9,704 research outputs found
The hyperbolic formal affine Demazure algebra
In the present paper we extend the construction of the formal (affine)
Demazure algebra due to Hoffnung, Malag\'on-L\'opez, Savage and Zainoulline in
two directions. First, we introduce and study the notion of an extendable
weight lattice in the Kac-Moody setting and show that all the definitions and
properties of the formal (affine) Demazure operators and algebras hold for such
lattices. Second, we show that for the hyperbolic formal group law the formal
Demazure algebra is isomorphic (after extending the coefficients) to the Hecke
algebra.Comment: Final version. Accepted for publication in Algebras and
Representation Theory. ALGE-D-15-0016
Parallel eigensolvers in plane-wave Density Functional Theory
We consider the problem of parallelizing electronic structure computations in
plane-wave Density Functional Theory. Because of the limited scalability of
Fourier transforms, parallelism has to be found at the eigensolver level. We
show how a recently proposed algorithm based on Chebyshev polynomials can scale
into the tens of thousands of processors, outperforming block conjugate
gradient algorithms for large computations
Bounding the Heat Trace of a Calabi-Yau Manifold
The SCHOK bound states that the number of marginal deformations of certain
two-dimensional conformal field theories is bounded linearly from above by the
number of relevant operators. In conformal field theories defined via sigma
models into Calabi-Yau manifolds, relevant operators can be estimated, in the
point-particle approximation, by the low-lying spectrum of the scalar Laplacian
on the manifold. In the strict large volume limit, the standard asymptotic
expansion of Weyl and Minakshisundaram-Pleijel diverges with the higher-order
curvature invariants. We propose that it would be sufficient to find an a
priori uniform bound on the trace of the heat kernel for large but finite
volume. As a first step in this direction, we then study the heat trace
asymptotics, as well as the actual spectrum of the scalar Laplacian, in the
vicinity of a conifold singularity. The eigenfunctions can be written in terms
of confluent Heun functions, the analysis of which gives evidence that regions
of large curvature will not prevent the existence of a bound of this type. This
is also in line with general mathematical expectations about spectral
continuity for manifolds with conical singularities. A sharper version of our
results could, in combination with the SCHOK bound, provide a basis for a
global restriction on the dimension of the moduli space of Calabi-Yau
manifolds.Comment: 32 pages, 3 figure
On the seismic modelling of rotating B-type pulsators in the traditional approximation
The CoRoT and Kepler data revolutionised our view on stellar pulsation. For
massive stars, the space data revealed the simultaneous presence of
low-amplitude low-order modes and dominant high-order gravity modes in several
B-type pulsators. The interpretation of such a rich set of detected
oscillations requires new tools. We present computations of oscillations for
B-type pulsators taking into account the effects of the Coriolis force in the
so-called traditional approximation. We discuss the limitations of classical
frequency matching to tune these stars seismically and show that the predictive
power is limited in the case of high-order gravity mode pulsators, except if
numerous modes of consecutive radial order can be identified.Comment: 8 pages, 4 figures. Paper submitted for publication in the
Proceedings of the 61st Fujihara Seminar: Progress in solar/stellar physics
with helio- and asteroseismology to appear in ASP Conference Serie
A note on some constants related to the zeta-function and their relationship with the Gregory coefficients
In this paper new series for the first and second Stieltjes constants (also
known as generalized Euler's constant), as well as for some closely related
constants are obtained. These series contain rational terms only and involve
the so-called Gregory coefficients, which are also known as (reciprocal)
logarithmic numbers, Cauchy numbers of the first kind and Bernoulli numbers of
the second kind. In addition, two interesting series with rational terms are
given for Euler's constant and the constant ln(2*pi), and yet another
generalization of Euler's constant is proposed and various formulas for the
calculation of these constants are obtained. Finally, in the paper, we mention
that almost all the constants considered in this work admit simple
representations via the Ramanujan summation
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