共查询到20条相似文献，搜索用时 343 毫秒
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2.
Peebles PJ 《The Astrophysical journal》2000,534(2):L127-L129
Dark matter modeled as a classical scalar field that interacts only with gravity and with itself by a potential that is close to quartic at large field values and approaches a quadratic form when the field is small would be gravitationally produced by inflation and, at the present epoch, could act like an ideal fluid with pressure that is a function only of the mass density. This could have observationally interesting effects on the core radii and solid-body rotation of dark matter halos and on the low-mass end of the primeval mass fluctuation power spectrum. 相似文献
3.
Theories with Lagrangians nonlinear in the curvature scalar can be reduced by appropriate transformations to a form similar to the Brans-Dicke model. This may enable us to have extended inflation in the early universe without the difficulties of introducing scalar fields. 相似文献
4.
Recent LHC data provides precise values of coupling constants of the Higgs field, however, these measurements do not determine its coupling with gravity. We explore this freedom to see whether Higgs field non-minimally coupled to Gauss–Bonnet term in 4-dimensions can lead to inflation generating the observed density fluctuations. We obtain analytical solution for this model and that the exit of inflation (with a finite number of e-folding) demands that the energy scale of inflation is close to Electro-weak scale. We compare the scalar and tensor power spectrum of our model with PLANCK data and discuss its implications. 相似文献
5.
A. de la Macorra 《Astroparticle Physics》2012,35(7):478-484
We present a model where inflation and Dark Matter takes place via a single scalar field ?. Without introducing any new parameters we are able unify inflation and Dark Matter using a scalar field ? that accounts for inflation at an early epoch while it gives a Dark Matter WIMP particle at low energies. After inflation our universe must be reheated and we must have a long period of radiation dominated before the epoch of Dark Matter. Typically the inflaton decays while it oscillates around the minimum of its potential. If the inflaton decay is not complete or sufficient then the remaining energy density of the inflaton after reheating must be fine tuned to give the correct amount of Dark Matter. An essential feature here, is that Dark Matter-Inflaton particle is produced at low energies without fine tuning or new parameters. This process uses the same coupling g as for the inflaton decay. Once the field ? becomes non-relativistic it will decouple as any WIMP particle, since n? is exponentially suppressed. The correct amount of Dark Matter determines the cross section and we have a constraint between the coupling g and the mass mo of ?. The unification scheme we present here has four free parameters, two for the scalar potential V(?) given by the inflation parameter λ of the quartic term and the mass mo. The other two parameters are the coupling g between the inflaton ? and a scalar filed φ and the coupling h between φ with standard model particles ψ or χ. These four parameters are already present in models of inflation and reheating process, without considering Dark Matter. Therefore, our unification scheme does not increase the number of parameters and it accomplishes the desired unification between the inflaton and Dark Matter for free. 相似文献
6.
We propose a new class of inflationary models in which the scalar field potential governing inflation is generated by the same nonperturbative gauge dynamics that may lead to supersymmetry breaking. Such models satisfy constraints from cosmic microwave background measurements for natural values of the fundamental parameters in the theory. In addition, they have two particularly interesting characteristics: a “blue” spectrum of scalar perturbations, and an upper bound on the total amount of inflation possible. 相似文献
7.
The evolution of a homogeneous, isotropic cosmological model driven by a nonminimally coupled scalar field is studied. The
potential for the quintessential inflation model proposed by Peebles and Vilenkin is selected as a scalar potential. Possible
scenarios for the cosmological dynamics are described in the conformal Einstein and Jordan representations. It is shown that,
unlike in models with a minimal scalar field, here a class of solutions exists for which the scalar field is fixed at finite
values during cosmological expansion.
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Translated from Astrofizika, Vol. 49, No. 3, pp. 487–498 (August 2006). 相似文献
8.
Marcelo Samuel Berman 《Astrophysics and Space Science》2007,310(3-4):205-207
We find a solution for exponential inflation in Brans–Dicke cosmology endowed with a cosmological term, which includes time-varying
shear and vorticity. We find that the scalar field and the scale factor increase exponentialy while shear, vorticity, energy
density, cosmic pressure and the cosmological term decay exponentialy for negative beta, where beta is defined in the text. 相似文献
9.
The aim of this paper is to study the warm inflation during intermediate era in the framework of locally rotationally symmetric Bianchi type I universe model. We assume that the universe is composed of inflaton and imperfect fluid having radiation and bulk viscous pressure. To this end, dynamical equations (first model field equation and energy conservation equations) under slow-roll approximation and in high dissipative regime are constructed. A necessary condition is developed for the realization of this anisotropic model. We assume both dissipation and bulk viscous coefficients variable as well as constant. We evaluate entropy density, scalar (tensor) power spectra, their corresponding spectral indices, tensor–scalar ratio and running of spectral index in terms of inflaton. These cosmological parameters are constrained using recent Planck and WMAP7 probe. 相似文献
10.
In this paper we have studied B-D theory and general scalar tensor theory of Gravitation for anisotropic cosmological model in the false vacuum state. The possibility of both exponential inflation and power function inflation are examined for constant or variable coupling parameter . Also asymptotic limit of the scalar field and are discussed. 相似文献
11.
