2,267 research outputs found
Modifications in the Spectrum of Primordial Gravitational Waves Induced by Instantonic Fluctuations
Vacuum to vacuum instantonic transitions modify the power spectrum of
primordial gravitational waves. We evaluate the new form of the power spectrum
for ordinary gravity as well as the parity violation induced in the spectrum by
a modification of General Relativity known as Holst term and we outline the
possible experimental consequences.Comment: V1: 8 pages. V2: 8 pages, some points clarified, typos corrected,
some references added, final result unchanged. V3: 8 pages, title changed,
presentation improved, discussion of phenomenological consequences added,
comments very welcome. V4: Discussion further improved, comments very very
welcom
From the Einstein-Cartan to the Ashtekar-Barbero canonical constraints, passing through the Nieh-Yan functional
The Ashtekar-Barbero constraints for General Relativity with fermions are
derived from the Einstein-Cartan canonical theory rescaling the state
functional of the gravity-spinor coupled system by the exponential of the
Nieh-Yan functional. A one parameter quantization ambiguity naturally appears
and can be associated with the Immirzi parameter.Comment: Minor changes, two references added, accepted for publication in
Phys. Rev.
Peccei--Quinn mechanism in gravity and the nature of the Barbero--Immirzi parameter
A general argument provides the motivation to consider the Barbero--Immirzi
parameter as a field. The specific form of the geometrical effective action
allows to relate the value of the Barbero--Immirzi parameter to other quantum
ambiguities through the analog of the Peccei--Quinn mechanism.Comment: Accepted for publication on Phys. Rev. Let
Dark Matter Prediction from Canonical Quantum Gravity with Frame Fixing
We show how, in canonical quantum cosmology, the frame fixing induces a new
energy density contribution having features compatible with the (actual) cold
dark matter component of the Universe. First we quantize the closed
Friedmann-Robertson-Walker (FRW) model in a sinchronous reference and determine
the spectrum of the super-Hamiltonian in the presence of ultra-relativistic
matter and a perfect gas contribution. Then we include in this model small
inhomogeneous (spherical) perturbations in the spirit of the Lemaitre-Tolman
cosmology. The main issue of our analysis consists in outlining that, in the
classical limit, the non-zero eigenvalue of the super-Hamiltonian can make
account for the present value of the dark matter critical parameter.
Furthermore we obtain a direct correlation between the inhomogeneities in our
dark matter candidate and those one appearing in the ultra-relativistic matter.Comment: 5 pages, to appear on Modern Physics Letters
Psychiatric profile of motor subtypes of de novo drug-naĂŻve Parkinson's disease patients
Background: Parkinson's disease (PD) is a heterogeneous neurodegenerative disorder. It is well established that different motor subtypes of PD evolve with different clinical courses and prognoses. The complete psychiatric profile underlying these different phenotypes since the very early stage of the disease is debated. Aims of the study: We aimed at investigating the psychiatric profile of the three motor subtypes of PD (akinetic-rigid, tremor-dominant, and mixed) in de novo drug-naĂŻve patients with PD. Methods: Sixty-eight patients with PD, divided into 39 akinetic-rigid (AR), seven mixed (MIX), and 22 tremor-dominant (TD) patients underwent a complete assessment of psychiatric, cognitive, and motor symptoms. Results: No significant differences were found among groups. Conclusions: Our results suggest that a differentiation of the psychiatric symptoms associated with specific motor subtypes of PD is not detectable in de novo drug-naĂŻve patients. Previous evidence that emerges later along the disease progression may be a consequence of the dopaminergic and nondopaminergic damage increase
Barbero-Immirzi field in canonical formalism of pure gravity
The Barbero-Immirzi (BI) parameter is promoted to a field and a canonical
analysis is performed when it is coupled with a Nieh-Yan topological invariant.
