball is calculated up to order λ ² for the case of SU(2) Yang-Mills theory.     

Electron-positron pair production by collisions of non-relativistic charged particles

The cross-section for (e ⁺,e ^?)-pair production in collisions of non-relativistic charged particles has been calculated to lowest order in the fine structure constant and leading power of the relative velocity of the colliding particles. Thus the deflection of colliding particles is included in one-photon-exchange approximation, while the Coulomb distortion of the (e ⁺,e ^?)-pair is omitted. We have laid particular emphasis on current conservation. The previously neglected contribution of the spatial part of the current turns out to be dominant.     

Spin effects and factorization in the Drell-Yan process

We discuss the idea that the nontrivial vacuum structure in QCD may induce transverse momentum and spin correlations of the initial state partons in Drell-Yan type reactions, i.e. in hadron-hadron collisions with production of a vector bosonV=γ ^*,Z,W ^±. Transverse momentum correlations are found to have practically no effect on observable quantities, but spin correlations have drastic consequences for the polarization density matrices of theV-bosons. We therefore propose measurements of theV polarization as a good test for the basic factorization hypothesis which, so far, has been assumed to be valid in numerous applications of the naive and QCD-improved parton model. We compare our ansatz for a spin correlation violating factorization with data from the NA 10 collaboration onγ ^* production inπ ^? N scattering. We find that the data give an indication of spin correlations of the partons in the initial state to be present.     

Charge polarization in compact lattice QED

We investigate the polarization cloud around static electric charges in the framework of compact lattice QED. We calculate the correlations of Polyakov loops with the electric charge densityψ ^? ψ normalized to the chiral condensate. It turns out that virtual anticharges screen static charges as expected from continuum QED. Charge polarization is more pronounced at strong couplings and extends to a longer range on the lattice in the weak coupling phase. In both phases the correlations decrease with larger fermion mass.     

Measuring transverse spin correlations by 4-particle correlations ine + e − → 2 jets

The azimuthal distribution of pairs of particles in a jet is sensitive to the transverse polarization of the quark initiating the jet, but with a sensitivity that involves a nonperturbative analyzing power. We show in detail how to measure the analyzing power from 4-hadron correlations ine ⁺ e ^?→2 jets. We explain the combinations of particle flavor that are likely to give the biggest effect.     

Inelastic hadron-nucleus interactions at 20 and 37 GeV/c

The experiment studies charged particle production for π^?, K^?, and $\text{p}$ interactions on nuclei at 20 and 37 GeV/c at the CERN SPS. A non-magnetic detector, consisting of CsI(Tl) scintillation and lucite ?erenkov counters, distinguishes between fast particles, mainly pions, and slow particles, mainly nucleons, with a cut at velocity β ≈ 0.7. Angular distributions, multiplicity distributions and correlations of slow and fast particles were analysed. It is shown that the measurement of the correlations can provide a critical test for different theoretical models of the hadron-nucleus interaction. At the energies studied so far a systematic deviation from KNO scaling is observed. This gives further support to the “standard picture” of the hadron-nucleus interaction and it contrasts with predictions of the coherent-tube model. The regularity observed for the angular distribution of fast secondaries as a function of the number of slow particles can only be explained by combining features predicted by different models.     

Non-perturbative QCD vacuum frome +e−→I=1 hadron data

We estimate the gluon vacuum condensate α _s 〈F ²〉 from thee ⁺e^?→I=1 hadron cross-section known below 2 GeV using moment sum rules ratios. We obtain α _s 〈F ²〉= (3.9±1.0)10^?2GeV⁴. We also re-evaluate the contribution of the dimension-six vacuum condensates to the above sum rule and test the factorization hypothesis of the four-quark operator. Useful rules for the evaluation of the dimension-six vacuum condensates contributions are given.     

Forward and backward multiplicities inK − p interactions at 110 GeV/c

Multiplicity distributions and correlations between charged particles in the forward and back-ward c.m. hemispheres are studied inK ^?p interactions at 110 GeV/c and compared with other data on mesonnucleon scattering. The interpretation in terms of a simple quark-parton picture assuming that the forward multiplicity is dominated by quark fragmentation and the backward multiplicity by diquark fragmentation is supported by the experimental fact that the forward and the backward mean multiplicities are approximately equal to half of thee ⁺ e ^? andpp multiplicities, respectively. The 110 GeV/cK ^?p data show significant correlations between the numbers of slow forward and slow backward particles, whereas the multiplicities of fast forward and fast backward particles are independent.     

Colour transparency and scaling properties of nuclear shadowing in deep inelastic scattering

We present the perturbative QCD analysis of nuclear shadowing in the deep inelastic scattering at smallx in terms of the spatial wave function ofq \(\bar q\) fluctuations of virtual photons. The wave function formalism makes it quite obvious that shadowing is the scaling, rather than the higher twist, 1/Q ², effect, contrary to a numerous recent claims. We demonstrate explicitly how the scaling shadowing comes from the large, hadronic, size quarkantiquark pairs even in the limit ofQ ²→∞, and why it should very slowly, ∞1/log (Q ²/m ²) decrease at very largeQ ². We argue in favor of the scaling triple-pomeron contribution to the nuclear shadowing and present predictions for a cross section of diffraction dissociation of virtual photons and for the mass spectrum of diffraction excitation, which can be checked at HERA and Fermilab. We predict strikingly different scaling properties of diffraction dissociation and nuclear shadowing for the longitudinal and transverse photons. Our, numerial predictions for shadowing are in good agreement with the recent EMC data.     

