1,668 research outputs found
Scattering phase shifts in quasi-one-dimension
Scattering of an electron in quasi-one dimensional quantum wires have many
unusual features, not found in one, two or three dimensions. In this work we
analyze the scattering phase shifts due to an impurity in a multi-channel
quantum wire with special emphasis on negative slopes in the scattering phase
shift versus incident energy curves and the Wigner delay time. Although at
first sight, the large number of scattering matrix elements show phase shifts
of different character and nature, it is possible to see some pattern and
understand these features. The behavior of scattering phase shifts in
one-dimension can be seen as a special case of these features observed in
quasi-one-dimensions. The negative slopes can occur at any arbitrary energy and
Friedel sum rule is completely violated in quasi-one-dimension at any arbitrary
energy and any arbitrary regime. This is in contrast to one, two or three
dimensions where such negative slopes and violation of Friedel sum rule happen
only at low energy where the incident electron feels the potential very
strongly (i.e., there is a very well defined regime, the WKB regime, where FSR
works very well). There are some novel behavior of scattering phase shifts at
the critical energies where -matrix changes dimension.Comment: Minor corrections mad
Four Dimensional Supergravity from String Theory
A derivation of N=1 supergravity action from string theory is presented.
Starting from a Nambu-Goto bosonic string, matter field is introduced to obtain
a superstring in four dimension. The excitation quanta of this string contain
graviton and the gravitino. Using the principle of equivalence, the action in
curved space time are found and the sum of them is the Deser-Zumino N=1
supergravity action. The energy tensor is Lorentz invariant due to
supersymmetry.Comment: 9 page
Study of quantum current enhancement, eigenenergy spectra and magnetic moments in a multiply connected system at equilibrium
A multiply connected system in both its open and closed form variations but
in equilibrium is studied using quantum waveguide theory. The system exhibits
remarkable features, in its open form variation we see current enhancement,
hitherto seen only in non-equilibrium systems in absence of magnetic flux. In
its closed form analog parity effects are broken. Further we analyse the global
and local current densities of our system and also show that the orbital
magnetic response of the system calculated from the current densities (and
inherently linked to the topological configuration) is qualitatively not same
as that calculated from the eigenenergy spectra.Comment: 10 pages, 15 figures, 3 table
Effect of spin-orbit coupling on zero-conductance resonances in asymmetrically coupled one-dimensional rings
The influence of Rashba spin-orbit coupling on zero conductance resonances
appearing in one dimensional ring asymmetrically coupled to two leads is
investigated. For this purpose, the transmission function of the corresponding
one-electron scattering problem is derived analytically and analyzed in the
complex energy plane with focus on the zero-pole structure characteristic of
transmission (anti)resonances. The lifting of real conductance zeros due to
spin-orbit coupling in the asymmetric Aharonov-Casher (AC) ring is related to
the breaking of spin reversal symmetry in analogy to the time-reversal symmetry
breaking in the asymmetric Aharonov-Bohm (AB) ring.Comment: 10 pages, 11 figure
Temperature enhanced persistent currents and " periodicity"
We predict a non-monotonous temperature dependence of the persistent currents
in a ballistic ring coupled strongly to a stub in the grand canonical as well
as in the canonical case. We also show that such a non-monotonous temperature
dependence can naturally lead to a periodicity of the persistent
currents, where =h/e. There is a crossover temperature , below
which persistent currents increase in amplitude with temperature while they
decrease above this temperature. This is in contrast to persistent currents in
rings being monotonously affected by temperature. is parameter-dependent
but of the order of , where is the level spacing
of the isolated ring. For the grand-canonical case is half of that for
the canonical case.Comment: some typos correcte
Three Generations of SUSY Standard Model of Nambu-Goto String
A four dimensional Superstring is constructed starting from a twenty six
dimensional bosonic string. Fermions are introduced by noting the Manselstam's
proof of equivalence of two fermions to one boson in 1+1 dimensions. The action
of the superstring is invariant under SO(6) SO(5). It has four bosonic
coordinates and twenty four Majorana fermions of SO(3,1) representing two
transverse modes of super fermions and conformal ghosts (b,c). The super
conformal ghosts () are the quanta of an extended Hilbert space
of the remaining longitudinal modes of two superfermions. The massless spectrum
obtained by quantising the action, contain vector mesons which are generators
of the SO(6)SO(5). Using Wilson loops, this product group is proven to
descend to without breaking
supersymmetry.Thus there are just three generations of quarks and leptons.Comment: 11 page
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