# Nikita Markarian’s mathblog

## Manifoldic homology and Chern-Simons formalism

Posted in Mathematics by nikitamarkarian on July 30, 2011

My preprint arXiv:1106.5352v1 is mostly inspired by the perfect explanation of Damien Calaque of the Kevin Costello’s project. Given a $e_n$-algebra $A$ and a compact parallelized $n$-manifold without borders $M$ a morphism from homology of the Lie algebra $L(A)$ associated with $A$ to some manifoldic homology is constructed in the preprint. I guess that for a proper $A$ this morphism gives perturbative Chern-Simons invariants of $M$ and that this construction is closely connected with the Costello’s approach. Some comments are under the cut. (more…)

## Universal enveloping e_n-algebra

Posted in Mathematics by nikitamarkarian on July 30, 2011

The universal enveloping $e_n$-algebra is a functor from the category of homotopy Lie algebras over $Q$ to the category of algebras over the operad of rational chains of the operad of little $n-$discs. For $n=1$ one get (the derived functor of) the usual universal enveloping algebra. (more…)

## Equivariant Hochschild homology

Posted in Mathematics by nikitamarkarian on April 18, 2011

Here is the appendix to the forthcoming paper “Crystalline characteristic classes via the Atiyah gerbe and generalized Chern-Weil construction”.

## Koszul duality for n-algebras

Posted in Mathematics by nikitamarkarian on February 19, 2011

Below there is a construction that from any augmented  dg algebra over the operad of chains on framed little $n$-discs produces a coalgebra over the same operad.

This construction generalizes the Koszul duality, for $n=1$ this is the usual Koszul duality for algebras.

Another case of this duality is from topology. Take a topological space $X$. Then $\Omega^n X$  is a module over framed little $n$-discs.  The union of symmetric powers of $X$ is a comodule over the (trivial) operad $Com$ and thus over framed discs (I am grateful to Victor Turchin for this observation). (Co)chains of this (co)modules over operads are dual to each other in our sence. This explains why one may calculate homology of mapping spaces from a $n$-manifold to $X$ either by means of the generalization of  the higher Hochschild homology or the spherical homology.

It seems that it is connected with work in progress of M. Ching and P. Salvatore “Geometric self-duality for the little discs operads” (I found it on the homepage of Michael Ching).

UPD: This Koszul duality is mentioned in the draft of J. Lurie’s “Higher algebra”(see e.g. example 7.3.6.7). Unfortunately, details are postponed for future work. See also “Moduli Problems for Ring Spectra”.

## Spherical homology of a Hycomm-algebra

Posted in Mathematics by nikitamarkarian on December 22, 2010

Spherical homology of a homotopy BV algebra was a subject of some previous posts.  By Hycomm=BV/Δ, a Hycomm- algebra is a special case af a homotopy BV algebra. Below I discuss how spherical homology of such an algebra looks like.

## On quantum cohomology

Posted in Mathematics by nikitamarkarian on May 5, 2010

Nowadays the theory of quantum cohomology is treated as a part of symplectic geometry. But it is not clear (for me) how much information about the symplectic structure does quantum cohomology contain. Perhaps, the situation is analagous to the Morse theory, where the definition is given in differential geometric terms (integral curves and so on) but the result is purely topological.

If one take as a starting point the paper of Witten and two papers of Givental (this and this), one may develop a theory of a different flavour sketched below. Conjecturally it coincides with the usual one, at least in some cases.

## Perturbative Chern-Simons theory and spherical homology

Posted in Mathematics by nikitamarkarian on March 22, 2010

I already made some unclear hints about connections between the perturbative Chern-Simons theory and spherical homology. Below I would like to clarify it. It seems that nearly everything I am going to say is known as “BV formalism”. But until I learn this language let me continue with my own.

Given a 3-manifold and a (say) $SU(n)$ connection on it with zero cohomology, the perturbative Chern-Simons theory gives an invariant of it, that is a power series of the quantization parameter. It would be plausible to make this invariant two-step: on get from the initial data some structure  (like a homotopy algebra  over a operad) and then take an invariant of it.

The structure involved is a 1-parametric family of homotopy BV algebras that is curvy trivial and trivialized . The spherical homology gives  invariants of this structure.

Let me explain and comment last two phrases.

## S-homology

Posted in Mathematics by nikitamarkarian on March 18, 2010

$S$-homology is an obvious generalization of the spherical homology. I already mentioned it here. In the present post I would like to summarise their properties.

UPD: Things described here and in some previous posts are particular cases of the topological chiral homology introduced in J. Lurie, “Derived Algebraic Geometry VI: E_k Algebras”. The only difference is that I need framed discs. I thank Damien for this comment.

UPD: Following M. Kapranov, I will use term manifoldic homology for the higher dimensional generalization of $S$-homology.

## TQFT as a generalization of spherical homology

Posted in Mathematics by nikitamarkarian on December 15, 2009

Speculating about the question posed in the end of this confused post I recognised, that the generalization involved makes some sense. Spherical homology is generalised in two directions. Firstly 2-sphere is replaced with any compact oriented 2-manifold. Secondly a BV (f2-)algebra is replaced with a cyclic 2-category. As a result one get a structure that strongly reminds TQFT up to decorations. By decorations I mean metric, counit and so on. This conjectural structure plays for cyclic 2-categories the same role as  Hochschild homology plays for (1-)categories.

## Homotopy cyclic 2-category

Posted in Mathematics by nikitamarkarian on December 9, 2009

In the paper “What do DG categories form?” D. Tamarkin introduced the notion of a homotopy 2-category. Its important feature is that for any object $X$ on $\mathop{Hom}(Id_X, Id_X)$ the operad of chains of little discs acts. Below  a notion of homotopy cyclic 2-category is introduced. For it the complex $\mathop{Hom}(Id_X, Id_X)$ is acted by the operad of chains of framed little discs.
(more…)