Features of diffractive scattering and the nature of the N1(1400) observed in NN→N(Nπ) reactions at 5.7 GeV/c

The results for the diffractive scattering contribution ($\text{F}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^0$) obtained in a cross channel isospin analysis of the $\text{N}\text{N}\text{→}\text{N}\text{(}\text{N}\text{π)}$ reactions at 5.7 GeV/c are compared with those obtained for other ZN → Z′(Nπ) reactions where Z stands for N, π and the carbon nucleus. The dependence of the diffractive scattering on the mass M_πN and the momentum transfer t seems very weakly related to the nature of Z and the incident momentum.A comparison between amplitudes of the isospin exchange I_ex = 0 and I_ex = 1 leading to $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ production shows that $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1492)}$ and $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(1670)}$ are produced essentialy through I_ex = 1.     

Interaction of NO and O2 with Pd(111) surfaces. II

At least three different types of oxygen atoms may be present in the surface region of Pd(111) which may be distinguished by their thermal, chemical, structural and electronic properties. Exposure to O₂ at low temperatures causes the formation of 2 × 2 and $\text{3}\text{×}\text{3}\text{R30°}$ structures from chemisorbed oxygen, the latter being probably stabilized by small amounts of H_ab or CO_ab on the surface. The initial sticking coefficient was estimated to be about s₀ ≈ 0.3, the adsorption energy ~55 kcal/mole. The photoelectron spectrum exhibits an additional maximum at 5 eV below E_F. During thermal desorption dissolution of oxygen in the bulk strongly competes; on the other hand absorbed oxygen may diffuse to the surface giving rise to high temperature peaks in the flash desorption spectra. High temperature (~1000 K) treatment of the sample with O₂ causes the formation of a more tightly bound surface species also characterized by a 2 × 2 LEED pattern which is chemically rather stable and which is considered to be a transition state to PdO. The latter compound is only formed by interaction with NO at about 1000 K via the reaction $\text{Pd}\text{+}\text{NO}\text{→}\text{PdO}\text{+}\text{1}\text{2N}{}_2$ which offers a rather high “virtual” oxygen pressure. This reaction leads to drastic changes of the photoelectron spectrum and is also identified within the LEED pattern.     

Autler-Townes effect in double optical resonance

Two frequency stabilized dye lasers and a sodium atomic beam are used to study the Autler-Townes effect in the aligned 3S_{$\text{1}\text{2}$}, F = 2, $\text{M}{}_{\mathrm{F}}\text{= 2 → 3P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, F = 3, M_F = 3, → 4D_{$\text{5}\text{2}$}, F = 4, M_F = 4 states. This system is to a very good approximation an isolated three-level atom. The Autler-Townes doublet splittings are measured as a function of the intensities of the two lasers and their detunings from resonance. The experimental results are in good agreement with theory.     

Adsorbate enhanced Ti-3d photoemission from layered TiSe2 surfaces

Angle resolved photoelectron spectra of 1T-TiSe₂ single crystals $\text{(}\text{h}\text{?}\text{ω = 21.2}\text{eV}\text{)}$ have been investigated as a function of exposure to H₂O, CO, N₂ and O₂ at room temperature. A significant enhancement of the Ti-3d emission near the Fermi energy E_F is observed for H₂O and CO exposures of several kL. As compared to the clean surface this emission extends over the entire Brillouin zone. The results indicate that by H₂O and CO adsorption the lowest d-subband is pulled below E_F possibly by local band bending. Additional relaxation effects at the surface associated with changes in d-band matrix elements may occur. The intensity of the Se-4p derived valence band emission down to 7 eV below E_F remains essentially unchanged.     

On the asymptotic behaviour of the mass operator near the Fermi energy

By taking due account of momentum conservation, it is shown that, when ω is near the Fermi energy ω_F, the imaginary part of the mass operator $\text{M(}\text{k}\text{, ω)}$ for an infinite Fermi system behaves like (ω ? ω_F)^p(k) where the exponent p(k) ? 2 depends on the interval in which $\text{|}\text{k}\text{|}$ is lying. In particular, the commonly asserted quadratic behaviour (ω ? ω_F² is shown to be true only for $\text{|}\text{k}\text{| ? 3k}{}_{\mathrm{<mtext>F</mtext>}}$. It is explicity assumed that the Fermi system admits a perturbative type treatment.     

