6,340 research outputs found
Moduli as Inflatons in Heterotic M-theory
We consider different cosmological aspects of Heterotic M-theory. In
particular we look at the dynamical behaviour of the two relevant moduli in the
theory, namely the length of the eleventh segment (pi rho) and the volume of
the internal six manifold (V) in models where supersymmetry is broken by
multiple gaugino condensation. We look at different ways to stabilise these
moduli, namely racetrack scenarios with or without non-perturbative corrections
to the Kahler potential. The existence of different flat directions in the
scalar potential, and the way in which they can be partially lifted, is
discussed as well as their possible role in constructing a viable model of
inflation. Some other implications such as the status of the moduli problem
within these models are also studied.Comment: 16 pages, 8 Postscript figures. Final version to appear in JHE
Cosmological Aspects of Heterotic M-theory
In this talk we discuss a few relevant aspects of heterotic M-theory. These
are the stabilization of the two relevant moduli (the length of the eleventh
segment (pi rho) and the volume of the internal six manifold (V)) in models
where supersymmetry is broken by multiple gaugino condensation and
non-perturbative corrections to the Kahler potential; the existence of almost
flat directions in the scalar potential; the possibility of lifting them, and
their role in constructing a viable model of inflation. Finally, we review the
status of the moduli problem within these models. TComment: LaTeX, 8 pages, 4 eps figures, uses ws-p8-50x6-00.cls; invited talk
at the International Workshop on Particle Physics and the Early Universe
(COSMO-99), Trieste, Italy, September 27 - October 2, 199
Stabilizing the Dilaton in Superstring Cosmology
We address the important issue of stabilizing the dilaton in the context of
superstring cosmology. Scalar potentials which arise out of gaugino condensates
in string models are generally exponential in nature. In a cosmological setting
this allows for the existence of quasi scaling solutions, in which the energy
density of the scalar field can, for a period, become a fixed fraction of the
background density, due to the friction of the background expansion. Eventually
the field can be trapped in the minimum of its potential as it leaves the
scaling regime. We investigate this possibility in various gaugino condensation
models and show that stable solutions for the dilaton are far more common than
one would have naively thought.Comment: 13 pages, LaTex, uses psfig.sty with 3 figure
Moduli Evolution in Heterotic Scenarios
We discuss several aspects of the cosmological evolution of moduli fields in
heterotic string/M-theory scenarios. In particular we study the equations of
motion of both the dilaton and overall modulus of these theories in the
presence of an expanding Universe and under different assumptions. First we
analyse the impact of their couplings to matter fields, which turns out to be
negligible in the string and M-theory scenarios. Then we examine in detail the
possibility of scaling in M-theory, i.e. how the moduli would evolve naturally
to their minima instead of rolling past them in the presence of a dominating
background. In this case we find interesting and positive results, and we
compare them to the analogous situation in the heterotic string.Comment: 12 pages, 4 postscript figure
Deterministic creation of stationary entangled states by dissipation
We propose a practical physical system for creation of a stationary
entanglement by dissipation without employing the environment engineering
techniques. The system proposed is composed of two perfectly distinguishable
atoms, through their significantly different transition frequencies, with only
one atom addressed by an external laser field. We show that the arrangement
would easily be realized in practice by trapping the atoms at the distance
equal to the quarter-wavelength of a standing-wave laser field and locating one
of the atoms at a node and the other at the successive antinode of the wave.
The undesirable dipole-dipole interaction between the atoms, that could be
large at this small distance, is adjusted to zero by a specific initial
preparation of the atoms or by a specific polarization of the atomic dipole
moments. Following this arrangement, we show that the dissipative relaxation
can create a stationary entanglement on demand by tuning the Rabi frequency of
the laser field to the difference between the atomic transition frequencies.
The laser field dresses the atom and we identify that the entangled state
occurs when the frequency of one of the Rabi sidebands of the driven atom tunes
to frequency of the undriven atom. It is also found that this system behaves as
a cascade open system where the fluorescence from the dressed atom drives the
other atom with no feedback.Comment: Published versio
Remote Preparation of Single-Photon "Hybrid" Entangled and Vector-Polarization States
Quantum teleportation faces increasingly demanding requirements for
transmitting large or even entangled systems. However, knowledge of the state
to be transmitted eases its reconstruction, resulting in a protocol known as
remote state preparation. A number of experimental demonstrations to date have
been restricted to single-qubit systems. We report the remote preparation of
two-qubit "hybrid" entangled states, including a family of vector-polarization
beams. Our single-photon states are encoded in the photon spin and orbital
angular momentum. We reconstruct the states by spin-orbit state tomography and
transverse polarization tomography. The high fidelities achieved for the
vector-polarization states opens the door to optimal coupling of down-converted
photons to other physical systems, such as an atom, as required for scalable
quantum networks, or plasmons in photonic nanostructures.Comment: Letter: 4 pages, 1 figure. Supplementary material: 1 pag
WMAP Constraints on a Quintessence Model
We use the results from the Wilkinson Microwave Anisotropy Probe (WMAP) for
the locations of peaks and troughs of the Cosmic Microwave Background (CMB)
power spectrum, together with constraints from large-scale structure, to study
a quintessence model in which the pure exponential potential is modified by a
polynomial factor. Our analysis, in the cosmological
parameters space shows that this quintessence model is favoured compared to
CDM for and relatively high values of early
quintessence; for , quintessence and CDM give similar results,
except for high values of early quintessence, in which case CDM is
favoured.Comment: 3 pages. Talk presented by N. M. C. Santos at the Tenth Marcel
Grossmann Meeting on General Relativity, Rio de Janeiro, July 200
Generation of time-bin entangled photons without temporal post-selection
We report on the implementation of a new interferometric scheme that allows
the generation of photon pairs entangled in the time-energy degree of freedom.
This scheme does not require any kind of temporal post-selection on the
generated pairs and can be used even with lasers with short coherence time.Comment: RevTex, 6 pages, 8 figure
Generation of Hyperentangled Photons Pairs
We experimentally demonstrate the first quantum system entangled in every
degree of freedom (hyperentangled). Using pairs of photons produced in
spontaneous parametric downconversion, we verify entanglement by observing a
Bell-type inequality violation in each degree of freedom: polarization, spatial
mode and time-energy. We also produce and characterize maximally hyperentangled
states and novel states simultaneously exhibiting both quantum and classical
correlations. Finally, we report the tomography of a 2x2x3x3 system
(36-dimensional Hilbert space), which we believe is the first reported photonic
entangled system of this size to be so characterized.Comment: 5 pages, 3 figures, 1 table, published versio
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