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In mathematics, an
E
n
{\displaystyle {\mathcal {E}}_{n}}
-algebra in a symmetric monoidal infinity category C consists of the following data:
An object
A
(
U
)
{\displaystyle A(U)}
for any open subset U of Rn homeomorphic to an n-disk.
A multiplication map:
μ
:
A
(
U
1
)
⊗
⋯
⊗
A
(
U
m
)
→
A
(
V
)
{\displaystyle \mu :A(U_{1})\otimes \cdots \otimes A(U_{m})\to A(V)}
for any disjoint open disks
U
j
{\displaystyle U_{j}}
contained in some open disk V
subject to the requirements that the multiplication maps are compatible with composition, and that
μ
{\displaystyle \mu }
is an equivalence if
m
=
1
{\displaystyle m=1}
. An equivalent definition is that A is an algebra in C over the little n-disks operad.
Examples
An
E
n
{\displaystyle {\mathcal {E}}_{n}}
-algebra in vector spaces over a field is a unital associative algebra if n = 1, and a unital commutative associative algebra if n ≥ 2.
An
E
n
{\displaystyle {\mathcal {E}}_{n}}
-algebra in categories is a monoidal category if n = 1, a braided monoidal category if n = 2, and a symmetric monoidal category if n ≥ 3.
If Λ is a commutative ring, then
X
↦
C
∗
(
Ω
n
X
;
Λ
)
{\displaystyle X\mapsto C_{*}(\Omega ^{n}X;\Lambda )}
defines an
E
n
{\displaystyle {\mathcal {E}}_{n}}
-algebra in the infinity category of chain complexes of
Λ
{\displaystyle \Lambda }
-modules.
See also
Categorical ring
Highly structured ring spectrum
References
http://www.math.harvard.edu/~lurie/282ynotes/LectureXXII-En.pdf
http://www.math.harvard.edu/~lurie/282ynotes/LectureXXIII-Koszul.pdf
External links
"En-algebra", ncatlab.org