49 research outputs found
Structure formation in the Lemaitre-Tolman model
Structure formation within the Lemaitre-Tolman model is investigated in a
general manner. We seek models such that the initial density perturbation
within a homogeneous background has a smaller mass than the structure into
which it will develop, and the perturbation then accretes more mass during
evolution. This is a generalisation of the approach taken by Bonnor in 1956. It
is proved that any two spherically symmetric density profiles specified on any
two constant time slices can be joined by a Lemaitre-Tolman evolution, and
exact implicit formulae for the arbitrary functions that determine the
resulting L-T model are obtained. Examples of the process are investigated
numerically.Comment: LaTeX 2e plus 14 .eps & .ps figure files. 33 pages including figures.
Minor revisions of text and data make it more precise and consistent.
Currently scheduled for Phys Rev D vol 64, December 15 issu
The physical meaning of the "boost-rotation symmetric" solutions within the general interpretation of Einstein's theory of gravitation
The answer to the question, what physical meaning should be attributed to the
so-called boost-rotation symmetric exact solutions to the field equations of
general relativity, is provided within the general interpretation scheme for
the ``theories of relativity'', based on group theoretical arguments, and set
forth by Erich Kretschmann already in the year 1917.Comment: 9 pages, 1 figure; text to appear in General Relativity and
Gravitatio
A modification of Einstein-Schrodinger theory that contains Einstein-Maxwell-Yang-Mills theory
The Lambda-renormalized Einstein-Schrodinger theory is a modification of the
original Einstein-Schrodinger theory in which a cosmological constant term is
added to the Lagrangian, and it has been shown to closely approximate
Einstein-Maxwell theory. Here we generalize this theory to non-Abelian fields
by letting the fields be composed of dxd Hermitian matrices. The resulting
theory incorporates the U(1) and SU(d) gauge terms of
Einstein-Maxwell-Yang-Mills theory, and is invariant under U(1) and SU(d) gauge
transformations. The special case where symmetric fields are multiples of the
identity matrix closely approximates Einstein-Maxwell-Yang-Mills theory in that
the extra terms in the field equations are 10^-13 of the usual terms for
worst-case fields accessible to measurement. The theory contains a symmetric
metric and Hermitian vector potential, and is easily coupled to the additional
fields of Weinberg-Salam theory or flipped SU(5) GUT theory. We also consider
the case where symmetric fields have small traceless parts, and show how this
suggests a possible dark matter candidate.Comment: latex2e, generalized from U(1)xSU(2) to U(1)xSU(d
Alternative scheme to generate a supersinglet state of three-level atoms
In this paper we propose an alternative scheme to generate a supersinglet
state of three three-level atoms via a single-mode of a cavity QED based on the
two-photon transitions described by the 'full microscopical Hamiltonian
approach'. In it, three three-level atoms prepared in suitable initial states
are sequentially sent through the cavity originally prepared in its vacuum
state. After an appropriate choice of the atom-cavity interaction times plus a
field detection the state that describes the whole atom-field system is
projected in the desired supersinglet state. The fidelity and success
probability of the state as well as the practical feasibility of the scheme are
discussed.Comment: 10 pages, 3 figures, 4 table
Gravitomagnetism and the Clock Effect
The main theoretical aspects of gravitomagnetism are reviewed. It is shown
that the gravitomagnetic precession of a gyroscope is intimately connected with
the special temporal structure around a rotating mass that is revealed by the
gravitomagnetic clock effect. This remarkable effect, which involves the
difference in the proper periods of a standard clock in prograde and retrograde
circular geodesic orbits around a rotating mass, is discussed in detail. The
implications of this effect for the notion of ``inertial dragging'' in the
general theory of relativity are presented. The theory of the clock effect is
developed within the PPN framework and the possibility of measuring it via
spaceborne clocks is examined.Comment: 27 pages, LaTeX, submitted to Proc. Bad Honnef Meeting on: GYROS,
CLOCKS, AND INTERFEROMETERS: TESTING GENERAL RELATIVITY IN SPACE (22 - 27
August 1999; Bad Honnef, Germany
Cosmological expansion and local systems: a Lema\^{i}tre-Tolman-Bondi model
We propose a Lema\^{i}tre-Tolman-Bondi system mimicking a two-body system to
address the problem of the cosmological expansion versus local dynamics. This
system is strongly bound but participates in the cosmic expansion and is
exactly comoving with the cosmic substratum
Gauged motion in general relativity and in Kaluza-Klein theories
In a recent paper [1] a new generalization of the Killing motion, the {\it
gauged motion}, has been introduced for stationary spacetimes where it was
shown that the physical symmetries of such spacetimes are well described
through this new symmetry. In this article after a more detailed study in the
stationary case we present the definition of gauged motion for general
spacetimes. The definition is based on the gauged Lie derivative induced by a
threading family of observers and the relevant reparametrization invariance. We
also extend the gauged motion to the case of Kaluza-Klein theories.Comment: 42 pages, revised version, typos correction along with some minor
changes, Revtex forma
Engineering a C-Phase quantum gate: optical design and experimental realization
A two qubit quantum gate, namely the C-Phase, has been realized by exploiting
the longitudinal momentum (i.e. the optical path) degree of freedom of a single
photon. The experimental setup used to engineer this quantum gate represents an
advanced version of the high stability closed-loop interferometric setup
adopted to generate and characterize 2-photon 4-qubit Phased Dicke states. Some
experimental results, dealing with the characterization of multipartite
entanglement of the Phased Dicke states are also discussed in detail.Comment: accepted for publication on EPJ
Energetics of the Einstein-Rosen spacetime
A study covering some aspects of the Einstein--Rosen metric is presented. The
electric and magnetic parts of the Weyl tensor are calculated. It is shown that
there are no purely magnetic E--R spacetimes, and also that a purely electric
E--R spacetime is necessarily static. The geodesics equations are found and
circular ones are analyzed in detail. The super--Poynting and the
``Lagrangian'' Poynting vectors are calculated and their expressions are found
for two specific examples. It is shown that for a pulse--type solution, both
expressions describe an inward radially directed flow of energy, far behind the
wave front. The physical significance of such an effect is discussed.Comment: 19 pages Latex.References added and updated.To appear in
Int.J.Theor.Phy
Minimum mass-radius ratio for charged gravitational objects
We rigorously prove that for compact charged general relativistic objects
there is a lower bound for the mass-radius ratio. This result follows from the
same Buchdahl type inequality for charged objects, which has been extensively
used for the proof of the existence of an upper bound for the mass-radius
ratio. The effect of the vacuum energy (a cosmological constant) on the minimum
mass is also taken into account. Several bounds on the total charge, mass and
the vacuum energy for compact charged objects are obtained from the study of
the Ricci scalar invariants. The total energy (including the gravitational one)
and the stability of the objects with minimum mass-radius ratio is also
considered, leading to a representation of the mass and radius of the charged
objects with minimum mass-radius ratio in terms of the charge and vacuum energy
only.Comment: 19 pages, accepted by GRG, references corrected and adde