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1.
Dark energy with the usually used equation of state p=γρ, where γ=const<0 is hydrodynamically unstable. To overcome this drawback we consider the cosmology of a perfect fluid with a linear equation
of state of a more general form p=α(ρ−ρ
0), where the constants α and ρ
0 are free parameters. The anisotropic Bianchi type-I cosmological model filled with dark energy has been considered. A generalized
equation of state for the dark energy component of the universe has been used. The exact solutions to the corresponding Einstein
field equations and the statefinder diagnostic pair i.e. {r,s} parameters have been obtained in three interesting cases (i) when ρ
Λ>0 and A>0 (ii) when ρ
Λ>0 and A<0 and (iii) when ρ
Λ<0 and A>0 at the singularities i.e. t→0 and t→±∞. 相似文献
2.
K. A. Bronnikov B. E. Meierovich 《Journal of Experimental and Theoretical Physics》2008,106(2):247-264
We consider (d
0 + 2)-dimensional configurations with global strings in two extra dimensions and a flat metric in d
0 dimensions, endowed with a warp factor e
2γ depending on the distance l from the string center. All possible regular solutions of the field equations are classified by the behavior of the warp
factor and the extradimensional circular radius r(l). Solutions with r → ∞ and r → const > 0 as l → ∞ are interpreted in terms of thick brane-world models. Solutions with r → 0 as l → l
c > 0, i.e., those with a second center, are interpreted as either multibrane systems (which are appropriate for large enough
distances l
c between the centers) or as Kaluza-Klein-type configurations with extra dimensions invisible due to their smallness. In the
case of the Mexican-hat symmetry-breaking potential, we build the full map of regular solutions on the (ɛ, Γ) parameter plane,
where ɛ acts as an effective cosmological constant and Γ characterizes the gravitational field strength. The trapping properties
of candidate brane worlds for test scalar fields are discussed. Good trapping properties for massive fields are found for
models with increasing warp factors. Kaluza-Klein-type models are shown to have nontrivial warp factor behaviors, leading
to matter particle mass spectra that seem promising from the standpoint of hierarchy problems.
The text was submitted by the authors in English. 相似文献
3.
S. D. Troitskaya 《Russian Journal of Mathematical Physics》2010,17(3):342-362
A class of solutions, decaying as t → ∞, of a two-dimensional model problem on the oscillations of an ideal rotating fluid in some domains with angular points
is constructed explicitly. The existence of solutions whose L
2-norms decrease more rapidly than any negative power of t is established. 相似文献
4.
For stationary cylindrically symmetric solutions of the Einstein-Maxwell equation we have shown that the “charged” solutions
of McCrea, Chitre et al. (CGN), Van den Bergh and Wils (VW) can be obtained from the seed metrics using generating conjecture.
The McCrea “charged” solution has as a seed vacuum metric the Van Stockum solution with a Killing vector (0, 0, 1, 0). The
CGN “charged” solution and the VW “charged” solution have the static seed metrics connected by the complex substitutiont → iz, z → it and the Killing vector which is a simple linear combination of∂
ϕ
and∂
t
Killing vectors (VW), respectively∂
ϕ
and∂
z
Killing vectors (CGN). 相似文献
5.
Quantum harmonic oscillators with spring constants k > 0 plus constant forces f exhibit rescaled and displaced Hermite—Gaussian wave functions, and discrete, lower bound spectra. We examine their limits
when (k, f) → (0, 0) along two different paths. When f → 0 and then k → 0, the contraction is standard: the system becomes free with a double continuous, positive spectrum, and the wave functions
limit to plane waves of definite parity. On the other hand, when k → 0 first, the contraction path passes through the free-fall system, with a continuous, nondegenerate, unbounded spectrum
and displaced Airy wave functions, while parity is lost. The subsequent f → 0 limit of the nonstandard path shows the dc hysteresis phenomenon of noncommuting contractions: the lost parity reappears
as an infinitely oscillating superposition of the two limiting solutions that are related by the symmetry.
The text was submitted by the authors in English.
On sabatical leave from Physics Department, Ben Gurion University of the Negev, Beer Sheva, Israel.
on leave from the Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Russia. 相似文献
6.
7.
The Einstein-Maxwell equations for non-static charged shear-free spherically symmetric perfect fluid distribution reduce to
a second-order non-linear differential equation in the radial parameter. Several solutions of this equation have been obtained
in earlier work without considering the general requirement for physical relevance of the solutions. Generally physically
acceptable relativistic fluid models demand that the solutions satisfy the reality conditions ρ ≥ 0, p ≥ 0, ρ
r
≤ 0, etc. throughout the fluid model. In this article the expression for density gradient ρ
x
(or ρ
r
) has been utilized to produce charged shear-free relativistic fluid models with non-positive density gradient (NDG)ρ
r
≤ 0. Eventually, we have found that none of the Riccati solutions have NDG including Vaidya metric. Also, the solutions with
NDG neither possess Lie-symmetries nor Painlevé property. Further, it is observed that the solutions with NDG have no uncharged
analogue. 相似文献
8.
