1,721,033 research outputs found
Quantum field theory of axion-photon mixing and vacuum polarization
No full textWe report on recent results obtained by analyzing axion-photon mixing in the framework of quantum field theory. We obtain corrections to the oscillation formulae and we reveal a new effect of the vacuum polarization due to the non-zero value of the vacuum energy for the component of the photon polarization mixed with the axion. The study of axion-photon mixing in curved space is also presented. Numerical analysis show that some quantum field theory effect of axion-photon mixing, in principle, could be detected experimentally
Cosmological Effects of Quantum Vacuum Condensates
No full textIn quantum field theory, many phenomena are characterized by a condensed structure of their vacua. Such a structure is responsible of a non trivial vacuum energy. Here we analyze disparate systems and we show that the thermal vacuum state for hot plasmas, the vacuum for boson field in curved space and the vacuum for mixed neutrinos have the state equation of dark matter, w = 0 , and values of the energy density which are in agreement with the one estimated for dark matter. Moreover, we show that the vacuum of axions mixed with photons has the state equation of the cosmological constant w = − 1 and a value of the energy density compatible with the one of dark energy
Boson mixing and flavor vacuum in the expanding Universe: A possible candidate for the dark energy
Full text linkWe analyze the boson mixing in curved spacetime and compute the expectation value of the energy-momentum tensor of bosons on the flavor vacuum in spatially flat Friedmann-Lemaître-Robertson-Walker metrics. We show that the energy-momentum tensor of the flavor vacuum behaves as the effective energy-momentum tensor of a perfect fluid. Assuming a fixed de Sitter background, we show that the equation of state can assume values in the interval [−1,1], and, in the flat space-time limit has a value −1, which is the one of the dark energy. The results here presented show that vacuum of mixed bosons like neutrino super-partners, can represent a possible component of the dark energy of the Universe
Fermion condensates induced by axial interactions and cosmological implications
No full textWe reveal the presence of a new source of axial current due to the condensed vacuum generated by the spin-spin interaction. To show this, we consider a quartic Dirac Lagrangian containing a spin-spin interaction term, possibly originating from torsion in Einstein-Cartan-like theories. We use a mean field approach to analyze the quantized theory. We show that the diagonalization of the field Hamiltonian defines a new vacuum state, energetically favored with respect to the free vacuum. Such a vacuum, which is a condensate of particle-antiparticle pairs, is characterized by a nontrivial expectation value of the axial current operator. The new source of axial current, here obtained, can have effects both at the atomic level and at the astrophysical-cosmological level depending on the origin of the spin-spin interaction term. The condensate spontaneously breaks Lorentz symmetry, therefore it implies the possibility of CPT violation in the early universe. Furthermore the condensate induces a new source term in the gravitational field equations and may affect the dark sector of the Universe at cosmological level
A background independent notion of causality
No full textWe develop a notion of causal order on a generic manifold as independent of the underlying differential and topological structure. We show that sufficiently regular causal orders can be recovered from a distinguished algebra of sets, which plays a role analogous to that of topologies and sigma algebras. We then discuss how a natural notion of measure can be associated to the algebra of causal sets
Landsat 9 Satellite Images Potentiality in Extracting Land Cover Classes in GEE Environment Using an Index-Based Approach: The Case Study of Savona City
No full textLand use and land cover modeling is an essential tool because it enables scientists and policymakers to foresee prospective changes in landscape heritage and examine trends to minimize potential dangers. To attain this purpose, a continuous stream of data needs be collected and examined. Landsat missions present a viable alternative since they have been collecting continuous data for five decades, and a new platform was launched at the end of September 2021 to avoid disrupting such a series. Consequently, the purpose of this research is to assess the quality of Landsat 9 data in extracting land use information using the index-based approach. Following the conclusion of the collection and pre-processing operations, two of the most often used vegetation indices, NDVI and MSAVI2, were derived from a Landsat 9 data covering Savona city, which was chosen as the pilot site due to its unique geomorphological characteristics. Lastly, maps accuracy was assessed by computing the confusion matrices, k estimator and overall, producer and users accuracy. The entire method was implemented in the free cloud computing platform Google Earth Engine by writing custom Java code. The generated land use/cover maps were both satisfactory, albeit the MSAVI2 had a greater overall accuracy (90.24% vs 79.60%) and K parameter (84.45% vs 71.70%) due to its ability to minimize soil spectral effect. Those findings are consistent with those derived from Landsat 8 images. This means that Landsat 9 is an excellent successor to Landsat 8
Neutrinos, mixed bosons, quantum reference frames and entanglement
No full textWe discuss the relevance of quantum reference frames in the description of mixed particle states. We show that the notion of a rest frame for mixed particles, which is classically ill-defined, can be introduced in the context of quantum frames. We discuss the possible implications, displaying a new form of frame-dependent entanglement that characterizes reactions involving mixed particles, and suggest a possible route to extract observables related to such an entanglement
Innovative method for linking anthropisation process to vulnerability
No full textCoastal areas have been gradually modified by humans to face emerging social needs. This phenomenon can be traced in the Amalfi Coast (Southern Italy) through the presence of terraces, constructed to make its steep slope habitable and arable. The current research is aimed to investigate the anthropisation process in Minori, and to identify the most vulnerable areas where debris flows. Two photogrammetric datasets, acquired in 1956 and 2017, respectively, were processed to generate two fine resolution digital elevation models and orthophotos, applied to calculate the normalised remaining vegetation index, the digital elevation model of differences, the new vulnerability expeditious index. The two orthophotos were also classified by applying the OBIA approach for extracting terraced areas. An increment of 800% of man-made infrastructures was detected, while the extension and the location of terraces was not subjected to any transformation. This implies a strong increment of vulnerability in the Minori municipality
Neutrino capture on tritium as a probe of flavor vacuum condensate and dark matter
Full text linkWe show that the study of neutrino capture on tritium, for non-relativistic neutrinos, can allow to distinguish among the various neutrino models, eventually prove the quantum field theory condensation effects and permit to test the hypothesis according to which the flavor vacuum energy gives a contribution to the dark matter of the universe. Indeed, we show that the capture rate depends on the neutrino model considered, and that it brings an imprint of the flavor vacuum condensate. Experiments like PTOLEMY, designed to reveal the cosmic neutrino background, then can give an indication of the existence of the dark matter component induced by neutrino mixing
Neutrino nature, total and geometric phase
No full textWe study the total and the geometric phase associated with neutrino mixing and we show that the phases produced by the neutrino oscillations have different values depending on the representation of the mixing matrix and on the neutrino nature. Therefore the phases represent a possible probe to distinguish between Dirac and Majorana neutrinos
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