870 research outputs found
Hawking radiation via tachyon condensation and its implications to tachyon cosmology
Hawking radiation can be derived from the collapsing process of matter to
form a black hole. In this work, we show in more detail that the freely
infalling process of a probe (D-)particle (or point-like object) in a
non-extreme black hole background is essentially a tachyon condensation
process. That is, a probe D-particle will behave as an unstable D-particle in
the near-horizon region of a non-extreme black hole. From this point of view,
Hawking radiation can be viewed as the thermal radiation from rolling tachyon
on an unstable D-particle (i.e., the infalling probe) at the Hagedorn
temperature. The result has interesting implications to tachyon cosmology: the
uniform tachyon rolling in cosmology can automatically create particle pairs at
late times, via a mechanism just like the Hawking radiation process near a
black hole. So this particle creation process can naturally give rise to a hot
universe with thermal perturbations beyond tachyon inflation, providing an
alternative reheating mechanism.Comment: 22 page
Global geoid model GGM2022
We provide an updated 5 5 global geoid model
GGM2022, which is determined based on the shallow layer method (Shen method).
First, we choose an inner surface below the EGM2008 global geoid by 15
m, and the layer bounded by the inner surface and the Earth's
geographical surface is referred to as the shallow layer. The Earth's
geographical surface is determined by the digital topographic model
DTM2006.0 combining with the DNSC2008 mean sea surface. Second, we formulate
the 3D shallow mass layer model using the refined 5 5
crust density model CRUSTre , which { is an improved 5 5 density model of the CRUST2.0 or CRUST1.0 with taking
into account the corrections of the areas covered by ice sheets and the
land-ocean crossing regions. Third, based on the shallow mass layer model and
the gravity field EGM2008 that is defined in the region outside the Earth's
geographical surface , we determine the gravity field model EGM2008s that is
defined in the whole region outside the inner surface , where the
definition domain of the gravity field is extended from the domain outside
to the domain outside . Fourth, based on the gravity field EGM2008s and
the geodetic equation (where is the geopotential constant on
the geoid and is the point on the geoid ), we determine a 5
5 global geoid, which is referred to as GGM2022.
Comparisons show that the GGM2022 fits the globally available GPS/leveling data
better than EGM2008 global geoid in the USA, Europe and the western part of
China.Comment: 17 pages, 25 figure
Stochastic stability and moment Lyapunov exponent for co-dimension two bifurcation system with a bounded noise
In this paper, the pth moment Lyapunov exponent of a co-dimension two bifurcation system that is parametrically excited by a real noise is investigated. By a linear stochastic transformation, the eigenvalue problem of moment Lyapunov exponent is obtained. Then through perturbation method, we deduce the joint probability density function of the phase processes and its eigenvalue problem, which is solved by a Fourier cosine series expansion. Thus, an infinite matrix yields and whose leading eigenvalue is the second order of the asymptotic expansion of the moment Lyapunov exponent. Because of the complexity of elements in matrix A, the eigenvalues of the low order sub-matrices of A are obtained by the truncation of n and the convergence of the eigenvalue sequence is numerically illustrated. Finally, the effects of the system and noise parameters on the moment Lyapunov exponent are discussed
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