High-statistics data on the γγ → π0η reaction will make it possible to conclude whether the K
+
K
−-loop rescattering mechanism, γγ → K
+
K
− → a
0(980) → π0η, is the main mechanism of the production of a
0(980) isovector resonance. This mechanism provides a reasonable value of 20–30 nb at the maximum for the manifestation of
a
0(980) in the γγ → π0η cross section. It also gives rise to a noticeable narrowing of the a
0(980) peak to its effective (observed) width ≈20–30 MeV in the γγ → π0η channel. The decay width averaged over the resonance mass distribution is 〈Γα
0 → K
+
K
− → γγ〉πη ≈ 0.13 keV. The experimental confirmation of this scenario would be important evidence in favor of the q
2
$
\bar q
$
\bar q
2 nature of light scalar mesons. 相似文献
9.
R. Escribano 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):454-457
The scalar contributions to the radiative decay φ→K
0ˉ0
γ are studied within the framework of the Linear Sigma Model (LσM). Theoretical predictions for the associated subprocesses φ→f
0
γ and φ→a
0
γ as well as the ratio φ→f
0
γ/a
0
γ are also given. 相似文献
10.
R. N. Garifullin B. I. Suleimanov 《Journal of Experimental and Theoretical Physics》2010,110(1):133-146
An analysis is presented of the effect of weak dispersion on transitions from weak to strong discontinuities in inviscid fluid
dynamics. In the neighborhoods of transition points, this effect is described by simultaneous solutions to the Korteweg—de
Vries equation u
t
′ + uu
x
″ + u
xxx
‴ = 0 and fifth-order nonautonomous ordinary differential equations. As x2 + t
2 →∞, the asymptotic behavior of these simultaneous solutions in the zone of undamped oscillations is given by quasi-simple
wave solutions to Whitham equations of the form r
i(t, x) = tli x/t2. 相似文献
11.
The correlations of the linear and circular polarizations in the system of two photons have been theoretically investigated.
The polarization of a two-photon state is described by the one-photon Stokes parameters and by the components of the correlation
“tensor” in the Stokes space. It is shown that in the case of two-photon decays π0 → 2γ, η → 2γ, K
L
0 → 2γ, K
S
0 → 2γ and the cascade process |0〉 → |1〉 + γ → |0〉 + 2γ(|0〉 and |1〉 are states with the spin 0 and 1, respectively) the final
two-photon state represents a characteristic example of the entangled (nonfactorizable) state, and the correlations between
the Stokes parameters in all these decays have the purely quantum character: the incoherence inequalities of the Bell type
for the components of the correlation “tensor”, established previously for the case of classical “mixtures”, are violated.
The general analysis of the registration procedure for two correlated photons by two one-photon detectors is performed. 相似文献
12.
We define a nonlinear model for fractional relaxation phenomena. We use ε-expansion method to analyse this model. By studying the fundamental solutions of this model we find that when t → 0 the model exhibits a fast decay rate and when t → ∞ the model exhibits a power-law decay. By analysing the frequency response we find a logarithmic enhancement for the relative
ratio of susceptibility. 相似文献
13.
High-statistics Belle data on the γγ → π0η reaction have been analyzed in order to reveal the mechanism of two-photon production and the nature of the a
0(980) resonance. The solution obtained for the γγ → π0η amplitude is in agreement with the predictions of the chiral theory for the πη-scattering length; with the strong coupling
of the a
0(980) resonance with the πη, K
$
\bar K
$
\bar K
, and πη′ channels; and with the key role of the a
0(980) → (K
$
\bar K
$
\bar K
+ π0η + π0η′) → γγ rescattering mechanisms in the a
0(980) → γγ decay. This picture is much in favor of the q
2
$
\bar q
$
\bar q
2 nature of a
0(980) resonance and is consistent with the properties of its partners, σ0(600) and f
0(980) resonances, in particular, with those manifested in the γγ → ππ reactions. The important role of vector exchanges in
the formation of the nonresonant background in the γγ → π0η reaction has been revealed. Preliminary information on the π0η → π0η reaction has been obtained. 相似文献
14.
