7,830 research outputs found
Approximating the radiatively corrected Higgs mass in the Minimal Supersymmetric Model
To obtain the most accurate predictions for the Higgs masses in the minimal
supersymmetric model (MSSM), one should compute the full set of one-loop
radiative corrections, resum the large logarithms to all orders, and add the
dominant two-loop effects. A complete computation following this procedure
yields a complex set of formulae which must be analyzed numerically. We discuss
a very simple approximation scheme which includes the most important terms from
each of the three components mentioned above. We estimate that the Higgs masses
computed using our scheme lie within 2 GeV of their theoretically predicted
values over a very large fraction of MSSM parameter space.Comment: 31 pages, 10 embedded figures, latex with psfig.sty the complete
postscript file of this preprint, including figures, is available via
anonymous ftp at ftp://www-ttp.physik.uni-karlsruhe.de/ttp95-09/ttp95-09.ps
or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Origin of the structural phase transition in Li7La3Zr2O12
Garnet-type Li7La3Zr2O12 (LLZO) is a solid electrolyte material with a
low-conductivity tetragonal and a high-conductivity cubic phase. Using
density-functional theory and variable cell shape molecular dynamics
simulations, we show that the tetragonal phase stability is dependent on a
simultaneous ordering of the Li ions on the Li sublattice and a
volume-preserving tetragonal distortion that relieves internal structural
strain. Supervalent doping introduces vacancies into the Li sublattice,
increasing the overall entropy and reducing the free energy gain from ordering,
eventually stabilizing the cubic phase. We show that the critical temperature
for cubic phase stability is lowered as Li vacancy concentration (dopant level)
is raised and that an activated hop of Li ions from one crystallographic site
to another always accompanies the transition. By identifying the relevant
mechanism and critical concentrations for achieving the high conductivity
phase, this work shows how targeted synthesis could be used to improve
electrolytic performance
The mechanics of shuffle products and their siblings
We carry on the investigation initiated in [15] : we describe new shuffle
products coming from some special functions and group them, along with other
products encountered in the literature, in a class of products, which we name
-shuffle products. Our paper is dedicated to a study of the latter
class, from a combinatorial standpoint. We consider first how to extend
Radford's theorem to the products in that class, then how to construct their
bi-algebras. As some conditions are necessary do carry that out, we study them
closely and simplify them so that they can be seen directly from the definition
of the product. We eventually test these conditions on the products mentioned
above
Recipe theorem for the Tutte polynomial for matroids, renormalization group-like approach
Using a quantum field theory renormalization group-like differential
equation, we give a new proof of the recipe theorem for the Tutte polynomial
for matroids. The solution of such an equation is in fact given by some
appropriate characters of the Hopf algebra of isomorphic classes of matroids,
characters which are then related to the Tutte polynomial for matroids. This
Hopf algebraic approach also allows to prove, in a new way, a matroid Tutte
polynomial convolution formula appearing in W. Kook {\it et. al., J. Comb.
Series} {\bf B 76} (1999).Comment: 14 pages, 3 figure
Spin Resistivity in the Frustrated Model
We study in this paper the resistivity encountered by Ising itinerant spins
traveling in the so-called frustrated simple cubic Ising lattice. For
the lattice, we take into account the interactions between nearest-neighbors
and next-nearest-neighbors, and respectively. Itinerant spins
interact with lattice spins via a distance-dependent interaction. We also take
into account an interaction between itinerant spins. The lattice is frustrated
in a range of in which we show that it undergoes a very strong
first-order transition. Using Monte Carlo simulation, we calculate the
resistivity of the itinerant spins and show that the first-order
transition of the lattice causes a discontinuity of .Comment: submitted for publicatio
Space-time domain decomposition for advection-diffusion problems in mixed formulations
This paper is concerned with the numerical solution of porous-media flow and
transport problems , i. e. heterogeneous, advection-diffusion problems. Its aim
is to investigate numerical schemes for these problems in which different time
steps can be used in different parts of the domain. Global-in-time,
non-overlapping domain-decomposition methods are coupled with operator
splitting making possible the different treatment of the advection and
diffusion terms. Two domain-decomposition methods are considered: one uses the
time-dependent Steklov--Poincar{\'e} operator and the other uses optimized
Schwarz waveform relaxation (OSWR) based on Robin transmission conditions. For
each method, a mixed formulation of an interface problem on the space-time
interface is derived, and different time grids are employed to adapt to
different time scales in the subdomains. A generalized Neumann-Neumann
preconditioner is proposed for the first method. To illustrate the two methods
numerical results for two-dimensional problems with strong heterogeneities are
presented. These include both academic problems and more realistic prototypes
for simulations for the underground storage of nuclear waste
Improved Perturbative QCD Approach to the Bottomonium Spectrum
Recently it has been shown that the gross structure of the bottomonium
spectrum is reproduced reasonably well within the non-relativistic boundstate
theory based on perturbative QCD. In that calculation, however, the fine
splittings and the S-P level splittings are predicted to be considerably
narrower than the corresponding experimental values. We investigate the
bottomonium spectrum within a specific framework based on perturbative QCD,
which incorporates all the corrections up to O(alpha_S^5 m_b) and O(alpha_S^4
m_b), respectively, in the computations of the fine splittings and the S-P
splittings. We find that the agreement with the experimental data for the fine
splittings improves drastically due to an enhancement of the wave functions
close to the origin as compared to the Coulomb wave functions. The agreement of
the S-P splittings with the experimental data also becomes better. We find that
natural scales of the fine splittings and the S-P splittings are larger than
those of the boundstates themselves. On the other hand, the predictions of the
level spacings between consecutive principal quantum numbers depend rather
strongly on the scale mu of the operator \propto C_A/(m_b r^2). The agreement
of the whole spectrum with the experimental data is much better than the
previous predictions when mu \simeq 3-4 GeV for alpha_S(M_Z)=0.1181. There
seems to be a phenomenological preference for some suppression mechanism for
the above operator.Comment: 26 pages, 16 figures. Minor changes, to be published in PR
Renormalization group-like proof of the universality of the Tutte polynomial for matroids
In this paper we give a new proof of the universality of the Tutte polynomial
for matroids. This proof uses appropriate characters of Hopf algebra of
matroids, algebra introduced by Schmitt (1994). We show that these Hopf algebra
characters are solutions of some differential equations which are of the same
type as the differential equations used to describe the renormalization group
flow in quantum field theory. This approach allows us to also prove, in a
different way, a matroid Tutte polynomial convolution formula published by
Kook, Reiner and Stanton (1999). This FPSAC contribution is an extended
abstract.Comment: 12 pages, 3 figures, conference proceedings, 25th International
Conference on Formal Power Series and Algebraic Combinatorics, Paris, France,
June 201
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