共查询到20条相似文献,搜索用时 31 毫秒
1.
Osamu Yasuda 《Nuclear Physics B》1984,246(1):170-188
Classical stability of Einstein spaces Sd1 ×?×Sdn(dj ? 2) against all fluctuations is investigated in euclidean gravity with a cosmological constant. It is shown that Sd is classically stable, while Sd1 ×?× Sdn(n ? 2) is classically unstable. As a generalization of this analysis it is proved that a compact Einstein space B1 ×?× Bn(n ? 2) which is a direct product of each Einstein space is classically unstable. Non-Einstein spaces M2 × S4 (M2 × S2 × S2) are also considered in six- dimensional Einstein-Maxwell theory and are shown to be classically stable (unstable). 相似文献
2.
3.
We prove that in the spectrum of the d = 4 theory obtained by Freund-Rubin compactification of d = 11 superconductivity, only fields of spin 0+ can give rise to classical instabilities. The criterion for stability in the 0+ sector can be expressed as a certain lower bound on the Lichnerowicz operator ΔL on the d = 7 compact space. Thus not only are supersymmetric vacua always stable but so are the corresponding non-supersymmetric vacua obtained by reversing the orientation of the compact space, since the 0+ spectrum is insensitive to the orientation. Examples are the orientation-reversed spaces with N = 0 obtained from the squashed seven-sphere with N = 1 and from SU(3) ×SU(2) ×U(1) spaces with N = 2 supersymmetry. Product spaces, on the other hand, are always unstable. Finally, we examine the massless sectors of the squashed seven-sphere vacua, and find an additional 135 massless scalars. 相似文献
4.
Using the gain-bandwidth method, the piezoelectric constant d14 of trigonal selenium has been deduced from measurements of the admittance and the electromechanical resonance frequencies of appropriately cut bars. The value was found to be |d14| = (2.54 ± 0.2) × 10?2C/N. 相似文献
5.
Pt/W/Cr/SiC Schottky-barrier diodes that retain good electrophysical parameters up to 450°C are studied. With the Auger electron spectroscopy (AES) method, it is shown that the thermal stability is provided by using a multilayer metal composition that ensures the metal/SiC interface stability. The surface-barrier structures obtained are tested for radiation hardness. They are irradiated by fast neutrons with a fluence of 4.42×1015 n/cm2 and attendant γ radiation with a dose of 8.67×105 R in the concentration range of N d-N a=1016−5×1017 cm−3. Irreversible modifications of the structures at N d-N a≤8×1016 cm−3 are found. The degradation of the parameters is inversely proportional to the doping level. 相似文献
6.
Peter J. Forrester 《Journal of statistical physics》2013,151(5):796-808
The exact value of the Lyapunov exponents for the random matrix product P N =A N A N?1?A 1 with each $A_{i} = \varSigma^{1/2} G_{i}^{\mathrm{c}}$ , where Σ is a fixed d×d positive definite matrix and $G_{i}^{\mathrm{c}}$ a d×d complex Gaussian matrix with entries standard complex normals, are calculated. Also obtained is an exact expression for the sum of the Lyapunov exponents in both the complex and real cases, and the Lyapunov exponents for diffusing complex matrices. 相似文献
7.
《Physics letters. A》1997,229(5):299-305
A hierarchy of N-dimensional systems is constructed starting from the standard continuous two-layer quasi-geostrophic model of the geophysical fluid dynamics. These models (“truncations”) preserve the Hamiltonian structure of the parent model and tend to it in the limit N → ∞. The construction is based on the known correspondence SU(N) → SDiff(T2) when N → ∞ between the finite-dimensional group of unitary unimodular N × N matrices and the group of symplectic diffeomorphisms of the torus and the fact that the above-mentioned continuous model has an intrinsic geometric structure related to SDiff(T2) in the case of periodic boundary conditions. A fast symplectic solver for these truncations is proposed and used to study the baroclinic instability. 7 相似文献
8.
The non-chiral N = 2, D = 10 supergravity theory is constructed using dimensional reduction from N = 1, D = 11 supergravity. It is shown that this theory may spontaneously compactify, yielding S4 × S2, CP2 × S2 and S2 × S2 × S2 spaces for the extra dimensions. 相似文献
9.
