27,288 research outputs found
Wigner Oscillators, Twisted Hopf Algebras and Second Quantization
By correctly identifying the role of central extension in the centrally
extended Heisenberg algebra h, we show that it is indeed possible to construct
a Hopf algebraic structure on the corresponding enveloping algebra U(h) and
eventually deform it through Drinfeld twist. This Hopf algebraic structure and
its deformed version U^F(h) are shown to be induced from a more fundamental
Hopf algebra obtained from the Schroedinger field/oscillator algebra and its
deformed version, provided that the fields/oscillators are regarded as
odd-elements of the super-algebra osp(1|2n). We also discuss the possible
implications in the context of quantum statistics.Comment: 23 page
Higher particle form factors of branch point twist fields in integrable quantum field theories
In this paper we compute higher particle form factors of branch point twist
fields. These fields were first described in the context of massive
1+1-dimensional integrable quantum field theories and their correlation
functions are related to the bi-partite entanglement entropy. We find analytic
expressions for some form factors and check those expressions for consistency,
mainly by evaluating the conformal dimension of the corresponding twist field
in the underlying conformal field theory. We find that solutions to the form
factor equations are not unique so that various techniques need to be used to
identify those corresponding to the branch point twist field we are interested
in. The models for which we carry out our study are characterized by staircase
patterns of various physical quantities as functions of the energy scale. As
the latter is varied, the beta-function associated to these theories comes
close to vanishing at several points between the deep infrared and deep
ultraviolet regimes. In other words, renormalisation group flows approach the
vicinity of various critical points before ultimately reaching the ultraviolet
fixed point. This feature provides an optimal way of checking the consistency
of higher particle form factor solutions, as the changes on the conformal
dimension of the twist field at various energy scales can only be accounted for
by considering higher particle form factor contributions to the expansion of
certain correlation functions.Comment: 25 pages, 4 figures; v2 contains small correction
Brownian motion meets Riemann curvature
The general covariance of the diffusion equation is exploited in order to
explore the curvature effects appearing on brownian motion over a d-dimensional
curved manifold. We use the local frame defined by the so called Riemann normal
coordinates to derive a general formula for the mean-square geodesic distance
(MSD) at the short-time regime. This formula is written in terms of
invariants that depend on the Riemann curvature tensor. We study the
n-dimensional sphere case to validate these results. We also show that the
diffusion for positive constant curvature is slower than the diffusion in a
plane space, while the diffusion for negative constant curvature turns out to
be faster. Finally the two-dimensional case is emphasized, as it is relevant
for the single particle diffusion on biomembranes.Comment: 16 pages and 3 figure
Theoretical Aspects of the Fractional Quantum Hall Effect in Graphene
We review the theoretical basis and understanding of electronic interactions
in graphene Landau levels, in the limit of strong correlations. This limit
occurs when inter-Landau-level excitations may be omitted because they belong
to a high-energy sector, whereas the low-energy excitations only involve the
same level, such that the kinetic energy (of the Landau level) is an
unimportant constant. Two prominent effects emerge in this limit of strong
electronic correlations: generalised quantum Hall ferromagnetic states that
profit from the approximate four-fold spin-valley degeneracy of graphene's
Landau levels and the fractional quantum Hall effect. Here, we discuss these
effects in the framework of an SU(4)-symmetric theory, in comparison with
available experimental observations.Comment: 12 pages, 3 figures; review for the proceedings of the Nobel
Symposium on Graphene and Quantum Matte
Electronic properties of graphene multilayers
We study the effects of disorder in the electronic properties of graphene
multilayers, with special focus on the bilayer and the infinite stack. At low
energies and long wavelengths, the electronic self-energies and density of
states exhibit behavior with divergences near half-filling. As a consequence,
the spectral functions and conductivities do not follow Landau's Fermi liquid
