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Mangano G.,Complesso Universitario Of Monte gelo | Mirizzi A.,University of Hamburg | Saviano N.,Durham University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The most general case of self-induced neutrino flavor evolution is described by a set of kinetic equations for a dense neutrino gas evolving in both space and time. Solutions of these equations have been typically worked out assuming that either the time (in the core-collapse supernova environment) or space (in the early Universe) homogeneity in the initial conditions is preserved through the evolution. In these cases, one can gauge away the homogeneous variable and reduce the dimensionality of the problem. In this paper, we investigate whether small deviations from an initial postulated homogeneity can be amplified by the interacting neutrino gas, leading to a new flavor instability. To this end, we consider a simple two-flavor isotropic neutrino gas evolving in time, and initially composed by only νe and ν̄e with equal densities. In the homogeneous case, this system shows a bimodal instability in the inverted mass hierarchy scheme, leading to the well-studied flavor pendulum behavior. This would lead to periodic pair conversions νeν̄e↔νxν̄x. To break space homogeneity, we introduce small amplitude space-dependent perturbations in the matter potential. By Fourier transforming the equations of motion with respect to the space coordinate, we then numerically solve a set of coupled equations for the different Fourier modes. We find that even for arbitrarily tiny inhomogeneities, the system evolution runs away from the stable pendulum behavior: the different modes are excited and the space-averaged ensemble evolves towards flavor equilibrium. We finally comment on the role of a time decaying neutrino background density in weakening these results. © 2014 American Physical Society.

Mirizzi A.,University of Hamburg | Mirizzi A.,National Institute of Nuclear Physics, Italy | Mangano G.,Complesso Universitario Of Monte gelo | Saviano N.,Durham University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We consider a simplified model for self-induced flavor conversions of a dense neutrino gas in two dimensions, showing new solutions that spontaneously break the spatial symmetries of the initial conditions. As a result of the symmetry breaking induced by the neutrino-neutrino interactions, the coherent behavior of the neutrino gas becomes unstable. This instability produces large spatial variations in the flavor content of the ensemble. Furthermore, it also leads to the creation of domains of different net lepton number flux. The transition of the neutrino gas from a coherent to incoherent behavior shows an intriguing analogy with a streaming flow changing from laminar to turbulent regime. These findings would be relevant for the self-induced conversions of neutrinos streaming-off a supernova core. © 2015 American Physical Society.

Paliathanasis A.,University of Naples Federico II | Paliathanasis A.,Complesso Universitario Of Monte gelo | Tsamparlis M.,National and Kapodistrian University of Athens
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We consider the two scalar field cosmology in a Friedmann Robertson Walker spatially flat spacetime where the scalar fields interact both in the kinetic part and the potential. We apply the Noether point symmetries in order to define the interaction of the scalar fields. We use the point symmetries in order to write the field equations in the normal coordinates, and we find that the Lagrangian of the field equations which admits at least three Noether point symmetries describes linear Newtonian systems. Furthermore, by using the corresponding conservation laws we find exact solutions of the field equations. Finally, we generalize our results to the case of N scalar fields interacting both in their potential and their kinematic part in a flat Friedmann Robertson Walker background. © 2014 American Physical Society.

Addazi A.,University of L'Aquila | Addazi A.,National Institute of Nuclear Physics, Italy | Esposito G.,Complesso Universitario Of Monte gelo
International Journal of Modern Physics A | Year: 2015

The realization of a nonlocal quantum field theory without losing unitarity, gauge invariance and causality is investigated. It is commonly retained that such a formulation is possible at tree level, but at quantum level acausality is expected to reappear at one loop. We suggest that the problem of acausality is, in a broad sense, similar to the one about anomalies in quantum field theory. By virtue of this analogy, we suggest that acausal diagrams resulting from the fermionic sector and the bosonic one might cancel each other, with a suitable content of fields and suitable symmetries. As a simple example, we show how supersymmetry can alleviate this problem in a simple and elegant way, i.e. by leading to exact cancellations of harmful diagrams, to all orders of perturbation theory. An infinite number of divergent diagrams cancel each other by virtue of the nonrenormalization theorem of supersymmetry. However, supersymmetry is not enough to protect a theory from all acausal divergences. For instance, acausal contributions to supersymmetric corrections to D-terms are not protected by supersymmetry. On the other hand, we show in detail how supersymmetry also helps in dealing with D-terms: divergences are not canceled but they become softer than in the nonsupersymmetric case. The supergraphs' formalism turns out to be a powerful tool to reduce the complexity of perturbative calculations. © 2015 World Scientific Publishing Company.

Sereno M.,Polytechnic University of Turin | Sereno M.,National Institute of Nuclear Physics, Italy | Covone G.,University of Naples Federico II | Covone G.,Complesso Universitario Of Monte gelo
Monthly Notices of the Royal Astronomical Society | Year: 2013

Mass and concentration of clusters of galaxies are related and evolving with redshift. We study the properties of a sample of 31 massive galaxy clusters at high redshift, 0.8̃ z̃ 1.5, using weak and strong lensing observations. Concentration is a steep function of mass, c200 ∞ M -0.83±0.39 200, with higher redshift clusters being less concentrated. Mass and concentration from the stacked analysis, M200 = (4.1 ± 0.4) × 1014M ̇h-1 and c200 = 2.3 ± 0.2, are in line with theoretical results extrapolated from the local Universe. Clusters with signs of dynamical activity preferentially feature high concentrations. We discuss the possibility that the whole sample is a mix of two different kinds of haloes. Overconcentrated clusters might be accreting haloes out of equilibrium in a transient phase of compression, whereas less concentrated ones might be more relaxed. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Mangano G.,Complesso Universitario Of Monte gelo
Nuclear and Particle Physics Proceedings | Year: 2015

I give an overview of what we do know from astrophysical data about some of neutrino properties and their role in cosmology. In particular, I focus on the number of effective neutrino species, active neutrino mass bounds and constraints on neutrino-antineutrino asymmetries. Finally, I also discuss the possibility of a non negligible abundance of eV mass scale sterile neutrino species in the early universe. © 2015 Elsevier B.V.

