7,095 research outputs found
Instanton counting in Class
We compute the instanton partition functions of SCFTs in
class . We obtain this result via orbifolding Dp/D(p-4) brane
systems and calculating the partition function of the supersymmetric gauge
theory on the worldvolume of D(p-4) branes. Starting with D5/D1 setups
probing a orbifold singularity we obtain
the instanton partition functions of 6d theories on in the presence of orbifold defects on via computing the 2d
superconformal index of the worldvolume theory on D1 branes wrapping the
. We then reduce our results to the 5d and to the 4d instanton partition
functions. For we check that we reproduce the known elliptic,
trigonometric and rational Nekrasov partition functions. Finally, we show that
the instanton partition functions of quivers in class
can be obtained from the class mother theory partition functions
with gauge factors via imposing the `orbifold condition'
with and
, on the Coulomb moduli and the mass parameters.Comment: 43 pages, 7 figure
Assembling homology classes in automorphism groups of free groups
The observation that a graph of rank can be assembled from graphs of
smaller rank with leaves by pairing the leaves together leads to a
process for assembling homology classes for and from
classes for groups , where the generalize
and . The symmetric group
acts on by permuting leaves, and for trivial
rational coefficients we compute the -module structure on
completely for . Assembling these classes then
produces all the known nontrivial rational homology classes for and
with the possible exception of classes for recently discovered
by L. Bartholdi. It also produces an enormous number of candidates for other
nontrivial classes, some old and some new, but we limit the number of these
which can be nontrivial using the representation theory of symmetric groups. We
gain new insight into some of the most promising candidates by finding small
subgroups of and which support them and by finding
geometric representations for the candidate classes as maps of closed manifolds
into the moduli space of graphs. Finally, our results have implications for the
homology of the Lie algebra of symplectic derivations.Comment: Final version for Commentarii Math. Hel
On cocliques in commutative Schurian association schemes of the symmetric group
Given the symmetric group and a multiplicity-free
subgroup , the orbitals of the action of on by left
multiplication induce a commutative association scheme. The irreducible
constituents of the permutation character of acting on are indexed by
partitions of and if is the second largest partition in
dominance ordering among these, then the Young subgroup
admits two orbits in its action on , which
are and its complement.
In their monograph [Erd\H{o}s-Ko-Rado theorems: Algebraic Approaches. {\it
Cambridge University Press}, 2016] (Problem~16.13.1), Godsil and Meagher asked
whether is a coclique of a graph in the commutative
association scheme arising from the action of on . If such a graph
exists, then they also asked whether its smallest eigenvalue is afforded by the
-module.
In this paper, we initiate the study of this question by taking .
We show that the answer to this question is affirmative for the pair of
groups , where and , or and is one of , or . For the pair , we also prove that the answer to this question
of Godsil and Meagher is negative
Large deviations for random matrices
We prove a large deviation result for a random symmetric n x n matrix with
independent identically distributed entries to have a few eigenvalues of size
n. If the spectrum S survives when the matrix is rescaled by a factor of n, it
can only be the eigenvalues of a Hilbert-Schmidt kernel k(x,y) on [0,1] x
[0,1]. The rate function for k is where h is the
Cramer rate function for the common distribution of the entries that is assumed
to have a tail decaying faster than any Gaussian. The large deviation for S is
then obtained by contraction.Comment: 13 pages. Appeared in Comm. on Stochastic Analysis, vol. 6 no. 1,
1-13, 201
On self-Mullineux and self-conjugate partitions
The Mullineux involution is a relevant map that appears in the study of the modular representations of the symmetric group and the alternating group. The fixed points of this map are certain partitions of particular interest. It is known that the cardinality of the set of these self-Mullineux partitions is equal to the cardinality of a distinguished subset of self-conjugate partitions. In this work, we give an explicit bijection between the two families of partitions in terms of the Mullineux symbol
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