206 research outputs found
Nonrelativistic isothermal fluid in the presence of a chameleon scalar field: Static and collapsing configurations
We consider a gravitating spherically symmetric nonrelativistic configuration
consisting of a massless chameleon scalar field nonminimally coupled to a
perfect isothermal fluid. The object of this paper is to show the influence of
the chameleon scalar field on the structure and evolution of an isothermal
sphere. For this system we find static, singular and regular solutions
depending on the form of the coupling function. A preliminary stability
analysis indicates that both stable and unstable solutions exist. For unstable
configurations, by choosing the special form of the coupling function, we
consider the problem of the gravitational collapse by applying the similarity
method.Comment: 16 pages, 3 figures, minor corrections to content, references added,
matches PRD accepted versio
Anisotropic neutron stars in gravity
We consider static neutron stars within the framework of gravity. The
neutron fluid is described by three different types of realistic equations of
state (soft, moderately stiff, and stiff). Using the observational data on the
neutron star mass-radius relation, it is demonstrated that the characteristics
of the objects supported by the isotropic fluid agree with the observations
only if one uses the soft equation of state. We show that the inclusion of the
fluid anisotropy enables one also to employ more stiff equations of state to
model configurations that will satisfy the observational constraints
sufficiently. Also, using the standard thin accretion disk model, we
demonstrate potentially observable differences, which allow us to distinguish
the neutron stars constructed within the modified gravity framework from those
described in Einstein's general relativity.Comment: 14 pages, 4 figures, minor corrections to content, new references
added, version published in PR
Thick brane solutions supported by two spinor fields
Stationary thick brane solutions supported by two spinor fields are
considered. Two spinor fields are used here to exclude the off-diagonal
components of the energy-momentum tensor of the spinor fields. The trapping of
a test scalar field on the brane is also considered.Comment: 6 pages, 2 fig'
Kaluza-Klein wormholes with the compactified fifth dimension
We consider wormhole solutions in five-dimensional Kaluza-Klein gravity in
the presence of a massless ghost four-dimensional scalar field. The system
possesses two types of topological nontriviality connected with the presence of
the scalar field and of a magnetic charge. Mathematically, the presence of the
charge appears in the fact that the part of a spacetime metric is the
Hopf bundle with fibre . We show that the fifth
dimension spanned on the sphere is compactified in the sense that
asymptotically, at large distances from the throat, the size of is equal
to some constant, the value of which can be chosen to lie, say, in the Planck
region. Then, from the four-dimensional point of view, such a wormhole contains
a radial magnetic (monopole) field, and an asymptotic four-dimensional observer
sees a wormhole with the compactified fifth dimension.Comment: 6 pages, 3 figure
Dirac stars supported by nonlinear spinor fields
We study configurations consisting of a gravitating spinor field with
a nonlinearity of the type . To ensure
spherical symmetry of the configurations, we use two spin- fields
forming a spin singlet. For such systems, we find regular stationary
asymptotically flat solutions describing compact objects. For negative values
of the coupling constant , it is shown that, by choosing physically
reasonable values of this constant, it is possible to obtain configurations
with masses comparable to the Chandrasekhar mass. It enables us to speak of an
astrophysical interpretation of the obtained systems, regarding them as Dirac
stars.Comment: 8 pages, 4 figures, minor corrections to content, new reference
added, version published in PR
Spinor field solutions in modified Weyl gravity
We consider modified Weyl gravity where a Dirac spinor field is nonminimally
coupled to gravity. It is assumed that such modified gravity is some
approximation for the description of quantum gravitational effects related to
the gravitating spinor field. It is shown that such a theory contains solutions
for a class of metrics which are conformally equivalent to the Hopf metric on
the Hopf fibration. For this case, we obtain a full discrete spectrum of the
solutions and show that they can be related to the Hopf invariant on the Hopf
fibration. The expression for the spin operator in the Hopf coordinates is
obtained. It is demonstrated that this class of conformally equivalent metrics
contains: (a) a metric describing a toroidal wormhole without exotic matter;
(b) a cosmological solution with a bounce and inflation; and (c) a transition
with a change in metric signature. A physical discussion of the results is
given. \end{abstract}Comment: 11page
Scalar model of SU(N) glueball \`a la Heisenberg
Nonperturbative model of glueball is studied. The model is based on the
nonperturbative quantization technique suggested by Heisenberg. 2- and 4-point
Green functions for a gauge potential are expressed in terms of two scalar
fields. The first scalar field describes quantum fluctuations of the subgroup
, and the second one describes quantum fluctuations of the
coset . An effective Lagrangian for the scalar fields is
obtained. The coefficients for all terms in the Lagrangian are calculated, and
it is shown that they depend on . It is demonstrated
that a spherically symmetric solution describing the glueball does exist.Comment: 2 figures, 8 page
Energy spectrum and the mass gap from nonperturbative quantization \`a la Heisenberg
Using approximate methods of nonperturbative quantization \`a la Heisenberg
and taking into account the interaction of gauge fields with quarks, we find
regular solutions describing the following configurations: (i) a spinball
consisting of two virtual quarks with opposite spins; (ii) a quantum monopole;
(iii) a spinball-plus-quantum-monopole system; and (iv) a
spinball-plus-quantum-dyon system. A comparison with quasi-particles obtained
by lattice and phenomenological analytical calculations is carried out. All
these objects (except the spinball) are embedded in a bag created by the
quantum coset condensate consisting of the SU(3)/(SU(2)~~U(1)) gauge
fields. The existence of these objects is due to the Meissner effect, which
implies that the SU(2)~~U(1) gauge fields are expelled from the
condensate. The physical interpretation of these solutions is proposed in two
different forms: (i) an approximate glueball model; and (ii) quantum
fluctuations in the coset condensate of the nonperturbative vacuum or in a
quark-gluon plasma. For the spinball and the spinball-plus-quantum-monopole
configuration, we obtain energy spectra, in which mass gaps are present. The
process of deconfinement is discussed qualitatively. It is shown that the
quantum chromodynamics constant appears in the
nonperturbative quantization \`a la Heisenberg as some constant controlling the
correlation length of quantum fields in a spacelike direction.Comment: 19 pages, 19 figure
Quantum Evolution of the Dilaton-Inflaton Model
The quantum evolution of a model of the universe with account of two scalar
fields ({\it dilaton} and {\it inflaton}) is considered. For this case, the
closed and flat models has been examined. It is shown that in both cases the
realization of conditions necessary for inflation is strongly depends on
coupling constant for dilaton and inflaton fields.Comment: 11 pages, 4 figure
Spinor brane
The thick brane model supported by a nonlinear spinor field is constructed.
The different cases with the various values of the cosmological constant
are investigated. It is shown that regular analytical
spinor thick brane solutions with asymptotically Minkowski (at ) or
anti-de Sitter spacetimes (at ) do exist.Comment: errors are correcte
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