Overlapping branes in M-theory

We construct new supersymmetric solutions of D = 11 supergravity describing n orthogonally “overlapping” membranes and fivebranes for n = 2,…,8. Overlapping branes arise after separating intersecting branes in a direction transverse to all of the branes. The solutions, which generalize known intersecting brane solutions, preserve at least 2⁻ⁿ of the supersymmetry. Each pairwise overlap involves a membrane overlapping a membrane in a 0-brane, a fivebrane overlapping a fivebrane in a 3-brane or a membrane overlapping a fivebrane in a string. After reducing n overlapping membranes to obtain n overlapping D-2-branes in D = 10, T-duality generates new overlapping D-brane solutions in type IIA and type IIB string theory. Uplifting certain type IIA solutions leads to the D = 11 solutions. Some of the new solutions reduce to dilaton black holes in D = 4. Additionally, we present a D = 10 solution that describes two D-5-branes overlapping in a string. T-duality then generates further D = 10 solutions and uplifting one of the type IIA solutions gives a new D = 11 solution describing two fivebranes overlapping in a string.     

Covariant first and second quantization of the N = 2, D = 10 Brink-Schwarz superparticle

Using a new type of harmonic superspace variables, we reduce the N = 2, D = 10 Brink-Schwarz (BS) superparticle to a system whose constraints are (i) first class, (ii) functionally independent and (iii) Lorentz covariant. We show that these features are essential for a correct covariant quantization. Q_BRST is first rank. By using it to second quantize the system, we obtain a covariant off-shell unconstrained superfield action of the linearized D = 10 type IIB supergravity. A corresponding procedure for the Green Schwarz (GS) superstring is conjectured.     

Covariant unconstrained superfield action for the linearized D = 10 super-Yang-Mills theory

A new type of D = 10 harmonic superspace with two generations of harmonics allows us to reduce the D = 10, N = 1 Brink-Schwarz (BS) superpaticle to a system whose constraints are all first class, functionally independent and Lorentz-covariant. Given these properties, the covariant BFV-BRST quantization of the system is straightforward. By second quantizing this system, we circumvent the no-go theorem which forbids the existence of a covariant off-shell unconstrained superfield action for the linearized D = 10 super-Yang-Mills theory.     

X-ray spectroscopy of multiply-charged ions from laser plasmas

Original results are reported on the observation and identification of spectra of multiply-charged ions in the range of λ ≈ 1.5–15 Å, which corresponds to transitions with a range of principal quantum number n. The main part of the review consists of tables with about a thousand spectral lines, which have been mainly observed in laser-plasma radiation, as well as in the solar corona and other laboratory sources at an electron temperature T_e≈10⁷°K. The accuracy for the wavelengths (Δλ) is the following: Δλ is equal to ≈ 0.0005 Å for λ ≈ 2.5 Å and it is equal to ≈ 0.003 Å for λ ≈ 15 Å. The spectral lines are considered for the following transitions: 1-n type for [H]-like ions (Z = 11–16)and [He]-like ions (Z = 11–26); 2-n type for [Li]-like ions (Z = 19–26), [Be]-like ions (Z = 22–34) and [Ne]-like ions (Z = 26–42); 3-n type [Co]- and [Ni]-like ions (Z = 73). The line-list contains about four hundred wavelengths for multiply-charged iron L-ions (Fe(XVII)-Fe(XXIV)) and is presented with identification of some of the transitions. The wavelengths and intensities of satellites of the [H]-like ions and [He]-like ions, which are caused by transitions from the doubly-excited autoionization states 2l2l′ and 1s2l2L′ of [He]-like ions (Z = 11–16) and [Li]-like ions (Z = 11–26), respectively, are also considered.     

Structural instability in new magnetic heusler compounds

The crystal structure and magnetic properties have been determined for a new series of compounds of the form Rh₂TSn. For T = Mn, Ni, or Cu, the room temperature structure is the fully ordered cubic Heusler structure. For T = V, Cr, Fe, or Co, a new structure is observed which is an exceptionally large tetragonal distortion of the Heusler structure (c/a = 1.18?1.27). The appearance of this tetragonal distortion is attributed to an electronic instability of the band Jahn-Teller type.     

Small-angle X-ray scattering on spinodal,nucleotic or coarsening processes in two-phase systems containing spherical,fibrillar or lamellar inhomogeneities

We study the effects of some of the most important and typical structural changes in two-phase systems on selected structural parameters obtained from small-angle x-ray scattering (SAXS) measurements. To limit the present study, it was assumed that the Phase, 1, embedded in the matrix

1. is monodispersed and homogeneous,
2. possesses one of the three most extreme shapes (spherical, fibrillar or lamellar) and
3. changes its behaviour

1. through type change (spinodal or nucleotic or coarsening), without changing the shape,
2. through a change of the shape only, or
3. through a) (type change) and b) (shape change) simultaneously.

