61,027 research outputs found
Contractions from to the M-theory superalgebra extended by additional fermionic generators
We study here the generalized Weimar-Woods contractions of the superalgebra
in order to obtain a suitable algebra that could
describe the gauge group of supergravity. The contracted superalgebras
are assumed to be given in terms of fermionic extensions of the M-theory
superalgebra. We show that the only superalgebra of this type obtained by
contraction is the only one for which the three-form of supergravity
cannot be trivialized. Therefore, supergravity cannot be connected in
this way with a contraction of
Pairing Correlations in Finite Systems: From the weak to the strong fluctuations regime
The Particle Number Projected Generator Coordinate Method is formulated for
the pairing Hamiltonian in a detailed way in the projection after variation and
the variation after projection methods. The dependence of the wave functions on
the generator coordinate is analyzed performing numerical applications for the
most relevant collective coordinates. The calculations reproduce the exact
solution in the weak, crossover and strong pairing regimes. The physical
insight of the Ansatz and its numerical simplicity make this theory an
excellent tool to study pairing correlations in complex situations and/or
involved Hamiltonians.Comment: Submitted to EPJ
Branching: the Essence of Constraint Solving
This paper focuses on the branching process for solving any constraint
satisfaction problem (CSP). A parametrised schema is proposed that (with
suitable instantiations of the parameters) can solve CSP's on both finite and
infinite domains. The paper presents a formal specification of the schema and a
statement of a number of interesting properties that, subject to certain
conditions, are satisfied by any instances of the schema.
It is also shown that the operational procedures of many constraint systems
including cooperative systems) satisfy these conditions.
Moreover, the schema is also used to solve the same CSP in different ways by
means of different instantiations of its parameters.Comment: 18 pages, 2 figures, Proceedings ERCIM Workshop on Constraints
(Prague, June 2001
A singularity-free space-time
We show that the solution published in Ref.1 is geodesically complete and
singularity-free. We also prove that the solution satisfies the stronger energy
and causality conditions, such as global hyperbolicity, causal symmetry and
causal stability. A detailed discussion about which assumptions in the
singularity theorems are not fulfilled is performed, and we show explicitly
that the solution is in accordance with those theorems. A brief discussion of
the results is given.Comment: Latex 2.09, 14 page
: Confronting theory and lattice simulations
We consider a recent -matrix analysis by Albaladejo {\it et al.}, [Phys.\
Lett.\ B {\bf 755}, 337 (2016)] which accounts for the and
coupled--channels dynamics, and that successfully describes the
experimental information concerning the recently discovered .
Within such scheme, the data can be similarly well described in two different
scenarios, where the is either a resonance or a virtual state. To
shed light into the nature of this state, we apply this formalism in a finite
box with the aim of comparing with recent Lattice QCD (LQCD) simulations. We
see that the energy levels obtained for both scenarios agree well with those
obtained in the single-volume LQCD simulation reported in Prelovsek {\it et
al.} [Phys.\ Rev.\ D {\bf 91}, 014504 (2015)], making thus difficult to
disentangle between both possibilities. We also study the volume dependence of
the energy levels obtained with our formalism, and suggest that LQCD
simulations performed at several volumes could help in discerning the actual
nature of the intriguing state
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