Enrique Guzmán 《Astrophysics and Space Science》1997,249(2):179-188
We have found that for the Bianchi types I–II–III–V in the Brans-Dicke theory, the scalar field of the theory φ has the same
form in the isotropic case. It is shown that the isotropization of the Universe occurs in a very short time when the Universe
is dominated by vacuum energy, proving that an isotropic Robertson-Walker model is a good approximation to use in the extended
inflation scenario.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
In this paper, we study the dynamics of warm inflation in which slow-roll inflation is driven by non-Abelian gauge fields. To this end, we use the geometry of locally rotationally symmetric Bianchi type I universe model. We construct dynamical equations, i.e., first model field equation, energy conservation equations and equation of motion under slow-roll approximation. In order to discuss inflationary perturbations, we evaluate parameters like scalar and tensor power spectra as well as scalar and tensor spectral indices. We also evaluate inflaton, directional Hubble parameter, slow-roll and perturbation parameters as well as tensor-scalar ratio as a function of inflaton during intermediate and logamediate inflationary eras. It is concluded that anisotropic inflationary universe model with non-Abelian gauge fields remains compatible with WMAP7. 相似文献
13.
Corrado Massa 《Astrophysics and Space Science》1997,253(2):285-289
The possibility that the deceleration parameter q might be a null constant is discussed; such possibilitiy is interesting
because solves the horizon problem and the flatness problem with no need of inflation. A simple way to get q = const = 0 is
explored: the way assumes Einstein's field equations without cosmological term and introduces a massless scalar field V with
negative energy density. Both in the early and in the present universe one finds the Whitrow-Randall relation Gut2 = const 1 G gravitational coupling, u mass-energy density, t cosmic time). The interaction between the V-field and the ordinary
matter is briefly discussed; as possible consequence of this interaction the true value of the Hubble parameter might be one
half the observed value.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Chameleon scalar field is a new model, which introduced to provide a mechanism for exhibiting accelerating universe. Chameleon
field has several interesting aspects, such as field dependence on the local matter density. For this model we introduce a
new kind of potential which has run away form and satisfies chameleon constraints. The results are acceptable in comparison
with the other potentials which studied up to now. 相似文献
15.
A. A. Saaryan 《Astrophysics》1995,38(1):55-67
The low-energy string gravitation is investigated for the case of reduction with a variable (in string units) inner space. A flat cosmological model of the corresponding four-dimensional theory is constructed. The model equations are analyzed qualitatively for a potential-dominated scalar field as the source. It is demonstrated that an extended inflation stage with one purely scalar dilaton field is possible here, in contrast with the case of a constant inner space. The pattern of cosmological evolution in various conformal representations is discussed.Translated from Astrofizika, Vol. 38, No. 1, pp. 99–119, January–March, 1995. 相似文献
16.
In the computation of density perturbation in inflation it is conventional to assume the inflation field to be in the vacuum state. There are, however, some advantages in relaxing this assumption. In an earlier paper we have estimated the density perturbations in a Gaussian coherent state using a toy-model. Here we extend this work by doing an exact analysis of this problem. The advantages of this method is discussed and the results are compared with earlier results 相似文献
17.
V. I. Dokuchaev Yu. N. Eroshenko S. G. Rubin D. A. Samarchenko 《Astronomy Letters》2010,36(11):773-779
A model for the formation of supermassive primordial black holes in galactic nuclei with the simultaneous suppression of the
formation of intermediate-mass black holes is presented. A bimodal mass function for black holes formed through phase transitions
in a model with a “Mexican hat” potential has been found. The classical motion of the phase of a complex scalar field during
inflation has been taken into account. Possible observational manifestations of primordial black holes in galaxies and constraints
on their number are discussed. 相似文献
18.
李元杰 《中国天文和天体物理学报》1992,(3)
我们利用含αR~2+γR_(μv)R~(μv)项的宇宙理论同带有一个标量场φ的Einstein理论之间的等价性,讨论了该宇宙的暴涨行为.结果表明,在D维空时(D>2)中,存在指数型的暴涨解. 相似文献
19.
Best-fitting values of the spectral index of the curvature perturbation are presented, assuming the ΛCDM cosmology. Apart from the spectral index, the parameters are the Hubble parameter, the total matter density and the baryon density. The data points are intended to represent all measurements that are likely to affect the result significantly. The cosmic microwave anisotropy is represented by the COBE normalization, and heights of the first and second peaks are given by the latest Boomerang and Maxima data. The slope of the galaxy correlation function and the matter density contrast on the 8 h −1 Mpc scale are each represented by a data point, as are the expected values of the Hubble parameter and matter density. The 'low-deuterium' nucleosynthesis value of the baryon density provides a final data point, the fit giving a value higher by about one standard deviation. The reionization epoch is calculated from the model by assuming that it corresponds to the collapse of a fraction f ≳10−4 of matter. We consider the case of a scale-independent spectral index, and also the scale-dependent spectral index predicted by running mass models of inflation. In the former case, the result is compared with the prediction of models of inflation based on effective field theory, in which the field value is small on the Planck scale. A detailed comparison is made with other fits, and other approaches to the comparison with theory. 相似文献
20.
The scalar equations of infinitesimal elastic gravitational motion for a rotating, slightly elliptical Earth are always used
to study the Earth's nutation and tides theoretically, while the determination of the integration of the equations depends,
to a certain extent, on the choice of a set of appropriate boundary conditions. In this paper, a continuity quantity related
to the displacement is first transformed from the elliptical reference boundary to the corresponding effective spherical domain,
and then converted from a vector (or tensor) form to a scalar form by generalized surface spherical harmonics expansion. All
the related components, including the displacement vector field (or the stress tensor field), are then decomposed into the
poloidal and toroidal field using the symmetry restrictions on the normal mode eigenfunctions. After truncation, the boundary
conditions are finally derived, in a scalar ordinary differential form. The process of the derivation is second order in ellipticity
and in full detail. Moreover, the other boundary conditions are also presented as second order in ellipticity at the end of
this paper.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献