Esposito G.,Complesso Universitario Of Monte gelo
International Journal of Geometric Methods in Modern Physics | Year: 2016

In the 60s, DeWitt discovered that the advanced and retarded Green functions of the wave operator on metric perturbations in the de Donder gauge make it possible to define classical Poisson brackets on the space of functionals that are invariant under the action of the full diffeomorphism group of spacetime. He therefore tried to exploit this property to define invariant commutators for the quantized gravitational field, but the operator counterpart of such classical Poisson brackets turned out to be a hard task. On the other hand, in the mathematical literature, it is by now clear that, rather than inverting exactly an hyperbolic (or elliptic) operator, it is more convenient to build a quasi-inverse, i.e. an inverse operator up to an operator of lower order which plays the role of regularizing operator. This approximate inverse, the parametrix, which is, strictly, a distribution, makes it possible to solve inhomogeneous hyperbolic (or elliptic) equations. We here suggest that such a construction might be exploited in canonical quantum gravity provided one understands what is the counterpart of classical smoothing operators in the quantization procedure. We begin with the simplest case, i.e. fundamental solution and parametrix for the linear, scalar wave operator; the next step are tensor wave equations, again for linear theory, e.g. Maxwell theory in curved spacetime. Last, the nonlinear Einstein equations are studied, relying upon the well-established Choquet-Bruhat construction, according to which the fifth derivatives of solutions of a nonlinear hyperbolic system solve a linear hyperbolic system. The latter is solved by means of Kirchhoff-type formulas, while the former fifth-order equations can be solved by means of well-established parametrix techniques for elliptic operators. But then the metric components that solve the vacuum Einstein equations can be obtained by convolution of such a parametrix with Kirchhoff-type formulas. Some basic functional equations for the parametrix are also obtained, that help in studying classical and quantum version of the Jacobi identity. © 2016 World Scientific Publishing Company.

Battista E.,Complesso Universitario Of Monte gelo | Esposito G.,Complesso Universitario Of Monte gelo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Recent work in the literature has studied the restricted three-body problem within the framework of effective-field-theory models of gravity. This paper extends such a program by considering the full three-body problem, when the Newtonian potential is replaced by a more general central potential which depends on the mutual separations of the three bodies. The general form of the equations of motion is written down, and they are studied when the interaction potential reduces to the quantum-corrected central potential considered recently in the literature. A recursive algorithm is found for solving the associated variational equations, which describe small departures from given periodic solutions of the equations of motion. Our scheme involves repeated application of a 2×2 matrix of first-order linear differential operators. © 2014 American Physical Society.

Mangano G.,Complesso Universitario Of Monte gelo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We consider the role of the zero-point energy of a quantum field in cosmology and show that the flow of trans-Planckian momenta due to redshift acts as a source for this energy, regularized with a cutoff Λ in physical momenta. In order to fulfill Bianchi identity, we generalize Einstein equations and discuss the corresponding Friedmann homogeneous and isotropic models. In case of a de Sitter phase, such as during inflation, the solution shows a logarithmic behavior of the Hubble parameter and a primordial spectrum of scalar perturbations characterized by the spectral index ns=1-Λ2/(3πmP2) with mP the Planck mass. We also discuss possible implications of the scenario on the late accelerating stage of the Universe at small redshifts and the emergence of a fluid characterized by an equation of state w=P/ρ=- 1+Λ2/(9πmP2). Primordial perturbation spectrum and dark energy parameter w are, thus, predicted to be connected by the simple relation w=-(2+ns)/3. © 2010 The American Physical Society.

Battista E.,Complesso Universitario Of Monte gelo | Esposito G.,Complesso Universitario Of Monte gelo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

One of the outstanding problems of classical celestial mechanics was the restricted three-body problem, in which a planetoid of small mass is subject to the Newtonian attraction of two celestial bodies of large mass, as it occurs, for example, in the Sun-Earth-Moon system. On the other hand, over the last decades, a systematic investigation of quantum corrections to the Newtonian potential has been carried out in the literature on quantum gravity. The present paper studies the effect of these tiny quantum corrections on the evaluation of equilibrium points. It is shown that, despite the extreme smallness of the corrections, there exists no choice of sign of these corrections for which all qualitative features of the restricted three-body problem in Newtonian theory remain unaffected. Moreover, first-order stability of equilibrium points is characterized by solving a pair of algebraic equations of fifth degree, where some coefficients depend on the Planck length. The coordinates of stable equilibrium points are slightly changed with respect to Newtonian theory, because the planetoid is no longer at equal distance from the two bodies of large mass. The effect is conceptually interesting but too small to be observed, at least for the restricted three-body problems available in the solar system. © 2014 American Physical Society.

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