72,030 research outputs found
Can new generations explain neutrino masses?
In this talk we explore the possibility that the smallness of the observed
neutrino masses is naturally understood in a modified version of the standard
model with N extra generations of fermions and N right-handed neutrinos, in
which light neutrino masses are generated at two loops. We find that with N = 1
it is not possible to fit the observed spectrum of masses and mixings while
with N = 2 it is. Within this extension, we analyse the parameters which are
allowed and the possible phenomenological signals of the model in future
experiments. Contribution to the proceedings of Les Rencontres de Moriond EW
2011, Young Scientist Forum
Theory of Electromagnetic Wave Transmission through Metallic Gratings of Subwavelength Slits
We present FDTD calculations for transmission of light and other
electromagnetic waves through periodic arrays of slits in a metallic slab. The
results show resonant, frequency dependent, transmittance peaks for
subwavelength widths of the slits which can be up to a factor of ten with
respect to those out of resonance. Although our conclusions agree with previous
work by Lezec and Thio as regards both the magnitude of the enhancement and the
lack of contribution of surface plasmon polaritons of the metal surface to this
effect, we derive an interpretation from a theory that deals with emerging
beam- Rayleigh anomalies of the grating, and with Fabry-Perot resonances of the
perforated slab considered as an effective medium.Comment: 12 pages 3 figure
Bosonic versus fermionic pairs of topological spin defects in monolayered high-T_c superconductors
The energy associated with bosonic and fermionic pairs of topological spin
defects in doped antiferromagnetic quantum spin-1/2 square lattice is estimated
within a resonating valence bond scenario, as described by a t-t'-J-like model
Hamiltonian, plus a t-perpendicular, responsible of a three-dimensional
screening of the electrostatic repulsion within the bosonic pairs. For
parameters appropriate for monolayered high-T_c superconductors, both fermionic
and bosonic pairs show x^2-y^2 symmetry. We find a critical value of doping
such that the energy of the bosonic pairs goes below twice the energy of two
fermionic pairs at their Fermi level. This finding could be related to the
onset of high-T_c superconductivity.Comment: 10 pages, 6 figures. To be published in Phys. Rev.
Light Collimation and Focussing by a Thin Flat Metallic Slab
We present experimental and theoretical work showing that a flat metallic
slab can collimate and focus light impinging on the slab from a punctual
source. The effect is optimised when the radiation is around the bulk, not at
the surface, plasma frequency. And the smaller the imaginary part of the
permittivity is, the better the collimation. Experiments for Ag in the visible
as well as calculations are presented. We also discuss the interesting case of
the Aluminium whose imaginary part of the permittivity is very small at the
plasma frequency in UV radiation. Generalization to other materials and
radiations are also discussed.Comment: 6 pages, 3 figures. To be published on Optics Lette
OS diversity for intrusion tolerance: Myth or reality?
One of the key benefits of using intrusion-tolerant systems is the possibility of ensuring correct behavior in the presence of attacks and intrusions. These security gains are directly dependent on the components exhibiting failure diversity. To what extent failure diversity is observed in practical deployment depends on how diverse are the components that constitute the system. In this paper we present a study with operating systems (OS) vulnerability data from the NIST National Vulnerability Database. We have analyzed the vulnerabilities of 11 different OSes over a period of roughly 15 years, to check how many of these vulnerabilities occur in more than one OS. We found this number to be low for several combinations of OSes. Hence, our analysis provides a strong indication that building a system with diverse OSes may be a useful technique to improve its intrusion tolerance capabilities
Overview of charmonium decays and production from Non-Relativistic QCD
I briefly review Non-Relativistic QCD and related effective theories, and
discuss applications to heavy quarkonium decay, and production in
electron-positron colliders.Comment: 8 pages, Invited talk at Charm 2010, Oct. 21-24, IHEP, Beijin
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