142,518 research outputs found
To Split or Not to Split, That Is the Question in Some Shallow Water Equations
In this paper we analyze the use of time splitting techniques for solving
shallow water equation. We discuss some properties that these schemes should
satisfy so that interactions between the source term and the shock waves are
controlled. This paper shows that these schemes must be well balanced in the
meaning expressed by Greenberg and Leroux [5]. More specifically, we analyze in
what cases it is enough to verify an Approximate C-property and in which cases
it is required to verify an Exact C-property (see [1], [2]). We also include
some numerical tests in order to justify our reasoning
Spin(7)-instantons, stable bundles and the Bogomolov inequality for complex 4-tori
Using gauge theory for Spin(7)-manifolds of dimension 8, we develop a
procedure, called Spin-rotation, which transforms a (stable) holomorphic
structure on a vector bundle over a complex torus of dimension 4 into a new
holomorphic structure over a different complex torus. We show non-trivial
examples of this procedure by rotating a decomposable Weil abelian variety into
a non-decomposable one. As a byproduct, we obtain a Bogomolov type inequality,
which gives restrictions for the existence of stable bundles on an abelian
variety of dimension 4, and show examples in which this is stronger than the
usual Bogomolov inequality.Comment: 40 pages, no figures; v2. To appear in Journal de math\'ematiques
pures et appliqu\'ee
Glueball-Meson Mixing
Calculations in unquenched QCD for the scalar glueball spectrum have
confirmed previous results of Gluodynamics finding a glueball at ~ 1750 MeV. I
analyze the implications of this discovery from the point of view of
glueball-meson mixing at the light of the experimental scalar sprectrum.Comment: 7 pages, 5 figure
AdS gravity and glueball spectrum
The glueball spectrum has attracted much attention since the formulation of
Quantum Chromodynamics. Different approaches give very different results for
their masses. We revisit the problem from the perspective of the AdS/CFT
correspondence.Comment: 4 pages, no figures, 5 table
Topology in the SU(Nf) chiral symmetry restored phase of unquenched QCD and axion cosmology
We investigate the topological properties of unquenched on the basis of
numerical results of simulations at fixed topological charge, recently reported
by Borsanyi et al.. We demonstrate that their results for the mean value of the
chiral condensate at fixed topological charge are inconsistent with the
analytical prediction of the large volume expansion around the saddle point,
and argue that the most plausible explanation for the failure of the saddle
point expansion is a vacuum energy density -independent at high
temperatures, but surprisingly not too high , a result which
would imply a vanishing topological susceptibility, and the absence of all
physical effects of the axial anomaly at these temperatures. We also
show that under a general assumption concerning the high temperature phase of
, where the symmetry is restored, the analytical prediction
for the chiral condensate at fixed topological charge is in very good agreement
with the numerical results of Borsanyi et al., all effects of the axial anomaly
should disappear, the topological susceptibility and all the
-derivatives of the vacuum energy density vanish and the theory becomes
-independent at any in the infinite volume limit.Comment: 18 pages, no figures, typos added in section 4, small changes in the
text and some references adde
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