E.S.R. and optical study of the interstitial h centres in heavily neutron irradiated Lif

The paramagnetic spectra of the hole-centres created in LiF by a heavy neutron irradiation at 78°K have been studied by E.S.R. and optical techniques. Samples which have been irradiated at a dose at least equal to $\text{10}{}^{19}\text{solneutrons}\text{cm}{}^2\text{exhibit}$, after they have been warmed at 200°K, several spectra related to 〈111〉-oriented asymmetric centres. These centres are stable up to 500°K. One of them, designated the H_N1 centre, has been studied in detail. The analysis of the paramagnetic spectrum shows that this defect is an interstitial fluorine atom which forms an asymmetric ($\text{F}{}^{\mathrm{<mtext>-</mtext><mtext>?1</mtext><mtext>3</mtext>}}\text{- F}{}^{\mathrm{<mtext>-</mtext><mtext>?2</mtext><mtext>3</mtext>}}$) molecule ion with a lattice fluorine ion. Optical experiments have shown that the excited Σ level is at 4.1 eV from the ground Σ level. Two excited π levels have been found at 2.5 and 2.1 eV. This asymmetric H centre is formed from a primary symmetric H centre, designated the H_N2 centre. The H_N2 centre is 〈110〉-oriented. The transformation of the symmetric H_N2 centre into the asymmetric H_N1 one is associated with important changes in the values of the isotropic hyperfine interaction and of the g_⊥ shift.     

A small U approach to the 4kF reflections in organic linear chain compounds

It is shown that a lattice distortion of wavevector 4k_F with an essentially one-dimensional correlation occurs in a one-dimensional metal when the intramolecular Coulomb interaction U is small compared with the band-width 4t; ($\text{U}\text{4t}\text{?}\text{1}\text{4}$). This one-dimensional property suppresses the real phase-transition temperature well below the mean-field transition, where fluctuative 4k_F distortions build up. This accounts for the 4k_F reflections observed in TTF-TCNQ and several other charge transfer compounds. The strong locking of the electrons to the lattice when the band is $\text{1}\text{4}$ (or$\text{1}\text{2}$) full, and weak locking when the band is $\text{1}\text{3}$ (or $\text{2}\text{3}$) full, are also accounted for.     

Right-handed weak currents in neutrino scattering

We investigate transition strengths of right-handed weak charged currents in deep inelastic neutrino scattering, exploiting the dominance of p, n valence quarks in the nucleon. The energy dependence of σ_t and the average quantities 〈y〉 and 〈Q²〉 are shown to provide sensitive measures of new quark production thresholds and right-handed currents in $\text{ν}\text{N}$ scattering. With our analysis, the present data give an upper bound on the right to left hand structure function ratio of $\text{F}{}_{\mathrm{<mtext>R</mtext>}}{}^{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{F}{}_{\mathrm{<mtext>L</mtext>}}{}^{\mathrm{<mtext>\nu </mtext><mtext>N</mtext>}}\text{≈}\text{1}\text{2}$, above a threshold of W≈7.5 GeV.     

Continuum limit of QED2 on a lattice

A path integral is defined for the vacuum expectation values of Euclidean QED₂ on a periodic lattice. Wilson's expression is used for the coupling between fermion and gauge fields. The action for the gauge field by itself is assumed to be a quadratic in place of Wilson's periodic action. The integral over the fermion field is carried out explicitly to obtain a Matthews-Salam formula for vacuum expectation values. For a combination of gauge and fermion fields $\text{G}$ on a lattice with spacing proportional to N^?1, N?Z⁺, the Matthews-Salam formula for the vacuum expectation 〈G〉_N has the form ($\text{G}$)_N=∫d_nu;W_N($\text{G}$,f), where dμ is an N-independent measure on a random electromagnetic field ? and $\text{W}{}_{\mathrm{N}}\text{(G, ?)}$ is an N-dependent function of ? determined by $\text{G}$. For a class of $\text{G}$ we prove that as N → ∞, $\text{W}{}_{\mathrm{N}}\text{(C, ?)}$ has a limit $\text{W(G, ?)}$ except possibly for a set of ? of measure zero. In subsequent articles it will be shown that ∫d_nu;W_N($\text{G}$,f) exists and lim_N→∞∫d_nu;W_N($\text{G}$,f).     

