563 research outputs found
Symplectic resolutions for multiplicative quiver varieties and character varieties for punctured surfaces
We study the algebraic symplectic geometry of multiplicative quiver varieties, which are moduli spaces of representations of certain quiver algebras, introduced by Crawley-Boevey and Shaw, called multiplicative preprojective algebras. They are multiplicative analogues of Nakajima quiver varieties. They include character varieties of (open) Riemann surfaces fixing conjugacy class closures of the monodromies around punctures, when the quiver is "crab-shaped". We prove that, under suitable hypotheses on the dimension vector of the representations, or the conjugacy classes of monodromies in the character variety case, the normalisations of such moduli spaces are symplectic singularities and that the existence of a symplectic resolution depends on a combinatorial condition on the quiver and the dimension vector. These results are analogous to those obtained by Bellamy and the first author in the ordinary quiver variety case, and for character varieties of closed Riemann surfaces. At the end of the paper, we outline some conjectural generalisations to moduli spaces of objects in 2-Calabi--Yau categories
Magnetism and superconductivity driven by identical 4 states in a heavy-fermion metal
The apparently inimical relationship between magnetism and superconductivity
has come under increasing scrutiny in a wide range of material classes, where
the free energy landscape conspires to bring them in close proximity to each
other. This is particularly the case when these phases microscopically
interpenetrate, though the manner in which this can be accomplished remains to
be fully comprehended. Here, we present combined measurements of elastic
neutron scattering, magnetotransport, and heat capacity on a prototypical heavy
fermion system, in which antiferromagnetism and superconductivity are observed.
Monitoring the response of these states to the presence of the other, as well
as to external thermal and magnetic perturbations, points to the possibility
that they emerge from different parts of the Fermi surface. This enables a
single 4 state to be both localized and itinerant, thus accounting for the
coexistence of magnetism and superconductivity.Comment: 4 pages, 4 figure
Poisson-de Rham homology of hypertoric varieties and nilpotent cones
We prove a conjecture of Etingof and the second author for hypertoric
varieties, that the Poisson-de Rham homology of a unimodular hypertoric cone is
isomorphic to the de Rham cohomology of its hypertoric resolution. More
generally, we prove that this conjecture holds for an arbitrary conical variety
admitting a symplectic resolution if and only if it holds in degree zero for
all normal slices to symplectic leaves.
The Poisson-de Rham homology of a Poisson cone inherits a second grading. In
the hypertoric case, we compute the resulting 2-variable Poisson-de
Rham-Poincare polynomial, and prove that it is equal to a specialization of an
enrichment of the Tutte polynomial of a matroid that was introduced by Denham.
We also compute this polynomial for S3-varieties of type A in terms of Kostka
polynomials, modulo a previous conjecture of the first author, and we give a
conjectural answer for nilpotent cones in arbitrary type, which we prove in
rank less than or equal to 2.Comment: 25 page
Classes on compactifications of the moduli space of curves through solutions to the quantum master equation
In this paper we describe a construction which produces classes in a
compactification of the moduli space of curves. This construction extends a
construction of Kontsevich which produces classes in the open moduli space from
the initial data of a cyclic A-infinity algebra. The initial data for our
construction is what we call a `quantum A-infinity algebra', which arises as a
type of deformation of a cyclic A-infinity algebra. The deformation theory for
these structures is described explicitly. We construct a family of examples of
quantum A-infinity algebras which extend a family of cyclic A-infinity
algebras, introduced by Kontsevich, which are known to produce all the
Miller-Morita-Mumford classes using his construction.Comment: This version includes an updated list of reference
Explaining Myanmar's Regime Transition: The Periphery is Central
In 2010, Myanmar (Burma) held its first elections after 22 years of direct military rule. Few compelling explanations for this regime transition have emerged. This article critiques popular accounts and potential explanations generated by theories of authoritarian ‘regime breakdown’ and ‘regime maintenance’. It returns instead to the classical literature on military intervention and withdrawal. Military regimes, when not terminated by internal factionalism or external unrest, typically liberalise once they feel they have sufficiently addressed the crises that prompted their seizure of power. This was the case in Myanmar. The military intervened for fear that political unrest and ethnic-minority separatist insurgencies would destroy Myanmar’s always-fragile territorial integrity and sovereignty. Far from suddenly liberalising in 2010, the regime sought to create a ‘disciplined democracy’ to safeguard its preferred social and political order twice before, but was thwarted by societal opposition. Its success in 2010 stemmed from a strategy of coercive state-building and economic incorporation via ‘ceasefire capitalism’, which weakened and co-opted much of the opposition. Having altered the balance of forces in its favour, the regime felt sufficiently confident to impose its preferred settlement. However, the transition neither reflected total ‘victory’ for the military nor secured a genuine or lasting peace
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