6,023 research outputs found
Local order and magnetic field effects on the electronic properties of disordered binary alloys in the Quantum Site Percolation limit
Electronic properties of disordered binary alloys are studied via the
calculation of the average Density of States (DOS) in two and three dimensions.
We propose a new approximate scheme that allows for the inclusion of local
order effects in finite geometries and extrapolates the behavior of infinite
systems following `finite-size scaling' ideas. We particularly investigate the
limit of the Quantum Site Percolation regime described by a tight-binding
Hamiltonian. This limit was chosen to probe the role of short range order (SRO)
properties under extreme conditions. The method is numerically highly efficient
and asymptotically exact in important limits, predicting the correct DOS
structure as a function of the SRO parameters. Magnetic field effects can also
be included in our model to study the interplay of local order and the shifted
quantum interference driven by the field. The average DOS is highly sensitive
to changes in the SRO properties, and striking effects are observed when a
magnetic field is applied near the segregated regime. The new effects observed
are twofold: there is a reduction of the band width and the formation of a gap
in the middle of the band, both as a consequence of destructive interference of
electronic paths and the loss of coherence for particular values of the
magnetic field. The above phenomena are periodic in the magnetic flux. For
other limits that imply strong localization, the magnetic field produces minor
changes in the structure of the average DOS.Comment: 13 pages, 9 figures, 31 references, RevTex preprint, submitted to
Phys. Rev.
Ongoing Mass Transfer in the Interacting Galaxy Pair NGC 1409/10
I present two-band HST STIS imaging, and WIYN spectral mapping, of ongoing
mass transfer in the interacting galaxy pair NGC 1409/10 (where NGC 1410 is the
Seyfert galaxy also catalogued as III Zw 55). Archival snapshot WFPC2 imaging
from the survey by Malkan et al. showed a dust feature stretching between the
galaxies, apparently being captured by NGC 1409. The new images allow estimates
of the mass being transferred and rate of transfer. An absorption lane
typically 0.25" (100 pc) wide with a representative optical depth tau_B = 0.2
cuts across the spiral structure of NGC 1410, crosses the 7-kpc projected space
between the nuclei, wraps in front of and, at the limits of detection, behind
NGC 1409, and becomes a denser (tau_B = 0.4) polar feature around the core of
NGC 1409. Combination of extinction data in two passbands allows a crude
three-dimensional recovery of the dust structure, supporting the front/back
geometry derived from colors and extinction estimates. The whole feature
contains of order solar masses in dust, implying about 2x10^7 solar
masses of gas, requiring a mass transfer rate averaging ~1 solar mass per year
unless we are particularly unlucky in viewing angle. Curiously, this
demonstrable case of mass transfer seems to be independent of the occurrence of
a Seyfert nucleus, since the Seyfert galaxy in this pair is the donor of the
material. Likewise, the recipient shows no signs of recent star formation from
incoming gas, although NGC 1410 has numerous luminous young star clusters and
widespread H-alpha emission.Comment: 27 pages, 9 figures. Accepted for the Astronomical Journal, March
200
Vacuum polarization by topological defects in de Sitter spacetime
In this paper we investigate the vacuum polarization effects associated with
a massive quantum scalar field in de Sitter spacetime in the presence of
gravitational topological defects. Specifically we calculate the vacuum
expectation value of the field square, . Because this investigation
has been developed in a pure de Sitter space, here we are mainly interested on
the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and
Quantum Gravity (MCCQG
A double coset ansatz for integrability in AdS/CFT
We give a proof that the expected counting of strings attached to giant
graviton branes in AdS_5 x S^5, as constrained by the Gauss Law, matches the
dimension spanned by the expected dual operators in the gauge theory. The
counting of string-brane configurations is formulated as a graph counting
problem, which can be expressed as the number of points on a double coset
involving permutation groups. Fourier transformation on the double coset
suggests an ansatz for the diagonalization of the one-loop dilatation operator
in this sector of strings attached to giant graviton branes. The ansatz agrees
with and extends recent results which have found the dynamics of open string
excitations of giants to be given by harmonic oscillators. We prove that it