We obtain a U(M) action for super membranes with central charges in the Light Cone Gauge (LCG). The theory realizes all of the symmetries and constraints of the supermembrane together with the invariance under a U(M) gauge group with M arbitrary. The worldvolume action has (LCG) N = 8 supersymmetry arid it corresponds to M parallel supermembranes minimally immersed on the target M g × T 2 (MIM2). In order to ensure the invariance under the symmetries and to close the corresponding algebra, a star-product determined by the central charge condition is introduced. It is constructed with a nonconstant symplectic two-form where curvature terms are also present. The theory is in the strongly coupled gauge-gravity regime. At low energies, the theory enters in a decoupling limit and it is described by an ordinary N = 8 SYM in the IR phase for any number of M2-branes. 相似文献
10.
In a diaphragm shock-tube, Ar, Kr and Xe plasmas were generated with equilibrium temperatures of 8,000 to 12,000 K. The electron densities were measured with a two-wavelength interferometer and varied from 4×1016 to 1.4×1017 cm-3. Emission profiles of spectral lines were recorded with a polychromator setup in 1 μs intervals using a fast data acquisition system. Width w and shift d turned out to be proportional to electron density Ne for the observed lines. Stark broadening parameters w/Ne and d/Ne are presented for 3 Ar(I), 4 Kr(I) and 5 Xe(I) lines in the visible region of the spectrum. 相似文献
11.
We present a new class of compactifying solutions for d = 11 supergravity. The internal 7-spaces are described by coset manifolds Npqr of the form SU(3) × U(1)/U(1) × U(1). The three integers p, q, r characterize the embedding of the stability subgroup U(1) × U(1) in SU(3) × U(1).Their supersymmetry content is quite remarkable. For a particular choice of p, q, r the isometry of Npqr is SU(3) × SU(2): in this case we find that N = 3 supersymmetry survives. For all the other values of p, q, r, supersymmetry is broken to N = 1, and the isometry group is SU(3) × U(1).We also find a class of solutions with internal photon curl Fαβγδ ≠ 0, breaking all supersymmetries. 相似文献
12.
《Physics letters. [Part B]》1988,214(3):387-392
The problem of gauge dependence of the effective action in multidimensional supergravities (SG) is investigated. As an example d=5 SGs are considered. The convenient gauge-dependent effective action (EA) and gauge-invariant Vilkovisky-De Witt EA in d=5, N=2, 4, 6, 8 SGs on the background R4×S1 with accuracy to linear curvature terms are obtained. The convenient three-gauge-parameter-dependent EA in d=5, N=2 gauged SG on the background R4×S1 is calculated. The Vilkovisky-De Witt EA in d=5 SGs on the background R4×S1 at non-zero temperature is also obtained. 相似文献
13.
The results of the investigation of dark-current relaxation in EuGa2S4 single crystals are reported. The depth and concentration of the traps are found to be Et = 0.79 eV and Nt = 1.64 × 1014 cm?3, respectively.The charge accumulation region (dc = 3.3 × 10?5 cm) and contact capacitance (Cc = 1.23 × 10?10 F) are also estimated. 相似文献
14.
N-Nitrodimethylamine is known to undergo a displacive structural phase transition at Tt~107 K, (atmospheric pressure) associated with a soft-mode observed in the low temperature phase Raman spectrum.The soft-model has already been assigned to a lattice vibration although crystallographic observations of the symmetry breaking distortion suggest that a coupling with an internal vibration should not be ruled out. To clarify this point neutron inelastic spectra have been recorded. They lead to a better assignment of both the high and low frequency vibrations and to the conclusion that no softening of an intramolecular mode is visible.High pressure (up to 3.5 Kbars) neutron scattering experiments are also described. They give both the directions and magnitudes (k1=0.33× 10?2, kb=1.17 × 10?2, k3 = 0.12× 10?2Kbar?1) of the isothermal principal compressibilities of DMN and the dependence of Tt on pressure ((dTt/dP)P=0 ~ + 4.3 Kbar?1). Spectroscopic and crystallographic data now available on DMN allow us to discuss the mechanism of the transition. An extension of Samara's rule to molecular crystals is attempted 相似文献
15.
