988 research outputs found
Numerical determination of entanglement entropy for a sphere
We apply Srednicki's regularization to extract the logarithmic term in the
entanglement entropy produced by tracing out a real, massless, scalar field
inside a three dimensional sphere in 3+1 flat spacetime. We find numerically
that the coefficient of the logarithm is -1/90 to 0.2 percent accuracy, in
agreement with an existing analytical result
The Semiclassical Limit of Loop Quantum Cosmology
The continuum and semiclassical limits of isotropic, spatially flat loop
quantum cosmology are discussed, with an emphasis on the role played by the
Barbero-Immirzi parameter \gamma in controlling space-time discreteness. In
this way, standard quantum cosmology is shown to be the simultaneous limit
\gamma \to 0, j \to \infty of loop quantum cosmology. Here, j is a label of the
volume eigenvalues, and the simultaneous limit is technically the same as the
classical limit \hbar \to 0, l \to \infty of angular momentum in quantum
mechanics. Possible lessons for semiclassical states at the dynamical level in
the full theory of quantum geometry are mentioned.Comment: 10 page
Is entanglement entropy proportional to area?
It is known that the entanglement entropy of a scalar field, found by tracing
over its degrees of freedom inside a sphere of radius , is
proportional to the area of the sphere (and not its volume). This suggests that
the origin of black hole entropy, also proportional to its horizon area, may
lie in the entanglement between the degrees of freedom inside and outside the
horizon. We examine this proposal carefully by including excited states, to
check probable deviations from the area law.Comment: 6 pages. Based on talk by S. Das at Theory Canada 1, Vancouver, 3
June, 2005. To be published in a special edition of the Canadian Journal of
Physics. Minor changes to match published versio
FRW cosmologies between chaos and integrability
A recent paper by Castagnino, Giacomini and Lara concludes that there is no
chaos in a conformally coupled closed Friedmann-Robertson-Walker universe,
which is in apparent contradiction with previous works. We point out that
although nonchaotic the quoted system is nonintegrable.Comment: Revtex, 2 pages, no figure
Where are the degrees of freedom responsible for black hole entropy?
Considering the entanglement between quantum field degrees of freedom inside
and outside the horizon as a plausible source of black hole entropy, we address
the question: {\it where are the degrees of freedom that give rise to this
entropy located?} When the field is in ground state, the black hole area law is
obeyed and the degrees of freedom near the horizon contribute most to the
entropy. However, for excited state, or a superposition of ground state and
excited state, power-law corrections to the area law are obtained, and more
significant contributions from the degrees of freedom far from the horizon are
shown.Comment: 6 pages, 4 figures, Invited talk at Theory Canada III, Edmonton,
Alberta, Canada, June 16, 200
Tinted Semi-Transparent Solar Panels Allow Concurrent Production of Crops and Electricity on the Same Cropland
Agrivoltaics describes concurrent agricultural production of crops and photovoltaic generation of electricity on the same cropland. By using tinted semi-transparent solar panels, this study introduces a novel element to transform the concept of agrivoltaics from just solar-sharing to selective utilisation of different light wavelengths. Agrivoltaic growth of basil and spinach was tested. When compared with classical agriculture, and based on the feed-in-tariff of the experimental location, agrivoltaic co-generation of biomass and electricity is calculated to result in an estimated financial gross gain up to +2.5% for basil and +35% for spinach. Marketable biomass yields did not change significantly for basil, while a statistically significant loss was observed for spinach. This was accompanied by a relative increase in the protein content for both plants grown under agrivoltaic conditions.
Agrivoltaics implemented with tinted solar panels improved the biomass production per unit amount of solar radiation up to 68%, with up to 63% increase in the ratio of leaf and stem biomass to root. Agrivoltaics can enrich the portfolio of farmers, mitigate risks associated with climate, and vastly enhance global photovoltaics capacity without compromising agricultural production.Leverhulme Trust RPG-2015-393
Italian Ministry of University and Research (to co-author A Schievano
The Value of Singularities
We point out that spacetime singularities play a useful role in gravitational
theories by eliminating unphysical solutions. In particular, we argue that any
modification of general relativity which is completely nonsingular cannot have
a stable ground state. This argument applies both to classical extensions of
general relativity, and to candidate quantum theories of gravity.Comment: 5 pages, no figures; a few clarifying comments adde
Relational Reality in Relativistic Quantum Mechanics
Up to now it has been impossible to find a realistic interpretation for the
reduction process in relativistic quantum mechanics. The basic problem is the
dependence of the states on the frame within which collapse takes place. A
suitable use of the causal structure of the devices involved in the measurement
process allows us to introduce a covariant notion for the collapse of quantum
states.Comment: 4 pages, final version accepted for publication in Phys. Lett.
Gravitational collapse in loop quantum gravity
In this paper we study the gravitational collapse in loop quantum gravity. We
consider the space-time region inside the Schwarzschild black hole event
horizon and we divide this region in two parts, the first one where the matter
(dust matter) is localized and the other (outside) where the metric is
Kantowski-Sachs type. We calculate the state solving Hamiltonian constraint and
we obtain a set of three difference equations that give a regular and natural
evolution beyond the classical singularity point in "r=0" localized.Comment: 16 pages, 2 figure
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