Breakdown of normal threshold dispersion relation for the vacuum polarization

Stating a concrete example, it is shown that the vacuum polarization develops anomalous singularities. The analytic structure of the vacuum polarization in these circumstances is discussed in some detail. It appears that its large q² behaviour is not linked anymore to the asymptotic form of the e⁺e^? total cross section. Since it is the large q² behaviour of the vacuum polarization which solely can be calculated in asymptotically free gauge theories (giving in leading order the naive quark model result), this is a warning to using the naive quark model result for the e⁺e^? total cross section as well in fitting the data.     

Semiinclusive two-particle correlations and independent cluster emission at ISR energies

Semiinclusive two-particle correlations are calculated in the independent cluster emission model. The resulting semi-inclusive correlation functions ?₂ⁿ(y₁ = y₂ = 0) agree rather than well experimental data, esp. with respect to the multiplicity dependence. The average number of charged particles per cluster found from comparison with semiinclusive data is 2.5 charged particles per cluster, a value found earlier also from analysis of inclusive correlations.     

Vacuum Stability of the Wrong Sign (−ϕ 6) Scalar Field Theory

We apply the effective potential method to study the vacuum stability of the bounded from above (?? ⁶) (unstable) quantum field potential. The stability (?E/?b = 0) and the mass renormalization (? ² E/?b ² = M ²) conditions force the effective potential of this theory to be bounded from below (stable). Since bounded from below potentials are always associated with localized wave functions, the algorithm we use replaces the boundary condition applied to the wave functions in the complex contour method by two stability conditions on the effective potential obtained. To test the validity of our calculations, we show that our variational predictions can reproduce exactly the results in the literature for the \(\mathcal {PT}\) -symmetric ? ⁴ theory. We then extend the applications of the algorithm to the unstudied stability problem of the bounded from above (?? ⁶) scalar field theory where classical analysis prohibits the existence of a stable spectrum. Concerning this, we calculated the effective potential up to first order in the couplings in d space-time dimensions. We find that a Hermitian effective theory is instable while a non-Hermitian but \(\mathcal {PT}\) -symmetric effective theory characterized by a pure imaginary vacuum condensate is stable (bounded from below) which is against the classical predictions of the instability of the theory. We assert that the work presented here represents the first calculations that advocates the stability of the (?? ⁶) scalar potential.     

Neutrino Self-Energy and Index of Refraction in Strong Magnetic Field: A New Approach

The Ritus E_p eigenfunction method is extended to the case of spin-1 charged particles in a constant electromagnetic field and used to calculate the one-loop neutrino self-energy in the presence of a strong magnetic field. From the obtained self-energy, the neutrino dispersion relation and index of refraction in the magnetized vacuum are determined within the field range m²_e?eB?M²_W. The propagation of neutrinos in the magnetized vacuum is anisotropic due to the dependence of the index of refraction on the angle between the directions of the neutrino momentum and the external field. Possible cosmological implications of the results are discussed.     

Heavy Majorana neutrinos in e + e − → W + W−

In this paper we investigate the effects of heavy Majorana neutrinos in the reaction e ⁺ e ^? → W ⁺ W ^?. We consider neutrino masses in the 1–10 TeV region. We show that at LEP II and NLC energies it is possible to use this processes to verify indirect evidence of heavy neutral particles with mixing angles of the order sin² α = 0.01. We discuss the unitarity restrictions that can be obtained for vector singlet and fermion-mirror-fermion models.     

Vacuum copies and perturbation theory in the 't hooft-veltman gauge of QED

The 't Hooft-Veltman gauge condition ?_μA_μ + A_μ² = 0 gives a version of quantum electrodynamics with many similarities to Yang-Mills theory, including the presence of Gribov gauge-fixing ambiguities. We exhibit and discuss some properties of a family of copies of the vacuum, emphasizing their bearing on perturbation theory and the choice of a vacuum state. It is shown that in a general gauge theory, the same perturbation series results from expanding about any gauge-copy of the vacuum.     

Bounds on radii and anomalous magnetic dipole moments of quarks and leptons from LEP,SLC and HERA

Leptons, quarks and gauge bosons are assumed to be pointlike particles in the Standard Model. Stringent bounds on the radii of quarks and leptons and their weak anomalous magnetic moments can be derived from the high-precision measurements at LEP and SLC. We find a model-independent bound ofR?10^?17 cm for quark and lepton radii. HERA will provide complementary information on the electromagnetic static properties of the quarks and the parameters of the charged quark currents.     

Properties of anomalous eμ events produced in e+e− annihilation

We present the properties of 105 events of the form e⁺ + e^? → e^+- + μ^? + missing energy, in which no other charged particles or photons are detected. The simplesthypothesis compatible with all the data is that these events come from the production of a pair of heavy leptons, the mass of the lepton being in the range 1.6 to 2.0 GeV/c²