2,384 research outputs found
Crossover from Luttinger liquid to Coulomb blockade regime in carbon nanotubes
We develop a theoretical approach to the low-energy properties of 1D electron
systems aimed to encompass the mixed features of Luttinger liquid and Coulomb
blockade behavior observed in the crossover between the two regimes. For this
aim we extend the Luttinger liquid description by incorporating the effects of
a discrete single-particle spectrum. The intermediate regime is characterized
by a power-law behavior of the conductance, but with an exponent oscillating
with the gate voltage, in agreement with recent experimental observations. Our
construction also accounts naturally for the existence of a crossover in the
zero-bias conductance, mediating between two temperature ranges where the
power-law behavior is preserved but with different exponent.Comment: 5 pages, 3 figure
New insight into WDVV equation
We show that Witten-Dijkgraaf-Verlinde-Verlinde equation underlies the
construction of N=4 superconformal multi--particle mechanics in one dimension,
including a N=4 superconformal Calogero model.Comment: 16 pages, no figures, LaTeX file, PACS: 04.60.Ds; 11.30.P
Extremal Black Hole and Flux Vacua Attractors
These lectures provide a pedagogical, introductory review of the so-called
Attractor Mechanism (AM) at work in two different 4-dimensional frameworks:
extremal black holes in N=2 supergravity and N=1 flux compactifications. In the
first case, AM determines the stabilization of scalars at the black hole event
horizon purely in terms of the electric and magnetic charges, whereas in the
second context the AM is responsible for the stabilization of the universal
axion-dilaton and of the (complex structure) moduli purely in terms of the RR
and NSNS fluxes. Two equivalent approaches to AM, namely the so-called
``criticality conditions'' and ``New Attractor'' ones, are analyzed in detail
in both frameworks, whose analogies and differences are discussed. Also a
stringy analysis of both frameworks (relying on Hodge-decomposition techniques)
is performed, respectively considering Type IIB compactified on and
its orientifolded version, associated with . Finally, recent results on the U-duality orbits and
moduli spaces of non-BPS extremal black hole attractors in , d=4 supergravities are reported.Comment: 1+74 pages, 2 Tables. Contribution to the Proceedings of the Winter
School on Attractor Mechanism 2006 (SAM2006), 20-24 March 2006, INFN-LNF,
Frascati, Ital
Consistent Batalin--Fradkin quantization of Infinitely Reducible First Class Constraints
We reconsider the problem of BRST quantization of a mechanics with infinitely
reducible first class constraints. Following an earlier recipe [Phys. Lett. B
381, 105, (1996)], the original phase space is extended by purely auxiliary
variables, the constraint set in the enlarged space being first stage of
reducibility. The BRST charge involving only a finite number of ghost variables
is explicitly constructed.Comment: 5 pages, LaTex. Minor corrections including the title. The version to
appear in Phys. Rev.
Intersecting Attractors
We apply the entropy formalism to the study of the near-horizon geometry of
extremal black p-brane intersections in D>5 dimensional supergravities. The
scalar flow towards the horizon is described in terms an effective potential
given by the superposition of the kinetic energies of all the forms under which
the brane is charged. At the horizon active scalars get fixed to the minima of
the effective potential and the entropy function is given in terms of U-duality
invariants built entirely out of the black p-brane charges. The resulting
entropy function reproduces the central charges of the dual boundary CFT and
gives rise to a Bekenstein-Hawking like area law. The results are illustrated
in the case of black holes and black string intersections in D=6, 7, 8
supergravities where the effective potentials, attractor equations, moduli
spaces and entropy/central charges are worked out in full detail.Comment: 1+41 pages, 2 Table
Single Wall Nanotubes: Atomic Like Behaviour and Microscopic Approach
Recent experiments about the low temperature behaviour of a Single Wall
Carbon Nanotube (SWCNT) showed typical Coulomb Blockade (CB) peaks in the zero
bias conductance and allowed us to investigate the energy levels of interacting
electrons. Other experiments confirmed the theoretical prediction about the
crucial role which the long range nature of the Coulomb interaction plays in
the correlated electronic transport through a SWCNT with two intramolecular
tunneling barriers. In order to investigate the effects on low dimensional
electron systems due to the range of electron electron repulsion, we introduce
a model for the interaction which interpolates well between short and long
range regimes. Our results could be compared with experimental data obtained in
SWCNTs and with those obtained for an ideal vertical Quantum Dot (QD).
For a better understanding of some experimental results we also discuss how
defects and doping can break some symmetries of the bandstructure of a SWCNT.Comment: 8 pages, 4 figure
Constant magnetic field and 2d non-commutative inverted oscillator
We consider a two-dimensional non-commutative inverted oscillator in the
presence of a constant magnetic field, coupled to the system in a
``symplectic'' and ``Poisson'' way. We show that it has a discrete energy
spectrum for some value of the magnetic field.Comment: 7 pages, LaTeX file, no figures, PACS number: 03.65.-
Doping- and size-dependent suppression of tunneling in carbon nanotubes
We study the effect of doping in the suppression of tunneling observed in
multi-walled nanotubes, incorporating as well the influence of the finite
dimensions of the system. A scaling approach allows us to encompass the
different values of the critical exponent measured for the tunneling
density of states in carbon nanotubes. We predict that further reduction of
should be observed in multi-walled nanotubes with a sizeable amount
of doping. In the case of nanotubes with a very large radius, we find a
pronounced crossover between a high-energy regime with persistent
quasiparticles and a low-energy regime with the properties of a one-dimensional
conductor.Comment: 4 pages, 2 figures, LaTeX file, pacs: 71.10.Pm, 71.20.Tx, 72.80.R
On Quantum Special Kaehler Geometry
We compute the effective black hole potential V of the most general N=2, d=4
(local) special Kaehler geometry with quantum perturbative corrections,
consistent with axion-shift Peccei-Quinn symmetry and with cubic leading order
behavior. We determine the charge configurations supporting axion-free
attractors, and explain the differences among various configurations in
relations to the presence of ``flat'' directions of V at its critical points.
Furthermore, we elucidate the role of the sectional curvature at the
non-supersymmetric critical points of V, and compute the Riemann tensor (and
related quantities), as well as the so-called E-tensor. The latter expresses
the non-symmetricity of the considered quantum perturbative special Kaehler
geometry.Comment: 1+43 pages; v2: typo corrected in the curvature of Jordan symmetric
sequence at page 2
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