To find the type of change for three basically different shapes of Phase 1 and to calculate its intensity (amount of the change) the following three SAXS parameters must be compared before and after the treatment of the system:

1. chord lengthl ₁ (and/or radius of gyrationR),
2. volume partw ₁ of the Phase 1, and
3. relative inner surfaceS _v of the system.

It is shown by this comparison that by the pure type change in the case of

1. spinodal change, all three SAXRS parameters are increasing or decreasing simultaneously and proportional to a power of the intensity of the change,
2. nucleotic change,l ₁ (and/orR) is unchanged, the other two (w ₁ andS _v ) are increasing or decreasing simultaneously and directly proportional to the intensity,
3. coarsening change,w ₁ is unchanged and anincreasing ofl ₁ is always accompanied by adecreasing ofS _v and vice versa.

In addition to this type change, the cases of mere changes of the shape (“shape change”) and finally of simultaneous type and/or shape change are studied. For the case of pure shape change the alteration of the dimensions (chord lengthl ₁ and/or radius of gyrationR) must be followed. The limitations of the analyses of the simultaneous type and/or shape change are discussed in detail.     

Structural studies of La \mathsf{_{1-x}}Sr\mathsf{_{x}}MnO \mathsf {_{3 + \delta}} (x = 0.1-1.0)

We report here for the first time (particularly for $x \ge 0.5$ ) a systematic structural study using Rietveld Profile Refinement of powder X-ray diffraction data on the series of polycrystalline compounds La_1-x Sr _x MnO $_{3 + \delta}$ (0.1 ≤ x ≤ 1.0). The iodometric redox titration results show that the compounds $0.1\le x\le 0.4$ and the end compound are oxygen excess and deficient respectively and the compounds in the compositional range 0.5 ≤ x ≤ 0.9 are oxygen stoichiometric within the experimental error. It is found that the structure remains hexagonal until x = 0.4 composition. On further doping, at x = 0.5 composition, a structural transition to orthorhombic phase is observed. Around this composition, very small variations in the Mn-O(2)-Mn and average Mn-Mn bond distances are observed. For above x = 0.5, until x = 0.8 composition, the structure remains orthorhombic with reduced orthorhombic distortion. For the next compound, x = 0.9, a mixed hexagonal and orthorhombic phase is observed where the hexagonal phase is 6 layered with stacking sequence of ABCACB type and the orthorhombic phase is more distorted than that of x = 0.8 composition. The end compound is a four layered hexagonal structure with stacking sequence ABAC type which is more distorted than ABCACB type. As one goes down the series, a decrease in the volume per formula unit and average Mn-O bond distance are observed except at x = 0.9 composition. The observed structural transitions from hexagonal to orthorhombic to layered hexagonal phase can be explained under the electrostatic limit.     

Superheating,supercooling, surface superconductivity and Ginzburg-Landau parameters of pure type-I superconductors and their alloys

We have measured the low-frequency differential susceptibility of several pure type 1 superconductors, viz. Sn, In, Tl, Pb and Hg, as a function of increasing or decreasing applied magnetic fields. Special emphasis was placed on the observation of metastable (superheated and supercooled) states. Experimental values of the Ginzburg-Landau parameter? at the transition temperatureT _c and of suitably defined temperature dependent parameters for superheating,? _sh(t), and for supercooling,? _sc(t), have been obtained and compared with theoretical estimates. The rapid drop in? _sh close toT _c observed in materials with??1 such as Sn, In, and Tl is interpreted as a manifestation of nonlocal electrodynamics. Supercooling of the normal state down to the bulk nucleation fieldH _c2, rather thanH _c3, has been achieved close toT _c in Cu-plated samples of Sn and In. The parameters? and?(t) have also been determined for a series of SnIn alloys spanning the range between type I and type II behavior. Supercooling of the superconducting surface sheath below the thermodynamic critical fieldH _c has been observed in these alloys as well as in pure Pb. The measured values of? are compared with estimates based on normal state parameters extracted from independent low temperature experiments. Corrections for energy gap anisotropy and electron-phonon retardation are typically below 10%. The strong temperature dependence of? _sc(t), observed in all the materials studied, is not explained by present theories, even in the concentrated alloys where anisotropy effects should be washed out.     

Elliptic index and superstring effective actions

Certain N = 1 supersymmetric string one-loop effective actions can be obtained directly from the path integral. As the computation is essentially the same as the one leading to the index of the Dirac-Ramond operator, they are determined by the gauge and gravitational anomaly structure of the theory. Specifically, we calculate the four-point effective action in ten dimensions, the corrections to the kinetic terms in d = 6 (including auxiliary fields) and the Fayet-Iliopoulos D-term in d = 4. We also compute the β-function of four-dimensional N = 2 theories from the elliptic genus in d = 6. Furthermore, we derive supersymmetry Ward type identities in terms of Kac-Moody characters, relating parity conserving with parity violating amplitudes.     

