11,559 research outputs found
Prospects for SIMPLE 2000: A large-mass, low-background Superheated Droplet Detector for WIMP searches
SIMPLE 2000 (Superheated Instrument for Massive ParticLE searches) will
consist of an array of eight to sixteen large active mass ( g)
Superheated Droplet Detectors(SDDs) to be installed in the new underground
laboratory of Rustrel-Pays d'Apt. Several factors make of SDDs an attractive
approach for the detection of Weakly Interacting Massive Particles (WIMPs),
namely their intrinsic insensitivity to minimum ionizing particles, high
fluorine content, low cost and operation near ambient pressure and temperature.
We comment here on the fabrication, calibration and already-competitive first
limits from SIMPLE prototype SDDs, as well as on the expected immediate
increase in sensitivity of the program, which aims at an exposure of 25
kg-day during the year 2000. The ability of modest-mass fluorine-rich detectors
to explore regions of neutralino parameter space beyond the reach of the most
ambitious cryogenic projects is pointed out.Comment: 19 pages, 10 figures included. New Journal of Physics, in pres
Dimer Decimation and Intricately Nested Localized-Ballistic Phases of Kicked Harper
Dimer decimation scheme is introduced in order to study the kicked quantum
systems exhibiting localization transition. The tight-binding representation of
the model is mapped to a vectorized dimer where an asymptotic dissociation of
the dimer is shown to correspond to the vanishing of the transmission
coefficient thru the system. The method unveils an intricate nesting of
extended and localized phases in two-dimensional parameter space. In addition
to computing transport characteristics with extremely high precision, the
renormalization tools also provide a new method to compute quasienergy
spectrum.Comment: There are five postscript figures. Only half of the figure (3) is
shown to reduce file size. However, missing part is the mirror image of the
part show
Collision and symmetry-breaking in the transition to strange nonchaotic attractors
Strange nonchaotic attractors (SNAs) can be created due to the collision of
an invariant curve with itself. This novel ``homoclinic'' transition to SNAs
occurs in quasiperiodically driven maps which derive from the discrete
Schr\"odinger equation for a particle in a quasiperiodic potential. In the
classical dynamics, there is a transition from torus attractors to SNAs, which,
in the quantum system is manifest as the localization transition. This
equivalence provides new insights into a variety of properties of SNAs,
including its fractal measure. Further, there is a {\it symmetry breaking}
associated with the creation of SNAs which rigorously shows that the Lyapunov
exponent is nonpositive. By considering other related driven iterative
mappings, we show that these characteristics associated with the the appearance
of SNA are robust and occur in a large class of systems.Comment: To be appear in Physical Review Letter
The Flux-Phase of the Half-Filled Band
The conjecture is verified that the optimum, energy minimizing magnetic flux
for a half-filled band of electrons hopping on a planar, bipartite graph is
per square plaquette. We require {\it only} that the graph has
periodicity in one direction and the result includes the hexagonal lattice
(with flux 0 per hexagon) as a special case. The theorem goes beyond previous
conjectures in several ways: (1) It does not assume, a-priori, that all
plaquettes have the same flux (as in Hofstadter's model); (2) A Hubbard type
on-site interaction of any sign, as well as certain longer range interactions,
can be included; (3) The conclusion holds for positive temperature as well as
the ground state; (4) The results hold in dimensions if there is
periodicity in directions (e.g., the cubic lattice has the lowest energy
if there is flux in each square face).Comment: 9 pages, EHL14/Aug/9
Far-UV Emissions of the Sun in Time: Probing Solar Magnetic Activity and Effects on Evolution of Paleo-Planetary Atmospheres
We present and analyze FUSE observations of six solar analogs. These are
single, main-sequence G0-5 strs selected as proxies for the Sun at several
stages of its main-sequence lifetime. The emission features in the FUSE
920-1180 A wavelength range allow for a critical probe of the hot plasma over
three decades in temperature. Using the flux ratio CIII 1176/977 as
diagnostics, we investigate the dependence of the electron pressure of the
transition region as a function of the rotation period, age and magnetic
activity. The results from these solar proxies indicate that the electron
pressure of the stellar ~10^5-K plasma decreases by a factor of about 70
between the young, fast-rotating magnetically active star and the old,
slow-rotating inactive star. Also, the observations indicate that the average
surface fluxes of emission features strongly decrease with increasing stellar
age and longer rotation period. The emission flux evolution with age or
rotation period is well fitted by power laws, which become steeper from cooler
chromospheric (10^4 K) to hotter coronal (10^7 K) plasma. The relationship for
the integrated (920-1180 A) FUSE flux indicates that the solar far-ultraviolet
emissions were about twice the present value 2.5 Gyr ago and about 4 times the
present value 3.5 Gyr ago. Note also that the FUSE/FUV flux of the Zero-Age
Main Sequence Sun could have been higher by as much as 50 times. Our analysis
