124 research outputs found
Carriers Multiplication in Neighboring Surfactant-free Silicon Nanocrystals Produced by 3D-surface Engineering in Liquid Medium
Luminescent Colloidal Silicon Nanocrystals Prepared by Nanoseconds Laser Fragmentation and Laser Ablation in Water
Effective action for Einstein-Maxwell theory at order RF**4
We use a recently derived integral representation of the one-loop effective
action in Einstein-Maxwell theory for an explicit calculation of the part of
the effective action containing the information on the low energy limit of the
five-point amplitudes involving one graviton, four photons and either a scalar
or spinor loop. All available identities are used to get the result into a
relatively compact form.Comment: 13 pages, no figure
Semiconducting quantum confined silicon-tin alloyed nanocrystals prepared by ns pulsed laser ablation in water
In this letter we demonstrate the material synthetic feasibility for semiconducting alloyed silicon-tin nanocrystals (SiSn-ncs) with quantum confinement effects. An environmentally friendly synthesis is achieved by ns laser ablation of SiSn amorphous target in water at ambient conditions. Plasmas generated in liquid by laser pulses are characterized by spatial confinement with very high pressure (GPa), which allowed the growth of SiSn-ncs via kinetic pathways. We further illustrate that surface engineering by a direct-current atmospheric-pressure microplasma is capable of tailoring SiSn-ncs surface properties without the need of lengthy surfactants and resulting in room temperature photoluminescence (PL); the PL peak wavelength is red-shifted by more than 250 nm with respect to the PL peak wavelengths observed for comparable elemental silicon nanocrystals
Geodetic precession and strong gravitational lensing in the dynamical Chern-Simons modified gravity
We have investigated the geodetic precession and the strong gravitational
lensing in the slowly-rotating black hole in the dynamical Chern-Simons
modified gravity theory. We present the formulas of the orbital period and
the geodetic precession angle for the timelike particles in the
circular orbits around the black hole, which shows that the change of the
geodetic precession angle with the Chern-Simons coupling parameter is
converse to the change of the orbital period with for fixed . We also
discuss the effects of the Chern-Simons coupling parameter on the strong
gravitational lensing when the light rays pass close to the black hole and
obtain that for the stronger Chern-Simons coupling the prograde photons may be
captured more easily, and conversely, the retrograde photons is harder to be
captured in the slowly-rotating black hole in the dynamical Chern-Simons
modified gravity. Supposing that the gravitational field of the supermassive
central object of the Galaxy can be described by this metric, we estimated the
numerical values of the main observables for gravitational lensing in the
strong field limit.Comment: 19 pages, 5 figures, more clarifications and references added,
accepted for publication in Classical and Quantum Gravit
A silicon nanocrystal/polymer nanocomposite as a down-conversion layer in organic and hybrid solar cells
Axions In String Theory
In the context of string theory, axions appear to provide the most plausible
solution of the strong CP problem. However, as has been known for a long time,
in many string-based models, the axion coupling parameter F_a is several orders
of magnitude higher than the standard cosmological bounds. We re-examine this
problem in a variety of models, showing that F_a is close to the GUT scale or
above in many models that have GUT-like phenomenology, as well as some that do
not. On the other hand, in some models with Standard Model gauge fields
supported on vanishing cycles, it is possible for F_a to be well below the GUT
scale.Comment: 62 pages, v2; references, acknowledgements and minor corrections
adde
Bounds on masses of bulk fields in string compactifications
In string compactification on a manifold X, in addition to the string scale
and the normal scales of low-energy particle physics, there is a Kaluza-Klein
scale 1/R associated with the size of X. We present an argument that generic
string models with low-energy supersymmetry have, after moduli stabilization,
bulk fields with masses which are parametrically lighter than 1/R. We discuss
the implications of these light states for anomaly mediation and gaugino
mediation scenarios.Comment: 15 page
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