共查询到20条相似文献,搜索用时 0 毫秒
1.
We introduce the idea of local symmetry breaking by impurities to explain the recently observed splitting of the J=0-->1 propagating excitation in doped Sm1-xYxS. While preserving the global cubic symmetry of the crystal, Y impurities change the local crystal-field environment of each Sm ion from cubic to tetragonal, thereby splitting the J=1 triplet into a m(i).J=0 level with energy Delta(1) and a m(i).J=+/-1 doublet with energy Delta(2)>Delta(1). A model with a randomly oriented quantization axis m(i) fits not only the observed mode frequencies but also their intensities, which strongly depends on the wave vector. 相似文献
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Bittner S Dietz B Günther U Harney HL Miski-Oglu M Richter A Schäfer F 《Physical review letters》2012,108(2):024101
We demonstrate the presence of parity-time (PT) symmetry for the non-Hermitian two-state Hamiltonian of a dissipative microwave billiard in the vicinity of an exceptional point (EP). The shape of the billiard depends on two parameters. The Hamiltonian is determined from the measured resonance spectrum on a fine grid in the parameter plane. After applying a purely imaginary diagonal shift to the Hamiltonian, its eigenvalues are either real or complex conjugate on a curve, which passes through the EP. An appropriate basis choice reveals its PT symmetry. Spontaneous symmetry breaking occurs at the EP. 相似文献
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I. V. Dzedolik 《Technical Physics》2006,51(7):932-937
Conditions for spontaneous symmetry breaking and generation of quasi-particles in an insulator through which an electromagnetic field propagates are considered. The order parameter of the system is determined. The mass spectrum of the quasi-particles is found in the cases of linear and nonlinear propagation through the medium with and without interfaces. 相似文献
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We investigate the use of UV-pump-UV-probe schemes to trace the evolution of nuclear wave packets in excited molecular states by analyzing the asymmetry of the electron angular distributions resulting from dissociative ionization. The asymmetry results from the coherent superposition of gerade and ungerade states of the remaining molecular ion in the region where the nuclear wave packet launched by the pump pulse in the neutral molecule is located. Hence, the variation of this asymmetry with the time delay between the pump and the probe pulses parallels that of the moving wave packet and, consequently, can be used to clock its field-free evolution. The performance of this method is illustrated for the H(2) molecule. 相似文献
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Spontaneous symmetry breaking of a
4 quantum of field theory in a time-dependent space-time, de Sitter space, is discussed in the Schrödinger picture. Instead of the usual cutoff method we use an-regularization procedure to deal with the divergent integrals. 相似文献
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S. Narison 《Physics letters. [Part B]》1984,142(3):168-172
Using a spectral function sum rules approach, we derive some constraints among the Goldstone parameters, the lowest dimension vacuum condensates and the mass of the chiral matter superfield in supersymmetric QCD (SQCD). These relations are consistent with previous results on SQCD and complement them. 相似文献
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A complex eigenvalue in the Bogoliubov–de Gennes equations for a stationary Bose–Einstein condensate in the ultracold atomic system indicates the dynamical instability of the system. We also have the modes with zero eigenvalues for the condensate, called the zero modes, which originate from the spontaneous breakdown of symmetries. Although the zero modes are suppressed in many theoretical analyses, we take account of them in this paper and argue that a zero mode can change into one with a pure imaginary eigenvalue by applying a symmetry breaking external perturbation potential. This emergence of a pure imaginary mode adds a new type of scenario of dynamical instability to that characterized by the complex eigenvalue of the usual excitation modes. For illustration, we deal with two one-dimensional homogeneous Bose–Einstein condensate systems with a single dark soliton under a respective perturbation potential, breaking the invariance under translation, to derive pure imaginary modes. 相似文献
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Hirofumi Yamada 《Zeitschrift fur Physik C Particles and Fields》1993,59(1):67-75
We study dynamical chiral symmetry breaking in massless QCD by the use of the generalized Hartree-Fock method. As the order parameter of chiral symmetry we choose the dynamical quark mass in the zero momentum limit which we call low energy quark mass. We calculate the low energy mass to the second order of diagrammatic expansion around shifted perturbative vacuum. We then show that the mass is finite and renormalization group invariant. After the improvement of the result by the method of effective charges we estimate the mass in the true vacuum under the gap and stationarity conditions and demonstrate that both of them produce non-zero mass proportional to a conventional scale, which breaks down the chiral symmetry. 相似文献
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A. Bouquet 《Zeitschrift fur Physik C Particles and Fields》1979,3(1):65-74
The implications of the breaking of SU (N) flavor symmetry are studied at the planar and cylinder levels of the Dual Topological Unitarization scheme. It is shown that the ρ intercept is constrained to lie between 0.51 and 0.54, and that SU (4) symmetry is necessarily more strongly broken that SU (3). The matrix structure of the cylinder bootstrap equations is shown to suppress many of the problems of the “cylinder extinction of the planar poles”, and to lead to a sensible singularity spectrum. 相似文献
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T. Li 《The European Physical Journal C - Particles and Fields》2002,24(4):595-612
We study the supersymmetric GUT models in which the supersymmetry and GUT gauge symmetry can be broken by a discrete symmetry.
