1,545 research outputs found
Resonant Raman scattering off neutral quantum dots
Resonant inelastic (Raman) light scattering off neutral GaAs quantum dots
which contain a mean number, N=42, of electron-hole pairs is computed. We find
Raman amplitudes corresponding to strongly collective final states
(charge-density excitations) of similar magnitude as the amplitudes related to
weakly collective or single-particle excitations. As a function of the incident
laser frequency or the magnetic field, they are rapidly varying amplitudes. It
is argued that strong Raman peaks should come out in the spin-density channels,
not related to valence-band mixing effects in the intermediate states.Comment: Accepted in Physical Review
Spin polarization and magneto-luminescence of confined electron-hole systems
A BCS-like variational wave-function, which is exact in the infinite field
limit, is used to study the interplay among Zeeman energies, lateral
confinement and particle correlations induced by the Coulomb interactions in
strongly pumped neutral quantum dots. Band mixing effects are partially
incorporated by means of field-dependent masses and g-factors. The spin
polarization and the magneto-luminescence are computed as functions of the
number of electron-hole pairs present in the dot and the applied magnetic
field.Comment: To appear in Phys. Rev.
Ground-state properties of tubelike flexible polymers
In this work we investigate structural properties of native states of a
simple model for short flexible homopolymers, where the steric influence of
monomeric side chains is effectively introduced by a thickness constraint. This
geometric constraint is implemented through the concept of the global radius of
curvature and affects the conformational topology of ground-state structures. A
systematic analysis allows for a thickness-dependent classification of the
dominant ground-state topologies. It turns out that helical structures,
strands, rings, and coils are natural, intrinsic geometries of such tubelike
objects
Studies of Prototype CsI(Tl) Crystal Scintillators for Low-Energy Neutrino Experiments
Crystal scintillators provide potential merits for the pursuit of low-energy
low-background experiments. A CsI(Tl) scintillating crystal detector is being
constructed to study low-energy neutrino physics at a nuclear reactor, while
projects are underway to adopt this technique for dark matter searches. The
choice of the geometrical parameters of the crystal modules, as well as the
optimization of the read-out scheme, are the results of an R&D program.
Crystals with 40 cm in length were developed. The detector requirements and the
achieved performance of the prototypes are presented. Future prospects for this
technique are discussed.Comment: 32 pages, 14 figure
SO(10) unified models and soft leptogenesis
Motivated by the fact that, in some realistic models combining SO(10) GUTs
and flavour symmetries, it is not possible to achieve the required baryon
asymmetry through the CP asymmetry generated in the decay of right-handed
neutrinos, we take a fresh look on how deep this connection is in SO(10). The
common characteristics of these models are that they use the see-saw with
right-handed neutrinos, predict a normal hierarchy of masses for the neutrinos
observed in oscillating experiments and in the basis where the right-handed
Majorana mass is diagonal, the charged lepton mixings are tiny.
In addition these models link the up-quark Yukawa matrix to the neutrino
Yukawa matrix Y^\nu with the special feature of Y^\nu_{11}-> 0 Using this
condition, we find that the required baryon asymmetry of the Universe can be
explained by the soft leptogenesis using the soft B parameter of the second
lightest right-handed neutrino whose mass turns out to be around 10^8 GeV. It
is pointed out that a natural way to do so is to use no-scale supergravity
where the value of B ~1 GeV is set through gauge-loop corrections.Comment: 26 pages, 2 figures. Added references, new appendix of a relevant fit
and improved comment
PSR J1119-6127 and the X-ray Emission from High Magnetic Field Radio Pulsars
The existence of radio pulsars having inferred magnetic elds in the magnetar regime suggests that possible transition objects could be found in the radio pulsar population. The discovery of such an object would contribute greatly to our understanding of neutron star physics. Here we report on unusual X-ray emission detected from the radio pulsar PSR J1119-6127 using XMM-Newton. The pulsar has a characteristic age of 1,700 yrs and inferred surface dipole magnetic eld strength of 4.1x10^13 G. In the 0.5-2.0 keV range, the emission shows a single, narrow pulse with an unusually high pulsed fraction of ~70%. No pulsations are detected in the 2.0-10.0 keV range, where we derive an upper limit at the 99% level for the pulsed fraction of 28%. The pulsed emission is well described by a thermal blackbody model with a high temperature of 2.4x10^6 K. While no unambiguous signature of magnetar-like emission has been found in high-magnetic-eld radio pulsars, the X-ray characteristics of PSR J1119-6127 require alternate models from those of conventional thermal emission from neutron stars. In addition, PSR J1119-6127 is now the radio pulsar with the smallest characteristic age from which thermal X-ray emission has been detected
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