4,058 research outputs found
The Field White Dwarf Mass Distribution
We revisit the properties and astrophysical implications of the field white
dwarf mass distribution in preparation of Gaia applications. Our study is based
on the two samples with the best established completeness and most precise
atmospheric parameters, the volume-complete survey within 20 pc and the Sloan
Digital Sky Survey (SDSS) magnitude-limited sample. We explore the modelling of
the observed mass distributions with Monte Carlo simulations, but find that it
is difficult to constrain independently the initial mass function (IMF), the
initial-to-final-mass relation (IFMR), the stellar formation history (SFH), the
variation of the Galactic disk vertical scale height as a function of stellar
age, and binary evolution. Each of these input ingredients has a moderate
effect on the predicted mass distributions, and we must also take into account
biases owing to unidentified faint objects (20 pc sample), as well as unknown
masses for magnetic white dwarfs and spectroscopic calibration issues (SDSS
sample). Nevertheless, we find that fixed standard assumptions for the above
parameters result in predicted mean masses that are in good qualitative
agreement with the observed values. It suggests that derived masses for both
studied samples are consistent with our current knowledge of stellar and
Galactic evolution. Our simulations overpredict by 40-50% the number of massive
white dwarfs (M > 0.75 Msun) for both surveys, although we can not exclude a
Salpeter IMF when we account for all biases. Furthermore, we find no evidence
of a population of double white dwarf mergers in the observed mass
distributions.Comment: 15 pages, 16 figures, accepted for publication in MNRA
Reply to `A comment on `The Cauchy problem of f(R) gravity''
We reply to a comment by Capozziello and Vignolo about the Cauchy problem of
Palatini f(R) gravity.Comment: 3 pages, late
Mott physics and first-order transition between two metals in the normal state phase diagram of the two-dimensional Hubbard model
For doped two-dimensional Mott insulators in their normal state, the
challenge is to understand the evolution from a conventional metal at high
doping to a strongly correlated metal near the Mott insulator at zero doping.
To this end, we solve the cellular dynamical mean-field equations for the
two-dimensional Hubbard model using a plaquette as the reference quantum
impurity model and continuous-time quantum Monte Carlo method as impurity
solver. The normal-state phase diagram as a function of interaction strength
, temperature , and filling shows that, upon increasing towards
the Mott insulator, there is a surface of first-order transition between two
metals at nonzero doping. That surface ends at a finite temperature critical
line originating at the half-filled Mott critical point. Associated with this
transition, there is a maximum in scattering rate as well as thermodynamic
signatures. These findings suggest a new scenario for the normal-state phase
diagram of the high temperature superconductors. The criticality surmised in
these systems can originate not from a T=0 quantum critical point, nor from the
proximity of a long-range ordered phase, but from a low temperature transition
between two types of metals at finite doping. The influence of Mott physics
therefore extends well beyond half-filling.Comment: 27 pages, 16 figures, LaTeX, published versio
Theory of spin and charge fluctuations in the Hubbard model
A self-consistent theory of both spin and charge fluctuations in the Hubbard
model is presented. It is in quantitative agreement with Monte Carlo data at
least up to intermediate coupling . It includes both
short-wavelength quantum renormalization effects, and long-wavelength thermal
fluctuations which can destroy long-range order in two dimensions. This last
effect leads to a small energy scale, as often observed in high temperature
superconductors. The theory is conserving, satisfies the Pauli principle and
includes three-particle correlations necessary to account for the incipient
Mott transition.Comment: J1K 2R1 10 pages, Revtex 3.0, 4 uuencoded postscript figures, report#
CRPS-93-4
Invariants of Lie Algebras with Fixed Structure of Nilradicals
An algebraic algorithm is developed for computation of invariants
('generalized Casimir operators') of general Lie algebras over the real or
complex number field. Its main tools are the Cartan's method of moving frames
and the knowledge of the group of inner automorphisms of each Lie algebra.
Unlike the first application of the algorithm in [J. Phys. A: Math. Gen., 2006,
V.39, 5749; math-ph/0602046], which deals with low-dimensional Lie algebras,
here the effectiveness of the algorithm is demonstrated by its application to
computation of invariants of solvable Lie algebras of general dimension
restricted only by a required structure of the nilradical.
Specifically, invariants are calculated here for families of real/complex
solvable Lie algebras. These families contain, with only a few exceptions, all
the solvable Lie algebras of specific dimensions, for whom the invariants are
found in the literature.Comment: LaTeX2e, 19 page
Disseminated Neoplasia and Clam Populations in a Canadian National Park-Kouchibouguac National Park.
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