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G. Lambiase

Publications and source records attributed to G. Lambiase.

At least 91 records · Page 5Linked to original sources
arXiv2001

Neutrino Oscillations in Caianiello's Quantum Geometry Model

Neutrino flavor oscillations are analyzed in the framework of Quantum Geometry model proposed by Caianiello. In particular, we analyze the consequences of the model for accelerated neutrino particles which experience an effective Schwarzschild geometry modified by the existence of an upper limit on the acceleration, which implies a violation of the equivalence principle. We find a shift of quantum mechanical phase of neutrino oscillations, which depends on the energy of neutrinos as E^3. Implications on atmospheric and solar neutrinos are discussed.

hep-ph↗
arXiv2001

Spin-Rotation Coupling in Muon g-2 Experiments

Spin-rotation coupling, or Mashhoon effect, is a phenomenon associated with rotating observers. We show that the effect exists and plays a fundamental role in the determination of the anomalous magnetic moment of the muon.

gr-qc↗
arXiv2001

Maximal Acceleration Effects in Kerr Space

We consider a model in which accelerated particles experience line--elements with maximal acceleration corrections that are introduced by means of successive approximations. It is shown that approximations higher than the first need not be considered. The method is then applied to the Kerr metric. The effective field experienced by accelerated test particles contains corrections that vanish in the limit $\hbar\to 0$, but otherwise affect the behaviour of matter greatly. The corrections generate potential barriers that are external to the horizon and are impervious to classical particles.

gr-qc↗
arXiv2001

Asymptotic Freedom in Curvature-Satured Gravity

For a spatially flat Friedmann model with line element $ds^2=a^2 [ da^2/B(a)-dx^2-dy^2-dz^2 ] $, the 00-component of the Einstein field equation reads $8πG T_{00}=3/a^2$ containing no derivative. For a nonlinear Lagrangian ${\cal L}(R)$, we obtain a second--order differential equation for $B$ instead of the expected fourth-order equation. We discuss this equation for the curvature-saturated model proposed by Kleinert and Schmidt. Finally, we argue that asymptotic freedom $G_{\rm eff}^{-1}\to 0$ is fulfilled in curvature-saturated gravity.

gr-qc↗
arXiv2001

Geometric classification of the torsion tensor in space-time

Torsion appears in literature in quite different forms. Generally, spin is considered to be the source of torsion, but there are several other possibilities in which torsion emerges in different contexts. In some cases a phenomenological counterpart is absent, in some other cases torsion arises from sources without spin as a gradient of a scalar field. Accordingly, we propose two classification schemes. The first one is based on the possibility to construct torsion tensors from the product of a covariant bivector and a vector and their respective space-time properties. The second one is obtained by starting from the decomposition of torsion into three irreducible pieces. Their space-time properties again lead to a complete classification. The classifications found are given in a U_4, a four dimensional space-time where the torsion tensors have some peculiar properties. The irreducible decomposition is useful since most of the phenomenological work done for torsion concerns four dimensional cosmological models. In the second part of the paper two applications of these classification schemes are given. The modifications of energy-momentum tensors are considered that arise due to different sources of torsion. Furthermore, we analyze the contributions of torsion to shear, vorticity, expansion and acceleration. Finally the generalized Raychaudhuri equation is discussed.

gr-qc↗
arXiv2001

Casimir energy of a dilute dielectric ball in the mode summation method

In the $(ε_1-ε_2)^2$--approximation the Casimir energy of a dilute dielectric ball is derived using a simple and clear method of the mode summation. The addition theorem for the Bessel functions enables one to present in a closed form the sum over the angular momentum before the integration over the imaginary frequencies. The linear in $(ε_1-ε_2)$ contribution into the vacuum energy is removed by an appropriate subtraction. The role of the contact terms used in other approaches to this problem is elucidated.

hep-th↗
arXiv2000

Casimir Energy of a Semi-Circular Infinite Cylinder

The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only a half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions which are the consequence of the edges or corners in the boundaries. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.

hep-th↗
arXiv2000

Supermassive boson stars: prospects for observational detection

In a recent work (Torres, Capozziello and Lambiase, Physical Review D62, 104012 (2000)), it was shown that a supermassive boson star could provide an alternative model for the galactic center, usually assumed as a black hole. Here we comment on some of the possibilities to actually detect this object, and how can it be distinguished from the standard and other alternative models.

