28 research outputs found
Random unitaries, Robustness, and Complexity of Entanglement
It is widely accepted that the dynamic of entanglement in presence of a
generic circuit can be predicted by the knowledge of the statistical properties
of the entanglement spectrum. We tested this assumption by applying a
Metropolis-like entanglement cooling algorithm generated by different sets of
local gates, on states sharing the same statistic. We employ the ground states
of a unique model, namely the one-dimensional Ising chain with a transverse
field, but belonging to different macroscopic phases such as the paramagnetic,
the magnetically ordered, and the topological frustrated ones. Quite
surprisingly, we observe that the entanglement dynamics are strongly dependent
not just on the different sets of gates but also on the phase, indicating that
different phases can possess different types of entanglement (which we
characterize as purely local, GHZ-like, and W-state-like) with different degree
of resilience against the cooling process. Our work highlights the fact that
the knowledge of the entanglement spectrum alone is not sufficient to determine
its dynamics, thereby demonstrating its incompleteness as a characterization
tool. Moreover, it shows a subtle interplay between locality and non-local
constraints.Comment: 14 pages, 11 figures, 1 tabl
Particle production and classical condensates in de Sitter space
The cosmological particle production in a expanding de Sitter universe
with a Hubble parameter is considered for various values of mass or
conformal coupling of a free, scalar field. One finds that, for a minimally
coupled field with mass (except for ),
the one-mode occupation number grows to unity soon after the physical
wavelength of the mode becomes larger than the Hubble radius, and afterwards
diverges as , where . However, for a field with ,
the occupation number of a mode outside the Hubble radius is rapidly
oscillating and bounded and does not exceed unity. These results, readily
generalized for cases of a nonminimal coupling, provide a clear argument that
the long-wavelength vacuum fluctuations of low-mass fields in an inflationary
universe do show classical behavior, while those of heavy fields do not. The
interaction or self-interaction does not appear necessary for the emergence of
classical features, which are entirely due to the rapid expansion of the de
Sitter background and the upside-down nature of quantum oscillators for modes
outside the Hubble radius.Comment: Revtex + 5 postscript figures. Accepted for Phys Rev D15. Revision of
Aug 1996 preprint limited to the inclusion and discussion of references
suggested by the referee
Phenolic Compounds and Peroxidases in Sunflower Near-Isogenic Lines After Downy Mildew Infection
Two near-isogenic lines of sunflower, resistant (+Pl6 gene) and susceptible (-P16 gene) to downy mildew were used in this paper. Secondary infection with a suspension of Plasmopara halstedii spores was done on the plants in the phase of first pair of leaves. In the samples taken 12 h after infection, content of phenolic compounds in methanolic extracts from frozen leaves was analysed by HPLC. POD activity was determined spectrophotmetrically and POD isoforms by isoelectrophoresis. Constitutive level of phenolic compounds and their accumulation after infection were higher in the susceptible than in the resistant line. Increased POD amount in leaf, constitutively present in NS-H-26R, was in correlation with increased guaiacol-dependent POD activity and low total phenolics contents. After infection, guaiacol- and chlorogenic acid-dependent POD activity significantly increased in both lines. Scopoletin-dependent POD activity was induced upon infection only in NS-H-26R. IEF electrophoresis revealed existance of four anionic isoforms of peroxidase in leaves of both lines. The main isoform with pI 5 was particularly intesified in the resistant line. In conclusion, scopoletin-dependent POD activity that was induced upon infection only in resistant NIL indicates a specific role of POD in coumarin metabolism that is possibly connected with the presence of Pl6 gene
Cascade Birth of Universes in Multidimensional Spaces
The formation mechanism of universes with distinctly different properties is
considered within the framework of pure gravity in a space of D > 4 dimensions.
