arXiv subjects

S. Bellucci

Publications and source records attributed to S. Bellucci.

At least 145 records · Page 8Linked to original sources

arXiv2003

Rashba effect in 2D mesoscopic systems with transverse magnetic field

We present semiclassical and quantum mechanical results for the effects of a strong magnetic field in Quantum Wires in the presence of Rashba Spin Orbit coupling. Analytical and numerical results show how the perturbation acts in the presence of a transverse magnetic field in the ballistic regime and we assume a strong reduction of the backward scattering interaction which could have some consequences for the Tomonaga-Luttinger transport. We analyze the spin texture due to the action of Spin Orbit coupling and magnetic field often referring to the semiclassical solutions that magnify the singular spin polarization: results are obtained for free electrons in a twodimensional electron gas and for electrons in a Quantum Wire. We propose the systems as possible devices for the spin filtering at various regimes.

cond-mat.mes-hall↗

arXiv2003

Crystal Undulator As A Novel Compact Source Of Radiation

A crystalline undulator (CU) with periodically deformed crystallographic planes is capable of deflecting charged particles with the same strength as an equivalent magnetic field of 1000 T and could provide quite a short period L in the sub-millimeter range. We present an idea for creation of a CU and report its first realization. One face of a silicon crystal was given periodic micro-scratches (grooves), with a period of 1 mm, by means of a diamond blade. The X-ray tests of the crystal deformation have shown that a sinusoidal-like shape of crystalline planes goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in CU, a novel compact source of radiation. The first experiment on photon emission in CU has been started at LNF with 800 MeV positrons aiming to produce 50 keV undulator photons.

physics.acc-ph↗

arXiv2003

Doping- and size-dependent suppression of tunneling in carbon nanotubes

We study the effect of doping in the suppression of tunneling observed in multi-walled nanotubes, incorporating as well the influence of the finite dimensions of the system. A scaling approach allows us to encompass the different values of the critical exponent $α$ measured for the tunneling density of states in carbon nanotubes. We predict that further reduction of $α$ should be observed in multi-walled nanotubes with a sizeable amount of doping. In the case of nanotubes with a very large radius, we find a pronounced crossover between a high-energy regime with persistent quasiparticles and a low-energy regime with the properties of a one-dimensional conductor.

cond-mat.str-el↗

arXiv2003

Renormalization of the energy-momentum tensor in noncommutative scalar field theory

We consider the one-loop renormalization of dimension four composite operators and the energy-momentum tensor in noncommutative ϕ^4 scalar field theory. Proper operator bases are constructed and it is proved that the bare composite operators are expressed via renormalized ones, with the help of a mixing matrix, whose explicit form is calculated. The corresponding matrix elements turn out to differ from the commutative theory. The canonically defined energy-momentum tensor is not finite and must be replaced by the "improved" one, in order to provide finiteness. The suitable "improving" terms are found.

hep-th↗

arXiv2003

Goldstone Superfield Actions for Partially Broken AdS5 Supersymmetry

We explicitly construct N=1 worldvolume supersymmetric minimal off-shell Goldstone superfield actions for two options of 1/2 partial spontaneous breaking of AdS5 supersymmetry SU(2,2|1) corresponding to its nonlinear realizations in the supercosets with the AdS5 and AdS5 X S1 bosonic parts. The relevant Goldstone supermultiplets are comprised, respectively, by improved tensor and chiral N=1 superfields. The second action is obtained from the first one by duality transformation. In the bosonic sectors they yield static-gauge Nambu-Goto actions for L3-brane on AdS5 and scalar 3-brane on AdS5 X S1.

hep-th↗

arXiv2002

AdS_2/CFT_1, Canonical Transformations and Superconformal Mechanics

We propose a simple conformal mechanics model which is classically equivalent to a charged massive particle propagating near the AdS_2\times S^2 horizon of an extreme Reissner-Nordström black hole. The equivalence holds for any finite value of the black hole mass and with both the radial and angular degrees of freedom of the particle taken into account. It is ensured by the existence of a canonical transformation in the Hamiltonian formalism. Using this transformation, we construct the Hamiltonian of a N=4 superparticle on AdS_2\times S^2 background.

