Ultraviolet Domain Research Articles

The bumps in the spectral energy distribution of active galactic nuclei

The spectral energy distribution of active galactic nuclei is investigated through calculations by composite models, which account for the coupled effect of the photoionizing flux from the active center and for shock propagation. The results show that bumps in the infrared, optical, and ultraviolet bands are produced by the emission of photoionized gas inside clouds of the narrow-line region; relatively strong radiation in the ultraviolet and X-ray domain is due to the high temperatures in the postshock region. Comparison with observational results show that a good fit can be obtained without assuming the contribution of an accretion disk, of starbursts, etc. 38 refs.

Ultraviolet photon detection and localization with Multiwire Chambers

The Multistep Proportional Chamber allows large gains (in excess of 10 6) in photosensitive gas mixtures to be obtained, thus constituting a convenient instrument for detection and localization of single photons in the ultraviolet domain. We describe the efficiency and localization properties of the device, as well as its applications for Cherenkov ring imaging.

Dynamic masses or quarks in quantum chromodynamics

Using Dyson-Schwinger equations we obtain an ultraviolet asymptotics for the dynamical mass of quark in QCD mD(p) = 〈qq〉 3 ḡ2(p2/μ2, g2 R) p2 ( ḡ2(p2/μ2, g2 R) g2 R )−d . We also determine a numerical value for the π meson decay constant fπ. Electronic version of the paper published in Russ. Phys. J. 25, 55 (1982). As is well known, strong interactions at high energies are approximately invariant with respect to the chiral symmetry group SUL(N) ⊗ SUR(N) (N is the number of different quark species). The Lagrangian of QCD – the most popular field-theoretical model of strong interactions – has the chiral symmetry group SUL(N)⊗ SUR(N) in approximation of massless quarks. The success of current algebra and PCAC hypothesis shows that the chiral symmetry SUL(N) ⊗ SUR(N) is spontaneously broken down to SU(N) symmetry. The spontaneous violation of the chiral symmetry reveals itself in nonvanishing vacuum expectation values 〈qq〉 and also in the appearance of dynamical mass for originally massless quarks. The problem of dynamical mass generation in massless theories has a long history. First, in refs. [1, 2] it has been shown in some concrete models that the generation of the dynamical mass can take place in quantum field theory. However, the consistent study of the problem of dynamical mass generation requires going beyond perturbation theory. It is obvious that this problem is rather nontrivial in the field theory because of the absence of the consistent methods different from perturbation theory. The purpose of the present paper is to investigate a possibility of generation of the dynamical mass of quarks in QCD. Using the Dyson-Schwinger equations we show that one can reliably determine the dependence of the dynamical mass of quarks m(p) on the momentum p in the ultraviolet domain due to the property of asymptotic freedom of strong interactions. In the following we will work in Euclidean space-time and in the transverse gauge (Landau gauge). The use of this gauge is convenient since the propagator of the massless quark is not renormalized in the leading logarithmic approximation. The Dyson-Schwinger equation for the quark propagator G(p) has the form G(p) = S(p) + g (2π)4 ∫ dk Γμ(p, k)G(k)Dμν(p− k)γν(λ /2). (1) Here S(p) is the propagator of free quarks, λ/2 are the generators of the fundamental representation of the group SU(N). Equation (1) is written for bare quantities. After performing the renormalization we find Z 2 G −1 R (p) = S (p) + g R (2π)4 ∫ dk Γ μ (p, k)GR(k)D R μν(p− k)γν(λ /2), where Z2 is the renormalization constant of the quark propagator. At the lowest order in g 2 R in the Landau gauge the renormalization constant of the quark propagator is equal to one Z2 = 1+O(g 4 R). Therefore in the leading logarithmic approximation we can set G(p) = m(p)−p. For the quantity m(p) we obtain the equation of the form m(p) = 4 (2π)4 ∫ dk m(k)ḡ((p− k)) (m2(k2) + k2)(p− k)2 where ḡ(p) = ḡ(p/μ, g R) = g 2 R/ ( 1 + (11− 2N/3) g R 16π2 ln p μ2 ) is the effective quark-gluon coupling constant. We split the region of integration into two subdomains determined by the requirements k > p (sub-domain (I)) and k < p (sub-domain (II))

Asymptotic freedom in the infinite-momentum frame

We study the renormalization of $\mathrm{SU}(N)$ Yang-Mills theory through one loop in the null-plane gauge. We choose as a measure of the effective coupling the off-shell four-gluon correlation function with all legs having zero transverse momentum. We find that, in addition to self-energy and vertex corrections, two-gluon exchange contributes to coupling-constant renormalization in an essential way. In this gauge, asymptotic freedom is due to a residual attraction between two gluons in the ultraviolet domain.

Solar abundance of iridium

By a method of spectrum synthesis, which yields log gfA, where g is the statistical weight of the lower level, f is the oscillator strength, and A is the abundance, an attempt is made to deduce the solar iridium abundance from one relatively unblended, but fairly weak IrI line, lambda 3220.78 A. If the Corliss-Bozman f-value for this line is adopted, we find log A(Ir) = 0.82 on the scale log A(H) = 12.00. The discordance with the value found from carbonaceous chondrites may arise from faulty f-values or from difficulties arising from line blending in this far ultraviolet domain of the solar spectrum.