374 research outputs found
Scale-dependent bias and the halo model
We use a simplified version of the halo model with a power law power spectrum
to study scale dependence in galaxy bias at the very large scales relevant to
baryon oscillations. In addition to providing a useful pedagogical explanation
of the scale dependence of galaxy bias, the model provides an analytic tool for
studying how changes in the Halo Occupation Distribution (HOD) impact the scale
dependence of galaxy bias on scales between 10 and 1000 Mpc/h, which is useful
for interpreting the results of complex N-body simulations. We find that
changing the mean number of galaxies per halo of a given mass will change the
scale dependence of the bias, but that changing the way the galaxies are
distributed within the halo has a smaller effect on the scale dependence of
bias at large scales. We use the model to explain the decay in amplitude of the
baryon oscillations as k increases, and generalize the model to make
predictions about scale dependent galaxy bias when redshift space distortions
are introduced.Comment: 13 pages, 2 figures; corrected typos, extended discussion of redshift
space distortions, matches published versio
Characterizing the Shapes of Galaxy Clusters Using Moments of the Gravitational Lensing Shear
We explore the use of the tangential component of weak lensing shear to
characterize the ellipticity of clusters of galaxies. We introduce an
ellipticity estimator, and quantify its properties for isolated clusters from
LCDM N-body simulations. We compare the N-body results to results from smooth
analytic models. The expected distribution of the estimator for mock
observations is presented, and we show how this distribution is impacted by
contaminants such as noise, line of sight projections, and misalignment of the
central galaxy used to determine the orientation of the triaxial halo. We
examine the radial profile of the estimator and discuss tradeoffs in the
observational strategy to determine cluster shape.Comment: 17 pages, 6 figures; added references, corrected typos, matches
published versio
Coulomb gap in one-dimensional disordered electronic systems
We study a one-dimensional system of spinless electrons in the presence of a
long-range Coulomb interaction (LRCI) and a random chemical potential at each
site. We first present a Tomonaga-Luttinger liquid (TLL) description of the
system. We use the bosonization technique followed by the replica trick to
average over the quenched randomness. An expression for the localization length
of the system is then obtained using the renormalization group method and also
a physical argument. We then find the density of states for different values of
the energy; we get different expressions depending on whether the energy is
larger than or smaller than the inverse of the localization length. We work in
the limit of weak disorder where the localization length is very large; at that
length scale, the LRCI has the effect of reducing the interaction parameter K
of the TLL to a value much smaller than the noninteracting value of unity.Comment: Revtex, 6 pages, no figures; discussions have been expanded in
several place
Friedel oscillations in a two-band Hubbard model for CuO chains
Friedel oscillations induced by open boundary conditions in a two-band
Hubbard model for CuO chains are numerically studied. We find that for
physically realistic parameters and close to quarter filling, these
oscillations have a 2k_F modulation according with experimental results on
YBa_2Cu_3O_{7-delta}. In addition, we predict that, for the same parameters, as
hole doping is reduced from quarter filling to half filling, Friedel
oscillations would acquire a 4k_F modulation, typical of a strongly correlated
electrons regime. The 4k_F modulation dominates also in the electron doped
region. The range of parameters varied is very broad, and hence the results
reported could apply to other cuprates and other strongly correlated compounds
with quasi-one dimensional structures. On a more theoretical side, we stress
the fact that the copper and oxygen subsystems should be described by two
different Luttinger liquid exponents.Comment: 7 pages, 7 eps figure
Spin chirality induced by the Dzyaloshinskii-Moriya interaction and the polarized neutron scattering
We discuss the influence of the Dzyaloshinskii-Moriya (DM) interaction in the
Heizenberg spin chain model for the observables in the polarized neutron
scattering experiments. We show that different choices of the parameters of DM
interaction may leave the spectrum of the problem unchanged, while the
observable spin-spin correlation functions may differ qualitatively.
Particularly, for the uniform DM interaction one has the incommensurate
fluctuations and polarization-dependent neutron scattering in the paramagnetic
phase. We sketch the possible generalization of our treatment to higher
dimensions.Comment: 4 pages, REVTEX, no figures, references added, to appear in PR
Attractor Solution of Phantom Field
In light of recent study on the dark energy models that manifest an equation
of state , we investigate the cosmological evolution of phantom field in
a specific potential, exponential potential in this paper. The phase plane
analysis show that the there is a late time attractor solution in this model,
which address the similar issues as that of fine tuning problems in
conventional quintessence models. The equation of state is determined by
the attractor solution which is dependent on the parameter in the
potential. We also show that this model is stable for our present observable
universe.Comment: 9 pages, 3 ps figures; typos corrected, references updated, this is
the final version to match the published versio
Systematic event generator tuning for the LHC
In this article we describe Professor, a new program for tuning model
parameters of Monte Carlo event generators to experimental data by
parameterising the per-bin generator response to parameter variations and
numerically optimising the parameterised behaviour. Simulated experimental
analysis data is obtained using the Rivet analysis toolkit. This paper presents
the Professor procedure and implementation, illustrated with the application of
the method to tunes of the Pythia 6 event generator to data from the LEP/SLD
and Tevatron experiments. These tunes are substantial improvements on existing
standard choices, and are recommended as base tunes for LHC experiments, to be
themselves systematically improved upon when early LHC data is available.Comment: 28 pages. Submitted to European Physical Journal C. Program sources
and extra information are available from
http://projects.hepforge.org/professor
Phantom Cosmology with Non-minimally Coupled Real Scalar Field
We find that the expansion of the universe is accelerating by analyzing the
recent observation data of type \textsc{I}a supernova(SN-Ia) .It indicates
that the equation of state of the dark energy might be smaller than -1,which
leads to the introduction of phantom models featured by its negative kinetic
energy to account for the regime of equation of state parameter .In this
paper the possibility of using a non-minimally coupled real scalar field as
phantom to realize the equation of state parameter is discussed.The main
equations which govern the evolution of the universe are obtained.Then we
rewrite them with the observable quantities.Comment: 12 pages, 2 figures. Accepted for publication in Gen.Rel.Gra
Low frequency response of a collectively pinned vortex manifold
A low frequency dynamic response of a vortex manifold in type-II
superconductor can be associated with thermally activated tunneling of large
portions of the manifold between pairs of metastable states (two-level
systems). We suggest that statistical properties of these states can be
verified by using the same approach for the analysis of thermal fluctuations
the behaviour of which is well known. We find the form of the response for the
general case of vortex manifold with non-dispersive elastic moduli and for the
case of thin superconducting film for which the compressibility modulus is
always non-local.Comment: 8 pages, no figures, ReVTeX, the final version. Text strongly
modified, all the results unchange
Antiferromagnetism in doped anisotropic two-dimensional spin-Peierls systems
We study the formation of antiferromagnetic correlations induced by impurity
doping in anisotropic two-dimensional spin-Peierls systems. Using a mean-field
approximation to deal with the inter-chain magnetic coupling, the intra-chain
correlations are treated exactly by numerical techniques. The magnetic coupling
between impurities is computed for both adiabatic and dynamical lattices and is
shown to have an alternating sign as a function of the impurity-impurity
distance, hence suppressing magnetic frustration. An effective model based on
our numerical results supports the coexistence of antiferromagnetism and
dimerization in this system.Comment: 5 pages, 4 figures; final version to appear in Phys. Rev.
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