No Arabic abstract
In our recent papers [Sh1,2], we introduced a {it twisted tensor product} of dg categories, and provided, in terms of it, {it a contractible 2-operad $mathcal{O}$}, acting on the category of small dg categories, in which the natural transformations are derived. We made use of some homotopy theory developed in [To] to prove the contractibility of the 2-operad $mathcal{O}$. The contractibility is an important issue, in vein of the theory of Batanin [Ba1,2], according to which an action of a contractible $n$-operad on $C$ makes $C$ a weak $n$-category. In this short note, we provide a new elementary proof of the contractibility of the 2-operad $mathcal{O}$. The proof is based on a direct computation, and is independent from the homotopy theory of dg categories (in particular, it is independent from [To] and from Theorem 2.4 of [Sh1]).
It is well-known that the pre-2-category $mathscr{C}at_mathrm{dg}^mathrm{coh}(k)$ of small dg categories over a field $k$, with 1-morphisms defined as dg functors, and with 2-morphisms defined as the complexes of coherent natural transformations, fails to be a strict 2-category. In [T2], D.Tamarkin constructed a contractible 2-operad in the sense of M.Batanin [Ba3], acting on $mathscr{C}at_mathrm{dg}^mathrm{coh}(k)$. According to Batanin loc.cit., it is a possible way to define a weak 2-category. In this paper, we provide a construction of {it another} contractible 2-operad $mathcal{O}$, acting on $mathscr{C}at_mathrm{dg}^mathrm{coh}(k)$. Our main tool is the {it twisted tensor product} of small dg categories, introduced in [Sh3]. We establish a one-side associativity for the twisted tensor product, making $(mathscr{C}at_mathrm{dg}^mathrm{coh}(k),overset{sim}{otimes})$ a skew monoidal category in the sense of [LS], and construct a {it twisted composition} $mathscr{C}oh_mathrm{dg}(D,E)overset{sim}{otimes}mathscr{C}oh_mathrm{dg}(C,D)tomathscr{C}oh_mathrm{dg}(C,E)$, and prove some compatibility between these two structures. Taken together, the two structures give rise to a 2-operad $mathcal{O}$, acting on $mathscr{C}at_mathrm{dg}^mathrm{coh}(k)$. Its contractibility is a consequence of a general result of [Sh3].
This article investigates duals for bimodule categories over finite tensor categories. We show that finite bimodule categories form a tricategory and discuss the dualities in this tricategory using inner homs. We consider inner-product bimodule categories over pivotal tensor categories with additional structure on the inner homs. Inner-product module categories are related to Frobenius algebras and lead to the notion of $*$-Morita equivalence for pivotal tensor categories. We show that inner-product bimodule categories form a tricategory with two duality operations and an additional pivotal structure. This is work is motivated by defects in topological field theories.
We show that the celebrated operad of pre-Lie algebras is very rigid: it has no non-obvious degrees of freedom from either of the three points of view: deformations of maps to and from the three graces of operad theory, homotopy automorphisms, and operadic twisting. Examining the latter, it is possible to answer two questions of Markl from 2005, including a Lie-theoretic version of the Deligne conjecture.
Given two small dg categories $C,D$, defined over a field, we introduce their (non-symmetric) twisted tensor product $Coverset{sim}{otimes} D$. We show that $-overset{sim}{otimes} D$ is left adjoint to the functor $Coh(D,-)$, where $Coh(D,E)$ is the dg category of dg functors $Dto E$ and their coherent natural transformations. This adjunction holds in the category of small dg categories (not in the homotopy category of dg categories $mathrm{Hot}$). We show that for $C,D$ cofibrant, the adjunction descends to the corresponding adjunction in the homotopy category. Then comparison with a result of To{e}n shows that, for $C,D$ cofibtant, $Coverset{sim}{otimes} D$ is isomorphic to $Cotimes D$, as an object of the homotopy category $mathrm{Hot}$.
Boris Shoikhet noticed that the proof of lemma 1 in section 2.3 of math.QA/0504420 contains an error. In this note I give a correct proof of this lemma which was suggested to me by Dmitry Tamarkin. The correction does not change the results of math.QA/0504420.