gr-qc↗
arXiv2000

Radiation from a uniformly accelerated charge in the outskirts of a wormhole throat

Using traversable wormholes as theoretical background, we revisit a deep question of general relativity: Does a uniformly accelerated charged particle radiate? We particularize to the recently proposed gravitational Čerenkov radiation, that happens when the spatial part of the Ricci tensor is negative. If $^{^{(3+1)}}R^i_{\phantom{i}i}< 0$, the matter threading the gravitational field violates the weak energy condition. In this case, the effective refractive index for light is bigger than 1, i.e. particles propagates, in that medium, faster than photons. This leads to a violation of the equivalence principle.

gr-qc↗
arXiv2000

Thin shell quantization in Weyl spacetime

We study the problem of quantization of thin shells in a Weyl-Dirac theory by deriving a Wheeler-DeWitt equation from the dynamics. Solutions are found which have interpretations in both cosmology and particle physics.

gr-qc↗
arXiv2000

Probing the galactic center by gravitational lensing

The nature of Galactic Center could be probed by lensing experiments capable of testing the spatial and velocity distributions of stars nearby and beyond it. Several hypotheses are possible (e.g. massive neutrino condensation, boson star) which avoid the shortcomings of the supermassive black hole model.

astro-ph↗
arXiv2000

Cerenkov radiation and scalar stars

We explore the possibility that a charged particle moving in the gravitational field generated by a scalar star could radiate energy via a recently proposed gravitational Čerenkov mechanism. We numerically prove that this is not possible for stable boson stars. We also show that soliton stars could have Čerenkov radiation for particular values of the boson mass, although diluteness of the star grows and actual observational possibility decreases for the more usually discussed boson masses. These conclusions diminish, although do not completely rule out, the observational possibility of actually detecting scalar stars using this mechanism, and lead us to consider other forms, like gravitational lensing.

gr-qc↗
arXiv2000

Newtonian Limit of Induced Gravity

We discuss the weak-field limit of induced gravity and show that results directly depend on the coupling and self-interaction potential of the scalar field. A static spherically symmetric exact solution is found and its conformal properties are studied. As an application, it is shown that the light deflection angle and the microlensing quantities can be parametrized by the coupling of the theory.

astro-ph↗
arXiv2000

A supermassive boson star at the galactic center?

We explore whether supermassive non-baryonic stars (in particular boson, mini-boson and non-topological soliton stars) might be at the center of some galaxies, with special attention to the Milky Way. We analyze, from a dynamical point of view, what current observational data show, concluding that they are compatible with a single supermassive object without requiring it to be a black hole. Particularly, we show that scalar stars fit very well into these dynamical requirements. The parameters of different models of scalar stars necessary to reproduce the inferred central mass are derived, and the possible existence of boson particles with the adequate range of masses is commented. Accretion to boson stars is also analyzed, and a comparison with another non-baryonic candidate, a massive neutrino ball, which is also claimed as an alternative to the central black hole, is given. Both models are capable to explain the nature of the object in Sgr A$^*$ without invoking the presence of a singularity. One difficult issue is why the accreted materials will not finally produce, in a sufficiently long time, a black hole. We provide an answer based on stellar disruption in the case of boson stars, and comment several suggestions for its possible solution in neutrino ball scenarios. Finally, we discuss the prospects for the observational detection of these supermassive scalar objects, using the new generation of X-ray and radio interferometry satellites.

astro-ph↗
arXiv2000

Inertial Effects on Berry's Phase of Neutrino Oscillations

The Berry phase of mixed states, as neutrino oscillations, is calculated in a accelerating and rotating reference frame. It turns out to be depending on the vacuum mixing angle, the mass--squared difference and on the coupling between the momentum of the neutrino and the spinorial connection. Berry's phase for solar neutrinos and its geometrical aspects are also discussed.

gr-qc↗
arXiv2000

Double Scalar-Tensor Gravity Cosmologies

We investigate homogeneous and isotropic cosmological models in scalar-tensor theories of gravity where two scalar fields are nonminimally coupled to the geometry. Exact solutions are found, by Noether symmetries, depending on the form of couplings and self-interaction potentials. An interesting feature is that we deal with the Brans-Dicke field and the inflaton on the same ground since both are nonminimally coupled and not distinguished {\it a priori} as in earlier models. This fact allows to improve dynamics to get successful extended inflationary scenarios. Double inflationary solutions are also discussed.

gr-qc↗