Three component model of cosmic ray spectra from 10 GeV to 100 PeV

A model to describe cosmic ray spectra in the energy region from 10 GeV to 100 PeV is suggested based on the assumption that Galactic cosmic ray flux is a mixture of fluxes accelerated by shocks from nova and supernova of different types. We analyze recent experimental data on cosmic ray spectra obtained in direct measurements above the atmosphere and data obtained with ground Extensive Air Shower arrays. The model of the three classes of cosmic ray sources is consistent with direct experimental data on cosmic ray elemental spectra and gives a smooth transition from the all particle spectrum measured in the direct experiments to the all particle spectrum measured with EAS.Comment: Revised version accepted for publication in Astronomy and Astrophysics, 5 pages, 6 figures, aa.cl

Lorentz Violating Inflation

We explore the impact of Lorentz violation on the inflationary scenario. More precisely, we study the inflationary scenario in the scalar-vector-tensor theory where the vector is constrained to be unit and time like. It turns out that the Lorentz violating vector affects the dynamics of the chaotic inflationary model and divides the inflationary stage into two parts; the Lorentz violating stage and the standard slow roll stage. We show that the universe is expanding as an exact de Sitter spacetime in the Lorentz violating stage although the inflaton field is rolling down the potential. Much more interestingly, we find exact Lorentz violating inflationary solutions in the absence of the inflaton potential. In this case, the inflation is completely associated with the Lorentz violation. We also mention some consequences of Lorentz violating inflation which can be tested by observations.Comment: 7 pages, 1 figur

The MRO-accompanied modes of Re-implantation into SiO2-host matrix: XPS and DFT based scenarios

The following scenarios of Re-embedding into SiO2-host by pulsed Re-implantation were derived and discussed after XPS-and-DFT electronic structure qualification: (i) low Re-impurity concentration mode -> the formation of combined substitutional and interstitial impurities with Re2O7-like atomic and electronic structures in the vicinity of oxygen vacancies; (ii) high Re-impurity concentration mode -> the fabrication of interstitial Re-metal clusters with the accompanied formation of ReO2-like atomic structures and (iii) an intermediate transient mode with Re-impurity concentration increase, when the precursors of interstitial defect clusters are appeared and growing in the host-matrix structure occur. An amplification regime of Re-metal contribution majority to the final Valence Band structure was found as one of the sequences of intermediate transient mode. It was shown that most of the qualified and discussed modes were accompanied by the MRO (middle range ordering) distortions in the initial oxygen subnetwork of the a-SiO2 host-matrix because of the appeared mixed defect configurations.Comment: 19 pages, 7 figures, accepted to J. Alloys and Compound

Electronic band gap reduction and intense luminescence in Co and Mn ion-implanted SiO2_2

Cobalt and manganese ions are implanted into SiO$_2$ over a wide range of concentrations. For low concentrations, the Co atoms occupy interstitial locations, coordinated with oxygen, while metallic Co clusters form at higher implantation concentrations. For all concentrations studied here, Mn ions remain in interstitial locations and do not cluster. Using resonant x-ray emission spectroscopy and Anderson impurity model calculations, we determine the strength of the covalent interaction between the interstitial ions and the SiO$_2$ valence band, finding it comparable to Mn and Co monoxides. Further, we find an increasing reduction in the SiO$_2$ electronic band gap for increasing implantation concentration, due primarily to the introduction of Mn- and Co-derived conduction band states. We also observe a strong increase in a band of x-ray stimulated luminescence at 2.75 eV after implantation, attributed to oxygen deficient centers formed during implantation.Comment: 8 pages, 6 figure

Vibrations induced by different charged oxygen vacancies in quartz-like GeO2

We have studied local configurations and vibrations of oxygen vacancies in different charged states in α-quartz GeO2 by computer simulation. First-principles potential of the Buckingham type has been used in calculations. The investigation of the lattice dynamics in defective crystal is performed using the phonon local density of states. The calculation of the densities of states is facilitated with Lanczos recursion. Frequencies of localized vibrations induced by oxygen vacancies are determined. © 2013 Elsevier B.V. All rights reserved

Hunting long-lived gluinos at the Pierre Auger Observatory

Eventual signals of split sypersymmetry in cosmic ray physics are analyzed in detail. The study focusses particularly on quasi-stable colorless R-hadrons originating through confinement of long-lived gluinos (with quarks, anti-quarks, and gluons) produced in pp collisions at astrophysical sources. Because of parton density requirements, the gluino has a momentum which is considerable smaller than the energy of the primary proton, and so production of heavy (mass ~ 500 GeV) R-hadrons requires powerful cosmic ray engines able to accelerate particles up to extreme energies, somewhat above 10^{13.6} GeV. Using a realistic Monte Carlo simulation with the AIRES engine, we study the main characteristics of the air showers triggered when one of these exotic hadrons impinges on a stationary nucleon of the Earth atmosphere. We show that R-hadron air showers present clear differences with respect to those initiated by standard particles. We use this shower characteristics to construct observables which may be used to distinguish long-lived gluinos at the Pierre Auger Observatory.Comment: 13 pages revtex, 9 eps figures. A ps version with high resolution figures is available at http://www.hep.physics.neu.edu/staff/doqui/rhadron_highres.p

Interstitial-oxygen induced localized vibrational properties in alpha-quartz

Local configurations and localized vibrations of oxygen interstitials in different charged states in alpha-quartz are investigated by computer calculations. First-principle potentials of the Buckingham type have been used in numerical modeling. The study of the lattice dynamics in defective crystal is performed using the phonon local density of states. Frequencies of localized vibrations induced by oxygen interstitials are determined. It is shown that the atomic configuration, type, number and frequency of localized vibrations depend on the sign and magnitude of the interstitial atom charge. © 2012 Elsevier B.V

Comparative Analysis of the Electronic Energy Structure of Nanocrystalline Polymorphs of Y2O3 Thin Layers: Theory and Experiments

The results of fabrication and characterization of atomic structure of nanocrystalline thin layers of Y2O3 in cubic and monoclinic phases is reported. Experimental data demonstrate crystalline ordering in nanocrystalline films with average grain size of ~10-14 nm both for cubic and monoclinic studied structures. Density Functional Theory (DFT) based simulations demonstrate insignificant differences of electronic structure of these phases in the bulk and on the surfaces. Theoretical modeling also pointed out the significant broadening of valence and conductive bands caused by means of energy levels splitting in agreement with experimental data (X-ray photoelectron and photoluminescence spectra). The presence of various intrinsic and extrinsic defects (including surface adsorption of carbon mono- and dioxide) does not promote visible changes in electronic structure of Y2O3 surface for both studied phases. Optical absorption and luminescence measurements indicate insignificant bandgap reduction of Y2O3 nanocrystalline layers and the very little contribution from defect states. Simulation of extrinsic compression and expanding demonstrate stability of the electronic structure of nanocrystalline Y2O3 even under significant strain. Results of comprehensive studies demonstrate that yttrium oxide based nanocrystalline layers are prospective for various optical applications as a stable material.Comment: 24 pages, 13 figures, accepted to Applied Surface Scienc