763 research outputs found
Naturalness in Cosmological Initial Conditions
We propose a novel approach to the problem of constraining cosmological
initial conditions. Within the framework of effective field theory, we classify
initial conditions in terms of boundary terms added to the effective action
describing the cosmological evolution below Planckian energies. These boundary
terms can be thought of as spacelike branes which may support extra
instantaneous degrees of freedom and extra operators. Interactions and
renormalization of these boundary terms allow us to apply to the boundary terms
the field-theoretical requirement of naturalness, i.e. stability under
radiative corrections. We apply this requirement to slow-roll inflation with
non-adiabatic initial conditions, and to cyclic cosmology. This allows us to
define in a precise sense when some of these models are fine-tuned. We also
describe how to parametrize in a model-independent way non-Gaussian initial
conditions; we show that in some cases they are both potentially observable and
pass our naturalness requirement.Comment: 35 pages, 8 figure
Simplest cosmological model with the scalar field II. Influence of cosmological constant
Continuing the investigation of the simplest cosmological model with the
massive real scalar non-interacting inflaton field minimally coupled to gravity
we study an influence of the cosmological constant on the behaviour of
trajectories in closed minisuperspace Friedmann-Robertson-Walker model. The
transition from chaotic to regular behaviour for large values of cosmological
constant is discussed. Combining numerical calculations with qualitative
analysis both in configuration and phase space we present a convenient
classification of trajectories.Comment: 12 pages with 2 gif figures and 2 eps figures, mprocl.sty, To appear
in International Journal of Modern Physics
Describing general cosmological singularities in Iwasawa variables
Belinskii, Khalatnikov, and Lifshitz (BKL) conjectured that the description
of the asymptotic behavior of a generic solution of Einstein equations near a
spacelike singularity could be drastically simplified by considering that the
time derivatives of the metric asymptotically dominate (except at a sequence of
instants, in the `chaotic case') over the spatial derivatives. We present a
precise formulation of the BKL conjecture (in the chaotic case) that consists
of basically three elements: (i) we parametrize the spatial metric by
means of \it{Iwasawa variables} ); (ii) we define, at
each spatial point, a (chaotic) \it{asymptotic evolution system} made of
ordinary differential equations for the Iwasawa variables; and (iii) we
characterize the exact Einstein solutions whose asymptotic
behavior is described by a solution of the
previous evolution system by means of a `\it{generalized Fuchsian system}' for
the differenced variables , , and by requiring that and tend to zero on the singularity. We also show that, in spite of the
apparently chaotic infinite succession of `Kasner epochs' near the singularity,
there exists a well-defined \it{asymptotic geometrical structure} on the
singularity : it is described by a \it{partially framed flag}. Our treatment
encompasses Einstein-matter systems (comprising scalar and p-forms), and also
shows how the use of Iwasawa variables can simplify the usual (`asymptotically
velocity term dominated') description of non-chaotic systems.Comment: 50 pages, 4 figure
Boundary Value Problem for Black Rings
We study the boundary value problem for asymptotically flat stationary black
ring solutions to the five-dimensional vacuum Einstein equations. Assuming the
existence of two additional commuting axial Killing vector fields and the
horizon topology of , we show that the only asymptotically flat
black ring solution with a regular horizon is the Pomeransky-Sen'kov black ring
solution.Comment: 21 pages, 1 figur
Some properties of the "String gas" with the equation of state
We show that the string gas - a perfect fluid with the equation of state possesses rather interesing properties. In Friedmann universes
its presence can can change the observable topology of the space; in the
spherically symmetric spacetimes it produces rather bizzare geometries and in a
way its influence on the rotation curves mimics the dark matter effects.Comment: 9 pages, 1 figur
Quantum diffraction and interference of spatially correlated photon pairs and its Fourier-optical analysis
We present one- and two-photon diffraction and interference experiments
involving parametric down-converted photon pairs. By controlling the divergence
of the pump beam in parametric down-conversion, the diffraction-interference
pattern produced by an object changes from a quantum (perfectly correlated)
case to a classical (uncorrelated) one. The observed diffraction and
interference patterns are accurately reproduced by Fourier-optical analysis
taking into account the quantum spatial correlation. We show that the relation
between the spatial correlation and the object size plays a crucial role in the
formation of both one- and two-photon diffraction-interference patterns.Comment: 10 pages, 13 figures, rev.
Joint Probabilities Reproducing Three EPR Experiments On Two Qubits
An eight parameter family of the most general nonnegative quadruple
probabilities is constructed for EPR-Bohm-Aharonov experiments when only 3
pairs of analyser settings are used. It is a simultaneous representation of 3
Bohr-incompatible experimental configurations valid for arbitrary quantum
states.Comment: Typo corrected in abstrac
On the Bogomol'nyi bound in Einstein-Maxwell-dilaton gravity
It has been shown that the 4-dimensional Einstein-Maxwell-dilaton theory
allows a Bogomol'nyi-type inequality for an arbitrary dilaton coupling constant
, and that the bound is saturated if and only if the (asymptotically
flat) spacetime admits a nontrivial spinor satisfying the gravitino and the
dilatino Killing spinor equations. The present paper revisits this issue and
argues that the dilatino equation fails to ensure the dilaton field equation
unless the solution is purely electric/magnetic, or the dilaton coupling
constant is given by , corresponding to the
Brans-Dicke-Maxwell theory and the Kaluza-Klein reduction of 5-dimensional
vacuum gravity, respectively. A systematic classification of the supersymmetric
solutions reveals that the solution can be rotating if and only if the solution
is dyonic or the coupling constant is given by . This
implies that the theory with cannot be embedded into
supergravity except for the static truncation. Physical properties of
supersymmetric solutions are explored from various points of view.Comment: v2: 23 pages, typos corrected, minor modifications, to appear in CQ
A model for time-dependent cosmological constant and its consistency with the present Friedmann universe
We use a model where the cosmological term can be related to the chiral gauge
anomaly of a possible quantum scenario of the initial evolution of the
universe. We show that this term is compatible with the Friedmann behavior of
the present universe.Comment: 5 pages, Revtex 4, twocolumn (minor corrections and improved
reference list. To appear in Classical and Quantum Gravity
Scalar Field Probes of Power-Law Space-Time Singularities
We analyse the effective potential of the scalar wave equation near generic
space-time singularities of power-law type (Szekeres-Iyer metrics) and show
that the effective potential exhibits a universal and scale invariant leading
x^{-2} inverse square behaviour in the ``tortoise coordinate'' x provided that
the metrics satisfy the strict Dominant Energy Condition (DEC). This result
parallels that obtained in hep-th/0403252 for probes consisting of families of
massless particles (null geodesic deviation, a.k.a. the Penrose Limit). The
detailed properties of the scalar wave operator depend sensitively on the
numerical coefficient of the x^{-2}-term, and as one application we show that
timelike singularities satisfying the DEC are quantum mechanically singular in
the sense of the Horowitz-Marolf (essential self-adjointness) criterion. We
also comment on some related issues like the near-singularity behaviour of the
scalar fields permitted by the Friedrichs extension.Comment: v2: 21 pages, JHEP3.cls, one reference adde
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