hep-th↗

arXiv2002

AdS/CFT Equivalence Transformation

We show that any conformal field theory in d-dimensional Minkowski space, in a phase with spontaneously broken conformal symmetry and with the dilaton among its fields, can be rewritten in terms of the static gauge (d-1)-brane on AdS_(d+1) by means of an invertible change of variables. This nonlinear holographic transformation maps the Minkowski space coordinates onto the brane worldvolume ones and the dilaton onto the transverse AdS brane coordinate. One of the consequences of the existence of this map is that any (d-1)-brane worldvolume action on AdS_(d+1)\times X^m (with X^m standing for the sphere S^m or more complicated curved manifold) admits an equivalent description in Minkowski space as a nonlinear and higher-derivative extension of some conventional conformal field theory action, with the conformal group being realized in a standard way. The holographic transformation explicitly relates the standard realization of the conformal group to its field-dependent nonlinear realization as the isometry group of the brane AdS_(d+1) background. Some possible implications of this transformation, in particular, for the study of the quantum effective action of N=4 super Yang-Mills theory in the context of AdS/CFT correspondence, are briefly discussed.

hep-th↗

arXiv2002

Making Micro- and Nano-beams by Channeling in Micro- and Nano-structures

A particle beam of very small cross-section is useful in many accelerator applications including biological and medical ones. We show the capability of the channeling technique using a micron-sized structure on a surface of a single crystal, or using a nanotube, to produce beam of a cross-section down to 1 square micrometer (or nanometer). The channeled beam can be deflected and thus well separated in angle and space from the primary and scattered particles. Monte Carlo simulation is done to evaluate the characteristics of a channeled microbeam. Emittances down to 0.1-0.001 nanometer radian, and flux up to 1 million particles per square micron per second, can be achieved for protons and ions.

physics.acc-ph↗

arXiv2002

On X-Ray Channeling in mu- and n-capillaries

In this work X-ray propagation in micro- and nano-size capillaries has been considered in the frame of a simple unified wave theory. It is shown that the diminishing of the channel sizes completely changes the mode of beam transportation, namely, we obtain the transformation of surface channeling in microcapillaries to bulk channeling in nanocapillaries (nanotubes).

physics.gen-ph↗

arXiv2002

Channeling of high energy beams in nanotubes

We present simulations of particle beam channeling in carbon nanotubes and evaluate the possibilities for experimental observation of channeling effect in straight and bent nanotubes at IHEP and LNF. Different particle species are considered: protons of 1.3 and 70 GeV, and positrons of 0.5 GeV. Predictions are made for the experiments, with analysis of requirements on the quality of nanosamples and resolution of the experimental set-up. Based on Monte Carlo simulations, the capabilities of nanotube channeling technique for particle beam steering are discussed.

physics.acc-ph↗

arXiv2002

Experimental Study For The Feasibility Of A Crystalline Undulator

We present an idea for creation of a crystalline undulator and report its first realization. One face of a silicon crystal was given periodic micro-scratches (trenches) by means of a diamond blade. The X-ray tests of the crystal deformation due to given periodic pattern of surface scratches have shown that a sinusoidal shape is observed on both the scratched surface and the opposite (unscratched) face of the crystal, that is, a periodic sinusoidal deformation goes through the bulk of the crystal. This opens up the possibility for experiments with high-energy particles channeled in crystalline undulator, a novel compact source of radiation.

physics.acc-ph↗

arXiv2002

Nanotube diameter optimal for channeling of high-energy particle beam

Channeling of particle beam in straight and bent single-wall nanotubes has been studied in computer simulations. We have found that the nanotubes should be sufficiently narrow in order to steer efficiently the particle beams, with preferred diameter in the order of 0.5-2 nm. Wider nanotubes, e.g. 10-50 nm, appear rather useless for channeling purpose because of high sensitivity of channeling to nanotube curvature. We have compared bent nanotubes with bent crystals as elements of beam steering technique, and found that narrow nanotubes have an efficiency of beam bending similar to that of crystals.

