4,366 research outputs found
Can the trace formula describe weak localisation?
We attempt to systematically derive perturbative quantum corrections to the
Berry diagonal approximation of the two-level correlation function (TLCF) for
chaotic systems. To this end, we develop a ``weak diagonal approximation''
based on a recent description of the first weak localisation correction to
conductance in terms of the Gutzwiller trace formula. This semiclassical method
is tested by using it to derive the weak localisation corrections to the TLCF
for a semiclassically disordered system. Unfortunately the method is unable to
correctly reproduce the ``Hikami boxes'' (the relatively small regions where
classical paths are glued together by quantum processes). This results in the
method failing to reproduce the well known weak localisation expansion. It so
happens that for the first order correction it merely produces the wrong
prefactor. However for the second order correction, it is unable to reproduce
certain contributions, and leads to a result which is of a different form to
the standard one.Comment: 23 pages in Latex (with IOP style files), 3 eps figures included, to
be a symposium paper in a Topical Issue of Waves in Random Media, 199
Itinerancy and Hidden Order in
We argue that key characteristics of the enigmatic transition at in indicate that the hidden order is a density wave formed within
a band of composite quasiparticles, whose detailed structure is determined by
local physics. We expand on our proposal (with J.A. Mydosh) of the hidden order
as incommnesurate orbital antiferromagnetism and present experimental
predictions to test our ideas. We then turn towards a microscopic description
of orbital antiferromagnetism, exploring possible particle-hole pairings within
the context of a simple one-band model. We end with a discussion of recent
high-field and thermal transport experiment, and discuss their implications for
the nature of the hidden order.Comment: 18 pages, 7 figures. v2 contains added referenc
Level and Eigenfunction Statistics in Billiards with Surface Scattering
Statistical properties of billiards with diffusive boundary scattering are
investigated by means of the supersymmetric sigma-model in a formulation
appropriate for chaotic ballistic systems. We study level statistics,
parametric level statistics, and properties of electron wavefunctions. In the
universal regime, our results reproduce conclusions of the random matrix
theory, while beyond this regime we obtain a variety of system-specific results
determined by the classical dynamics in the billiard. Most notably, we find
that level correlations do not vanish at arbitrary separation between energy
levels, or if measured at arbitrarily large difference of magnetic fields.
Saturation of the level number variance indicates strong rigidity of the
spectrum. To study spatial correlations of wavefunction amplitudes, we
reanalyze and refine derivation of the ballistic version of the sigma-model.
This allows us to obtain a proper matching of universal short-scale
correlations with system-specific ones.Comment: 19 pages, 5 figures included. Minor corrections, references adde
Climatological aspects of the optical properties of fine/coarse mode aerosol mixtures
Aerosol mixtures composed of coarse mode desert dust combined with fine mode combustion generated aerosols (from fossil fuel and biomass burning sources) were investigated at three locations that are in and/or downwind of major global aerosol emission source regions. Multiyear monitoring data at Aerosol Robotic Network sites in Beijing (central eastern China), Kanpur (Indo-Gangetic Plain, northern India), and Ilorin (Nigeria, Sudanian zone of West Africa) were utilized to study the climatological characteristics of aerosol optical properties. Multiyear climatological averages of spectral single scattering albedo (SSA) versus fine mode fraction (FMF) of aerosol optical depth at 675 nm at all three sites exhibited relatively linear trends up to similar to 50% FMF. This suggests the possibility that external linear mixing of both fine and coarse mode components (weighted by FMF) dominates the SSA variation, where the SSA of each component remains relatively constant for this range of FMF only. However, it is likely that a combination of other factors is also involved in determining the dynamics of SSA as a function of FMF, such as fine mode particles adhering to coarse mode dust. The spectral variation of the climatological averaged aerosol absorption optical depth (AAOD) was nearly linear in logarithmic coordinates over the wavelength range of 440-870 nm for both the Kanpur and Ilorin sites. However, at two sites in China (Beijing and Xianghe), a distinct nonlinearity in spectral AAOD in logarithmic space was observed, suggesting the possibility of anomalously strong absorption in coarse mode aerosols increasing the 870 nm AAOD
Measurement of the branching ratio of pi^0 -> e^+e^- using K_L -> 3 pi^0 decays in flight
The branching ratio of the rare decay pi^0 -> e^+e^- has been measured in
E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. The
pi^0's were produced in fully-reconstructed K_L -> 3 pi^0 decays in flight. We
observed 275 candidate pi^0 -> e^+e^- events, with an expected background of
21.4 +- 6.2 events which includes the contribution from Dalitz decays. We
measured BR(pi^0 -> e^+e^-, x>0.95) = (6.09 +- 0.40 +- 0.24) times 10^{-8},
where the first error is statistical and the second systematic. This result is
the first significant observation of the excess rate for this decay above the
unitarity lower bound.Comment: New version shortened to PRL length limit. 5 pages, 4 figures.
