523 research outputs found
Beating in electronic transport through quantum dot based devices
Electronic transport through a two-level system driven by external electric
field and coupled to (magnetic or non-magnetic) electron reservoirs is
considered theoretically. The basic transport characteristics such as current
and tunnel magnetoresistance (TMR) are calculated in the weak coupling
approximation by the use of rate equation connected with Green function
formalism and slave-boson approach. The time dependent phenomenon is considered
in the gradient expansion approximation. The results show that coherent beats
pattern can be observed both in current and TMR. The proposed system consisting
of two quantum dots attached to external leads, in which the dots' levels can
be tuned independently, can be realized experimentally to test this well known
physical phenomenon. Finally, we also indicate possible practical applications
of such device.Comment: 9 pages, 9 figure
Glueball Spin
The spin of a glueball is usually taken as coming from the spin (and possibly
the orbital angular momentum) of its constituent gluons. In light of the
difficulties in accounting for the spin of the proton from its constituent
quarks, the spin of glueballs is reexamined. The starting point is the
fundamental QCD field angular momentum operator written in terms of the
chromoelectric and chromomagnetic fields. First, we look at the restrictions
placed on the structure of glueballs from the requirement that the QCD field
angular momentum operator should satisfy the standard commutation
relationships. This can be compared to the electromagnetic charge/monopole
system, where the quantization of the field angular momentum places
restrictions (i.e. the Dirac condition) on the system. Second, we look at the
expectation value of this operator under some simplifying assumptions.Comment: 11 pages, 0 figures; added references and some discussio
Neutrino oscillations in matter of varying density
We consider two-family neutrino oscillations in a medium of
continuously-varying density as a limit of the process in a series of
constant-density layers. We construct analytic expressions for the conversion
amplitude at high energies within a medium with a density profile that is
piecewise linear. We compare some cases to understand the type of effects that
depend on the order of the material traversed by a neutrino beam.Comment: 10 page
On Neutrinos and Fermionic Mass Patterns
Recent data on neutrino mass differences are consistent with a hierarchical
neutrino mass structure strikingly similar to what is observed for the other
fermionic masses.Comment: 8pages, 2figure
Color dielectric model with two scalar fields
SU(2) Yang-Mills theory coupled in a non-minimal way to two scalar fields is
discussed. For the massless scalar fields a family of finite energy solutions
generated by an external, static electric charge is found. Additionally, there
is a single solution which can be interpreted as confining one. Similar
solutions have been obtained in the magnetic sector. In case of massive scalar
fields the Coulomb problem is investigated. We find that asymptotic behavior of
the fields can also, for some values of the parameter of the model, give
confinement of the electric charge. Quite interesting one glueball--meson
coupling gives the linear confining potential. Finally, it is shown that for
one non-dynamical scalar field we derive the color dielectric generalization of
the Pagels--Tomboulis model.Comment: 20 pages, LaTeX, Accepted for publication in Eur. Phys. J.
The Problem of Large Leptonic Mixing
Unlike in the quark sector where simple permutation symmetries can
generate the general features of quark masses and mixings, we find it
impossible (under conditions of hierarchy for the charged leptons and without
considering the see-saw mechanism or a more elaborate extension of the SM) to
guarantee large leptonic mixing angles with any general symmetry or
transformation of only known particles. If such symmetries exist, they must be
realized in more extended scenarios.Comment: RevTeX, 4 pages, no figure
- …