We show how N = 8 supersymmetry can break spontaneously to N = 1 at the Planck scale via a Kaluza-Klein compactification of d = 11 supergravity on the squashed seven-sphere. Features unique to Kaluza-Klein supergravity are (i) the massless gravitino of the N = 1 phase comes from a massiveN = 8 supermultiplet, (ii) the scalars developing nonzero VEVs also belong to massive N = 8 supermultiplets, (iii) parity remains unbroken when N = 8 breaks to N = 1.Next we ask whether the resulting N = 1 theory can provide a realistic SU(3) × SU(2) × U(1) unification and speculate that it might if some of the gauge bosons and fermions are composite as in the EGMZ model. In contrast to their model, however, we avoid unwanted helicities and problems with their non-compact E7. Moreover, we suggest a scheme in which the electroweak SU(2) × U(1) is a subgroup of the d = 11 general coordinate group but that the strong SU(3) is a subgroup of the d = 11 local Lorentz group and are not, therefore, to be combined into a GUT. The special properties of the seven-sphere also suggest a possible solution of the cosmological constant problem involving fermion condensates. 相似文献
16.
M.J. Duff 《Nuclear Physics B》1983,219(2):389-411
N = 1 supergravity in d = 11 dimensions spontaneously compactifies on S7 to an N = 8 supergravity in d = 4 with a local SO(8) × SO(8) invariance, probably enlargeable to SO(8) × SU(8). Apart from group manifolds, S7 is the only compact manifold to admit an absolute parallelism. This permits (a) a “squashing” of S7 which gives expectation values to the scalar fields and (b) a parallelizing “torsion” which gives expectation values to the pseudoscalars. This correspondence between extrema of the d = 4 effective potential and solutions of the d = 11 field equations provides a Kaluza-Klein origin for the spontaneous breakdown of gauge symmetries, discrete symmetries, and supersymmetries. It also puts a new perspective on the puzzle of the cosmological constant. 相似文献
17.
The paper reports on the barrier mid-wave infrared InAs/InAsSb (xSb = 0.4) type-II superlattice detector operating below thermoelectrical cooling. AlAsSb with Sb composition, xSb = 0.97; barrier doping, ND < 2×1016 cm?3 leading to valence band offset below 100 meV in relation to the active layer doping, ND = 5×1015 cm?3 was proved to be proper material not introducing extra barrier in valence band in the analyzed temperature range in XBn architectures. The detectivity of the simulated structure was assessed at the level of ~ 1011 Jones at T ~ 100 K assuming absorber thickness, d = 3 μm. The detector’s architecture for high frequency response operation, τs = 420 ps (T ~ 77 K) was presented with a reduced active layer of d = 1 μm. 相似文献
18.
Integral yields of spontaneous emission at wavelengths of 1.73, 2.03, and 2.65 μm have been measured upon excitation of pure xenon by a pulsed electron beam. These yields have been analyzed and experimental data have been obtained on time constants of radiative transitions 5d[3/2]1 → 6p[5/2]2, 5d[3/2]1 → 6p[3/2]1, and 5d[3/2]1 → 6p[1/2]0 of XeI, which appeared to be equal to (2300 ± 400) × 10?9, (300 ± 40) × 10?9, and (1300 ± 200) × 10?9 s, respectively. It is shown that the experimental data are in a qualitative agreement with the results of computational and theoretical investigations. The results of averaging the experimental and calculated data are proposed for use as recommended values of the corresponding constants. 相似文献
19.
《Infrared physics》1993,34(1):75-81
This paper presents a numerical analysis of infrared (IR) plasma reflectivity minimum in ultra heavily doped (UHD) n-Si (impurity concentration N up to 6 × 1021cm−3) by using a self-consistent method (SCM) and a complex physical model. The necessity of taking into account the dependence of effective mass on impurity concentration is shown. The scattering on defects (Ndef = 5 × 1017 cm−3) and dislocation (Ndis = 5 × 1011 cm−2) is included. The approximate relation for the wavelength λm(N) of the reflectivity minimum is given. The results obtained are compared with the experimental results for n-Si and satisfactory agreement is found. 相似文献
20.
I. I. Bondouk F. Machali Z. A. Saleh 《Zeitschrift für Physik A Hadrons and Nuclei》1970,236(2):170-175
The angular distributions of the polarization of protons from C12(d,p)C13(g.s) reaction were measured at 200 keV intervals for deuteron energies from 1.40 to 2.40 MeV. Elastic scattering on C12 at 45 ° (lab) was used to analyze the polarization. Positive sign of the polarization corresponds to the vector productK d ×K p . The maximum polarization observed is about 30%. The results are not similar to those obtained from the mirror reaction C12(d,n)N13 in the same deuteron energy range. 相似文献