Published in Phys. Rev. Let
Measurements of the rare decay K_{L} -> e^{+} e^{-} e^{+} e^{-}
We observe 441 K_{L} -> e^{+} e^{-} e^{+} e^{-} candidate events with a
background of 4.2 events and measure B(K_{L} -> e^{+} e^{-} e^{+} e^{-}) =
(3.72 \pm 0.18(stat) \pm 0.23(syst)) \times 10^{-8} in the KTeV/E799II
experiment at Fermilab. Using the distribution of the angle between the planes
of the e^{+} e^{-} pairs, we measure the CP parameters beta_{CP} = -0.23 \pm
0.09(stat) \pm 0.02(syst) and gamma_{CP} = -0.09 \pm 0.09(stat) \pm 0.02(syst).
We also present the first detailed study of the e^{+} e^{-} invariant mass
spectrum in this decay mode.Comment: 14 pages, 4 figure
Constraints from Solar and Reactor Neutrinos on Unparticle Long-Range Forces
We have investigated the impact of long-range forces induced by unparticle
operators of scalar, vector and tensor nature coupled to fermions in the
interpretation of solar neutrinos and KamLAND data. If the unparticle couplings
to the neutrinos are mildly non-universal, such long-range forces will not
factorize out in the neutrino flavour evolution. As a consequence large
deviations from the observed standard matter-induced oscillation pattern for
solar neutrinos would be generated. In this case, severe limits can be set on
the infrared fix point scale, Lambda_u, and the new physics scale, M, as a
function of the ultraviolet (d_UV) and anomalous (d) dimension of the
unparticle operator. For a scalar unparticle, for instance, assuming the
non-universality of the lepton couplings to unparticles to be of the order of a
few per mil we find that, for d_UV=3 and d=1.1, M is constrained to be M >
O(10^9) TeV (M > O(10^10) TeV) if Lambda_u= 1 TeV (10 TeV). For given values of
Lambda_u and d, the corresponding bounds on M for vector [tensor] unparticles
are approximately 100 [3/Sqrt(Lambda_u/TeV)] times those for the scalar case.
Conversely, these results can be translated into severe constraints on
universality violation of the fermion couplings to unparticle operators with
scales which can be accessible at future colliders.Comment: 13 pages, 3 figures. Minor changes due to precision in numerical
factors and correction in figure labels. References added. Conclusions remain
unchange
Radiative Decay Width Measurements of Neutral Kaon Excitations Using the Primakoff Effect
We produce a sample consisting of 147 candidate events, with minimal
backgrounds, of the mixed axial vector pair K1(1270)-K1(1400) by exciting Kl's
in the Coulomb field of lead and report the first measurements of the radiative
widths Gamma_r(K1(1400)) = 280.8+-23.2(stat)+-40.4(syst) keV and
Gamma_r(K1(1270)) = 73.2+- 6.1(stat)+-28.3(syst) keV. We also place 90% CL
upper limits Gamma_r(K*(1410)) < 52.9 keV for the vector state and
Gamma_r(K2*(1430)) < 5.4 keV for the tensor state. These measurements allow for
significant tests of quark-model predictions of radiative widths for the
low-lying vector mesons.Comment: PRL-size article, 4 figure
Mixmaster: Fact and Belief
We consider the dynamics towards the initial singularity of Bianchi type IX
vacuum and orthogonal perfect fluid models with a linear equation of state.
Surprisingly few facts are known about the `Mixmaster' dynamics of these
models, while at the same time most of the commonly held beliefs are rather
vague. In this paper, we use Mixmaster facts as a base to build an
infrastructure that makes it possible to sharpen the main Mixmaster beliefs. We
formulate explicit conjectures concerning (i) the past asymptotic states of
type IX solutions and (ii) the relevance of the Mixmaster/Kasner map for
generic past asymptotic dynamics. The evidence for the conjectures is based on
a study of the stochastic properties of this map in conjunction with dynamical
systems techniques. We use a dynamical systems formulation, since this approach
has so far been the only successful path to obtain theorems, but we also make
comparisons with the `metric' and Hamiltonian `billiard' approaches.Comment: 34 pages, 10 figure
On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode
A major, albeit serendipitous, discovery of the SOlar and Heliospheric
Observatory mission was the observation by the Extreme Ultraviolet Telescope
(EIT) of large-scale Extreme Ultraviolet (EUV) intensity fronts propagating
over a significant fraction of the Sun's surface. These so-called EIT or EUV
waves are associated with eruptive phenomena and have been studied intensely.
However, their wave nature has been challenged by non-wave (or pseudo-wave)
interpretations and the subject remains under debate. A string of recent solar
missions has provided a wealth of detailed EUV observations of these waves
bringing us closer to resolving their nature. With this review, we gather the
current state-of-art knowledge in the field and synthesize it into a picture of
an EUV wave driven by the lateral expansion of the CME. This picture can
account for both wave and pseudo-wave interpretations of the observations, thus
resolving the controversy over the nature of EUV waves to a large degree but
not completely. We close with a discussion of several remaining open questions
in the field of EUV waves research.Comment: Solar Physics, Special Issue "The Sun in 360",2012, accepted for
publicatio
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