First, with the ansatz that there exist discrete symmetries in the branes' neighborhoods, we discuss the general reflection
symmetries and GUT breaking on and . In those models, the extra dimensions can be large and the KK states can be set arbitrarily heavy. Second, considering that
the extra space manifold is the annulus or the disc , we can define any symmetry and break any 6-dimensional N=2 supersymmetric SU(M) models down to the 4-dimensional N=1 supersymmetric models for the zero modes. In particular, there might exist the interesting scenario on where just a few KK states are light, while the others are relatively heavy. Third, we discuss the complete global discrete
symmetries on and study the GUT breaking.
Received: 12 February 2002 / Published online: 14 June 2002 相似文献
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Jacob D. Bekenstein 《Foundations of Physics》1986,16(5):409-422
It is pointed out that the Higgs field may be supplanted by an ordinary Klein-Gordon field conformally coupled to the space-time curvature, and with very small, real, rest mass. Provided there is a bare cosmological constant of order of its square mass, this field can induce spontaneous symmetry breaking with a mass scale that can be as large as the Planck-Wheeler mass, but may be smaller. It can thus play a natural role in grand unified theories. In the theory presented here the physical cosmological constant is small, being of order of the squared mass, and can meet observational constraints without having to be cancelled accurately. The physical gravitational constant differs somewhat from the coupling constant in Einstein's equation, and is temperature dependent in the broken symmetry regime. Symmetry restoration occurs at high temperature.Research supported by the Arnow Chair in Astrophysics. 相似文献
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D. Atkinson P. W. Johnson M. Koopmans 《Zeitschrift fur Physik C Particles and Fields》1987,34(1):99-101
By applying bifurcation theory to a truncated Dyson-Schwinger equation for the quark propagator in massless QCD, we show that dynamical symmetry breaking occurs at a certain critical value of the coupling constant. Essential ingredients are (a) an effective dynamical mass for the gluon, and (b) a running coupling constant. 相似文献
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We analyze the atomic dynamics in an ac driven periodic optical potential which is symmetric in both time and space. We experimentally demonstrate that in the presence of dissipation the symmetry is broken, and a current of atoms through the optical lattice is generated as a result. 相似文献
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J.F. Luciani 《Nuclear Physics B》1978,135(1):111-130
We look for solutions of the Einstein-Yang-Mills equations in a 4 + D dimensional space-time. We find solutions where the first 4 dimensions are a flat Minkowskian space-time, while the D others are a compact, space-like manifold of small size. Such solutions can be obtained for an arbitrary compact gauge group K and are invariant under a sub-group G of K related to the space-time geometry. This shows that 4 + D dimensional gravity can give a mechanism for the super-strong symmetry breaking needed in grand unified field theories without introducing Higgs scalars. 相似文献
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The soft mode dynamics and related properties of perovskite, ABO3-type crystals have been studied using the operator form of the model Hamiltonian proposed by Pytte. The correlations have
been evaluated using the double time thermal Green’s function technique and Dyson’s equation. Without any decoupling, the
higher order correlations, appearing in the dynamical equation, have been evaluated using the renormalized Hamiltonian. The
dielectric properties are directly related to the optical soft mode. The phonon width and shift have been calculated for different
structural phases. The analysis of the temperature dependence of microwave loss tangent and dielectric constant explains the
experimental results. 相似文献