15,459 research outputs found
Geometric modular action for disjoint intervals and boundary conformal field theory
In suitable states, the modular group of local algebras associated with
unions of disjoint intervals in chiral conformal quantum field theory acts
geometrically. We translate this result into the setting of boundary conformal
QFT and interpret it as a relation between temperature and acceleration. We
also discuss aspects ("mixing" and "charge splitting") of geometric modular
action for unions of disjoint intervals in the vacuum state.Comment: Dedicated to John E. Roberts on the occasion of his 70th birthday; 24
pages, 3 figure
The Hall Algebras of Surfaces I
We study the derived Hall algebra of the partially wrapped Fukaya category of
a surface. We give an explicit description of the Hall algebra for the disk
with m marked intervals and we give a conjectural description of the Hall
algebras of all surfaces with enough marked intervals. Then we use a
functoriality result to show that a graded version of the HOMFLY-PT skein
relation holds among certain arcs in the Hall algebras of general surfaces.Comment: 63 page
Algebraic foundations for qualitative calculi and networks
A qualitative representation is like an ordinary representation of a
relation algebra, but instead of requiring , as
we do for ordinary representations, we only require that , for each in the algebra. A constraint
network is qualitatively satisfiable if its nodes can be mapped to elements of
a qualitative representation, preserving the constraints. If a constraint
network is satisfiable then it is clearly qualitatively satisfiable, but the
converse can fail. However, for a wide range of relation algebras including the
point algebra, the Allen Interval Algebra, RCC8 and many others, a network is
satisfiable if and only if it is qualitatively satisfiable.
Unlike ordinary composition, the weak composition arising from qualitative
representations need not be associative, so we can generalise by considering
network satisfaction problems over non-associative algebras. We prove that
computationally, qualitative representations have many advantages over ordinary
representations: whereas many finite relation algebras have only infinite
representations, every finite qualitatively representable algebra has a finite
qualitative representation; the representability problem for (the atom
structures of) finite non-associative algebras is NP-complete; the network
satisfaction problem over a finite qualitatively representable algebra is
always in NP; the validity of equations over qualitative representations is
co-NP-complete. On the other hand we prove that there is no finite
axiomatisation of the class of qualitatively representable algebras.Comment: 22 page
Representations of nets of C*-algebras over S^1
In recent times a new kind of representations has been used to describe
superselection sectors of the observable net over a curved spacetime, taking
into account of the effects of the fundamental group of the spacetime. Using
this notion of representation, we prove that any net of C*-algebras over S^1
admits faithful representations, and when the net is covariant under Diff(S^1),
it admits representations covariant under any amenable subgroup of Diff(S^1)
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