provides the conjectured diagonalization leading to harmonic oscillators.Comment: 33 pages, 3 figures; v2: references adde
Electronic Phase Separation Transition as the Origin of the Superconductivity and the Pseudogap Phase of Cuprates
We propose a new phase of matter, an electronic phase separation transition
that starts near the upper pseudogap and segregates the holes into high and low
density domains. The Cahn-Hilliard approach is used to follow quantitatively
this second order transition. The resulting grain boundary potential confines
the charge in domains and favors the development of intragrain superconducting
amplitudes. The zero resistivity transition arises only when the intergrain
Josephson coupling is of the order of the thermal energy and phase
locking among the superconducting grains takes place. We show that this
approach explains the pseudogap and superconducting phases in a natural way and
reproduces some recent scanning tunneling microscopy dataComment: 4 pages and 5 eps fig
Euclidean Scalar Green Function in a Higher Dimensional Global Spacetime
We construct the explicit Euclidean scalar Green function associated with a
massless field in a higher dimensional global monopole spacetime, i.e., a
-spacetime with which presents a solid angle deficit. Our
result is expressed in terms of a infinite sum of products of Legendre
functions with Gegenbauer polynomials. Although this Green function cannot be
expressed in a closed form, for the specific case where the solid angle deficit
is very small, it is possible to develop the sum and obtain the Green function
in a more workable expression. Having this expression it is possible to
calculate the vacuum expectation value of some relevant operators. As an
application of this formalism, we calculate the renormalized vacuum expectation
value of the square of the scalar field, , and the
energy-momentum tensor, , for the global monopole
spacetime with spatial dimensions and .Comment: 18 pages, LaTex format, no figure
Nonplanar integrability at two loops
In this article we compute the action of the two loop dilatation operator on
restricted Schur polynomials that belong to the su(2) sector, in the displaced
corners approximation. In this non-planar large N limit, operators that
diagonalize the one loop dilatation operator are not corrected at two loops.
The resulting spectrum of anomalous dimensions is related to a set of decoupled
harmonic oscillators, indicating integrability in this sector of the theory at
two loops. The anomalous dimensions are a non-trivial function of the 't Hooft
coupling, with a spectrum that is continuous and starting at zero at large N,
but discrete at finite N.Comment: version to appear in JHE
Econometric analysis of Australian emissions markets and electricity prices
© 2014 Elsevier Ltd. Emissions trading schemes aim to reduce the emissions in certain pollutants using a market based scheme where participants can buy and sell permits for these emissions. This paper analyses the efficiency of the two largest schemes in Australia, the NSW Greenhouse Gas Abatement Scheme and the Mandatory Renewable Energy Trading Scheme, through their effect on the electricity prices from 2004 to 2010. We use a long run structural modelling technique for thefirst time on this market. It provides a practical long-run approach to structural relationships which enable the determination of the effectiveness of the theoretical expectations of these schemes. The generalised forecast error variance decomposition analysisfinds that both schemes' emissions prices have little effect on electricity prices. Generalised impulse response function analysis support thisfinding indicating that when shocks are applied to electricity by the two schemes it returns to equilibrium very quickly. This indicates that these schemes are not having the effect anticipated in their legislation
Giant Gravitons - with Strings Attached (III)
We develop techniques to compute the one-loop anomalous dimensions of
operators in the super Yang-Mills theory that are dual to open
strings ending on boundstates of sphere giant gravitons. Our results, which are
applicable to excitations involving an arbitrary number of open strings,
generalize the single string results of hep-th/0701067. The open strings we
consider carry angular momentum on an S embedded in the S of the
AdSS background. The problem of computing the one loop anomalous
dimensions is replaced with the problem of diagonalizing an interacting Cuntz
oscillator Hamiltonian. Our Cuntz oscillator dynamics illustrates how the
Chan-Paton factors for open strings propagating on multiple branes can arise
dynamically.Comment: 66 pages; v2: improved presentatio
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