Higher orders in N−1 in the Gross-Neveu model

We study higher-order terms in the N expansion of the two-dimensional model field theory of Gross and Neveu. The quantity $\text{M}{}_{\mathrm{\sigma }}\text{2M}{}_{\mathrm{<mtext>F</mtext><mtext>?1</mtext>}}$ (M_F is the fermion mass, M_σ is the scalar bound-state mass), is conjectured to deviate from zero in O(N^?4). Order N^?1 corrections are found to leave unchanged both the symmetry-breaking, and the absence of zeros of the Callan-Symanzik function β for real non-zero coupling constant. Behavior of β for complex coupling constant is altered considerably by the corrections; consequences are discussed.We obtain the following additional results: proof that the model is renormalizable without the necessity of additional interactions; construction of a perturbation theory in the asymmetric vacuum; proof of a lemma on fermion-antifermion thresholds in two-dimensional space-time; derivation of closed formulae for arbitrary one-loop integrals in two-dimensional space-time.     

Ni-Zr amorphous alloys: Low temperature specific heat and superconductivity

The specific heat (C_p) of the amorphous alloys Ni_100-xZr_x for x = 75, 65, 55 and 35 was measured from 0.8K to 40K and the composition trends of the transition temperature T_c, the enhanced density of states at the Fermi level N_γ(_F) and the Debye temperatures θ_D(0), θ_D(T) established. For the three superconducting compositions (x=75, 65, 55) N_γ(E_F increases rapidly with increasing [Zr] in agreement with the trend in amorphous Cu-Zr alloys. However, for the Zr-Ni alloys the bare density of states $\text{N}{}_0\text{(E}{}_{\mathrm{F}}\text{) =}\text{N}{}_{\mathrm{\gamma }}\text{(E}{}_{\mathrm{F}}\text{)}\text{(1 + λ}{}_{\mathrm{p}}\text{)}$ increases strongly with [Zr] in contrast to the Zr-Cu alloys where it is reported to be almost constant. We conclude that for the Ni-Zr alloys the electron-ion matrix element <I²> decreases with increasing [Zr]. Other results are related to recent photoemission studies of these alloys.     

Peierls transitions in semimetallic one dimensional charge transfer salts

Peierls transitions in one dimensional charge transfer salts in which both donor and acceptor molecules have even valency such as TTF-TCNQ have been studied. Transitions involving macroscopic occupation of phonon states of wavevector $\text{k}{}_{\mathrm{<mtext>F</mtext>}}\text{(TTF)}\text{+ k}{}_{\mathrm{<mtext>F</mtext>}}\text{(TCNQ)}\text{=}\text{1}\text{2}\text{G}$ and |k_F(TTF) ? k_F (TCNQ)| can occur as well as transitions of wavevector 2k_F(TTF) [and 2k_F(TCNQ)].     

A study of ππ → NN partial-wave amplitudes using hyperbolic dispersion relations

We investigate $\text{ππ →}\text{N}\text{N}$ partial-wave amplitudes, using a spin separation method based on hyperbolic dispersion relations. Partial-wave amplitudes with J ? 3 are dominant in the pseudophysical region between the ππ and $\text{N}\text{N}$ thresholds, but we find clear evidence for J = 4 and J = 5 contributions from regions near and above the $\text{N}\text{N}$ threshold. We isolate J = 2 and J = 3 partial waves and determine the couplings of f₀(1270) and g (1680). Knowing the high-spin contributions, we are able to eliminate thse and to study s- and p-waves. We find evidence for small p-wave contributions above the ?, having the same sign as the ? contributions. We develop methods for determining the I = J = 0 ππ scattering length a₀⁰ and find a₀⁰ = 0.30 ± 0.15.     

Interaction of NO with a Ni (111) surface

The interaction of NO with a Ni (111) surface was studied by means of LEED, AES, UPS and flash desorption spectroscopy. NO adsorbs with a high sticking probability and may form two ordered structures (c4 × 2 and hexagonal) from (undissociated) NO_ad. The mean adsorption energy is about 25 $\text{kcal}\text{mole}$. Dissociation of adsorbed NO starts already at ?120°C, but the activation energy for this process increases with increasing coverage (and even by the presence of preadsorbed oxygen) up to the value for the activation energy of NO desorption. The recombination of adsorbed nitrogen atoms and desorption of N₂ occurs around 600 °C with an activation energy of about 52 $\text{kcal}\text{mole}$. A chemisorbed oxygen layer converts upon further increase of the oxygen concentration into epitaxial NiO. A mixed layer consisting of N_ad + O_ad (after thermal decomposition of NO) exhibits a complex LEED pattern and can be stripped of adsorbed oxygen by reduction with H₂. This yields an N_ad overlayer exhibiting a 6 × 2 LEED pattern. A series of new maxima at ≈ ?2, ?8.8 and ?14.6 eV is observed in the UV photoelectron spectra from adsorbed NO which are identified with surface states derived from molecular orbitals of free NO. N_ad as well as O_ad causes a peak at ?5.6 eV which is derived from the 2p electrons of the adsorbate. The photoelectron spectrum from NiO agrees closely with a recent theoretical evaluation.     

