Let A be a finite algebra and let C be the clone of term operations of A. A set of tuples is called and algebraic set, if it is the set of all solutions of a system of equations over A. These algebraic sets are the main objects of study in the so-called universal algebraic geometry initiated by Boris Plotkin. It is straightforward to verify that algebraic sets are always closed under C*, the centralizer of the clone C. We are interested in algebras for which the converse is also true, i.e., where solution sets of systems of equations can be characterized as C*-closed sets of tuples. We prove that this holds if and only if the algebra is polymorphism-homogeneous, and we determine such algebras in several classes of algebras, namely

two-element algebras,

finite lattices,

finite semilattices,

finite abelian groups,

finite monounary algebras.

This is joint work with Endre Tóth (University of Szeged).

Solution sets and polymorphism-homogeneity

Wed, Dec. 2 3pm (via zoom)

Math Phys

Andrew Hamilton (CU Boulder Astrophysics Department)

X

The spinors of the group Spin(N) of rotations in N spacetime dimensions are indexed by a bitcode with [N/2] bits. A well-known promising grand unified group that contains the standard-model group is Spin(10). Fermions in the standard model are described by five bits durgb, consisting of two weak bits d and u, and three color bits r, g, b. If a sixth bit T is added, necessary to accommodate a time dimension, then the enlarged Spin(11,1) algebra contains the standard-model and Dirac algebras as commuting subalgebras, unifying all four forces. The largest subgroup of Spin(11,1) that commutes with the Poincare group is Spin(5)xSpin(6), suggesting that the latter is a partial unification on the way to complete unification in Spin(11,1). The Spin(5)xSpin(6) algebra contains a subalgebra with precisely the properties of the electroweak Higgs field. The Spin(5)xSpin(6) symmetry contains, and is spontaneously broken by, a U(1) symmetry related to the U_{B-L}(1) symmetry. Grand unification is associated with a change in the dimensionality of spacetime.

Unification of the four forces in the Spin(11,1) geometric algebra

Thu, Dec. 3 1pm (Zoom (vir…

Rep Theory

Chiara Damiolini (Rutgers University)

X

In this talk I will discuss certain properties of sheaves of covacua and conformal blocks attached to modules over vertex operator algebras. After briefly recalling how these objects are constructed from a geometric point of view, I will focus on the conditions required to construct Cohomological Field Theories from these sheaves. If time permits I will also discuss open problems which naturally arise. This is based on joint works with A. Gibney and N. Tarasca.

Consider the Mal’tsev condition on a variety which asserts the existence of an n-ary term p satisfying some equations of the form p(x_1 , . . . , x_n ) = y. Such a Mal’tsev condition can be reformulated within the internal language of an abstract category, using the so-called ‘matrix method’ of Z. Janelidze. The corresponding categorical condition is captured by a matrix of positive integers, and is formally called a closedness property of internal relations, or a ‘matrix property’ for short. Some of these properties follow from (conjunctions of) others, for example, the matrix property corresponding to the equations defining a majority term follows from the matrix property corresponding to a Pixley term. This then is the categorical theorem corresponding the fact that if p(x, y, z) is a Pixley term, then m(x, y, z) = p(x, p(x, y, z), z) is a majority term. The main aim of this talk is to present some recent work together with Z. Janelidze and P.-A. Jacqmin which has produced an algorithm for deciding implications of (conjunctions of) matrix properties in the light context of left-exact categories. Such implications of matrix properties are context sensitive, i.e., they depend on what further conditions the base category satisfies. In particular, we will see that implications of matrix properties in the context of varieties of algebras can be different from the context of left exact categories.

A classification of left exact categories motivated from universal algebra