Height Fluctuations in the Honeycomb Dimer Model 总被引:1,自引:0,他引:1
Richard Kenyon 《Communications in Mathematical Physics》2008,281(3):675-709
We study a model of random surfaces arising in the dimer model on the honeycomb lattice. For a fixed “wire frame” boundary
condition, as the lattice spacing ϵ → 0, Cohn, Kenyon and Propp [3] showed the almost sure convergence of a random surface to a non-random limit shape Σ0. In [12], Okounkov and the author showed how to parametrize the limit shapes in terms of analytic functions, in particular
constructing a natural conformal structure on them. We show here that when Σ0 has no facets, for a family of boundary conditions approximating the wire frame, the large-scale surface fluctuations (height
fluctuations) about Σ0 converge as ϵ → 0 to a Gaussian free field for the above conformal structure. We also show that the local statistics of the fluctuations
near a given point x are, as conjectured in [3], given by the unique ergodic Gibbs measure (on plane configurations) whose slope is the slope
of the tangent plane of Σ0 at x. 相似文献
15.
Optical nuclear polarization technique is used to study metastable properties of the gold donor center in silicon. A model
of a deep defect’s symmetry changing C
3V
→ C
1h
→ D
2d
with its charge state (D− → D0 → D+) is proposed to account for the observed optically induced quenching and regeneration of Au0 centers. 相似文献
16.
This paper is contributed to explore all possible single peakon solutions for the Degasperis–Procesi (DP) equation m
t
+ m
x
u + 3mu
x
= 0, m = u − u
xx
. Our procedure shows that the DP equation either has cusp soliton and smooth soliton solutions only under the inhomogeneous boundary condition lim|x|→ ∞
u =A ≠0, or possesses the regular peakon solutions ce
− |x − ct| ∈ H
1 (c is the wave speed) only when lim|x|→ ∞
u = 0 (see Theorem 4.1). In particular, we first time obtain the stationary cuspon solution of the DP equation. Moreover we present new cusp solitons (in the space of ) and smooth soliton solutions in an explicit form. Asymptotic analysis and numerical simulations are provided for smooth
solitons and cusp solitons of the DP equation.
相似文献
17.
Hai-Yang Cheng 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):647-653
The parametersχ
1,2, which measure nonfactorizable soft gluon contributions to hadronic weak decays of mesons, are updated by extracting them
from the data ofD, B→PP, VP decays (P: pseudoscalar meson,V: vector meson). It is found thatχ
2 ranges from −0.36 to −0.60 in the decays fromD→Kπ toD
+→φπ
+,D→K*π, while it is of order 10% with a positive sign inB→ψK, Dπ, D*π, Dρ decays. Therefore, the effective parametera
2 is process dependent in charm decay, whereas it stays fairly stable inB decay. This is in accordance with the picture that nonfactorizable soft gluon effects become stronger when the relative momentum
of the decay particles becomes smaller. As forD, B→VV decays, the presence of nonfactorizable terms in general prevents a possible definition of effectivea
1 anda
2. This is reinforced by the observation of a large longitudinal polarization fraction inB→ψK* decay, implying nonfactorizable effects contributing differently toS-, P- andD-wave amplitudes. We found thatA
1
nf
/A
1>0>A
2
nf
/A
2,V
nf/V (nf standing for nonfactorization) forB→ψK* decay and 0>A
1
nf
/A
1>A
2
nf
/A
2,V
nf/V forD→K*ρ decay. A measurement of longitudinally and transversely polarized decay rates Γ
L
and Γ
T
in color-suppressed decay modesB
0→D*0
ρ
0,D*0
ω andD
+→φρ
+ is urged. 相似文献
18.
Preliminary data on the reactions e
+
e
−→φ→γ f
0(980)→γπ0π0 together with data on ππ scattering and the reactions J/ψ→φπ+π− and K
−
p→π +π−(Λ,Σ) are analyzed. The analysis shows that the mass of the f
0(980) meson is
= 950 MeV, and BR(φ→γf
0→γπ0π0)≃ 1× 10−4, indicating that the f
0(980) resonance is of a four-quark nature.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 445–449 (10 April 1998) 相似文献
19.
T. Branz T. Gutsche V. Lyubovitskij 《The European Physical Journal A - Hadrons and Nuclei》2008,37(3):303-317
We discuss a possible interpretation of the f
0(980)-meson as a hadronic molecule —a bound state of K and mesons. Using a phenomenological Lagrangian approach we calculate the strong f
0(980) → ππ and electromagnetic f
0(980) → γγ decays. The compositeness condition provides a self-consistent method to determine the coupling constant between
f
0 and its constituents, K and . Form factors governing the decays of the f
0(980) are calculated by evaluating the kaon loop integrals. The predicted f
0(980) → ππ and f
0(980) → γγ decay widths are in good agreement with available data and results of other theoretical approaches. 相似文献
20.
N. N. Achasov 《Physics of Atomic Nuclei》2007,70(5):862-863
It is argued that the realization of gauge invariance condition as a consequent of cancellation between the ϕ → γf
0 → γπ
0
π
0 resonance contribution and the ϕ → γπ
0
π
0 background one, suggested by A.V. Anisovich et al., Yad. Fiz. 68, 1614 (2005), is misleading.
The text was submitted by the author in English. 相似文献