The emergence of the Planck scale and its relationship to the inflaton mass are
discussed.Comment: 10 p., minor correction
Quantum Cosmology and Open Universes
Quantum creation of Universes with compact spacelike sections that have
curvature either closed, flat or open, i.e. are studied. In the
flat and open cases, the superpotential of the Wheeler De Witt equation is
significantly modified, and as a result the qualitative behaviour of a typical
wavefunction differs from the traditional closed case. Using regularity
arguments, it is shown that the only consistent state for the wavefunction is
the Tunneling one. By computing the quantum probabilities for the curvature of
the sections, it is shown that quantum cosmology actually favours that the
Universe be open, . In all cases sufficient inflation
e-foldings is predicted: this is an improvement over classical measures that
generally are ambiguous as to whether inflation is certain to occur.Comment: 11 pages, Revtex, 7 figures. Accepted for publication in PRD. New
material and important corrections added in response to referee's repor
Space for Both No-Boundary and Tunneling Quantum States of the Universe
At the minisuperspace level of homogeneous models, the bare probability for a
classical universe has a huge peak at small universes for the Hartle-Hawking
`no-boundary' wavefunction, in contrast to the suppression at small universes
for the `tunneling' wavefunction. If the probability distribution is cut off at
the Planck density (say), this suggests that the former quantum state is
inconsistent with our observations. For inhomogeneous models in which
stochastic inflation can occur, it is known that the idea of including a volume
factor in the observational probability distribution can lead to arbitrarily
large universes' being likely. Here this idea is shown to be sufficient to save
the Hartle-Hawking proposal even at the minisuperspace level (for suitable
inflaton potentials), by giving it enough space to be consistent with
observations.Comment: LaTeX, 20 pages, no figures, blank lines removed, page break inserte
Accelerating Cosmologies and Inflation from M/Superstring Theories
We review the recent developments in obtaining accelerating cosmologies
and/or inflation from higher-dimensional gravitational theories, in particular
superstring theories in ten dimensions and M-theory in eleven dimensions. We
first discuss why it is difficult to obtain inflationary behavior in the
effective low-energy theories of superstring/M-theory, i. e. supergravity
theories. We then summarize interesting solutions including S-branes that give
rise to accelerating cosmologies and inflationary solutions in M-theory with
higher order corrections. Other approaches to inflation in the string context
are also briefly discussed.Comment: 38 pages, Invited review to be published in IJMPA, v2: slightly
expanded and refs. added, v3, v4: typos corrected, published versio
Stochastic Inflation:The Quantum Phase Space Approach
In this paper a quantum mechanical phase space picture is constructed for
coarse-grained free quantum fields in an inflationary Universe. The appropriate
stochastic quantum Liouville equation is derived. Explicit solutions for the
phase space quantum distribution function are found for the cases of power law
and exponential expansions. The expectation values of dynamical variables with
respect to these solutions are compared to the corresponding cutoff regularized
field theoretic results (we do not restrict ourselves only to \VEV{\F^2}).
Fair agreement is found provided the coarse-graining scale is kept within
certain limits. By focusing on the full phase space distribution function
rather than a reduced distribution it is shown that the thermodynamic
interpretation of the stochastic formalism faces several difficulties (e.g.,
there is no fluctuation-dissipation theorem). The coarse-graining does not
guarantee an automatic classical limit as quantum correlations turn out to be
crucial in order to get results consistent with standard quantum field theory.
Therefore, the method does {\em not} by itself constitute an explanation of the
quantum to classical transition in the early Universe. In particular, we argue
that the stochastic equations do not lead to decoherence.Comment: 43 page
Recovering the effective cosmological constant in extended gravity theories
In the framework of extended gravity theories, we discuss the meaning of a
time dependent "cosmological constant" and give a set of conditions to recover
asymptotic de Sitter behaviour for a class of cosmological models independently
of initial data. To this purpose we introduce a time-dependent (effective)
quantity which asymptotically becomes the true cosmological constant. We will
deal with scalar-tensor, fourth and higher than fourth-order theories.Comment: 24 pages, Latex, submitted to Gen.Rel.and Gra