19,309 research outputs found
The Minimal Length and Large Extra Dimensions
Planck scale physics represents a future challenge, located between particle
physics and general relativity. The Planck scale marks a threshold beyond which
the old description of spacetime breaks down and conceptually new phenomena
must appear. Little is known about the fundamental theory valid at Planckian
energies, except that it necessarily seems to imply the occurrence of a minimal
length scale, providing a natural ultraviolet cutoff and a limit to the
possible resolution of spacetime.
Motivated by String Theory, the models of large extra dimensions lower the
Planck scale to values soon accessible. These models predict a vast number of
quantum gravity effects at the lowered Planck scale, among them the production
of TeV-mass black holes and gravitons. Within the extra dimensional scenario,
also the minimal length comes into the reach of experiment and sets a
fundamental limit to short distance physics.
We review the status of Planck scale physics in these effective models.Comment: 18 pages, 5 figures, brief review to appear in Mod. Phys. Let.
Quantum Dot in 2D Topological Insulator: The Two-channel Kondo Fixed Point
In this work, a quantum dot couples to two helical edge states of a 2D
topological insulator through weak tunnelings is studied. We show that if the
electron interactions on the edge states are repulsive, with Luttinger liquid
parameter , the system flows to a stable two-channel fixed point at
low temperatures. This is in contrast to the case of a quantum dot couples to
two Luttinger liquid leads. In the latter case, a strong electron-electron
repulsion is needed, with , to reach the two-channel fixed point. This
two-channel fixed point is described by a boundary Sine-Gordon Hamiltonian with
a dependent boundary term. The impurity entropy at zero temperature is
shown to be . The impurity specific heat is when , and when . We
also show that the linear conductance across the two helical edges has
non-trivial temperature dependence as a result of the renormalization group
flow.Comment: 4+\epsilon page
Generalized Uncertainty Principle, Extra-dimensions and Holography
We consider Uncertainty Principles which take into account the role of
gravity and the possible existence of extra spatial dimensions. Explicit
expressions for such Generalized Uncertainty Principles in 4+n dimensions are
given and their holographic properties investigated. In particular, we show
that the predicted number of degrees of freedom enclosed in a given spatial
volume matches the holographic counting only for one of the available
generalizations and without extra dimensions.Comment: LaTeX, 13 pages, accepted for publication in Class. Quantum Gra
Generalized commutation relations and Non linear momenta theories, a close relationship
A revision of generalized commutation relations is performed, besides a
description of Non linear momenta realization included in some DSR theories. It
is shown that these propositions are closely related, specially we focus on
Magueijo Smolin momenta and Kempf et al. and L.N. Chang generalized
commutators. Due to this, a new algebra arises with its own features that is
also analyzed.Comment: accepted version in IJMP
Re-examination of electronic transports through a quantum wire coupled to a quantum dot
In this paper we re-examine the problem of electronic transports through a
system consisting of a quantum dot which has well-defined discrete energy
levels connected to an infinite quantum wire, using the bosonization method and
phase shift representation, we show that all previously known results can be
obtained through our method in a very simple way. Furthermore, the evolution of
the system from ultraviolet to infrared critical fixed points appears naturally
our method.Comment: latex, 26 pages, to appear in Phys. Rev. B61, January 15/200
Many Body Effects on Electron Tunneling through Quantum Dots in an Aharonov-Bohm Circuit
Tunneling conductance of an Aharonov-Bohm circuit including two quantum dots
is calculated based on the general expression of the conductance in the linear
response regime of the bias voltage. The calculation is performed in a wide
temperature range by using numerical renormalization group method. Various
types of AB oscillations appear depending on the temperature and the potential
depth of the dots. Especially, AB oscillations have strong higher harmonics
components as a function of the magnetic flux when the potential of the dots is
deep. This is related to the crossover of the spin state due to the Kondo
effect on quantum dots. When the temperature rises up, the amplitude of the AB
oscillations becomes smaller reflecting the breaking of the coherency.Comment: 21 pages, 11 PostScript figures, LaTeX, uses jpsj.sty epsbox.st
Spin-charge separation and Kondo effect in an open quantum dot
We study a quantum dot connected to the bulk by single-mode junctions at
almost perfect conductance. Although the average charge of
the dot is not discrete, its spin remains quantized: or ,
depending (periodically) on the gate voltage. This drastic difference from the
conventional mixed-valence regime stems from the existence of a broad-band,
dense spectrum of discrete levels in the dot. In the doublet state, the Kondo
effect develops at low temperatures. We find the Kondo temperature and
the conductance at .Comment: 4 pages, 1 figur
Weakly collisional Landau damping and three-dimensional Bernstein-Greene-Kruskal modes: New results on old problems
Landau damping and Bernstein-Greene-Kruskal (BGK) modes are among the most
fundamental concepts in plasma physics. While the former describes the
surprising damping of linear plasma waves in a collisionless plasma, the latter
describes exact undamped nonlinear solutions of the Vlasov equation. There does
exist a relationship between the two: Landau damping can be described as the
phase-mixing of undamped eigenmodes, the so-called Case-Van Kampen modes, which
can be viewed as BGK modes in the linear limit. While these concepts have been
around for a long time, unexpected new results are still being discovered. For
Landau damping, we show that the textbook picture of phase-mixing is altered
profoundly in the presence of collision. In particular, the continuous spectrum
of Case-Van Kampen modes is eliminated and replaced by a discrete spectrum,
even in the limit of zero collision. Furthermore, we show that these discrete
eigenmodes form a complete set of solutions. Landau-damped solutions are then
recovered as true eigenmodes (which they are not in the collisionless theory).
For BGK modes, our interest is motivated by recent discoveries of electrostatic
solitary waves in magnetospheric plasmas. While one-dimensional BGK theory is
quite mature, there appear to be no exact three-dimensional solutions in the
literature (except for the limiting case when the magnetic field is
sufficiently strong so that one can apply the guiding-center approximation). We
show, in fact, that two- and three-dimensional solutions that depend only on
energy do not exist. However, if solutions depend on both energy and angular
momentum, we can construct exact three-dimensional solutions for the
unmagnetized case, and two-dimensional solutions for the case with a finite
magnetic field. The latter are shown to be exact, fully electromagnetic
solutions of the steady-state Vlasov-Poisson-Amp\`ere system
Viscous Brane Cosmology with a Brane-Bulk Energy Interchange Term
We assume a flat brane located at y=0, surrounded by an AdS space, and
consider the 5D Einstein equations when the energy flux component of the
energy-momentum tensor is related to the Hubble parameter through a constant Q.
We calculate the metric tensor, as well as the Hubble parameter on the brane,
when Q is small. As a special case, if the brane is tensionless, the influence
from Q on the Hubble parameter is absent. We also consider the emission of
gravitons from the brane, by means of the Boltzmann equation. Comparing the
energy conservation equation derived herefrom with the energy conservation
equation for a viscous fluid on the brane, we find that the entropy change for
the fluid in the emission process has to be negative. This peculiar effect is
related to the fluid on the brane being a non-closed thermodynamic system. The
negative entropy property for non-closed systems is encountered in other areas
in physics also, in particular, in connection with the Casimir effect at finite
temperature.Comment: 12 pages, latex, no figure
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