SU(6) symmetry breaking effects in deep inelastic scattering

The fact that the N and Δ states of the $\text{56}$ baryons are not degenerate in mass is shown to imply that the deep inelastic scattering ratio F_2n(x)/F_2p(x) should approach $\text{1}\text{4}$ as x → 1. The rate of approach is predicted to be approximatel linear in x. The possibility of observing analogous effects in other large momentum transfer processes is also discussed.     

Nonorthogonality corrections in the method of correlated basis functions

A set of normalized linearly independent basis functions φ₁, φ₂, …, φ_j, … generates matrix representatives $\text{H}$ and $\text{N}$ of the Hamiltonian operator and the identity. An orthonormal basis $\text{φ}{}_1$, $\text{φ}{}_2$, …, $\text{φ}{}_{\mathrm{j}}$, … generated by a Löwdin transformation is characterized by the distance in Hilbert space between $\text{φ}{}_{\mathrm{j}}$ and φ_j. The choice of positive definite $\text{N}$${}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ minimizes these distances and maximizes the diagonal elements of $\text{N}$${}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. Again for positive definite $\text{N}$${}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and a finite basis, 1 ? j ? p, the analysis yields a general theorem on Trace $\text{N}$${}^{\mathrm{<mtext>?n</mtext><mtext>2</mtext>}}$ (? p for all positive and negative integral values of n except n = ?1 and ? p for n = ?1).Sufficient conditions are determined which permit the application of the binomial theorem to the evaluation of the transform of $\text{H}$. Approximate formulas for the energy eigenvalues through third order in nondiagonal matrix elements are presented in a compact form containing characteristic nonorthogonality corrections depending on the exterior or interior location of the matrix element in the perturbation formulas.     

Johnson noise and absolute temperature

Experimental evidence using Josephson junction devices has suggested that Johnson noise in copper fails to be proportional to absolute temperature below 10 millikelvin. A microscopic theory is presented which gives the Johnson noise temperature $\text{T}{}_{\mathrm{<mtext>J</mtext>}}\text{= ?}{}_0{}^1\text{XT}{}_0$ coth ($\text{XT}{}_0\text{T}$) dX where $\text{T}{}_0\text{=}\text{hν}{}_{\mathrm{<mtext>F</mtext>}}\text{2kN}$. For copper, the calculated T₀ = 3.84 mK agrees closely with the value extracted from experimental data, 3.89 mK. Within a few percent, $\text{T}{}_{\mathrm{<mtext>J</mtext>}}\text{? (}\text{T}{}_0\text{2}\text{)}$ coth ($\text{T}{}_0\text{2T}$), and this adequately fits the available experimental data. ν_F is the fermi velocity and N is the length of the resistor. The Johnson noise parameter “T₀” presumably can measure ν_F along different crystal orientations.     

Semi-simple real subal gebras of non-compact semi-simple real lie algebras V

The investigation of the problem of embedding a semi-simple real Lie algebra $\text{L}$ in a non-compact semi-simple real Lie algebra $\text{L}$ is extended to the case when $\text{L}$ and/or $\text{L}$ is exceptional. Matrix representations for all the exceptional Lie algebras are calculated. Detailed procedures are given, which, together with those given in previous papers, allow the construction of all embeddings of $\text{L}$ in $\text{L}$, when their complex extensions are A₁, B₁, C₁, D₁, E₆, E₇, E₈, F₄, G₂ or a direct sum of any two of there. The procedures are illustrated by examples, including all real semi-simple Lie subalgebras of real forms of G₂ and sub-algebras of real forms of F₄ whose complex extensions are B₄ or A₁ (representation (16) + (9)). Because of its physical significance, all embeddings of SL (2, C) in real forms of F₄ and E₆ are given. Many of these are new results.