physics.acc-ph↗

arXiv2001

Quantum mechanics of superparticle with 1/4 supersymmetry breaking

We study quantum mechanics of a massive superparticle in d=4 which preserves 1/4 of the target space supersymmetry with eight supercharges, and so corresponds to the partial breaking N=8 down to N=2. Its worldline action contains a Wess-Zumino term, explicitly breaks d=4 Lorentz symmetry and exhibits one complex fermionic kappa-symmetry. We perform the Hamiltonian analysis of the model and quantize it in two different ways, with gauge-fixed kappa-symmetry and in the Gupta-Bleuler formalism. Both approaches give rise to the same supermultiplet structure of the space of states. It contains three irreducible N=2 multiplets with the total number of (4+4) complex on-shell components. These states prove to be in one-to-one correspondence with the de Rham complex of p-forms on a three-dimensional subspace of the target x-manifold. We analyze the vacuum structure of the model and find that the non-trivial vacua are given by the exact harmonic one- and two-forms. Despite the explicit breaking of the d=4 Lorentz symmetry in the fermionic sector, the d=4 mass-shell condition is still valid in the model.

hep-th↗

arXiv2001

Energy conditions and classical scalar fields

Attention has been recently called upon the fact that the weak and null energy conditions and the second law of thermodynamics are violated in wormhole solutions of Einstein's theory with classical, nonminimally coupled, scalar fields as material source. It is shown that the discussion is only meaningful when ambiguities in the definitions of stress-energy tensor and energy density of a nonminimally coupled scalar are resolved. The three possible approaches are discussed with emphasis on the positivity of the respective energy densities and covariant conservation laws. The root of the ambiguities is traced to the energy localization problem for the gravitational field.

hep-th↗

arXiv2001

Crossover from marginal Fermi liquid to Luttinger liquid behavior in carbon nanotubes

We study graphene-based electron systems with long-range Coulomb interaction by performing an analytic continuation in the number of dimensions. We characterize in this way the crossover between the marginal Fermi liquid behavior of a graphite layer and the Luttinger liquid behavior at $D = 1$. The former persists for any dimension above $D = 1$. However, the proximity to the $D = 1$ fixed-point strongly influences the phenomenology of quasi-onedimensional systems, giving rise to an effective power-law behavior of observables like the density of states. This applies to nanotubes of large radius, for which we predict a lower bound of the corresponding exponent that turns out to be very close to the value measured in multi-walled nanotubes.

cond-mat.str-el↗

arXiv2001

Scalar gravitational waves and Einstein frame

The response of a gravitational wave detector to scalar waves is analysed in the framework of the debate on the choice of conformal frames for scalar-tensor theories. A correction to the geodesic equation arising in the Einstein conformal frame modifies the geodesic deviation equation. This modification is due to the non-metricity of the theory in the Einstein frame, yielding a longitudinal mode that is absent in the Jordan conformal frame.

hep-th↗

arXiv2001

Superbranes and Super Born-Infeld Theories from Nonlinear Realizations

We describe, on a few instructive examples, a systematic way of deducing the superfield equations of motion of superbranes in the approach of partial breaking of global supersymmetry (PBGS) from the nonlinear-realizations formalism. For D-branes these equations simultaneously represent the appropriate supersymmetric Born-Infeld theories. We also discuss how to construct an off-shell superfield action for the $N=2, d=4$ Dirac-Born-Infeld theory corresponding to the partial supersymmetry breaking $N=4 \to N=2$ in $d=4$.

hep-th↗

arXiv2001

Towards the complete N=2 superfield Born-Infeld action with partially broken N=4 supersymmetry

We propose a systematic way of constructing $N=2, d=4$ superfield Born-Infeld action with a second nonlinearly realized N=2 supersymmetry. The latter, together with the manifest N=2 supersymmetry, form a central-charge extended $N=4, d=4$ supersymmetry. We embed the Goldstone-Maxwell N=2 multiplet into an infinite-dimensional off-shell supermultiplet of this N=4 supersymmetry and impose an infinite set of covariant constraints which eliminate all extra N=2 superfields through the Goldstone-Maxwell one. The Born-Infeld superfield Lagrangian density is one of these composite superfields. The constraints can be solved by iterations to any order in the fields. We present the sought N=2 Born-Infeld action up to the 10th order. It encompasses the action found earlier by Kuzenko and Theisen to the 8th order from a self-duality requirement. This is a strong indication that the complete N=2 Born-Infeld action with partially broken N=4 supersymmetry is also self-dual.

hep-th↗