13,983 research outputs found
QCD thermodynamics at zero and non-zero density
We present recent results on thermodynamics of QCD with almost physical light
quark masses and a physical strange quark mass value. These calculations have
been performed with an improved staggerd action especially designed for finite
temperature lattice QCD. In detail we present a calculation of the transition
temperature, using a combined chiral and continuum extrapolation. Furthermore
we present preliminary results on the interaction measure and energy density at
almost realistic quark masses. Finally we disscuss the response of the pressure
to a finite quark chemical potential. Within the Taylor expansion formalism we
calculate quark number susceptibilities and leading order corrections to finite
chemical potential. This is particularly usefull for mapping out the critical
region in the QCD phase diagram.Comment: Invited talk at 3rd International Workshop on Critical Point and
Onset of Deconfinement, Florence, Italy, 3-6 Jul 200
Lattice QCD at Finite Density
I discuss different approaches to finite density lattice QCD. In particular,
I focus on the structure of the phase diagram and discuss attempts to determine
the location of the critical end-point. Recent results on the transiton line as
function of the chemical potential () are reviewed. Along the
transition line, hadronic fluctuations have been calculated, which can be used
to characterize properties of the Quark Gluon plasma and eventually can also
help to identify the location of the critical end-point in the QCD phase
diagram on the lattice and in heavy ion experiments. Furthermore, I comment on
the structure of the phase diagram at large .Comment: Plenary talk at XXIVth International Symposium on Lattice Field
Theory (Lattice 2006). Version to appear as PoS (LAT2006) 021; references
adde
Chiral perturbation theory for lattice QCD with a twisted mass term
Quantum Chromodynamics on a lattice with Wilson fermions and a chirally
twisted mass term for two degenerate quark flavours is considered in the
framework of chiral perturbation theory. The pion mass and decay constant are
calculated in next-to-leading order including terms linear in the lattice
spacing .Comment: 5 pages, LaTeX2e, typos corrected, 2 references adde
Towards an M5-Brane Model I: A 6d Superconformal Field Theory
We present an action for a six-dimensional superconformal field theory
containing a non-abelian tensor multiplet. All of the ingredients of this
action have been available in the literature. We bring these pieces together by
choosing the string Lie 2-algebra as a gauge structure, which we motivated in
previous work. The kinematical data contains a connection on a categorified
principal bundle, which is the appropriate mathematical description of the
parallel transport of self-dual strings. Our action can be written down for
each of the simply laced Dynkin diagrams, and each case reduces to a
four-dimensional supersymmetric Yang--Mills theory with corresponding gauge Lie
algebra. Our action also reduces nicely to an M2-brane model which is a
deformation of the ABJM model. While this action is certainly not the desired
M5-brane model, we regard it as a key stepping stone towards a potential
construction of the (2,0)-theory.Comment: 1+39 pages, v3: minor improvements, published versio
The Non-Abelian Self-Dual String and the (2,0)-Theory
We argue that the relevant higher gauge group for the non-abelian
generalization of the self-dual string equation is the string 2-group. We then
derive the corresponding equations of motion and discuss their properties. The
underlying geometric picture is a string structure, i.e. a categorified
principal bundle with connection whose structure 2-group is the string 2-group.
We readily write down the explicit elementary solution to our equations, which
is the categorified analogue of the 't Hooft-Polyakov monopole. Our solution
passes all the relevant consistency checks; in particular, it is globally
defined on and approaches the abelian self-dual string of charge
one at infinity. We note that our equations also arise as the BPS equations in
a recently proposed six-dimensional superconformal field theory and we show
that with our choice of higher gauge structure, the action of this theory can
be reduced to four-dimensional supersymmetric Yang-Mills theory.Comment: v3: 1+42 pages, presentation improved, typos fixed, published versio
Efficient Management of Short-Lived Data
Motivated by the increasing prominence of loosely-coupled systems, such as
mobile and sensor networks, which are characterised by intermittent
connectivity and volatile data, we study the tagging of data with so-called
expiration times. More specifically, when data are inserted into a database,
they may be tagged with time values indicating when they expire, i.e., when
they are regarded as stale or invalid and thus are no longer considered part of
the database. In a number of applications, expiration times are known and can
be assigned at insertion time. We present data structures and algorithms for
online management of data tagged with expiration times. The algorithms are
based on fully functional, persistent treaps, which are a combination of binary
search trees with respect to a primary attribute and heaps with respect to a
secondary attribute. The primary attribute implements primary keys, and the
secondary attribute stores expiration times in a minimum heap, thus keeping a
priority queue of tuples to expire. A detailed and comprehensive experimental
study demonstrates the well-behavedness and scalability of the approach as well
as its efficiency with respect to a number of competitors.Comment: switched to TimeCenter latex styl
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