It is shown that, in the effective theory, the BI field is a canonical
pseudoscalar minimally coupled with gravity. This framework is argued to be
more natural than the one of the usual Holst action. Potential consequences in
relation with inflation and the quantum theory are briefly discussed.Comment: 10 page
ECONOMY AND ENVIRONMENT OF THE GREEK COLONIAL SYSTEM IN SOUTHERN ITALY: POLLEN AND NPPS EVIDENCE OF GRAZING FROM THE RURAL SITE OF FATTORIA FABRIZIO (VI-IV CENT. BC; METAPONTO, BASILICATA)
this paper reports a study case showing integrated analyses of microscopic records from an archaeological site of southern italy. pollen and non pollen palynomorphs-Npps were found in archaeological layers and were basic in reconstructing both the past environment and the economic activities of the site. the site, Fattoria Fabrizio, is a modest 4th-cenury bc farmhouse of the chora (rural territory) of the Greek city (polis) of Metaponto (basilicata). pollen analyses in addition to the study of Npps have been particularly worthwhile for palaeoenvironmental and palaeoeconomical reconstructions of this site and others in the chora. the pollen spectra delineate an open plant landscape, with scanty woodlands and presence of local wet environments. Olea pollen is fairly well represented in all samples, suggesting that this tree was an important element of the agricultural economy of the chora. shrubby grasslands and a well-developed macchia characterized the territory, probably as result of grazing activities by sheep and goats. accordingly, the high percentages of poaceae and cichorieae pollen, together with coprophilous fungal spores (such as Sordaria type and Sporormiella type), suggest that pastoral activities were widely practiced. the low number of cerealia pollen grains suggests that the inhabitants’ fields covered small areas or were quite far from the farmhouse
Chirality of tensor perturbations for complex values of the Immirzi parameter
In this paper we generalise previous work on tensor perturbations in a de
Sitter background in terms of Ashtekar variables to cover all complex values of
the Immirzi parameter gamma (previous work was restricted to imaginary gamma).
Particular attention is paid to the case of real gamma. Following the same
approach as in the imaginary case, we can obtain physical graviton states by
invoking reality and torsion free conditions. The Hamiltonian in terms of
graviton states has the same form whether gamma has a real part or not; however
changes occur for the vacuum energy and fluctuations. Specifically, we observe
a gamma dependent chiral asymmetry in the vacuum fluctuations only if gamma has
an imaginary part. Ordering prescriptions also change this asymmetry. We thus
present a measurable result for CMB polarisation experiments that could shed
light on the workings of quantum gravity.Comment: 6 pages, 1 figur
On the Generalized Einstein-Cartan Action with Fermions
From the freedom exhibited by the generalized Einstein action proposed in
[1], we show that we can construct the standard effective Einstein-Cartan
action coupled to the fermionic matter without the usual current-current
interaction and therefore an effective action which does not depend neither on
the Immirzi parameter nor on the torsion. This establishes the equivalence
between the Einstein-Cartan theory and the theory of the general relativity
minimally coupled to the fermionic matter.Comment: 8 pages, Added references, Corrected typos, Accepted in Class. Quant.
Gra
Humans and Water in Desert “Refugium” Areas: Palynological Evidence of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
Saharan anthropic deposits from archaeological sites, located along wadis or close to lakes, and sedimentary sequences from permanent and dried basins demonstrate that water has always been an attractive environmental feature, especially during periods of drought. This paper reports on two very different examples of Holocene sites where “humans and water” coexisted during dry periods, as observed by stratigraphic, archaeological and palynological evidence. Independent research was carried out on the Jefara Plain (Libya, 32°N) and the Gobero area (Niger, 17°N), at the extreme northern and southern limits of the Sahara, respectively. The histories of the Jefara and Gobero areas, as revealed by the archaeological and palaeoenvironmental reconstructions, suggest that these areas were likely to have been visited and exploited for a long time, acting as anthropic refugia, and therefore they have been profoundly transformed. Human presence and actions have conditioned the local growing of plants and selected a more or less synanthropic flora. Today, modern conservation strategies should take into consideration that water reservoirs, which are crucial for the long-term conservation of biodiversity, have provided refugia in the past just as they presently do under global warming conditions
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