14,162 research outputs found
Joint Bayesian Estimation of Quasar Continua and the Lyman-Alpha Forest Flux Probability Distribution Function
We present a new Bayesian algorithm making use of Markov Chain Monte Carlo
sampling that allows us to simultaneously estimate the unknown continuum level
of each quasar in an ensemble of high-resolution spectra, as well as their
common probability distribution function (PDF) for the transmitted Ly
forest flux. This fully automated PDF regulated continuum fitting method models
the unknown quasar continuum with a linear Principal Component Analysis (PCA)
basis, with the PCA coefficients treated as nuisance parameters. The method
allows one to estimate parameters governing the thermal state of the
intergalactic medium (IGM), such as the slope of the temperature-density
relation , while marginalizing out continuum uncertainties in a fully
Bayesian way. Using realistic mock quasar spectra created from a simplified
semi-numerical model of the IGM, we show that this method recovers the
underlying quasar continua to a precision of and at
and , respectively. Given the number of principal component spectra,
this is comparable to the underlying accuracy of the PCA model itself. Most
importantly, we show that we can achieve a nearly unbiased estimate of the
slope of the IGM temperature-density relation with a precision of
at , at , for an ensemble of ten mock
high-resolution quasar spectra. Applying this method to real quasar spectra and
comparing to a more realistic IGM model from hydrodynamical simulations would
enable precise measurements of the thermal and cosmological parameters
governing the IGM, albeit with somewhat larger uncertainties given the
increased flexibility of the model.Comment: 21 pages (+ Appendix), accepted at Ap
Supersolidity and phase diagram of softcore bosons in a triangular lattice
We study the softcore extended Bose Hubbard model in a two-dimensional
triangular lattice by using the quantum Monte Carlo methods. The ground state
phase diagram of the system exhibits a very fruitful structure. Except the Mott
insulating state, four kinds of solid states with respect to the commensurate
filling factors and are identified. Two of them (CDW II
and CDW III) are newly predicted. In incommensurate fillings, superfluid,
spuersolid as well as phase separation states are detected . As in the case for
the hardcore bosons, a supersolid phase exists in while it is
unstable towards the phase separation in . However, this instability
is refrained in due to the softening of the bosons and then a
supersolid phase survives.Comment: 4 pages, 5 figure
Protocluster Discovery in Tomographic Ly Forest Flux Maps
We present a new method of finding protoclusters using tomographic maps of
Ly Forest flux. We review our method of creating tomographic flux maps
and discuss our new high performance implementation, which makes large
reconstructions computationally feasible. Using a large N-body simulation, we
illustrate how protoclusters create large-scale flux decrements, roughly 10
Mpc across, and how we can use this signal to find them in flux maps.
We test the performance of our protocluster finding method by running it on the
ideal, noiseless map and tomographic reconstructions from mock surveys, and
comparing to the halo catalog. Using the noiseless map, we find protocluster
candidates with about 90% purity, and recover about 75% of the protoclusters
that form massive clusters (). We
construct mock surveys similar to the ongoing COSMOS Lyman-Alpha Mapping And
Tomography Observations (CLAMATO) survey. While the existing data has an
average sightline separation of 2.3 Mpc, we test separations of 2 - 6
Mpc to see what can be tolerated for our application. Using
reconstructed maps from small separation mock surveys, the protocluster
candidate purity and completeness are very close what was found in the
noiseless case. As the sightline separation increases, the purity and
completeness decrease, although they remain much higher than we initially
expected. We extended our test cases to mock surveys with an average separation
of 15 Mpc, meant to reproduce high source density areas of the BOSS
survey. We find that even with such a large sightline separation, the method
can still be used to find some of the largest protoclusters.Comment: 18 pages, 12 figure
Linear scaling computation of the Fock matrix. IX. Parallel computation of the Coulomb matrix
We present parallelization of a quantum-chemical tree-code [J. Chem. Phys.
{\bf 106}, 5526 (1997)] for linear scaling computation of the Coulomb matrix.
Equal time partition [J. Chem. Phys. {\bf 118}, 9128 (2003)] is used to load
balance computation of the Coulomb matrix. Equal time partition is a
measurement based algorithm for domain decomposition that exploits small
variation of the density between self-consistent-field cycles to achieve load
balance. Efficiency of the equal time partition is illustrated by several tests
involving both finite and periodic systems. It is found that equal time
partition is able to deliver 91 -- 98 % efficiency with 128 processors in the
most time consuming part of the Coulomb matrix calculation. The current
parallel quantum chemical tree code is able to deliver 63 -- 81% overall
efficiency on 128 processors with fine grained parallelism (less than two heavy
atoms per processor).Comment: 7 pages, 6 figure
Interlayer couplings and the coexistence of antiferromagnetic and d-wave pairing order in multilayer cuprates
A more extended low density region of coexisting uniform antiferromagnetism
and d-wave superconductivity has been reported in multilayer cuprates, when
compared to single or bilayer cuprates. This coexistence could be due to the
enhanced screening of random potential modulations in inner layers or to the
interlayer Heisenberg and Josephson couplings. A theoretical analysis using a
renormalized mean field theory, favors the former explanation. The potential
for an improved determination of the antiferromagnetic and superconducting
order parameters in an ideal single layer from zero field NMR and infrared
Josephson plasma resonances in multilayer cuprates is discussed.Comment: 6 pages, 2 figure
Theory for Gossamer and Resonating Valence Bond Superconductivity
We use an effective Hamiltonian for two-dimensional Hubbard model including
an antiferromagnetic spin-spin coupling term to study recently proposed
gossamer superconductivity. We formulate a renormalized mean field theory to
approximately take into account the strong correlation effect in the partially
projected Gutzwiller wavefucntions. At the half filled, there is a first order
phase transition to separate a Mott insulator at large Coulomb repulsion U from
a gossamer superconductor at small U. Away from the half filled,the Mott
insulator is evolved into an resonating valence bond state, which is
adiabatically connected to the gossamer superconductor.Comment: 10 pages, 13 figure
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