suggests that the strong FUV emissions of the young Sun may have played a
crucial role in the developing planetary system, in particular through the
photoionization, photochemical evolution and possible erosion of the planetary
atmospheres. (abridged)Comment: 15 pages, 8 figures, accepted for publication in Ap
Search for an exosphere in sodium and calcium in the transmission spectrum of exoplanet 55 Cancri e
[Abridged] The aim of this work is to search for an absorption signal from
exospheric sodium (Na) and singly ionized calcium (Ca) in the optical
transmission spectrum of the hot rocky super-Earth 55 Cancri e. Although the
current best-fitting models to the planet mass and radius require a possible
atmospheric component, uncertainties in the radius exist, making it possible
that 55 Cancri e could be a hot rocky planet without an atmosphere. High
resolution (R110000) time-series spectra of five transits of 55 Cancri e,
obtained with three different telescopes (UVES/VLT, HARPS/ESO 3.6m &
HARPS-N/TNG) were analysed. Targeting the sodium D lines and the calcium H and
K lines, the potential planet exospheric signal was filtered out from the much
stronger stellar and telluric signals, making use of the change of the radial
component of the orbital velocity of the planet over the transit from -57 to
+57 km/sec. Combining all five transit data sets, we detect a signal
potentially associated with sodium in the planet exosphere at a statistical
significance level of 3. Combining the four HARPS transits that cover
the calcium H and K lines, we also find a potential signal from ionized calcium
(4.1 ). Interestingly, this latter signal originates from just one of
the transit measurements - with a 4.9 detection at this epoch.
Unfortunately, due to the low significance of the measured sodium signal and
the potentially variable Ca signal, we estimate the p-values of these
signals to be too high (corresponding to <4) to claim unambiguous
exospheric detections. By comparing the observed signals with artificial
signals injected early in the analysis, the absorption by Na and Ca are
estimated to be at a level of approximately 2.3 and 7.0 respectively, relative to the stellar spectrum.Comment: 15 pages, 8 figures, submission updated after English language
editing, submission updated to correct a mistaken cross-reference noticed in
A&A proo
Multifractals Competing with Solitons on Fibonacci Optical Lattice
We study the stationary states for the nonlinear Schr\"odinger equation on
the Fibonacci lattice which is expected to be realized by Bose-Einstein
condensates loaded into an optical lattice. When the model does not have a
nonlinear term, the wavefunctions and the spectrum are known to show fractal
structures. Such wavefunctions are called critical. We present a phase diagram
of the energy spectrum for varying the nonlinearity. It consists of three
portions, a forbidden region, the spectrum of critical states, and the spectrum
of stationary solitons. We show that the energy spectrum of critical states
remains intact irrespective of the nonlinearity in the sea of a large number of
stationary solitons.Comment: 5 pages, 4 figures, major revision, references adde
A map from 1d Quantum Field Theory to Quantum Chaos on a 2d Torus
Dynamics of a class of quantum field models on 1d lattice in Heisenberg
picture is mapped into a class of `quantum chaotic' one-body systems on
configurational 2d torus (or 2d lattice) in Schr\" odinger picture. Continuum
field limit of the former corresponds to quasi-classical limit of the latter.Comment: 4 pages in REVTeX, 1 eps-figure include
Water vapor on supergiants. The 12 micron TEXES spectra of mu Cephei
Several recent papers have argued for warm, semi-detached, molecular layers
surrounding red giant and supergiant stars, a concept known as a MOLsphere.
Spectroscopic and interferometric analyses have often corroborated this general
picture. Here, we present high-resolution spectroscopic data of pure rotational
lines of water vapor at 12 microns for the supergiant mu Cephei. This star has
often been used to test the concept of molecular layers around supergiants.
Given the prediction of an isothermal, optically thick water-vapor layer in
Local Thermodynamic Equilibrium around the star (MOLsphere), we expected the 12
micron lines to be in emission or at least in absorption but filled in by
emission from the molecular layer around the star. Our data, however, show the
contrary; we find definite absorption. Thus, our data do not easily fit into
the suggested isothermal MOLsphere scenario. The 12 micron lines, therefore,
put new, strong constraints on the MOLsphere concept and on the nature of water
seen in signatures across the spectra of early M supergiants. We also find that
the absorption is even stronger than that calculated from a standard,
spherically symmetric model photosphere without any surrounding layers. A cool
model photosphere, representing cool outer layers is, however, able to
reproduce the lines, but this model does not account for water vapor emission
at 6 microns. Thus, a unified model for water vapor on mu Cephei appears to be
lacking. It does seem necessary to model the underlying photospheres of these
supergiants in their whole complexity. The strong water vapor lines clearly
reveal inadequacies of classical model atmospheres.Comment: Accepted for publication in the Astrophysical Journa
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