On the formation of a random color magnetic quantum liquid in QCD

It is shown that a quantum state consisting of a condensate of color magnetic flux tubes is formed in QCD for a rather weak coupling g²/4π = 0.37. This result is obtained in a systematic search for energy minimizing forms of the QCD unstable magnetic mode. The magnetic field is argued to be of a “random” type with 〈H〉 = 0 and 〈H²〉 ≠ 0 at any point.     

On inflation in the heterotic superstring model

The possibility is considered of achieving inflation in the field-theory limit of the E₈ X E₈ superstring model, which is an N = 1 supergravity theory possessing a “no-scale” SU(n, 1)/SU(n) × U(1) structure. It is shown that neither type I inflation (due to higher-derivative terms O(R²)), nor inflation due to a SUSY-breaking gaugino-condensation potential, is possible, essentially because of the absence of free dimensionless parameters. Kaluza-Klein type inflation is ruled out because the internal space is Ricci flat. The occurence of type II inflation (due to some gauge singlet “inflation” field φ) depends upon the form of the superpotential F and of the Kähler potential G, but this also seems not to be possible, unless the >SU(n, 1) symmetry can be broken in a particular way. Hence, some new type of compactification scheme may be called for, or a different type of inflation.     

On a theory of spin systems with competing anisotropies

On the basis of a quantum treatment of Me_1?cFe_cX (Me = Mn, Ni, Co, X = Cl₂, CO₃, etc.) type random systems it is shown that parallel with order parameters such as magnetizations of mixed magnetic crystal ordering subsystems there is one more order parameter determining the angle between them.     

High pressure X-ray diffraction study on p-FeS2, m-FeS2 and MnS2 to 340 kbar: A possible high spin-low spin transition in MnS2

Pyrite p-FeS₂, marcasite m-FeS₂ and MnS₂2 have been investigated using the high-pressure X-ray diffraction technique to 340 kbar. MnS2 undergoes a pressure-induced phase transition at about 140 kbar from the pyrite to the marcasite type phase with a volume contraction of about 15%. The high-pressure marcasite type m-MnS₂ is found to belong to the B type of marcasite with an axial ratio $\text{c}\text{a}\text{= 0.76}$ and $\text{c}\text{b}\text{= 0.62.}$ p-FeS₂ and m-FeS₂ do not undergo any phase transition in the pressure range investigated. The high spin p-MnS₂ has been found to be much more compressible (B_o = 760 kbar, B′_o = 5.4) than the low spin p-FeS₂ (B_o = 2154 kbar, B′_o = 5.5) and m-FeS₂ (B₀ = 1465 kbar, B′_o = 4.9) while the high-pressure m-MnS₂ has comparable compressibility (B_o = 2138 kbar, B′₀ = 5.0) with those of low spin p-FeS₂ and m-FeS₂. The p-MnS₂-m-MnS₂ phase transition might be accompanied by a high spin-low spin transition of Mn²⁺.     

Magnetic ordering in NdRh2Si2 and ErRH2Si2

Neutron diffraction and magnetization study of polycrystalline NdRh₂Si₂ and ErRh₂Si₂ was performed in the temperature range from 4.2 to 293 K. Both compounds are of ThCr₂Si₂ type crystal structure and exhibit antiferromagnetic ordering below T_N = 53 K and T_N = 12.8 K respectively. The magnetic structure wave vector is τ = [0, 0, 1].     

Structure and the electrical and magnetic properties of perovskite-like Gd x Cu3V4O12 oxide

A new perovskite-like compound Gd _x Cu₃V₄O₁₂ (x = 0.67?0.73) is synthesized under high pressures (P = 4?9 GPa) and at high temperatures (T = 1000°C). Its structure (space group Im3, Z = 2, a = 7.2930(5) ?) is estrablished by X-ray analysis. The bond lengths and bond angles are determined. The temperature dependences of electrical resistivity (10?C300 K) and magnetic susceptibility are studied. The high-pressure Gd _x Cu₃V₄O₁₂ phase is found to have a semi-conductor type of conductivity and paramagnetic properties.     

Liquid 3He droplets: Energy systematics and magic numbers

Ground state properties of ³He clusters are investigated in the framework of the Hartree-Fock theory using an effective interaction of phenomenological type. Binding energies and density distributions are evaluated for clusters up to N = 168 atoms. The analysis yields magic number effects at N = 40 and 70. The method predicts the existence of a minimum number of particles forming a bound droplet around N = 20.     

A new polymorphic transition of FeTaO4 under high pressure

A phase transition of FeTaO₄ was observed under high pressures from the rutile type structure to the wolframite type structure, and the boundary between the two phases was found to be expressible approximately by p(kbar) = 0.065 T(K) + 52.