971 research outputs found
Can Theta/N Dependence for Gluodynamics be Compatible with 2 pi Periodicity in Theta ?
In a number of field theoretical models the vacuum angle \theta enters
physics in the combination \theta/N, where N stands generically for the number
of colors or flavors, in an apparent contradiction with the expected 2 \pi
periodicity in \theta. We argue that a resolution of this puzzle is related to
the existence of a number of different \theta dependent sectors in a finite
volume formulation, which can not be seen in the naive thermodynamic limit V ->
\infty. It is shown that, when the limit V -> \infty is properly defined,
physics is always 2 \pi periodic in \theta for any integer, and even rational,
values of N, with vacuum doubling at certain values of \theta. We demonstrate
this phenomenon in both the multi-flavor Schwinger model with the bosonization
technique, and four-dimensional gluodynamics with the effective Lagrangian
method. The proposed mechanism works for an arbitrary gauge group.Comment: minor changes in the discussion, a few references are adde
Inverting the Supersymmetric Standard Model Spectrum: from Physical to Lagrangian Ino Parameters
We examine the possibility of recovering the supersymmetric (and soft
supersymmetry breaking) Lagrangian parameters as direct {\em analytical}
expressions of appropriate physical masses, for the unconstrained (but CP and
R-parity conserving) minimal supersymmetric standard model. We concentrate
mainly on the algebraically non-trivial "inversion" for the ino parameters, and
obtain, for given values of , simple analytical expressions for the
, and parameters in terms of three arbitrary input physical
masses, namely either two chargino and one neutralino masses, or alternatively
one chargino and two neutralino masses. We illustrate and discuss in detail the
possible occurrence of ambiguities in this reconstruction. The dependence of
the resulting ino Lagrangian parameters upon physical masses is illustrated,
and some simple generic behaviour uncovered in this way. We finally briefly
sketch generalizing such an inversion to the full set of MSSM Lagrangian
parameters.Comment: Latex, 28 pages, 6 figures, 1 table, some typos corrected, one
paragraph extended in section 4.2. Version to appear in Phys. Rev.
Bounded Delay and Concurrency for Earliest Query Answering
International audienceEarliest query answering is needed for streaming XML processing with optimal memory management. We study the feasibility of earliest query answering for node selection queries. Tractable queries are distinguished by a bounded number of concurrently alive answer candidates at every time point, and a bounded delay for node selection. We show that both properties are decidable in polynomial time for queries defined by deterministic automata for unranked trees. Our results are obtained by reduction to the bounded valuedness problem for recognizable relations between unranked trees
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