theory. In particular, we show that the quasiparticle decay rate has a minimum
as a function of energy, there is a universal minimum value for the in-plane
conductivity of order e^2/h per plane and, unexpectedly, the c-axis
conductivity is enhanced by disorder at low doping, leading to an enormous
conductivity anisotropy at low temperatures.Comment: 4 pages, 4 figure. Reference to exciting new ARPES results on
graphite added (we thank A. Lanzara for sharing the paper prior to its
publication
5D Black Holes and Strings with Higher Derivatives
We find asymptotically flat black hole and string solutions to 5D
supergravity in the presence of higher derivative terms. In some cases,
including the fundamental heterotic string solution, the higher derivative
terms smooth out naked singularities into regular geometries carrying zero
entropy. We also compute corrections to the entropy of 5D Calabi-Yau black
holes, and discuss the relation to previous results.Comment: 33 pages, 2 figs., harvmac; v2: typos corrected, references added v3:
refs correcte
Rational sequences for the conductance in quantum wires from affine Toda field theories
We analyse the expression for the conductance of a quantum wire which is
decribed by an integrable quantum field theory. In the high temperature regime
we derive a simple formula for the filling fraction. This expression involves
only the inverse of a matrix which contains the information of the asymptotic
phases of the scattering matrix and the solutions of the constant thermodynamic
Bethe ansatz equations. Evaluating these expressions for minimal affine Toda
field theory we recover several sequences of rational numbers, which are
multiples of the famous Jain sequence for the filling fraction occurring in the
context of the fractional quantum Hall effect. For instance we obtain for -minimal affine Toda field theory. The matrices
involved have in general non-rational entries and are not part of previous
classification schemes based on integral lattices.Comment: 9 pages Latex, version to appear in Journal of Physics
Gauge invariance and finite width effects in radiative two-pion tau lepton decay
The contribution of the rho^{\pm} vector meson to the tau -> pi pi nu gamma
decay is considered as a potential source for the determination of the magnetic
dipole moment of this light vector meson. In order to keep gauge-invariance of
the whole decay amplitude, a procedure similar to the fermion loop-scheme for
charged gauge bosons is implemented to incorporate the finite width effects of
the rho^{\pm} vector meson. The absorptive pieces of the one-loop corrections
to the propagators and electromagnetic vertices of the rho^{\pm} meson and
W^{\pm} gauge boson have identical forms in the limit of massless particles in
the loops, suggesting this to be a universal feature of spin-one unstable
particles. Model-dependent contributions to the tau -> pi pi nu gamma decay are
suppressed by fixing the two-pion invariant mass distribution at the rho meson
mass value. The resulting photon energy and angular distribution is relatively
sensitive to the effects of the rho magnetic dipole moment.Comment: 22 pages, 4 postscript figures, references and comments on relevance
of perturbative treatment of rho electromagnetic vertex are added, accepted
for pub. in Phys. Rev.
Applications of quantum integrable systems
We present two applications of quantum integrable systems. First, we predict
that it is possible to generate high harmonics from solid state devices by
demostrating that the emission spectrum for a minimally coupled laser field of
frequency to an impurity system of a quantum wire, contains multiples
of the incoming frequency. Second, evaluating expressions for the conductance
in the high temperature regime we show that the caracteristic filling fractions
of the Jain sequence, which occur in the fractional quantum Hall effect, can be
obtained from quantum wires which are described by minimal affine Toda field
theories.Comment: 25 pages of LaTex, 4 figures, based on talk at the 6-th international
workshop on conformal field theories and integrable models, (Chernogolovka,
September 2002
Surface superconductivity in multilayered rhombohedral graphene: Supercurrent
The supercurrent for the surface superconductivity of a flat-band
multilayered rhombohedral graphene is calculated. Despite the absence of
dispersion of the excitation spectrum, the supercurrent is finite. The critical
current is proportional to the zero-temperature superconducting gap, i.e., to
the superconducting critical temperature and to the size of the flat band in
the momentum space
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