88,964 research outputs found
Cosmological Information from Lensed CMB Power Spectra
Gravitational lensing distorts the cosmic microwave background (CMB)
temperature and polarization fields and encodes valuable information on
distances and growth rates at intermediate redshifts into the lensed power
spectra. The non-Gaussian bandpower covariance induced by the lenses is
negligible to l=2000 for all but the B polarization field where it increases
the net variance by up to a factor of 10 and favors an observing strategy with
3 times more area than if it were Gaussian. To quantify the cosmological
information, we introduce two lensing observables, characterizing nearly all of
the information, which simplify the study of non-Gaussian impact, parameter
degeneracies, dark energy models, and complementarity with other cosmological
probes. Information on the intermediate redshift parameters rapidly becomes
limited by constraints on the cold dark matter density and initial amplitude of
fluctuations as observations improve. Extraction of this information requires
deep polarization measurements on only 5-10% of the sky, and can improve Planck
lensing constraints by a factor of ~2-3 on any one of the parameters w_0, w_a,
Omega_K, sum(m_nu) with the others fixed. Sensitivity to the curvature and
neutrino mass are the highest due to the high redshift weight of CMB lensing
but degeneracies between the parameters must be broken externally.Comment: 19 pages, 16 figures, submitted to PR
Controllable magnetic correlation between two impurities by spin-orbit coupling in graphene
Two magnetic impurities on the edge of a zigzag graphene nanoribbon strongly
interact with each other via indirect coupling, which can be mediated by
conducting carriers. By means of Quantum Monte Carlo (QMC) simulations, we find
that the spin-orbit coupling and the chemical potential in
system can be used to drive the transition of local-spin exchange from
ferromagnetism to anti-ferromagnetism. Since the tunable ranges for
and in graphene are experimentally reachable, we thus open the
possibilities for its device application. The symmetry in spatial distribution
is broken by the vertical and the transversal spin-spin correlations due to the
effect of spin-orbit coupling, leading to the spatial anisotropy of spin
exchange, which distinguish our findings from the case in normal Fermi liquid.Comment: 7 pages, 3 figures and 1 table. This paper has been accepted in
Scientific Report
Mode-locking of incommensurate phase by quantum zero point energy in the Frenkel-Kontorova model
In this paper, it is shown that a configuration modulated system described by
the Frenkel-Kontorova model can be locked at an incommensurate phase when the
quantum zero point energy is taken into account. It is also found that the
specific heat for an incommensurate phase shows different parameter-dependence
in sliding phase and pinning phase. These findings provide a possible way for
experimentalists to verify the phase transition by breaking of analyticity.Comment: 6 pages in Europhys style, 3 eps figure
CMB Lensing Reconstruction on the Full Sky
Gravitational lensing of the microwave background by the intervening dark
matter mainly arises from large-angle fluctuations in the projected
gravitational potential and hence offers a unique opportunity to study the
physics of the dark sector at large scales. Studies with surveys that cover
greater than a percent of the sky will require techniques that incorporate the
curvature of the sky. We lay the groundwork for these studies by deriving the
full sky minimum variance quadratic estimators of the lensing potential from
the CMB temperature and polarization fields. We also present a general
technique for constructing these estimators, with harmonic space convolutions
replaced by real space products, that is appropriate for both the full sky
limit and the flat sky approximation. This also extends previous treatments to
include estimators involving the temperature-polarization cross-correlation and
should be useful for next generation experiments in which most of the
additional information from polarization comes from this channel due to
sensitivity limitations.Comment: Accepted for publication in Phys. Rev. D; typos correcte
Leggett mode in a strong-coupling model of iron arsenide superconductors
Using a two-orbital model of the superconducting phase of the pnictides, we
compute the spectrum of the Leggett mode -- a collective excitation of the
phase of the superconducting gap known to exist in multi-gap superconductors --
for different possible symmetries of the superconducting order parameter.
Specifically, we identify the small regions of parameter space where the
Leggett mode lies below the two-particle continuum, and hence should be visible
as a sharp resonance peak. We discuss the possible utility of the Leggett mode
in distinguishing different momentum dependencies of the superconducting gap.
We argue that the observation of a sharp Leggett mode would be consistent with
the presence of strong electron-electron correlations in iron-based
superconductors. We also emphasize the importance of the orbital character of
the Leggett mode, which can result in an experimental observation of the mode
in channels other than
Model Wavefunctions for the Collective Modes and the Magneto-roton Theory of the Fractional Quantum Hall Effect
We construct model wavefunctions for the collective modes of fractional
quantum Hall systems. The wavefunctions are expressed in terms of symmetric
polynomials characterized by a root partition and a "squeezed" basis, and show
excellent agreement with exact diagonalization results for finite systems. In
the long wavelength limit, the model wavefunctions reduce to those predicted by
the single-mode approximation, and remain accurate at energies above the
continuum of roton pairs.Comment: 4 pages, 3 figures, minor changes for the final prl versio
- …